Effect of crystallization temperature on the interactive crystallization behavior of poly(l -lactide)-block-poly(ethylene glycol) copolymer

Accepted Manuscript Effect of Crystallization Temperature on the Interactive Crystallization Behavior of Poly(L-lactide)-block-Poly(ethylene glycol) Copolymer Jingjing Yang, Yongri Liang, Charles C. Han PII:

S0032-3861(15)30272-X

DOI:

10.1016/j.polymer.2015.09.067

Reference:

JPOL 18153

To appear in:

Polymer

Received Date: 19 July 2015 Revised Date:

20 September 2015

Accepted Date: 26 September 2015

Please cite this article as: Yang J, Liang Y, Han CC, Effect of Crystallization Temperature on the Interactive Crystallization Behavior of Poly(L-lactide)-block-Poly(ethylene glycol) Copolymer, Polymer (2015), doi: 10.1016/j.polymer.2015.09.067. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT

Graphical Abstract: after PEG crystals melted at 70 oC

after PEG blocks crystallized

after crystallization of PLLA blocks

o

Tc,PLLA=70 C o

2

70 oC

o

Tc,PLLA=110 C

Tc,PLLA=110 C

Iq

30 oC

o

Tc,PLLA=70 C

Iq

Iq

2

2

o

Tc,PLLA=70 C

o

0.04

0.06

-1

0.08

0.10

0.12

0.02

0.04

0.06

q (Å ) o

0.08

0.10

0.12

o

o

Tc,PLLA=70 C

o

o

Tc,PLLA=110 C

Tc,PLLA=110 C

16

18

20

22

24

8

10

12

14

16

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0.06

-1

0.08

0.10

0.12

18

2θ (degree)

20

22

24

8

10

12

o

Tc,PLLA=70 C

13.34 o 13.34

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14

2θ (degree)

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12

70 oC

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10

0.04

o

o

13.4

30 oC

8

0.02

q (Å )

13.43

o

Tc,PLLA=70 C Intensity (a.u.)

Intensity (a.u.)

13.31 o 13.34

-1

q (Å )

Intensity (a.u.)

0.02

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Tc,PLLA=110 C

o

Tc,PLLA=110 C

14

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2θ (degree)

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ACCEPTED MANUSCRIPT

Effect of Crystallization Temperature on the Interactive Crystallization Behavior of

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Poly(L-lactide)-block-Poly(ethylene glycol) Copolymer Jingjing Yanga,c , Yongri Liangb,c* and Charles C. Hanc*

School of Materials and Chemical Engineering, Xi’an Technological University, Xi’an 710032, China

College of Materials Science and Engineering, Beijing Key Laboratory of Special

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b

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a

Elastomer Composite Materials, Beijing Institute of Petrochemical Technology, Beijing, 102617, China

State Key Laboratory of Polymer Physics and Chemistry, Joint Laboratory of

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c

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Polymer Science and Materials, Chinese Academy of Sciences, Beijing 100190, China

Corresponding Authors: Yongri Liang (E-mail: [email protected]), Tel: +86 10 81292129

Charles C. Han (E-mail: [email protected]), Tel: +86 10 82618089, Fax: +86 10 62521519 1

ACCEPTED MANUSCRIPT ABSTRACT:

Crystallization behaviors of

crystalline-crystalline diblock copolymers are

important in understanding the structure evoluation. In this work, we investigated

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effects of crystallization temperature on the interactive crystallization behavior of crystalline-crystalline diblock copolymer of poly(L-lactide)-block-poly(ethylene glycol)

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copolymer (PLLA-b-PEG) with differential scanning calorimetry (DSC), polarized optical microscopy (POM), atomic force microscopy (AFM), small and wide angle

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X-ray scattering (SAXS/WAXS) and Fourier transform infrared (FTIR) spectroscopy techniques. SAXS results showed that during the two-step crystallization process PEG blocks should crystallize within spaces from interlamellar or interfibrillar of PLLA crystals, and the microstructure formation in PLLA-b-PEG copolymer was greatly

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dependent on TC,PLLA (crystallization temperature of PLLA). Moreover, crystal nucleation and crystallization rate of PEG blocks were also dependent on Tc,PLLA. On

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the other hand, almost reversible crystalline structure changes of PLLA crystals was induced by crystallization and melting of PEG blocks. And the extent of crystalline

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structure change of PLLA blocks by PEG crystallization was increased with Tc,PLLA increasing.

Keywords:

Poly(L-lactide)-block-poly(ethylene

crystallization behavior,

glycol)

copolymer,

interactive

SAXS/WAXS

2

ACCEPTED MANUSCRIPT Introduction The subject of crystallization in block copolymers has attracted much attention in the past few decades as reviewed by several researchers.[1-5] Recently,

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crystalline-crystalline diblock copolymer has been received even more attention. It is because that those systems can produce much more special superstructures and morphologies. The crystallization behavior and structure formation in double

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crystalline diblock copolymer systems are expected to be much more complex than

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those in crystalline-amorphous diblock copolymers, because of the additional competition between crystallization events of the two crystallizable components. For example, in crystalline-crystalline copolymer systems with two crystalline blocks (C1 and C2) possessing very different melting temperatures (Tm,C1 and Tm,C2, e.g.

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Tm,C1>Tm,C2), if phase segregation strength between two blocks is weak, the crystallization of block C1 may destroy the preexisting microphase-separated microdomains, when the crystallization temperature is higher than Tm,C2 (first stage of

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two-step crystallization process). If the segregation strength is sufficiently strong, the

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crystallization of C1 block will be confined in the microphase-separated microdomains. During the subsequent crystallization process (i.e., second stage of two-step crystallization process, the crystallization temperature is lower than Tm,C2), the crystallization of C2 block may be confined within the confined spaces established by the foregoing crystallization of C1 block in both cases of strong and weak microphase separation systems. When crystalline-crystalline diblock copolymers crystallize by one step crystallization process (i.e., rapidly cooled from the molten state to Tc that below

3

ACCEPTED MANUSCRIPT both Tm,C1 and Tm,C2), a competitive and (or) concurrent crystallization between the two components may take place. However, the mechanism and details of how does the crystallization behavior between the two blocks can interact with each other are still

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not quite understood Up to now, only a few works have focused on the subject of interactive crystallization in double crystalline block copolymers. Cong et al.[6] emphasized the

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idea of single molecular force generating mechanism in the study of confined

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crystallization behavior of PEO block in poly(lactic acid)-block-poly(ethylene oxide) copolymer (PLLA-b-PEO), with PLLA block crystallized at different crystallization temperatures. They reported that through varying crystallization temperature of PLLA, different strains could be imposed on the PEO block and the nucleation rate of PEO

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block was also affected. They think the crystallization of one block could generate strains between the connected two blocks; and the crystallization was tunable through controlling the crystallization temperture. Nojima et al.[7] reported the interactive

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crystallization behavior in the strongly segregated double crystalline block copolymer

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of poly(β-propiolactone)-block-linear low density polyethylene (PPL-b-PE) with close crystallization temperatures. When PPL-b-PE sample was cooled from the melt at constant rate (i.e., nonisothermal crystallization), PE blocks crystallized first followed by the PPL crystallization, where the crystallization of PPL blocks was overlapped with the late stage of PE crystallization (coincident crystallization). The crystallization of PPL blocks significantly affects the crystallization process of PE blocks, vice versa. When PPL-b-PE was isothermally crystallized, such coincident crystallization was not

4

ACCEPTED MANUSCRIPT observed and both blocks crystallized separately. Similar interactive crystallization behavior is also reported by Lin et al.[8] recently. They studied the interactive crystallization

kinetics

in

diblock

copolymer

of

syndiotactic

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polypropylene-block-poly(ε-caprolactone) (sPP-b-PCL). In both cases of two stage crystallization (Tm,PCL
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structure and transformed it into a crystalline lamellar morphology. During the

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two-stage crystallization process, PCL blocks were found to exhibit a faster crystallization at a given Tc,PCL, when sPP blocks crystallized at a higher Tc,sPP. This interactive crystallization behavior was mainly ascribed to the degree of stretching on PCL blocks, which was influenced by sPP crystallization. That is, the formation of

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thicker sPP crystals at higher Tc,sPP induced greater stretching on the PCL blocks, which enhanced the primary nucleation rate of PCL block during the PCL crystallization. Moreover, the effect of crystallization of C2 on the structure of C1 has

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been mentioned by Hamley et al in the double crystalline PLLA-b-PCL diblock

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copolymer system.[9-10] Their results indicated that the subsequent isothermal crystallization of PCL at 42 oC led to a rearrangement of the lamellar superstructure of PLLA, together with a change in PLLA unit cell parameters. However, the microstructure

evolution

and

interactive

crystallization

behavior

of

crystalline/crystalline diblock copolymer have not been fully understood so far. In this work, we used PLLA-b-PEG as the model copolymer to invsetigate the microstructure

evolution

and

the

interactive

crystallization

behavior

of

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ACCEPTED MANUSCRIPT double-crystalline diblock copolymers. Here, we focused on the Tc,PLLA dependent microstructure fromation and interaction between PLLA and PEG crystallization on the microscale in double crystalline PLLA-b-PEG diblock copolymer. Moreover, effects of

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Tc,PLLA on the confined crystallization of PEG blocks was also studied. Experimental Section Materials and Characterization

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The PLLA-b-PEG copolymer sample was provided by Ji’nan Daigang Co, Ltd, in

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China. The number-average molecular weight (Mn) and polydispersity index (PDI) of PLLA-b-PEG were 10090 and 1.25, respectively. The Mn of PLLA block was 4900, which was determined by 1H NMR spectra based on the known Mn of PEG block (Mn,PEG=5000). Detailed characterization of PLLA-b-PEG can be found in our previous

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work.[11] The melting temperatures of PLLA and PEG blocks in PLLA-b-PEG copolymer were determined 130 and 52.5 oC by differential scanning calorimetry (DSC, Q2000, TA) with a heating rate of 2 oC/min, respectively.

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Sample Preparation and Annealing

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PLLA-b-PEG samples were crystallized by a two-stage crystallization process using a Linkam hot stage (LTS 350). Samples were pre-heated at 160 °C for 5 min to eliminate thermal history and then rapidly quenched to Tc,PLLA (between melting temperatures of PLLA and PEG; that is, Tm , PLLA > Tc ,PLLA > Tm, PEG ) for isothermal crystallization of PLLA block for 6 h in the first stage crystallization process. Subsequently (i.e. second stage crystallization process), quickly quenched to 30 °C (< Tm,PEG ) for 2 h to achieve crystallization of PEG block.

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ACCEPTED MANUSCRIPT Polarized Optical Microscopy The polarized optical microscopy (POM) observations were performed with an Olympus BX51 optical microscope equipped with a hot stage (Linkam LTS350) and

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the ROM images were recorded by a C-5050ZOOM camera. Atomic Force Microscopy

Atomic force microscopy (AFM) images of PLLA-b-PEG copolymers were

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obtained by a Nanoscope multimode ⅢA (Bruker Co.) with tapping mode. A

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high-temperature heater accessory was used to control the sample temperature during in-situ AFM analysis. A silicon cantilever tip was used for measurements of the AFM images. The resonance frequency was about 300 KHz and the scan rate was 20 µm/s. The scanning density was 512 lines per frame.

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DSC Measurements

The nonisothermal crystallization behavior of PEG blocks in PLLA-b-PEG copolymer was recorded by DSC (Q2000, TA). PLLA-b-PEG samples were firstly

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isothermally crystallized at Tc,PLLA for 6 h; and then cooled from Tc,PLLA to 0 oC with a o

C/min. The crystallinity of PEG (Xw) was calculated by

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cooling rate of 2

Xw

∫ =

T

T0

(dH / dT )dT f × ∆H m0

× 100% , where T0 is onset temperature of crystallization of PEG.

f is the weight fraction of PEG block in the block copolymer. dH/dT and ∆Hm0 (8.66 kJ/mol)[12] are the rate of heat evolution and the equilibrium melting enthalpy of PEG, respectively.

FTIR Spectroscopy FTIR spectra were obtained on a Bruker Equinox 55 spectrometer equipped with 7

ACCEPTED MANUSCRIPT a MCT detector. The sample was casted on a KBr plate for FTIR spectra measurement and the INSTEC STC200 hot stage was used to control the sample temperature. The resolution was 2 cm-1 and the scan was repeated 32 times.

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Synchrotron SAXS/WAXS Measurements Synchrotron small and wide angle x-ray scattering (SAXS and WAXS) measurements were performed at BL16B1 beamline in Shanghai Synchrotron

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Radiation Facility (SSRF), China, respectively. Two-dimensional (2D) Mar165

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detectors were used to collect the 2D SAXS and WAXS patterns, respectively. The wavelength of the incident X-ray was 1.24 Å, and the sample to detector distance (SDD) was 2820 and 127.9 mm for SAXS and WAXS, respectively. The silver behenate (AgC22H43O2) and silicon powder were used as standard materials for

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calibration of the scattering vector of SAXS and WAXS patterns, respectively. The air and parasitic scattering were subtracted from original SAXS and WAXS data, respectively. An INSTEC (STC200) hot stage was used to control sample temperatures

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in SAXS experiments, which was calibrated by temperature calibrator (Fluker 724)

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with K type of very fine thermocouple (Omega) before use. And the sample temperature was controlled by a Linkam (CSS 450) hot stage during the WAXS experiments.

SAXS Analysis

The normalized 1D correlation function (γ1(r)) is defined as[13-14] ∞

γ 1 (r ) = ∫ I (q)q 2 cos(qr )dq / Q 0

(1)

8

ACCEPTED MANUSCRIPT Where, I(q) is scattering intensity, q is scattering vector defined as q =

4π sin θ

λ

( 2 θ is the scattering angle) and r is the direction along lamellar stack. The scattering invariant, Q is defined as ∞

Q = ∫ I (q)q 2 dq

(2)

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0

Because of the finite q range of experimental SAXS data, extrapolation of the 1D SAXS data to both the low and high q ranges are necessary for the integration of the

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intensity, I(q). Extrapolation to low q was performed using an intensity profiles based

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on Guinier’s law,[15] and the extension of the intensity to large q values can be accomplished by using Porod-Ruland model.[16] The parasitic scattering and thermal fluctuation were corrected before analysis of normalized 1D correlation function.

Results and Discussion

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Tc,PLLA Dependent Crystal morphology of PLLA-b-PEG

Tc,PLLA dependent POM crystal morphology of PLLA-b-PEG copolymers was shown in Figure 1. When Tc,PLLA was at 110 oC, dendrite crystalline morphology of

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PLLA-b-PEG was observed in Figure 1(a). Whereas, typical Maltese cross spherulite

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was observed when Tc,PLLA was at 70 oC, as shown in Figure 1(b). It implied that the crystal morphology of PLLA blocks was greatly affected by Tc,PLLA. The birefringence of all PLLA-b-PEG samples were changed, when PEG blocks crystallized at 30 oC, as shown in Figure 1 (a` and b`). In order to confirm the cause of birefringence changes, after the two-step crystallizaiton of PLLA-b-PEG copolymers, a following heating process was carryied out. After PEG crystals melted at 65 oC, the birefringence of samples could recover to the condition that before crystallization of PEG, as shown in

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ACCEPTED MANUSCRIPT Figure 1 (a`` and b``). It implied that the following crystallization of the PEG block

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could affect the microstructure of PLLA-b-PEG copolymer.

Figure 1. POM images of PLLA-b-PEG copolymer obtained after crystallization at 70 o

C (a) and 110 oC (b) for 6 h and then obtained after crystallization at 30 oC (a`, b`);

and melting at 65 oC (a``, b``). The thickness of all POM samples was about 20 µm.

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Detailed crystalline morphology on the submicron length scale in PLLA-b-PEG copolymers with different thermal histories was studied by AFM, as shown in Figure 2

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(a and b). When Tc,PLLA was 70 oC, edge-on like lamellar formed in the sample. When Tc,PLLA was 110 oC, both edge-on like and flat-on like lamellar formed in the sample.

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After remelting PEG crystals at 65 oC for 1 h, in-situ AFM resutls shown in Figure 2 (a` and b`) demonstrated that the crystallization of PEG blocks was confined in the framework of PLLA crystals. The AFM and POM results indicated that the crystallization of PEG may be influenced by the space from interlamellar stack (or interfibrillar) of PLLA blocks, which was also reported in the last paper.[11] In this work, we pay more attention to understand the effect of crystallization temperature on microstructure formation of PLLA-b-PEG copolymer. 10

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Figure 2. AFM (height (H) and phase (P)) images of PLLA-b-PEG copolymers with

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PLLA blocks crystalalized at different temperatures and PEG blocks crystallized at 30 o

C. (a) crystallization temperature of PLLA blocks (Tc,PLLA) was 70 oC, (b) Tc,PLLA=80 C, (c) Tc,PLLA=90 oC, (d) Tc,PLLA=100 oC, (e) Tc,PLLA=110 oC, (f) Tc,PLLA=115 oC. And

the image size is 5 µm×5 µm.

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Tc,PLLA Dependent Lamellar Structure Changes of PLLA-b-PEG In our previous work in-situ SAXS results has proved the microstructure formation

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of PLLA and PEG blocks in PLLA-b-PEG diblock copolymer on one condition.[11] Here the effect of Tc,PLLA on the lamellar structure of PLLA-b-PEG copolymers was

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developed further. Figure 3 showed SAXS profiles of crystallized PLLA-b-PEG samples with different thermal histories (different Tc,PLLA) obtained at room

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temperature (@ 30 oC) and temperature (@ 70 oC) above the melting temperature of PEG crystals, respectively. As shown in Figure 3(B), SAXS profiles of crystallized PLLA-b-PEG samples at 70 oC showed an intense scattering peak (peak 1) at around 0.030 Å-1 (q1) and a weak and broad scattering peak (peak 2) at around 0.057 Å-1 (q2). Since PEG crystals melted at 70 oC, Peak 1 corresponds to the long period of PLLA lamellar structure (LS), while peak 2 corresponds to microphase separated structure induced by PLLA crystallization.[11] Moreover, q1 was decreased with increasing 11

ACCEPTED MANUSCRIPT (B)

o

@70 C

Iq

2

q1 q2

(e) (d) (c)

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(b) (a)

(A)

o

Iq

2

@30 C

(e)

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(d)

(c)

0.02

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(b) (a)

0.04

0.06

0.08

-1

0.10

0.12

q (Å )

Figure 3. Lorentz-corrected 1D SAXS profiles of crystallized PLLA-b-PEG copolymer samples with different thermal histories obtained at (A) 30 and (B) 70 oC.

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PLLA-b-PEG copolymers crystallized at different Tc,PLLA and the same PEG block crystallization temperature at 30 oC: (a) Tc,PLLA=70 oC, (b) Tc,PLLA=80 oC, (c) Tc,PLLA=90 C, (d) Tc,PLLA=100 oC, (e) Tc,PLLA=110 oC.

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o

Tc,PLLA, which meant that the long period of PLLA LS increased as Tc,PLLA increases.

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As shown in Figure 3(A), when PEG blocks also crystallized, peak 1 (q1) shifted to higher scattering vector and the intensity of peak 1 was significantly reduced. However, intensity of peak 2 was stronger than those in corresponding curves shown in Figure 3 (B). Those results demonstrated that PEG blocks crystallized in the interlamellar regions of PLLA crystals. It is because that the electron density difference between two adjacent PLLA lamellar crystals was reduced by insertion of PEG crystals. In addition, the relative intensity of peak 1 and 2 was strongly influenced by Tc,PLLA as shown in 12

ACCEPTED MANUSCRIPT Figure 3. For example, the relative intensity ratio of peak 1 and 2 was 0.8 for Tc,PLLA= 70 oC and 1.3 for Tc,PLLA= 110 oC. As a result, the microstructure formation of PLLA-b-PEG copolymer samples was strongly affected by Tc,PLLA. o

C o

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(B) 70 γ1(r)

(e): Tc,PLLA=110 C o

(d): Tc,PLLA=100 C o

(c): Tc,PLLA=90 C o

(b): Tc,PLLA=80 C o

(A) 30

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(a): Tc,PLLA=70 C

o

C

o

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γ1(r)

(e): Tc,PLLA=110 C o

(d): Tc,PLLA=100 C o

(c): Tc,PLLA=90 C o

(b): Tc,PLLA=80 C o

(a): Tc,PLLA=70 C

0

100

200

300

400

500

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r (Å)

Figure 4. Normalized 1D correlation function of crystallized PLLA-b-PEG with

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different Tc,PLLA obtained at (A) 30 and (B) 70 oC.

The 1D correlation function (1DCF) was employed to analyze microstructure

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parameters of lamellar structure in PLLA-b-PEG samples. Figure 4 (A) and (B) showed the 1DCF of crystallized PLLA-b-PEG with different thermal histories (different Tc,PLLA) obtained at 30 and 70 oC, respectively. To establish the structure model and analysis method of 1DCF, crystallized PLLA-b-PEG sample with 70 oC of Tc,PLLA was used as a model example to interpret the 1DCF. And 1DCF profiles of crystallized PLLA-b-PEG at 70 and 30 oC, corresponding models of structure and electron density profile were shown in Figure 5. 13

ACCEPTED MANUSCRIPT The electron densities of amorphous and crystalline phases are 345 and 406 e/nm3 for PEG, and 396 and 410 e/nm3 for PLLA, respectively. As shown in Figure 5 (A(b)), in the γ1(r) versus r plot of crystallized PLLA-b-PEG samples at 70 oC, the long period

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of PLLA LS (LPLLA,@70) was obtained from the first maximum value in the plot and the crystalline phase thickness (lc,PLLA) of PLLA block was obtained by the intersection of the linear regression in the autocorrelation triangle with the “baseline” (γ1(r) equals to

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the first minimum) in the plot. The value of L@70 obtained by 1DCF was in good

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agreement with long period value (LB,@70) obtained by Bragg’s law from the corresponding Lorentz-corrected 1D SAXS profiles. For instance, values of L@70 and LB,@70 for the PLLA-b-PEG sample with 70 oC of Tc,PLLA were 19.1 and 19.6 nm

(qmax=0.032Å-1), respectively. The amorphous phase thickness of PLLA lamella at 70 o

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C (la@70) including both PLLA and PEG amorphous layers was calculated by la@70

=L@70-lc,PLLA. The number of chain folding in PLLA crystals and amorphous thickness of PLLA blocks (or the interface thickness of PLLA crystals) can be calculated

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theoretically. If the end group is neglected, the fully extended chain length of PLLA

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block, L0,PLLA, can be calculated by L0,PLLA =Lm×N, where Lm is the length of the repeat unit along the chain axis in the helical state and N is the polymerization degree. And, possible numbers of chain folding (Nf) in PLLA crystals can be estimated by Nf = (L0,PLLA/lc,PLLA)-1, assuming the absence of end chain defect in the PLLA crystals. Thus, L0,PLLA was calculated as L0,PLLA= (2.88/10)×(4900/72)=19.6 nm, and Nf was calculated

as Nf=(19.6/6.6)-1≈1. Accordingly, assuming absence of the chain ends in lamellar crystals and neglect length of the loop, residual chain length of PLLA on PLLA

14

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crystalline interface (i.e. the thickness of PLLA amorphous layer) at 70 oC (la,PLLA,@70)

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Figure 5. (A) Normalized 1D correlation function of crystallized PLLA-b-PEG with Tc,PLLA=70 oC obtained at (a) 30 oC and (b) 70 oC. The schematic models of the

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lamellar structure of PLLA and its density profiles at (B) 70 oC and (C) 30 oC.

can be calculated as la,PLLA@70 = (L0,PLLA-lc,PLLA×(Nf+1))/(Nf+1) = (19.6-6.6×(1+1))/(1+1) =3.2 nm. Actually, the amorphous thickness of PLLA block at Tc,PLLA should be smaller than the calculated value due to chain relaxation. Based on the lamellar structure model at 70 oC as shown in Figure 5 (B), microphase separated PEG domain size could be calculated as LPEG@70=L@70-lc,PLLA-2×la,PLLA@70=(19.1-6.6-3.2)=9.3 nm.

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ACCEPTED MANUSCRIPT The volume fraction of PEG domain in the PLLA LS was calculated by (9.3/19.1)=0.49, which was in good agreement with the volume fraction calculated by molecular weight (0.52). Therefore, the calculation value of la,PLLA@70 and LPEG@70 are

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reasonable. When PLLA-b-PEG samples subsequently crystallized at 30 oC, PEG crystals were crystallized in interlamellar regions of PLLA, partially or fully (i.e. partial or full

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insertion model), and crystals can grow into interfibrillar regions of PLLA crystals.

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And we have demonstrated that PLLA and PEG blocks existed as individual lamellar structures in PLLA-b-PEG copolymer in the last paper. The 1DCF of crystallized PLLA-b-PEG is a superposition of two periodic structures from PLLA and PEG.[11] For instance, 1DCF of crystallized PLLA-b-PEG copolymer at 30 °C showed two

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different periodic peaks as shown in Figure 4 (A) and Figure 5 (A(a)). The first intersection of the linear regression in the autocorrelation triangle with γ1(r) equal to the first minimum of γ1(r) can be attributed to amorphous thickness (la,PEG@30) of PEG

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LS and the first maximum value can be attributed to long period of PEG LS

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(LPEG@30).[11] Accordingly, crystalline layer thickness of PEG was calculated by lc,PEG= LPEG@30 - la,PEG@30. Furthermore, the second maximum peak in the 1CDF can be

attributed to the long period of PLLA-b-PEG copolymer (L@30=LPLLA+PEG), including crystalline phase of PLLA, amorphous phase of PLLA, amorphous phase of PEG and crystalline phase of PEG, since the crystalline phase of PLLA and PEG have similar electron density. The PLLA amorphous layer (interface thickness of PLLA crystals) (la,PLLA@30) at 30 oC could be calculated as la,PLLA,@30=LPLLA+PEG-LPEG, @30-lc,PLLA, based

16

ACCEPTED MANUSCRIPT on the PLLA LS model at 30 oC shown in Figure 5(C). The amorphous thickness of PLLA at 30 oC (la,PLLA@30) showed similar value with calculated la,PLLA,@70. Detailed lamellar structure parameters were summarized in Table 1.

PLLA-b-PEG copolymer. Tc,PLLA (oC) Crystalline phase thickness of PLLA (lc,PLLA ) (Å)

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Table 1. Tc,PLLA dependent lamellar structure parameters of PLLA and PEG blocks in

70

80

90

100

110

66

71

75

77

81

Long period of PLLA LS at 70 C by 1DCF (L @ 70) (Å)

191

202

214

216

226

Long period of PLLA LS at 70 oC by Bragg’s law (L B,@ 70 ) (Å)

196

205

215

217

224

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o

Calculated amorphous phase thickness of PLLA LS at 70 oC ( la, @70 ) (Å)

125

132

139

140

145

Calculated amorphous phase thickness of PLLA at 70 oC, la,PLLA @70 (Å)

32

27

23

21

17

1

1

1

1

1

93

104

116

118

128

Calculated volume fraction of PEG domain in the LS of PLLA

0.49

0.51

0.54

0.55

0.57

Amorphous phase thickness of PEG at 30 oC la,PEG,@30 (Å)

46

38

36

44

37

Long period of PEG at 30 oC, LPEG,@30 (Å)

115

115

120

128

129

Long period at 30 C (L@30=LPLLA+PEG) by 1DCF (Å)

207

215

220

215

224

Calculated crystalline phase thickness of PEG, lc,PEG@30 (Å)

69

77

84

84

92

Calculated Amorphous phase thickness of PLLA at 30 oC, la,PLLA @30 (Å)

26

29

25

10

14

Calculated numbers of chain folding (Nf) Calculated domain size of PEG at 70 oC, L PEG@ 70

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o

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(Å)

As shown in Table 1, we found that the crystalline layer thickness of PLLA

(lc,PLLA@70) was slightly increased with Tc,PLLA increasing; while the la,PLLA@70 value was slightly decreased. The domain size of PEG at 70 oC (LPEG,@ 70) and crystalline layer thickness of PEG (lc,PEG@30 ) was also increased with Tc,PLLA increasing. For example,

17

ACCEPTED MANUSCRIPT lc,PEG was 6.9 nm for Tc,PLLA=70 oC and 9.2 nm for Tc,PLLA=110 oC, which was

increased about 33%. Based on SAXS analysis, Tc,PLLA dependent crystalline and amorphous layer thicknesses of PLLA and PEG were plotted in Figure 6. It was clear

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that increasing the TC,PLLA leads to an increase of lamellar thickness of PLLA (lc,PLLA@70) crystals, as well as the crystalline layer thickness of PEG blocks. When the homopolymer crystallized from melt state, the formed lamellar crystal thickness is

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related to the reciprocal degree of supercooling temperature. However, in the case of

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crystalline block copolymers, our results implied that the crystallization of crystalline block is also strongly influenced by tethering block. For instance, during the two-step crystallization process, PEG blocks in PLLA-b-PEG samples (with different Tc,PLLA) crystallized at the same temperature (30 oC) possessed different layer thickness. In this

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case, both of confined space and tethered PLLA block could influence the crystallization behavior of PEG block, when PEG blocks subsequently crystallized at 30 oC. SAXS analysis results indicated that PEG domian size at 70 oC was increased

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with increasing Tc,PLLA. It implied that amorphous PEG chains were more stretched at

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higher Tc,PLLA. Therefore, we considered that the crystallization and lamellar thickness of PEG blocks should be related to the degree of PEG chain stretching at molten state. DSC results shown later in Figure 9 further supported this hypothesis. DSC results showed that the onset crystallization temperature of PEG block were slightly increased with Tc,PLLA increasing. The confined space might affect the crystal growth of PEG blocks, and the nucleation is strongly relative to the tethered PLLA chains on the interface of PLLA lamellar crystals.[17] As shown in Table 1 or Figure 6, lc,PEG

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ACCEPTED MANUSCRIPT increased with la,PLLA@70 decreasing. It implied that the short length of PLLA amorphous layer formed by PLLA crystallization at higher Tc,PLLA is more effective in facilitating the streching of PEG chains through the internal force. In other word, the

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nucleation and growth of PEG block in PLLA-b-PEG samples with higher Tc,PLLA were more easier than those with lower Tc,PLLA. Therefore, we suggested that the tethered PLLA blocks rather than the size of confined sapce is the main factor to influence

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crystallization behavior of PEG blocks. Tc,PLLA dependent PEG lamellar crystal

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thickness was owing to the stretched PEG chains formed by internal force generated by PLLA crystallization, which was dependent on chain folding in PLLA crystals and the amorphous thickness of PLLA blocks at the PLLA lamellar crystal interface. Moreover, compared with lower Tc,PLLA (for example 70 oC), more stronger internal force can be

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(lc,PLLA@70) (la,PLLA@30)

60

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Layer thickness (

????

)

90

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generated by amorphous layer of PLLA at higher Tc,PLLA (for example, 110 oC).

(lc,PEG@30) (la,PEG@30)

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45 30 15

70

80

90

100

110

o

Tc,PLLA ( C)

Figure 6. Tc,PLLA dependent crystalline and amorphous thicknesses of PLLA and PEG blocks in PLLA-b-PEG copolymer samples.

Tc,PLLA Dependent Crystal Structure Changes of PLLA

19

ACCEPTED MANUSCRIPT The crystallization of PEG blocks can also influence the crystalline structure of PLLA blocks in PLLA-b-PEG; because PEG blocks are connected to PLLA blocks by covalent bonds. Figure 7 showed selected in-situ WAXS patterns of PLLA-b-PEG

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samples during the two-step crystallization process. As shown in Figure 7(a) and (c), the diffraction peak of (200/110) planes of PLLA appeared at 13.34° for crystallization at 70 oC, and 13.31° for crystallization at 110 oC. After PEG blocks crystallized at 30 o

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C as shown in Figure 7(b) and (d), the diffraction peak appeared at 2θ=18.7°

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correaponded to (032)/( 1 24)/(112) crystal planes of PEG crystals. And the diffraction peak of (120) crystal plane of PEG crystals appeared at 2θ=15.34°, which was overlapped with the diffraction peak of (203) crystal plane of PLLA crystals. Moreover, after PEG blocks subsequently crystallized at 30 oC, the diffraction peak of (110/200)

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planes shifted from 13.34 to 13.40° for the PLLA-b-PEG sample with Tc,PLLA at 70 oC; while those shifted from 13.31 to 13.43° for the PLLA-b-PEG sample with Tc,PLLA at 110 oC, as shown in Figure 7. It indicated that the α-form PLLA crystal appearred by

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crystallization of PEG at 30 °C. In addition, we found that the diffraction peak position

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shifting of the (110/200) planes in the sample with Tc,PLLA at 110 oC was larger than that in the sample with Tc,PLLA at 70 oC. This implied that the PEG crystallization induced PLLA crystal structure change was influenced by the Tc,PLLA. It was owing to the PEG crystallization generated internal force, which was also dependent on the Tc,PLLA as well as the chain length of amorphous PLLA layer in crystallized PLLA lamella. Moreover, the reheating process of crystallized PLLA-b-PEG samples shown in Figure S1 further confirmed that the crystalline structure change of PLLA crystals

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ACCEPTED MANUSCRIPT was induced by PEG crystallization. 13.4

Intensity (a.u.)

13.34

(a) (b)

(c) (d)

13.43

8

12

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Intensity (a.u.)

13.31

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16

20

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2θ (degree)

Figure 7. WAXS patterns of PLLA-b-PEG copolymer before ((a) and (c)) and after ((b) and (d)) PEG block crystallized at 30 oC after PLLA block crystallized at different Tc,PLLA during the two-step crystallization process. Tc,PLLA is 70 oC in (a) and (b), while

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Tc,PLLA is 110 oC in (c) and (d).

It has been reported that PLLA has α- and α΄-form crystal modifications.[18-20]

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The diffraction peaks at 13.41° and 15.34° are corresponding to the (110/200) and (203) planes of PLLA α-form crystal, respectively, and the diffraction peaks at 13.17° and

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15.02° are corresponding to the (200/110) and (203) planes of PLLA α΄-form crystal,when the wavelength of X-ray was 0.124 nm.[20] The α-form crystal PLLA is more stable than α΄-form crystal. The metastable α΄-form can transform into more ordered α-form during the heating process, which induced the diffraction peak shift.[21] The phenomenon of peak position shifting was also reported in the PLLA-b-PCL copolymer by Hamley et al..[9-10] In their case, the peak intensity of the crystalline PLLA was reduced and the peak position was increased from 2θ=14.71˚ to 21

ACCEPTED MANUSCRIPT 2θ=14.83˚(@λ=0.14 nm), when PCL crystallized. And they gave two possible reasons for this phenomenon. One possibility is that to accommodate the crystallization of PCL, rearrangement of PLLA chains occurs, which is accomplished by local melting and

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change of unit cell. The other possibility is that a change in the structure factor could occur, since the unit cell is distorted. In our case, it was possible that at Tc,PLLA PLLA blocks formed a mixture of α-form and α΄-form crystal and then metastable α΄-form

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crystals transformed into stable α-form PLLA crystals due to PEG blocks

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crystallization. This assumption could be partialy proved by the following FTIR results. However, after PEG crystals melted at 70 oC, it was interesting that the crystalline structure of PLLA could almost recover to the state before PEG crystallization, as shown in Figure S1. This behavior has not been reported in PLLA homopolymers yet.

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The precise mechanism of reversible crystalline structure change of PLLA blocks was not clear now. One possibility may be the internal force generated by PEG crystallization was relaxed after PEG crystals melted.

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The structure changes of PLLA-b-PEG before and after crystallization of PEG

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were also investigated by in-situ FTIR. FTIR spectra of PLLA-b-PEG samples were shown in Figure 8. Typical FTIR spectra of α and α΄-form PLLA crystals were shown in Figure S2-S3. The characteristic bands of PEG are identified at 2867, 1280, 1061, 948(964) and 843 cm-1, and the characteristic bands of PLLA are identified at 1759, 1386, 1210, 1134 and 1044 cm-1. Moreover, according to literatures[20, 22-23], the carbonyl stretching vibration in the infrared spectra of PLLA crystals generally shows complex splitting with components at 1776, 1759 and 1749 cm-1 in the region of

22

ACCEPTED MANUSCRIPT 1800-1700 cm-1. In contrast, PLLA α΄-form crystals show a single peak at 1759 cm-1 in the region of 1800-1700 cm-1. As shown in Figure 8 (A), the absorbance of peaks at 1759 and 1749 cm-1 was increased after crystallization of PEG and that absorbance

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change was increased with Tc,PLLA increasing. This implied that perfect α-form PLLA crystals formed in PLLA-b-PEG copolymers and the absorption peak intensity change dependent on Tc,PLLA, which was in good agreement with in-situ WAXS results.

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Furthermore, bands in the region 1300-1050 cm-1 reflect the conformation of

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C-CO-O backbone and CH3 group, according to literatures.[24-25] The 1210 cm-1 band is assigned to νas(C-CO-O)+ras(CH3) and the 1134 cm-1 band is a typical band relative to the CH3 group. And these bands are also sensitive to the PLLA crystalline phase. In Figure 8 (B), the absorbance of bands at 1210 and 1134 cm-1 were obviously increased

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after crystallization of PEG blocks. For example, the absorbance band at 1210 cm-1 increased about 4.0%, 7.9%, 18.2% and 37.5% for Tc,PLLA of 70, 90, 100 and 110 oC, respectively, after crystallization of PEG. It demonstrated that the crystalline

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microstructure of PLLA crystals was greatly affect by PEG crystallization and this

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influence was dependent on Tc,PLLA. Reheating process of the crystallized samples shown in Figure S4 implied that this change was almost reversible. Those evidences supported that the effect of PEG crystallization on PLLA crystalline phase was dependent on Tc,PLLA. It also further gave more evidences that the crystallization of PEG blocks induced crystalline structure changes of PLLA crystals are strongly dependent on Tc,PLLA.

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ACCEPTED MANUSCRIPT (a),(b),(c) and (d) (a'),(b'),(c') and (d')

1776

1749

Absorbance

1759

(A)

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(d) and (d') (c) and (c') (b) and (b') (a) and (a')

1800

1780

1760

1740

1720

-1

1250

1200

1150

1700

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1135

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1186

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Absorbance

(a) (a`) (b) (b`)

1200

(B)

1210

Wavenumber (cm )

1100

-1

(c) (c`) (d) (d`)

1050

Wavenumber (cm )

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Figure 8. FTIR spectra in the (A) 1800-1700 cm-1 and (B) 1250-1050 cm-1 region of PLLA-b-PEG samples before and after PEG block crystallized at 30 oC with PLLA

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block fully crystallized at different Tc,PLLA. (a)-(d) are the spectra of samples with PLLA block crystallized at 70 (a), 90 (b), 100 (c) and 110 oC (d) before PEG crystallization. (a`)-(d`) are the corresponding spectra of those samples subsequently PEG crystallized at 30 oC. The spectra have been shifted for an easier visualization.

Tc,PLLA Dependent Confined Crystallization of PEG blocks In our previous article, we have demonstrated that the crystallization of PEG was confined in the framework of PLLA crystals.[11] Here, the effect of PLLA

24

ACCEPTED MANUSCRIPT crystallization temperature on the crystallization behavior of PEG was further studied by DSC. Figure 9 (A) showed DSC thermograms of PLLA-b-PEG samples obtained during the cooling process after the PLLA block fully crystallized at a certain Tc,PLLA.

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All samples showed an intense crystallization peak at around 35 oC (Tc1,PEG) and a weak crystallization peak at around 25 oC (Tc2,PEG) in DSC curves. And Tc1,PEG increased with Tc,PLLA increasing. In general, fractionated crystallization behaviors are

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ascribed to different nucleation mechanisms[26] or different confined crystallization

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mechanisms[27]. In our case, this fractionated crystallization behavior of PEG were mainly attributed to different confined crystallization mechanism; because the crystallization of PEG block can be confined in the interlamellar and interfibrillar regions of PLLA crystals.[11] The corresponding crystallinity (Xw%) of PEG blocks

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over temperature plots of PLLA-b-PEG samples with PLLA crystallized at different Tc,PLLA were dispalyed in Figure 9(B). Based on the crystallinity change during the cooling process, we considered that Tc1,PEG and Tc2,PEG should respectively correspond

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PLLA crystals.

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to the confined crystallization of PEG in the interlamellar and interfibrillar regions of

The ability of crystal nucleation can be estimated from the onset crystallization

temperature of exothermic peak (T0) and the crystallization rate can be estimated by half-time of crystallization, t1/2. During the nonisothermal crystallization process, t1/2 can be calculated as t1/ 2 = (T0 - Tt1 / 2 )/R , where Tt1/2 and R is respectively the temperature where the crystallinity reached to half maximum and the cooling rate. The onset crystallization temperature of Tc1,PEG (To) was increased from 36.7 to 39.9 oC,

25

ACCEPTED MANUSCRIPT (A) Tc2,PEG

(b) (a)

Tc1,PEG

10

50

(a) (b) (c) (d) (e)

40

50

60

2.2

t1/2 (min)

Xw%

60

40 o Temperature ( C)

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30

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(B)

20

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Exo

(e) (d) (c)

30 20

2.0 1.8 1.6 1.4

10

70

80

90

100

110

o

0

Tc,PLLA ( C)

40

30

20

10

0

o

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Temperature ( C)

Figure 9. (A) DSC thermograms of PLLA-b-PEG samples obtained during non-isothermal crystallization preocess with a cooling rate of 2 oC/min after full

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crystallization of PLLA blocks at a certain Tc,PLLA. (B) the crystallinity (Xw%) of PEG blocks obtained from curves in (A) during the cooling process and the insert is the t1/2

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of PEG block over Tc,PLLA plot. In the Figures: (a) Tc,PLLA=70 oC, (b) Tc,PLLA=80 oC, (c) Tc,PLLA=90 oC, (d) Tc,PLLA=100 oC, and (e) Tc,PLLA=110 oC. when Tc,PLLA increased from 70 to 90 oC, and then kept almost constant with Tc,PLLA increasing, as shown in Figure 9(A). It meant the crystallization nucleation of PEG blocks was affected by Tc,PLLA. Moreover, the plot of t1/2 of PEG block over Tc,PLLA in PLLA-b-PEG samples was inserted in Figure 9(B). It was clear that the t1/2 for Tc1,PEG was decreased with Tc,PLLA increasing. It meant that the crystallization rate of PEG was 26

ACCEPTED MANUSCRIPT larger in samples with higher Tc,PLLA. Furthermore, the total crystallinity, Xw%, also showed similar behaviors with To. Thus, DSC results indicated that the crystal nucleation and crystallization rate of PEG were strongly dependent on Tc,PLLA. The

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crystallization of PLLA blocks greatly affected the confined crystallization of PEG blocks in this double crystalline PLLA-b-PEG copolymer. In-situ SAXS experiments shown in Figure S5 further confirmed this conclusion. And Our DSC results are

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consistent with the similar work reported by Cong et al.[6], although the cooling rate

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was different.

Conclusions

In this work, the PLLA crystallization temperature dependent interactive crystallizaion behaviors of double crystalline PLLA-b-PEG copolymer was

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investigated. Effect of Tc,PLLA on the microstructure formation of PLLA-b-PEG copolymer, the confined crystallization of PEG blocks and PEG crystallization induced

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structure changes of PLLA crystals were analyzed. The SAXS results indicated that the lamellar crystal thicknesses of PLLA and PEG were obviously increased with Tc,PLLA

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increasing. Because for the constant chain length of PLLA block, the thickness of amorphous phase at interface of PLLA lamella was decreased with increasing the thickness of PLLA crystal. The internal force between PLLA and PEG blocks was enhanced as Tc,PLLA increased. As a result the confined crystallization including crystal nucleation and the crystallization rate of PEG blocks was greatly dependent on Tc,PLLA. In-situ WAXS and FTIR results demonstrated that the following crystallizaiton of PEG blocks in turn could affect the crystalline structure of PLLA crystals. And the extent of 27

ACCEPTED MANUSCRIPT crystalline structure change of PLLA blocks was increased with Tc,PLLA increasing. In a word, both confined crystallization behavior of PEG blocks and PEG crystallization induced structure changes of PLLA crystals were strongly influenced by Tc,PLLA.

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Acknowledgments

This research work was supported by National Natural Science Foundation of

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China (No. 21004070 and No. 21374125). The synchrotron in-situ SAXS/WAXS experiments were supported by Shanghai Synchrotron Radiation Facility in China

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(16B1/14B1).

REFERENCES

Hamley IW. Advances in Polymer Science 1999;148:113-137.

[2]

Hamley IW. Developments in block copolymer science and technology.

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[1]

Chichester: Wiley Online Library, 2004. [3]

Müller AJ, Arnal ML,Balsamo V. Lecture Notes in Physics : Progress in Understanding of Polymer Crystallization 2007;714:229-259. Müller

AJ,

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V,Arnal

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2005;190:1-63.

[6]

Castillo RV,Müller AJ. Progress in polymer science 2009;34(6):516-560.

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[5]

Cong Y, Liu H, Wang D, Zhao B, Yan T, Li L, Chen W, Zhong Z, Lin

MC,Chen HL. Macromolecules 2011;44(15):5878.

[7] [8]

Nojima S, Fukagawa Y,Ikeda H. Macromolecules 2009;42(24):9515-9522.

Lin MC, Chen HL, Su WB, Su CJ, Jeng US, Tzeng FY, Wu JY, Tsai JC,Hashimoto T. Macromolecules 2012;45:5114-5127.

[9]

Hamley I, Parras P, Castelletto V, Castillo R, Müller A, Pollet E, Dubois P,Martin C. Macromolecular Chemistry and Physics 2006;207(11):941-953.

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Hamley IW, Castelletto V, Castillo RV, Müller AJ, Martin CM, Pollet E,Dubois P. Macromolecules 2005;38(2):463-472.

[11]

Yang J, Liang Y, Luo J, Zhao C,Han CC. Macromolecules 2012;45:4254-4261.

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Thomas EL, Lotz B,Cheng SZ. Macromolecules 2008;41(13):4794-4801. Strobl GR,Schneider MJ. Journal of Polymer Science: Polymer Physics Edition 1980;18(6):1343-1359. [14]

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University Press New York, 2000.

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Massa MV, Carvalho JL,Dalnoki-Veress K. Physical review letters

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Hoogsteen W, Postema A, Pennings A, Ten Brinke G,Zugenmaier P. Macromolecules 1990;23(2):634-642.

De Santis P,Kovacs A. Biopolymers 1968;6(3):299-306.

[20]

Zhang J, Duan Y, Sato H, Tsuji H, Noda I, Yan S,Ozaki Y. Macromolecules

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Kawai T, Rahman N, Matsuba G, Nishida K, Kanaya T, Nakano M, Okamoto

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H, Kawada J, Usuki A,Honma N. Macromolecules 2007;40(26):9463-9469. Meaurio

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Chemistry B 2006;110(11):5790-5800.

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ACCEPTED MANUSCRIPT Dear Editor, Manuscript ID: JPOL 18153 Title: "Effect of Crystallization Temperature on the Interactive Crystallization

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Behavior of Poly(L-lactide)-block-Poly(ethylene glycol) Copolymer" by Yang, Jingjing; Liang, Yongri; Han, Charles.

We appreciate all of your patience for our paper. And we are very sorry for our

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delay. The problems you mentioned should be revised as follows:

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Figure 2. AFM (height and phase) images of PLLA-b-PEG copolymers with PLLA blocks crystallized at different temperatures ((a) Tc,PLLA=70 oC, (b) Tc,PLLA=110 oC) and PEG blocks crystallized at 30 oC. (a`) and (b`) are the corresponding AFM images after PEG crystals melted at 65 oC, respectively. And the image size is 5 µm×5 µm.

Charles C. Han

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Sincerely Yours,

State Key Laboratory of Polymer Physics and Chemistry, Joint Laboratory of Polymer Science and Materials,

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Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Haidian, Beijing 100190, P.R.China,

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Phone: +86-10-8261-8089 Fax: +86-10-6252-1519

Email: [email protected]

ACCEPTED MANUSCRIPT Highlights 1. Effects of crystallization temperature of PLLA on the interactive crystallization behaviors of the PLLA-b-PEG copolymer were studied.

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2. The crystallization temperature of PLLA blocks greatly affected the crystalline microstructure of PLLA-b-PEG copolymer and the confined crystallization behavior of PEG blocks.

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3. Almost reversible crystalline structure change of PLLA crystals was induced

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by crystallization and melting of PEG blocks in PLLA-b-PEG copolymer.

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Supporting Information for

Effect of Crystallization Temperature on the Interactive

glycol) Copolymer by

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Crystallization Behavior of Poly(L-lactide)-block-Poly(ethylene

School of Materials and Chemical Engineering, Xi’an Technological University,

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a

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Jingjing Yanga,c, Yongri Liangb,c*and Charles C. Hanc*

Xi’an 710032, China b

College of Materials Science and Engineering, Beijing Institute of Petrochemical

c

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Technology, Beijing, 102617, China

State Key Laboratory of Polymer Physics and Chemistry, Joint Laboratory of

Polymer Science and Materials, Chinese Academy of Sciences, Beijing 100190,

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China

1. WAXS results of crystallized PLLA-b-PEG samples before and after PEG crystals remelted.

2D wide angle x-ray scattering (WAXS) experiments of the crystallized

PLLA-b-PEG samples before and after PEG crystals remelted at 70 oC were performed

on

the

Rigaku

SAXS/WAXS

instrument

with

a

1.2

KW

MicroMAX-007HF rotating anode (40 KV and 30 mA) x-ray generator equipped with a Cu anode (The wavelength of x-ray beam was 0.1545 nm). The image plate (IP)

ACCEPTED MANUSCRIPT detector (size: 150 mm×150 mm, Fuji co.) was used to record the 2D WAXS patterns. The exposure time was set for 10 minutes. 2D WAXS patterns were calibrated using Silicon powder with a known crystal diffraction peak of 2θ = 28.44o. 16.60

(b)

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Intensity (a.u.)

70-30-H70 80-30-H70 90-30-H70 100-30-H70 110-30-H70

19.0

Intensity (a.u.)

70-30-RT 80-30-RT 90-30-RT 100-30-RT 110-30-RT

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22.21

(a)

19.13

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23.3

22.41

14

16

18

20

2θ (degree)

22

24

Figure S1. WAXS patterns of the crystallized PLLA-b-PEG samples with different

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Tc,PLLA (a) and those after PEG crystals remelted at 70 oC (b).

Typical diffraction peak at about 16.7° in Figure S1(a) belongs to (200/110)

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crystal planes of PLLA.1 It was obvious that crystallized PLLA-b-PEG samples with

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differnent Tc,PLLA had the same α-form PLLA crystalline structure. But the diffraction peak position of PLLA was transferred to lower 2θ region (16.6°) after PEG crystals remelted, as shown in Figure S1(b). It implied that the crystallization of PEG block induced reconstruction of PLLA crystals. Moreover, this crystal reconstruction behavior shown in Figure S1 was the reversible process of our in-situ WAXS resutls during the two-step crystallization process of PLLA-b-PEG copolymer. This result demonstrated that the interactive crystallization behavior between PLLA and PEG

ACCEPTED MANUSCRIPT blocks affected the microstructure formation. A similar feature was also reported by Hamely et al. in PLLA-b-PCL copolymer system.2 2. Typical FTIR Spectra of PLLA-b-PEG Copolymer and PLLA and PEG Homopolymers.

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As shown in Figure S2, the typical FTIR spectra of crystallized and amorphous PLLA-b-PEG copolymer, PLLA homopolymer crystallized at 120 and 70 oC and PEO

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homopolymer were displayed. It was clear that the FTIR spectrum of PLLA-b-PEG copolymer is a superposition of PLLA and PEG and both blocks could crystallize in

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smaples. Compared with the sepctra of PLLA homopolymer and PEG homopolymer, the characteristic bands of PEG are identified at 2867, 1280, 1061, 948(964) and 843 cm-1, while the characteristics bands of PLLA are identified at 1759, 1386, 1210 and 1044 cm-1. Moreover, PLLA homopolymer crystallized at different temperature

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possess different crystalline structure. It was reported when Tc was 120 oC, α form PLLA crystals formed; while α΄ form PLLA crystals was fomed, when Tc belows 120 C.3 The difference between the IR spectra of order α and disorder α΄ form PLLA was

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depicted in the enlarged FTIR spectra as shown in Figure S2(B)-(D). In the C=O

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stretching region, which is typical to PLLA block, different spliting peaks appear in α and α΄ form PLLA. In 1220∼1180 cm-1 region, which was assigned to νas(C-CO-O)+ras(CH3),

relative absorbance of 1210/1182 peaks was significantly

decreased in α΄ form PLLA crystals. So it is reasonable to investigate the crystallization of PLLA block based on the the FTIR spectra in the C=O stretching region and 1220∼1180 cm-1 region.

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(e) (d)

1200

0.4

α α´

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1.0

α

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1600

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3000

α

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α´ (b)

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α

2

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1212

4

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1749

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843

Absorbance

6

2.5

1759

(B)

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(A)

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1150

1100

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1050

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Figure S2. (A) The typical FTIR spectra of PLLA-b-PEG copolymer and homopolymer PLLA and PEO: (a) the FTIR spectrum of crystallized PEO homopolymer; (b) the FTIR spectrum of PLLA homopolymer crystallized at 70 oC; (c)

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the FTIR spectrum of PLLA homopolymer crystallized at 120 oC; (d) the FTIR spectrum of PLLA-b-PEG copolymer at molten state; (e) the FTIR spectrum of PLLA-b-PEG copolymer with both block crystallized. (B)—(D) are the enlarged

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FTIR spectra of α΄ (b) and α (c) form PLLA crystals.

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Figure S3 displayed FTIR spectra during heating process of PLLA homopolymer fully crystallized at 70 and 120 oC. It was obvious that below 90 oC neither the bands in C=O stretching region (1800-1700 cm-1) nor the bands in 1300-1000 cm-1 region changed with temperature. It implied that fully cystallized PLLA remained stable below 90 oC. Moreover, from Figure S3(a2) and (b2) we can see that the band at 1134 cm-1 is sensitive to the crystalline state of PLLA. With temperature increasing the peak intensity decreased and the peak position shift from 1134 to 1125 cm-1 (after

ACCEPTED MANUSCRIPT crystals were fully melted).

Absorbance 1800

1780

1760

1740

1720

-1

(a2) 1210

1700

1300

1250

1760

1740

1720

1700

-1

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Wavenumber (cm )

1150

1100

-1

1050

1134

1000

30C 40C 50C 60C 70C 80C 90C 180C

1210

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1780

(b2)

Absorbance

Absorbance

30C 40C 50C 60C 70C 80C 90C

1776

1800

1200

Wavenumber (cm )

1759

1749

1125

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Wavenumber (cm )

(b1)

35C 40C 50C 60C 70C 80C 90C 180C

1134

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35C 40C 50C 60C 70C 80C 90C

1759

Absorbance

(a1)

1300

1250

1200

1125

1150

1100

1050

1000

-1

Wavenumber (cm )

Figure S3. (a) FTIR spectra during the heating process of PLLA homopolymer crystallized at 70 oC in regions 1800-1700 cm-1 (a1) and 1300-1000 cm-1 (a2); (b)

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FTIR spectra during the heating process of PLLA homopolymer crystallized at 120 oC

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in regions 1800-1700 cm-1 (b1) and 1300-1000 cm-1 (b2).

In-situ crystallization process of PLLA-b-PEG samples with PLLA blocks fully

crystallized at different Tc,PLLA (70, 90, 100, 110oC) and the same PEG crsytallization temperature (30 oC), and the following reheating prcess were studied by FTIR. Selected FTIR spectra of PLLA-b-PEG samples during in-situ experiment were shown in Figure S4 in 1800-1000 cm-1 region. Existance and disappearance of the typical crystalline bands at about 1061 cm-1 was chosen to indicate the crystallization

ACCEPTED MANUSCRIPT and melt process of PEG crystals, respectively. And peak intensity of typical crystalline bands at 1759 and 1210 cm-1 were chosen to analyze the crystallinity of PLLA blocks. As shown in Figure S4, when PEG blocks crystallized, peak intensity of

70iso6h 70-30iso 70-30-H70

1.0 0.8 0.6 0.4

0.9 0.6

0.3 0.2 1750

1200

1100 -1

Wavenumber (cm )

1.5

Absorbance

0.3

1750

1200

1200

1100

1100

-1

110iso6h 110-30iso 110-30iso-H70

1000

1.2 0.9 0.6 0.3

0.0 1800

1750

1200

1100

1000

-1

Wavenumber (cm )

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Wavenumber (cm )

1000

-1

1.5

0.9 0.6

1750

Wavenumber (cm )

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Absorbance

1000

1.8

100iso6h 100-30iso 100-30iso-H70

1.2

0.0 1800

0.0 1800

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0.0 1800

90iso6h 90-30iso 90-30iso-H70

1.2

Absorbance

Absorbance

1.2

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1.4

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bands at 1759 and 1210 cm-1 were both increased, no matter what Tc,PLLA was chosen.

Figure S4. FTIR spectra in the 1800-1000 cm-1 region of PLLA-b-PEG samples

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during in-situ isothermal crystallization and reheating FTIR experiment. FTIR spectra of PLLA-b-PEG samples at Tc,PLLA (70, 90, 100, 110oC) after PLLA blocks fully crystallized for 6h, FTIR spectra of PLLA-b-PEG samples at 30 oC when PEG blocks begun to crystallize and FTIR spectra of reheating precess of crystallized PLLA-b-PEG sanmples at 70 oC.

This result implied that the crystallization of PEG could induced further crystallization of PLLA blocks. Moreover this influence was also dependent on

ACCEPTED MANUSCRIPT Tc,PLLA, since the peak intensity increasement degree of typical bands at 1759 and 1210 cm-1 increased as Tc,PLLA increases. During the following reheating process, the typical band at 1061 cm-1 of PEG totally disappeared when temperature reached to

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about 70 oC as shown in Figure S4. It demonstrated that at 70 oC PEG crystals totally melted in PLLA-b-PEG samples with different Tc,PLLA. And the peak intensity of bands at 1759 and 1210 cm-1 were both decreased, which further confirmed that the

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crystallinity change of PLLA blocks was indeed induced by PEG crystallization. This

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result prove the existance of stretching interaction between PLLA and PEG block, during crystallization process of PEG. 3. In-situ SAXS Experiments

In order to trace the confined crystallization of PEG block, we have done the

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time-resolved and temperature-resolved SAXS experiments. During the isothermal crystallization process, two limit crystallization temperature of PLLA (Tc,PLLA= 70 and 110 oC) were chosen. And after the crystallization of PLLA block completed, PEG

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block was crystallized at 30 oC. Figure S5(A) shows the Lorentz-corrected SAXS

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profiles of PLLA-b-PEG copolymer obtained at selected crystallization time during the two-step isothermal crystallizaiton process of PLLA-b-PEG copolymer. And Figure S5(B) shows the corresponding 1DCF of PLLA-b-PEG copolymer after PLLA block fully crystallized at 70 and 110 oC and then when PEG block also fully crystallized at 30 oC. It was clear that the scattering peak 1 shfited from 0.0315 to 0.035043 Ǻ-1, as shown in Figure S5(a) after the crystallization of PEG block. This demonstrated that the long period decreased from 19.9 to 17.9 nm and the change was

ACCEPTED MANUSCRIPT about 10.1%. From Figure S5(b), we can see that the scattering peak 1 shfited from 0.0272 to 0.0314 Ǻ-1, which implies that the long period decreased about 13.2% from 23.1 to 20.0 nm. Concerning with the crystallinity of PEG blocks in the smaples was

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about 0.54 and 0.6 (to block) with Tc1 at 70 and 110 oC (data was obtained from in-situ WAXS), respectively; the thermal shrinkage due to density change of PEG was about 9.3% and 11.5%, respectively, which is smaller than the long period change.

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Furthermore, the scattering intensity of peak 1 greatly decreased after PEG blocks

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crystallized. So insertion mode confined crystallization does exist in these samples. On the other hand, based on the crystallinity of PEG block, we can determined the lamellar thicknesses of PEG block are 8 and 9 nm when Tc1 at 70 and 110 oC, respectively. This result further determined that the crystallization of PEG block was

(A)

q1

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confined harder when PLLA crystallized at lower crystallization temperature. (B)

70C for 1min 70C for 30min 70C-30C for 5min

(a)

1.0

(C)

70C 70C-30C

(d)

110C 110C-30C

0.6 0.4

114

γ (r) 1

Iq

2

0.8

0.2

q2

EP

0.0

-0.4

la,PEG

-0.6

110C for 12min 110C for 90min 110C-30C for 10min

1.0 0.8

0.02

0.04

0.06 -1

q (Å )

0.6 0.4

133

γ (r) 1

Iq

2

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(b)

-0.2

0.2 0.0 -0.2 -0.4 la,PEG

0.08

0.10

-0.6 0

50

100

150

200

250

300

350

400

r (Å)

Figure S5. (A) Lorentz-corrected 1D SAXS profiles of PLLA-b-PEG copolymer obtained at selected crystallization time during the in-situ two-step isothermal crystallizaiton process of PLLA-b-PEG copolymer: (a) with the crystallization

ACCEPTED MANUSCRIPT temperature of PLLA block at 70 oC and that of PEG block at 30 oC; (b) with the crystallization temperature of PLLA block at 70 oC and that of PEG block at 30 oC. (B) Normalized 1D correlation function of PLLA-b-PEG copolymer samples before and after PEG block crystallized during the two-step crystallization process. (c) is

1.

Zhang, J.; Duan, Y.; Sato, H.; Tsuji, H.; Noda, I.; Yan, S.; Ozaki, Y. Macromolecules 2005, 38,

8012-8021. 2.

Hamley, I.; Parras, P.; Castelletto, V.; Castillo, R.; Müller, A.; Pollet, E.; Dubois, P.; Martin, C.

Macromolecular Chemistry and Physics 2006, 207, 941-953.

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Zhang, J.; Tashiro, K.; Tsuji, H.; Dombs, A. Macromolecules 2008, 41, 1352-1357.

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3.

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corresponding to (a) and (d) is cprresponding to (b).