Synthesis and self-assembly in aqueous solution of amphiphilic diblock copolymers containing hyperbranched polyethylene

Accepted Manuscript Synthesis and self-assembly in aqueous solution of amphiphilic diblock copolymers containing hyperbranched polyethylene BiYun Mai, Ran Liu, ZhiYun Li, Shuo Feng, Qing Wu, HaiYang Gao, GuoDong Liang, FangMing Zhu PII:

S0032-3861(14)01116-1

DOI:

10.1016/j.polymer.2014.12.017

Reference:

JPOL 17475

To appear in:

Polymer

Received Date: 24 August 2014 Revised Date:

21 October 2014

Accepted Date: 8 December 2014

Please cite this article as: Mai B, Liu R, Li Z, Feng S, Wu Q, Gao H, Liang G, Zhu F, Synthesis and selfassembly in aqueous solution of amphiphilic diblock copolymers containing hyperbranched polyethylene, Polymer (2015), doi: 10.1016/j.polymer.2014.12.017. 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.

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Graphical Abstract

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Synthesis and self-assembly in aqueous solution of amphiphilic diblock

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copolymers containing hyperbranched polyethylene BiYun Mai,1 Ran Liu,1 ZhiYun Li,1 Shuo Feng,1 Qing Wu,1,

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GuoDong Liang1, 2 and FangMing Zhu*1, 2

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HaiYang Gao,1,

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DSAPM Lab, Institute of polymer Science, School of Chemistry and Chemical Engineering, Sun Yat-Sen University, 510275, China

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Key Lab for Polymer Composite and Functional Materials of Ministry of Education,

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School of Chemistry and Chemical Engineering, Sun Yat-Sen University,

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Guangzhou, 510275, China

E-mail: [email protected]

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*Corresponding author

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Tel: +86-20-84113250

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Fax: +86-20-84114033

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ACCEPTED MANUSCRIPT ABSTRACT: In this paper, the well-defined amphiphilic diblock copolymers,

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hyperbranched polyethylene-b-poly(ethylene oxide) (HBPE-b-PEO) and hyperbranched

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polyethylene-b-poly(acrylic acid) (HBPE-b-PAA), were synthesized by combing chain

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walking ethylene polymerization in the presence of 4-vinylbenzyl chloride catalyzed

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with Pd-α-diimine and click chemistry or atom transfer radical polymerization (ATRP).

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The self-assembly behavior in water, a selective solvent for PEO and PAA, and the

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micelle morphology of HBPE-b-PEO and HBPE-b-PAA were investigated by laser

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light scattering (LLS), transmission electron microscopy (TEM) and atomic force

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microscopy (AFM). The resultant diblock copolymers can self-assemble into spherical

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vesicles as demonstrated by LLS and TEM, which become collapsed on mica surface

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during drying as showed by AFM.

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Keywords: hyperbranched polyethylene; amphiphilic diblock copolymers; laser light

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scattering

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1. Introduction Since the explorations made by Brookhart et al. and Guan et al. over a dozen years

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ago [1, 2], hyperbranched polyethylene (HBPE) obtained at low pressure based on

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“chain walking” polymerization (CWP) using Pd-α-diimine catalyst has attracted

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considerable attention due to its unique chain structure. Distinct from linear

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polyethylene (PE), HBPE has structure and topology similar to that of dendrimer, and

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possesses some strikingly superior material properties, such as improved processability

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[3, 4], enhanced solubility [5-7] and low melt viscosity [8-10]. For low- and

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medium-molecular-weight HBPE, it is even an oily liquid at room temperature [10]. To

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date, HBPE has been found its application for lubricant formulation [8-10], polymer

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extrusion processing [3, 4] and solubilization of carbon nanotubes in organic solvents

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[5-7].

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Another potential application for HBPE is as a building block for constructing

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polymers of various well-defined chain architectures [11-14], for instance, the

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hyperbranched-linear block copolymers [11, 12]. It has been demonstrated that

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dendritic-linear block copolymers have interesting self-assembling feature, novel

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interfacial properties, and special phase separation behavior, promising applications in

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thin film, drug delivery, biomaterials and coatings [15-17]. Unfortunately, dendritic

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structure often requires tedious synthetic procedures. Hyperbranched structure, as an

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alternative, is much easier to synthesize and incurs lower cost [18, 19]. HBPE is such an

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option, which can easily obtain at low pressure catalyzed by Pd-α-diimine catalyst.

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ACCEPTED MANUSCRIPT There have been a few studies on hyperbranched-linear diblock copolymers containing

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an HBPE block reported in the literature [11, 12]. Utilizing the unique reaction of

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styrene derivatives with cationic Pd species, Ye et al. demonstrated a quantitative

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end-capping chemistry for efficient synthesis of narrowly distributed telechelic

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hyperbranched polyethylenes (HBPEs) containing a functional ω-terminal group (i.e.,

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mono end-capped HBPEs with only one functional group at the ω chain end) [11]. Later,

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these mono end-capped HBPEs were successfully used as precursors for further

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synthesis of diblock copolymers of HBPE and polystyrene (HBPE-b-PS) or poly(methyl

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methacrylate) (HBPE-b-PMMA) via atom transfer radical polymerization (ATRP) [12].

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Note that, all the blocks of these reported hyperbranched-linear diblock copolymers

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containing an HBPE block are hydrophobic. In order to exploit their application in

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biomaterials or drug delivery, it is necessary to synthesize several HBPE diblock

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copolymers with a hydrophilic block.

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On the other hand, a number of dendritic / hyperbranched polyethylene graft

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copolymers have been synthesized by combining CWP with ATRP, reversible addition

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fragmentation transfer (RAFT) polymerization or click chemistry. Chen et al. first

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developed a tandem CWP-ATRP approach for constructing dendritic polyethylene with

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reactive surface functionalities [20]. Later, Zhang et al. showed the synthesis of HBPE

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tethered with PMMA side chains (HBPE-g-PMMA) via a similar procedure [13]. Our

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group also developed a tandem CWP-RAFT approach for the synthesis of HBPE

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grafted with poly(N, N-dimethylaminoethyl methacrylate) chains (HBPE-g-PDMAEMA)

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[14]. More recently, we further grafted poly(ethylene oxide) (PEO) chains onto a

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dendritic polyethylene core (DPE-g-PEO) through CWP combining azide-alkyne click

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chemistry [21]. The self-assembly of various hyperbranched polymers and linear-hyperbranched

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polymers have been widely investigated in the literature [22-27]. However, only one

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study has been concerned about amphiphilic polymers containing HBPE segments [14].

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The self-assembly of amphiphilic HBPE graft copolymers tethered with water-soluble

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chains in water was first investigated by our group recently [14]. These HBPE graft

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copolymers have been found to self-assemble into vesicles in aqueous solution. To date,

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there is still a lack of studies on the self-assembly of amphiphilic HBPE diblock

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copolymers (i.e., hyperbranched-linear diblock copolymers consisting of an HBPE

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block and a water-soluble linear block). Furthermore, it is essential to measure the exact

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nanostructures of the hydrated state aggregates when concerning their specific

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applications. So far, the nanostructures of the HBPE-based aggregates are investigated

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on the basis of transmission electron microscopy (TEM) and atomic force microscopy

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(AFM) observations [14]. Note that both measurements are performed after the

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aggregates become dry. Considering the HBPE block as an oily liquid at room

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temperature, the morphologies of the aggregates might change during the sample

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preparation. Thus, it is necessary to measure the nanostructures in aqueous solution for

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the HBPE-based aggregates.

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ACCEPTED MANUSCRIPT In this study, we employed the general technique of end-capping chemistry to

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synthesize two HBPE precursors. Then click chemistry and ATRP were respectively

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carried out to obtain two amphiphilic hyperbranched-linear diblock copolymers,

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hyperbranched polyethylene-b-poly(ethylene oxide) (HBPE-b-PEO) and hyperbranched

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polyethylene-b-poly(acrylic acid) (HBPE-b-PAA). Both diblock copolymers consisting

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of a long HBPE block and a short water-soluble block were used to study their

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self-assembly in aqueous solution. A detailed laser light-scattering (LLS) study on the

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HBPE-based aggregates was reported, providing the clear nanostructures for the

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hydrated state aggregates in aqueous solution. TEM and AFM observations were also

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used to give an image for the aggregates in their dried state.

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2. Experimental Section

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2.1 General Procedure and Materials

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All manipulations of air- and / or moisture-sensitive compounds were carried out

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under a dry argon atmosphere by using standard Schlenk techniques or under a dry

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argon atmosphere in glovebox unless otherwise noted. The Pd-α-diimine catalyst

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[(Ar-N=C(Me)-C(Me)=N-Ar)-Pd(II)(Me) (N≡CMe)]+ BAF- [Ar=2,6-(iPr)2C6H3] (1)

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was prepared according to the literature [1, 28, 29]. Dichloromethane was refluxed over

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CaH2 and distilled before use. Toluene was refluxed over potassium with benzophenone

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as indicator and distilled under argon atmosphere prior to use. N, N-dimethylformamide

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(DMF) and tert-butyl acrylate (tBuA) were obtained from Aladdin and distilled under

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vacuum before use. CuCl (97%, Aladdin) and CuBr (99%, Aldrich) were purified by

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ACCEPTED MANUSCRIPT washing with acetic acid, ethanol, and diethyl ether in order. 4-vinylbenzyl chloride

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(VBC, 90%), N, N, N’, N”, N”-pentamethyldiethylenetriamine (PMDETA, 99%), NaN3

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(99%) and CF3COOH (99%) were obtained from Aldrich and used without further

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purification. Mono-alkynyl-terminated PEO (PEO2k-≡, Mn = 2.0 × 103 g mol-1) was

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synthesized according to the literature [30]. Other reagents if not specified were

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purchased from Sinopharm Chemical Reagent Co. Ltd and used as received.

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2.2 Synthesis of Mono VBC End-Capped Hyperbranched Polyethylene (HBPE-VBC)

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Two mono VBC end-capped hyperbranched polyethylenes (HBPE-VBC-1 and

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HBPE-VBC-2) were synthesized according to the method reported by Li and Ye [11].

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Typically, ethylene “living” polymerizations were carried out with 0.1 mmol

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Pd-α-diimine catalyst (1) at 15 °C under ethylene pressure of 1 atm. in 50 mL

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dichloromethane. After a prescribed period of polymerization time, VBC of 300 equiv

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to the catalyst was injected to allow end-capping of PE chains for 1 h. Volatile

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components were removed by a rotary evaporator to yield a yellow product. The

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product was redissolved in petroleum ether, filtered through a short plug containing

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neutral alumina and silica gel to remove catalyst residues, and precipitated by a large

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amount of methanol for three times. The final colorless oily product was dried overnight

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under vacuum at 50 °C.

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2.3 Synthesis of Azido-Terminated HBPE (HBPE-N3)

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To a Schlenk flask equipped with a magnetic stirring bar, HBPE-VBC-1 (1.044g,

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5.60×10-5mol), NaN3 (0.036g, 5.60×10-4mol) and 30 mL DMF/toluene (2:3 v/v) 7

ACCEPTED MANUSCRIPT solution were introduced under N2. The reaction mixture was placed in an oil bath held

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at 80 °C. After stirring for 18 h, the polymer solution was diluted with 20 mL toluene,

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and washed with large amount of water. The organic layer was collected and dried over

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anhydrous MgSO4. The solvent was removed under vacuum, yielding a colorless oily

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product.

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2.4 Synthesis of HBPE-b-PEO

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HBPE-N3 (0.988g, 5.30×10-5mol), PEO2k-≡ (0.128g, 6.40×10-5mol, 1.2 equiv to

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azido group), CuBr (1.5 equiv to azido group) and 20 mL anhydrous toluene were

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added to a 50-mL Schlenk flask under N2. The mixture was degassed through three

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freeze-pump-thaw cycles and then left under N2. Degassed PMDETA (1.5 equiv to

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azido group) was then injected via gastight syringe. The mixture was stirred at 100 °C

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for 18 h in an oil bath. After reaction, the solvent was removed under vacuum. The

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resultant solid was dissolved in THF and precipitated into an excess of water / methanol

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(1:1 v/v) mixture to remove the copper catalyst and excess PEO. This dissolution /

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precipitation procedure was repeated until the polymer became colorless. The final

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product was dried overnight under vacuum at 50 °C, yielding a semitransparent viscous

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solid.

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2.5 Synthesis of HBPE-b-PtBuA

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The synthesis of HBPE-b-PtBuA was accomplished by the ATRP of tBuA with

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HBPE-VBC-2 as macroinitiator. A typical procedure [12] was started with the ratio of

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reagents [tBuA]0 / [HBPE-VBC-2]0 / [CuCl]0 / [PMDETA]0 = 1700 / 1 / 8 / 8.8. 8

ACCEPTED MANUSCRIPT HBPE-VBC-2 (5.78×10-5mol), PMDETA (5.09×10-4mol), tBuA (9.83×10-2mol), and

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toluene (15 mL) were placed in a 50-mL Schlenk flask under N2 and degassed through

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bubbling with dry N2 for 15min. CuCl (4.63×10-4mol) was then added to the mixture

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under N2. The mixture was degassed through three freeze-pump-thaw cycles and then

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stirred at 90 °C for 24 h in an oil bath. The raw product was obtained by precipitation

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using acidified methanol, washed with a large amount of methanol three times. The

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product was then dissolved in THF and passed through a neutral alumina column to

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remove the copper catalysts. The final viscous product was dried overnight under

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vacuum at 50 °C.

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2.6 Synthesis of HBPE-b-PAA

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HBPE-b-PtBuA (1.505g, 4.56×10-5mol) was dissolved in CH2Cl2 (20 mL) in a dry

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50 mL round-bottomed flask. CF3COOH (2.5 mL, 3.3×10-2mol, 10 equiv to tert-butyl)

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was added dropwise. The reaction mixture was allowed to stir for 1 day. The solvent

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and excess CF3COOH were removed by reduced pressure. The resultant solid was

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washed with acetone and purified by dialysis. The final product was dried overnight

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under vacuum at 50 °C, yielding a semitransparent viscous solid.

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2.7 Self-Assembly of HBPE-b-PEO and HBPE-b-PAA in Water

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The HBPE-b-PEO or HBPE-b-PAA was first dissolved in THF to form a molecular

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solution at a concentration of 5.0 mg mL−1 at room temperature. Subsequently, a certain

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amount of ultrapure water was slowly added dropwise into the THF solution. And then

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ACCEPTED MANUSCRIPT the resultant solution was transferred into a dialysis tube (MWCO = 3000) and dialyzed

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against ultrapure water to remove the THF at room temperature.

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2.8 Measurements

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H NMR spectra were performed on a Varian Unity INOVA 300 spectrometer at

room temperature. Molecular weight and molecular weight distribution (Mw / Mn) were

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determined by GPC against narrow molecular weight distribution polystyrene standards

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on Waters 2414 refractive index detector at 40 °C with THF as solvent.

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A commercial LLS spectrometer (Brookhaven BI-200SM) with a BI-9000AT digital

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correlator and a He-Ne laser at 532 nm was used. The samples were placed in an

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index-matching decalin bath with temperature control within ± 0.2 °C. Each solution

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was clarified by passing through a 0.45 µm nylon filter to remove dust. Both stock

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solutions were diluted to a proper concentration for the LLS measurement. The samples

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were equilibrated in the decalin bath at 25 °C for 30 min before data collection. In static

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LLS, the average radius of gyraton (Rg) and the averaged molar mass (Mw) of the

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aggregates were determined. In dynamic LLS, the Laplase inversion of each measured

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intensity time-correlated function in a dilute solution can result in a characteristic line

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width distribution G(Γ). For a purely diffusive relaxation, G(Γ) can be converted to a

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hydrodynamic radius (Rh) distribution by using the Stokes-Einstein equation.

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TEM observations were conducted at 25 °C using a JEM100CX instrument

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operating at an accelerating voltage of 100 kV. For sample preparation, 1 drop of the

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HBPE-b-PEO or HBPE-b-PAA aqueous solution used for the DLS measurement was

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ACCEPTED MANUSCRIPT deposited on a carbon-coated copper grid. Excess solution was swept away by touching

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the edge of the grid with a small piece of filter paper. For staining, a drop of 1.0 wt. %

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phosphotungstic acid was added to the sample on the grid. After 1 min, excess staining

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agent was swept away by filter paper, and the grid was dried under room temperature

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before measurement.

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AFM measurements were performed in the tapping mode under ambient conditions

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on SPA300HV Probe station (Japan). The samples were prepared by spin-coating the

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two solutions used for the DLS measurement on freshly cleaved mica and dried at

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ambient temperature for a week. Scan rate of 1.0 Hz was used.

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3. Results and Discussion

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3.1 Synthesis of HBPE-b-PEO and HBPE-b-PAA

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As shown in Scheme 1, HBPE-b-PEO was synthesized through three steps. Firstly,

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mono VBC end-capped hyperbranched polyethylenes (HBPE-VBC) was provided by

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employing VBC as an end-capping agent for quenching Pd-α-diimine catalyzed “living”

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polyethylene chains [11]. Figure 1a shows a typical 1H NMR spectrum of the resultant

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HBPE-VBC with Mn = 1.70 × 104 g mol-1, Mw / Mn = 1.02 as determined by GPC. Some

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characteristic signals (a-c) attributable to the incorporated VBC end-capping group can

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be clearly observed, which are consistent with the literature [11]. The obtained

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HBPE-VBC-1 was then converted to HBPE-N3 by the transformation of terminal

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chlorine into azido group via reaction with NaN3. The 1H NMR spectrum of HBPE-N3

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is shown in Fig. 1b, the signals of methylene group (c’) completely shift from 4.50 ppm

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ACCEPTED MANUSCRIPT to 4.30 ppm, indicating the quantitative end group transformation from chlorine to azido

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group. Click coupling reaction of HBPE-N3 with PEO2k-≡ was performed with CuBr /

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PMDETA as catalyst in toluene at 100 °C for 18 h. Note that an excess of PEO2k-≡ was

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used to ensure the complete consumption of HBPE-N3. The unreacted PEO2k-≡ and

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catalyst were removed by washing with a large amount of water and methanol. As

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shown in Fig. 2, the GPC profile of the resultant HBPE-b-PEO reveals monomodal and

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quite symmetric peak (Mw / Mn = 1.03) and Mn = 2.04 × 104 g mol-1 more than that of

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the HBPE-VBC-1 precursor. Furthermore, the characteristic signals from the

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corresponding protons of both building blocks are found in the 1H NMR spectrum for

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HBPE-b-PEO as shown in Fig. 1c. The characteristic resonance peaks of the triazole

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ring appear at 7.50 ppm (f) and the characteristic signal of −CH2CH2O− in PEO block at

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3.65 ppm (h). These results further support the successful preparation of the

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well-defined HBPE-b-PEO diblock copolymer by the combination of CWP and click

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chemistry.

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Scheme 1 Synthetic route for the preparation of HBPE-b-PEO and HBPE-b-PAA block

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copolymers.

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Fig. 1 1H NMR spectra of HBPE-VBC-1 (a), HBPE-N3 (b) and HBPE-b-PEO (c).

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Fig. 2 GPC traces of HBPE-VBC-1 and HBPE-b-PEO.

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HBPE-b-PtBuA was prepared via ATRP using CuCl / PMDETA as catalyst and

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HBPE-VBC as macroinitiator in toluene at 90 °C for 24 h [11, 12]. The typical GPC

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traces of both macroinitiators and corresponding block copolymers were shown in

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Figure 3, revealing a monomodal and quite symmetric elution peak with a narrow

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molecular weight distribution (Mw / Mn < 1.10). Compared to the HBPE-VBC

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ACCEPTED MANUSCRIPT macroinitiator, the elution peak of HBPE-b-PtBuA clearly shifts toward higher

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molecular weight of 3.30 × 104 g mol-1, indicating an effective ATRP reaction. The

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resultant HBPE-b-PtBuA was then hydrolyzed to HBPE-b-PAA. As shown in Fig. 4, the

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characteristic signals of the tert-butyl group at 1.4-1.5 ppm (Figure 4b) completely

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disappear, indicating 100 % hydrolysis of PtBuA blocks.

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Fig. 3 GPC traces of HBPE-VBC-2 and HBPE-b-PtBuA.

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Fig. 4 1H NMR spectra of (a) HBPE-b-PtBuA and (b) HBPE-b-PAA (CDCl3 as solvent).

3.2 Self-Assembly of HBPE-b-PEO and HBPE-b-PAA in Aqueous Solution

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ACCEPTED MANUSCRIPT The aggregates of HBPE-b-PEO and HBPE-b-PAA in aqueous solution were

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prepared by solvent diffusion method with THF as a co-solvent [31]. After the THF was

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removed completely by dialysis against ultrapure water, the aqueous dispersion of the

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resultant diblock copolymers appeared as a bluish, translucent and stable micellar

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solution. Information about the Rh and size distribution of the micelles in aqueous

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solution detected at 25 °C was provided by dynamic LLS at C = 0.1 mg mL−1. As shown

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in Fig. 5, the Rh distribution demonstrates an aggregation of polymer chains in aqueous

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solution because the average Rh () of 52.0 nm for HBPE-b-PEO and 66.5 nm for

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HBPE-b-PAA are much larger than that of individual chains. Furthermore, the Mw and

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of the micelles were provided by static LLS based on the angular and

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concentration dependence of the average excess scattering intensity in the concentration

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ranges from 2.6 to 47.0 mg L-1 for HBPE-b-PEO and 4.6 to 69.0 mg L-1 for

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HBPE-b-PAA. Figure 6 shows the Zimm-plots of HBPE-b-PEO and HBPE-b-PAA in

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aqueous solution. On the basis of eq (1), the Mw and of the micelles could be

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calculated to be 6.28×107 g mol-1 and 55.0 nm for HBPE-b-PEO, and 4.17×107 g mol-1

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and 68.8 nm for HBPE-b-PAA from the intercept of [KC/Rvv(q)]q→0, C→0.

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KC 1 1 ≈ (1 + 〈 Rg 2 〉 q 2 ) + 2 A2C Rvv(q ) Mw 3

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(1)

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Where K = 4π2n2(dn/dC)2/(NAλ04) and q = (4πn/λ0) sin(θ/2) with NA, dn/dC, n, λ0 and θ

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being Avogadro’s number, the specific refractive index increment, the solvent refractive

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index, the wavelength of the light in vacuo, and the scattering angle, respectively. A2 is

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ACCEPTED MANUSCRIPT the second virial coefficient. The Rg / Rh ratios are calculated to be 1.06 and 1.03 for the

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HBPE-b-PEO and HBPE-b-PAA micelles respectively, indicating that more mass of the

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spherical micelles distributes closer to the surface, which suggests a vesicle structure

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[32-35]. The TEM observations of HBPE-b-PEO and HBPE-b-PAA micelles in the

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dried state (Fig. 7) also confirm the existence of vesicles. However, the diameters of ca.

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206 nm for HBPE-b-PEO and ca. 172 nm for HBPE-b-PAA by TEM were observed to

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be higher than those in solution by LLS measurements resulting from collapsing of the

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spherical vesicles on the grid.

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aqueous solution at 25 °C.

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Fig. 5 Rh distributions of the aggregates of HBPE-b-PEO (a) and HBPE-b-PAA (b) in

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Fig. 6 Zimm plots of HBPE-b-PEO (a) and HBPE-b-PAA (b) aggregates in aqueous

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solution at 25 °C.

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ACCEPTED MANUSCRIPT Figure 8 shows the AFM images for the self-assembled micelles of HBPE-b-PEO

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and HBPE-b-PAA in aqueous solution. The samples were prepared by spin-coating the

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micellar solutions on mica substrate, and were imaged in tapping mode. On the basis of

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surface analysis constructed from the AFM images, the diameters and heights of the

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nanoparticles in the dried state were measured to be 200.0 nm and 7.0 nm for

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HBPE-b-PEO, and 170.0 nm and 9.0 nm for HBPE-b-PAA, respectively. The very low

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ratios of height to diameter suggest that the vesicles become collapsed on the substrate

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surface during drying. A possible illustration of the self-assembly of HBPE-b-PEO or

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HBPE-b-PAA in aqueous solution and the morphology transition of their

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self-assembled vesicles on mica surface is shown in Fig. 9. The amphiphilic

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HBPE-b-PEO or HBPE-b-PAA was first dissolved in THF to form a molecular solution.

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Then the self-assembly was occurred during the addition of water into the THF solution.

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The self-assembled vesicles were formed after the THF was removed by dialysis against

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water, as confirmed by LLS and TEM. In the hydrated state vesicles self-assembled in

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aqueous solution, the hydrophilic PEO or PAA blocks can only be able to locate in the

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exterior of the vesicle wall and the hydrophobic HBPE blocks locate in the interior of

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the vesicle wall [14]. Once these self-assembled vesicles are transferred from aqueous

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solution to mica surface and dried at 25 °C, they change into spherical corona ones as

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observed by AFM.

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Fig. 7 TEM images for the vesicle micelles of HBPE-b-PEO (a) and HBPE-b-PAA (b)

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at 25 °C.

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at 25 °C.

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Fig. 8 AFM images for the vesicle micelles of HBPE-b-PEO (a) and HBPE-b-PAA (b)

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Fig. 9 Schematic illustration of the self-assembly of HBPE-b-PEO or HBPE-b-PAA in

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water and the morphology transition of their self-assembled vesicles on mica surface at

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25 °C.

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4. Conclusions In summary, two amphiphilic diblock copolymers consisting of a hydrophobic

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HBPE block and a hydrophilic PEO or PAA block with lower molecular weight than

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HBPE, HBPE-b-PEO and HBPE-b-PAA, have been successfully synthesized by the

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combination of ethylene “chain walking” polymerization and click chemistry or ATRP.

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The HBPE-b-PEO and HBPE-b-PAA can self-assemble into spherical vesicles as

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demonstrated by LLS and TEM. Moreover, spherical corona micelles are observed by

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AFM when they are transferred from aqueous solution to mica surface as a result of

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collapse of vesicles during drying.

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Acknowledgements

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This work was supported by the National Natural Science Foundation of China

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(21174167), the NSF of Guangdong Province (S2013030013474) and the Guangdong

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Province Higher School Science and Technology Innovation Key Project.

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Highlights

Two well-defined linear-hyperbranched diblock copolymers were synthesized.




The diblock copolymers consist of a long HBPE block and a short water-soluble block.




They have been found to self-assemble into vesicles in aqueous solution.




A clear structural characterization was provided for the hydrated state vesicles.




The vesicles showed a morphology transition when they became dried on mica surface.

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