Synthesis of telechelic perfluorocarbon functionalized polystyrene and polybutylmethacrylate and characterization of their blends

Polymer 69 (2015) 58e65

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Synthesis of telechelic perfluorocarbon functionalized polystyrene and polybutylmethacrylate and characterization of their blends Victoria A. Piunova, Thieo E. Hogen-Esch* Loker Hydrocarbon Research Institute and Department of Chemistry, University of Southern California, Los Angeles, CA 90089-1661, USA

a r t i c l e i n f o

a b s t r a c t

Article history: Received 14 February 2015 Received in revised form 26 May 2015 Accepted 27 May 2015 Available online 29 May 2015

Telechelic (T) and end-functionalized (E) perfluorocarbon (RF ¼ C7F15 and C13F27) polystyrene with molecular weights (MWs) of about 15 k and 30 k and the corresponding isobaric polybutylmethacrylate (PS/PBMA) were synthesized by a combination of ATRP and Cu (I) catalyzed click-coupling reactions. Blends (1/1 w/w) of the E and T-type PS and PBMA having nearly identical MWs of 15 and 30 kDa and RF contents were compared using TEM, AFM, DSC and optical transmittance. The TEMs and AFMs of the isobaric E and T-type blends showed large increases in compatibility of the T-polymer blends as indicated by its much smaller domain sizes. For instance, at MW of about 30 k the blend of T-type C7F15 functionalized PS and PBMA showed well-defined TEM domains whereas the blend of the C13F27 endfunctionalized polymers only showed ill-defined m-sized domains. © 2015 Elsevier Ltd. All rights reserved.

Keywords: Polystyrene-poly(n-butylmethacrylate) blends Fluorocarbon end groups Self-assembly

1. Introduction The introduction of perfluorocarbon groups as pendent or end groups in vinyl polymers has been of interest for some time as its presence has given rise to robust effects in aqueous [1e9] and non aqueous [10e12] solutions and in the solid state both at the polymer surface [13e17] and in the bulk [18e21]. The effects of Rf end-groups have been investigated recently. For instance, the blends of polystyrene (PS) and poly(nbutylmethacrylate) (PBMA) with molecular weights (MWs) ranging between 7 k and 25 k and end-functionalized with perfluorocarbon groups (RF) (C4F9 e C13F27) exhibit greatly increased miscibilities at very low RF contents (<5 wt%) [22,23]. In this case pronounced “fluorophilic” intermolecular interactions, due in part to the exceptionally low cohesive energy densities of perfluorocarbons [24], are especially effective in mediating lower PSPBMA interfacial energies compared with the corresponding RF pendent groups [25]. Furthermore, the interactions can be tuned by changing RF lengths and hence fluorophilic association strengths [22]. Differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) indicate that most blends, within prescribed limits of polymer MW and RF lengths, retain properties of the PS and PBMA components. The bulk phase typically consists of sub-

* Corresponding author. http://dx.doi.org/10.1016/j.polymer.2015.05.044 0032-3861/© 2015 Elsevier Ltd. All rights reserved.

micron lamellar type structures but without any long range (>1 m) order typical of the PS-b-PBMA block copolymers. The degree of compatibility of these blends is determined largely by RF mass content. Thus, submicron (10e200 nm) domains in the bulk or at the surface are seen by TEM and AFM respectively with two glass transition temperatures being observed. For the blends with large RF contents (>3 wt%) very small (<10 nm) domains and single Tg's are typically observed [22]. However, blends of telechelic RF functionalized polymers functionalized with associating groups may demonstrate a different phase behavior than the blends of the corresponding end-functionalized counterparts with the same RF content. Here, we report on the synthesis and characterization of 1/1 (w/ w) blends telechelic C7F15 functionalized PS and PBMA (RF-PS and RF-PBMA) and compare these with the blends of the corresponding C13F27 end functionalized polymers with approximately the same RF contents. Thus, in this case, blend compatibilities, as reflected in the sizes of their micro domains, may be expected to increase. For instance, studies of analogous A/B blends of polymers with specific associating groups (hydrogen bonding, ionic-donor acceptor interactions) indicate that compatibilities in blends of telechelic polymers tend to increase compared with that of the endfunctionalized polymer blends with the same mole or weight fractions of the associating groups [26e28]. However, some studies have demonstrated diminished compatibility in telechelic polymer blends compared to the corresponding end-functionalized analogs [29]. As demonstrated by Elliott and Fredrickson [30] both cases are

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possible, the outcome being determined by a number of factors including the type of association (complementary or noncomplementary), inter-or intramolecular association strength between the functional end groups, the value of binary interaction parameter c, the MW and its distribution. Blends of such telechelic polymers chains may link into a variety of supramolecular aggregates. Provided that the association between the end groups is strong and value of c is low, the formation of quasi block-copolymers is possible hence improving compatibility and hence decreasing phase separation by lowering interfacial tension [31,32]. However, for the case of weak association between identical end groups, the formation of aggregates between identical chains (AeA or BeB) is thermodynamically preferable leading to increased phase separation. Here we report the synthesis and blend formation of C7F15 endfunctionalized telechelic polystyrene (F7T-PS)/poly n-butylmethacrylate (F7T-PBMA) and compare these with the blends of C13F27 end-functionalized polymers having nearly the same RF content. We show that, besides the RF content, the telechelic character of the RF- PS and RF- PBMA blends shows qualitatively better compatibilities as shown by much smaller domains especially at higher MW (30 k). The synthesis of telechelic polymers bearing identical functionalities at their both extremities is typically accomplished by means of anionic polymerization [13]. Thus, a desirable functional group may be introduced by reacting living polymer dianion with a suitable electrophile [33,34]. However, anionic polymerizations tend to be experimentally demanding and less versatile than “living” radical, i.e. Atom Transfer Radical Polymerization (ATRP), where halogen chain-end functionality can be modified further via nucleophilic substitution or radical coupling to yield telechelic polymers [35e37]. 2. Experimental section 2.1. Materials All chemicals were purchased from Aldrich and used as received unless otherwise noted. Copper (I) Bromide (99.999%) was purified by stirring in acetic acid. After filtration, it was washed with 2propanol and then dried in vacuum. Styrene (S) and n-butyl methacrylate (BMA) were freshly distilled after being stirred over CaH2 overnight. Fluorinated alcohols for the synthesis of initiators were purchased from SynQuest Labs, Inc. Silica wafers for AFM studies (University Wafer, P/100 Prime Grade) were rinsed successively with deionized water, acetone and blow dried before sample deposition. 2.2. Synthesis of RF end-functionalized PS and PBMA The synthesis of 1H,1H-perfluorooctyl-2-bromoisobutyrate (PFOBIB) and 1H,1H-perfluorotetradecyl-2-bromoisobutyrate (PFTDBIB) ATRP initiators was carried out according to published procedures [38,39]. The telechelic C7F15-PS and C7F15-PBMA precursors and the C13F27-PS and C13F27-PBMA were prepared by atom transfer polymerization (ATRP) using [Initiator]:[CuBr]:[Ligand] ratios of 1:1:2. In a typical example, a 25 mL Schlenk flask was charged with 52.2 mg (0.364 mmol) CuBr degassed and refilled with argon three times. Varying amounts of distilled monomer and 0.184 ml (0.728 mmol) of N,N,N0 ,N00 ,N00 -pentamethyldiethylenetriamine (PMDETA) ligand were added to the flask. The system was then degassed and refilled with argon three times. The flask was immersed in an oil bath at 90  C and the polymerization was initiated by the injection of 200 (or 309) mg (0.364 mmol) of the

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initiator. The polymerization progress was monitored by taking aliquots of reaction mixture every 30 min followed by SEC analysis. To ensure the quantitative presence of bromine at the chain ends (PSeBr or PBMA-Br) the polymerizations were stopped at about 50% of monomer conversion by exposing the reaction mixture to air. To remove residual copper catalyst the reaction mixture was diluted with THF sufficient to afford freely flowing solution and passed through an activated neutral aluminum oxide plug. The polymer was then precipitated in a large excess of aqueous (30 vol. % H2O) methanol, characterized by SEC and dried in vacuum at 25BC to a constant mass. 2.3. Preparation of a-azido-u-1,1-dihydroperfluorooctyl-endfunctionalized PS (APSRF) and a-azido-u-1,1-dihydroperfluorooctyl PBMA (APBRF) These were synthesized using published procedure [40]. In a typical experiment the bromine end-functionalized polystyrene (PSeBr, 7500 g/mol, 1 g, 0.13 mmol), sodium azide (130 mg, 2 mmol) and degassed dimethylformamide (DMF, 5 ml) were stirred at room temperature for 24 h under argon. The polymer was purified by filtration through a glass filter followed by precipitation in 20 ml of water. The resulting polymer was dried under vacuum at 25  C for 24 h. The same procedure was applied toward the synthesis of azide end-functionalized PBMA. 2.4. Synthesis of telechelic C7F15 -functionalized polymers The synthesis of telechelic polymers was carried out according to earlier published procedure [41,42]. Thus, [(500 mg, 0.066 mmol), copper bromide (10 mg, 0.066 mmol) and N,N,N0 ,N00 ,N00 -pentamethyldiethylenetriamine PMDETA (28 mL, 0.132 mmol) were added into a Schlenk flask capped with a septum. Degassed dry toluene (3 ml) was added to the flask via syringe and three freezeepumpethaw cycles were performed. Propargylic ether (0.033 mmol; 3.4 mL) was added to the reaction mixture via a micro syringe. The reaction, carried out at room temperature, was monitored by periodic withdrawal and GPC analysis of aliquots (Fig. 2). Upon completion, (10e14 days) the reaction mixture was exposed to air, diluted with 3 ml of THF and filtered through a short silica column to remove copper salts. The filtrate was concentrated by rotary evaporation to ~2 ml and the polymer was precipitated quantitatively by addition of the polymer solution to 20 ml of aqueous (30 vol.% H2O) methanol. The resulting polymer was separated from the uncoupled polymer by fractionation. Thus, 200 ml aliquots of methanol were added incrementally to 50 ml of crude RF-PS-RF solutions (5 mg/ml) in toluene leading to sequential polymer precipitates that were filtered and analyzed by SEC. The same procedures were used in the synthesis of a, u e bis(1,10 dihydroperfluorooctyl) PBMA. It was reported that Cu(II) salts combined with reducing agents (for example sodium ascorbate or hydrazine) also catalyze coupling reaction in aqueous media [43]. This system was also used for the above coupling reactions. To improve polymer solubilities, reactions were performed in THF/H2O (70/30 vv%) in the presence of CuSO4. However, no traces of coupled product were detected after several days (data not shown). 2.5. Sample preparation for AFM, TEM, DSC and optical studies. AFM studies RF-PS/RF-PBMA 1/1(wt/wt) blends with matching MW and perfluorocarbon content were prepared by spin coating 50 ml of a 2 g/L filtered polymer blend solution in toluene onto cleaned silica

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wafers (0.5  0.5 inch.) at 4500 rpm for 60 s followed by annealing at 120  C at ~106 Torr for 24 h. Four polymer blends with 1/1 (wt/ wt) were prepared: F7-15 kT, F13-15 kE, F7-30 kT, F13-30 kE. TEM samples of less than 100e120 nm in thickness were obtained by ultra-microtomy of a bulk blend solid sample sandwiched between two blocks of cured epoxy resin. Samples for optical transmittance (OT) experiments were prepared by drop casting of a 100 ml ((2 g/ L 1/1 w/w) toluene polymer blend solutions onto a cleaned cover glass. The thickness (~2 mm) of the resulting films was assumed to be that of the films cast onto silica wafers using identical methods and measured by ellipsometry. DSC samples were prepared by evaporation of 1 ml of 1/1 (w/w) 5 wt% polymer blend solutions in toluene followed by vacuum drying at room temperature for 24 h. The dried samples were weighted, (about 4e6 mg) transferred to aluminum pans, covered with lids and crimped. Glass transition temperature was measured in the second heating ramp at 10  C per minute. 2.6. Instrumentation SEC measurements were carried out using a Shimadzu Prominence LC-20AT solvent delivery unit equipped with a guard column and PLgel 5 mm MIXED-C column (Polymer Laboratories), a Shimadzu refractive index detector RID-10A, a Wyatt light scattering detector Dawn DSP and a Waters 484 UV detector. Calibration was based on PS standards (Scientific Polymer Products). A Varian 400 MHz Mercury NMR spectrometer was used for 1H and 19F NMR analysis. AFM images were recorded on a Nanoscope III microscope using tapping mode with Si tips (Tap300, Budget Sensor, 300 kHz, 40 N/m). TEM images were obtained with FEI Tecnai G2 microscope (200 kV). UVeVis measurements were carried out on a Cary 14 UVeVis spectrophotometer. DSC measurements were carried out with a Shimazu DSC 7 calorimeter at a heating rate 10  C/min. Samples were first subjected to heating to 150  C, and then cooled down to 40  C at the maximum cooling rate. The Tg was measured in the second heating ramp. 3. Results and discussion 3.1. Synthesis Perfluorocarbon end-functionalized PS (RF-PS) and RF-PBMA were prepared by Cu(I)Br catalyzed ATRP using perfluorocarbon functionalized initiators to yield bromine end functionalized PS and PBMA (Scheme 1) [22,23].

In order to ensure the highest possible bromine endfunctionalization and to avoid chain transfer to solvent, polymerizations were carried out under solvent free conditions and were stopped at monomer conversions between 50 and 70% [40,44]. The 1 H NMR spectrum of the isolated Br end -functionalized polystyrene (PSeBr) clearly shows the terminal methine resonance at 4.5 ppm and indicating the absence of vinyl protons generated by disproportionation side reactions, consistent with a quantitative bromine end-group functionalization. (Fig. 1) Bromine end-functionalized PS and PBMA were converted subsequently into the corresponding azides by reaction with excess of NaN3 in DMF/THF (2/1) at room temperature for 24 h (Scheme 1). The quantitative formation of azide-terminated polystyrene (RF-PSN3) was confirmed by 1H NMR, which showed a complete disappearance of the methine resonance at 4.5 ppm and did not indicate a competing elimination as no vinyl protons were seen (Fig. 1B). The presence of the azide functionality in the PBMA was confirmed by FT-IR spectrometry that showed a weak absorption at 2101 cm1 is in agreement with literature data [45]. The SEC data indicated that all samples with the exception of sample F13-PBMA-30 k had a narrow PDI (<1.20, Table 1) consistent with well-controlled polymerizations. After azide functionalization polymer “click coupling” with bispropargyl ether was carried out in DMF under argon at room temperature in the presence of Cu(I)Br/PMDETA (Scheme 1, Tables 1 and 2). Conversions were determined by comparing the areas of the SEC peaks of coupled product and corresponding precursor (Fig. 2). SEC based conversions of ~68% for polystyrene and 60% for PBMA were achieved in 14 days (Table 2, runs 1 and 3). Hence it was necessary to separate the telechelic polymers from uncoupled polymers by SEC monitored fractionations as described in Experimental section. The replacement of DMF with toluene did not affect the reaction time and proved successful also (Table 2 # 4e6). Slightly higher conversions of PBMA were achieved in some cases (Table 2, # 4). The use of CuI instead of the more air-sensitive CuBr [46] shortened reaction times by several days and conversions of ~70% for functionalized PS and PBMA were achieved in 10 days. The long reaction times could be attributed to excluded volume effects. It is also possible that perfluorocarbon association may impede the coupling reactions but this is not clear at present [47,48]. As indicated above, the high degree of coupling in the subsequent steps (Table 2) retroactively confirmed high degrees of bromine/azide end functionalization for RF- PBMA.

Scheme 1. Synthesis of a-azido-u-perfluoroalkyl PS (PMMA) precursors and their coupling with bispropargyl ether to give telechelic bis (1,1 dihydroperfluorocarbon) functionalized PS and PBMA.

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Fig. 1. 1H NMR spectra of a-bromo- u-1,1-dihydroperfluorooctyl polystyrene (F7E-PS-7 k) (A) and a-azido- u 1,1-dihydroperfluorooctylpolystyrene.

Fig. 2. SEC traces Representative GPC traces of click coupling reaction. Polymer: F7TPS- 15 k, Mn ¼ 13.6 kDa.

3.2.1. Blend properties RF-PS/RF-PBMA and blends of the corresponding telechelic RF polymers of roughly the same MW were formed by dissolution in toluene followed by slow evaporation and annealing at 120  C for 24 h. Optical transmission of polymer blend films is a relatively convenient way to qualitatively evaluate the occurrence of polymer domains with sizes that are comparable to that of the optical wavelengths [49e51]. The optical transmission of blends of telechelic RF- functionalized PS/PBMA (F7T-15 K, F7T-30 K) were compared with blends of the end-functionalized polymers with about the same overall RF content (Fig. 3). Although thin films of F7T-15 K as well as the F13E15 K were nearly completely transparent above about 350 nm, the corresponding F13E-30 K and F7T-30 K blends gave translucent films (70 and 80% transmission respectively above 400 nm) with the telechelic polymer blend being clearly more transparent above 400 nm (Fig. 3). It is interesting that in this case there is virtually no dependence on wavelength, indicating some residual refractive index variations over large domain sizes.

3.2. Blends of telechelic polymers Following synthesis of the telechelic polymers the blends of PSPBMA blends were formed as indicated in the Experimental Section. Precursor sample numbers following F represent the number of perfluorinated carbons on the RF groups. The letter “T” designates telechelic polymers followed by a number giving the MW in thousands. Blends are designated accordingly. For example, F7T30 K represents a 1/1 (wt/wt) blend containing C7F15 functionalized telechelic PS and PBMA with a MW of about 30,000 whereas the F13-30 k blend has a MW of about 30,000 and a single C13F27 end group (Table 2).

3.2.2. AFM and TEM studies Thin films of the F7T-15 K and the F13e15 K blends give relatively smooth AFM surfaces with calculated root mean square roughness (RMSR) of 0.53 and 0.60 nm respectively (Fig. 4). Much greater differences are seen for the end efunctionalized and telechelic blends with the same MW and composition. Thus, the F7T-30 K films are relatively “smooth” in part but show “boomerang shaped ” depressions (lengths of ~500 nm) and root mean square roughness (RMSR) and mean grain areas (MGA) of 1.5 nm and about 6000 nm [2] respectively. Clearly, the F13E-30 K polymer blend is very different and shows phase-separated, and large (4e10 mm) ellipsoidal macrophase sized depressions with

Table 1 SEC characterization of RF-End-Functionalized PS and PBMA. Polymera

Mna (x103)

PDIa

RF wt.%

Polymer

Mna (x103)

PDIa

RF wt.%

F7-PS-7K F7-PS-15K

7.2 13.1 11.5 13.1 29.8

1.11 1.13 1.12 1.05 1.1

4.6 2.7 2.9 4.9 2.0

F7-PBMAe7K F7-PBMA-15K

7.4 15.4

1.19 1.18

4.2 2.0

F13-PBMA-15Kb F13-PBMA-30Kb

13.5 32.4

1.12 1.32

4.4 2.2

F13-PS-15Kb F13-PS-30Kb a b

SEC data based on PS standards. From Ref. [22].

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Table 2 Coupling of PS- and PBMA-azides with bis-propargyl ether. F7-azide precursors

Telechelic F7-T polymers Mn (x103)

Run/polymer 1. 2. 3. 4. 5. 6. a b c d e f

a

F7-PS-N3 F7-PS-N3a F7-PS-N3b,c F7-PBMA-N3a F7-PBMA-N3b F7-PBMA-N3b,c

7.2 13.1 11.5 7.4 15.4 15.4

PDIa 1.10 1.13 1.12 1.18 1.20 1.20

Conv. % 68 70 71 60 77 73

Rxne (days) 14 14 10 14 14 10

Mn (x103) d

13.6 28.9d 22.0 15.3d 30.4d 29.1

PDI

RF (wt.%)f

1.06 1.04 1.05 1.10 1.05 1.07

5.1 2.5 e 4.4 2.3 2.5

In the presence of PMDETA (0.1 eq), CuBr (0.1 eq) in DMF. Click reaction carried out in toluene. CuI (0.1 eq) instead of CuBr. F7-T polymers used in the TEM and AFM studies. Reaction time in days. Calculated based on weight average MW.

dispersed in a continuous matrix with RMSR and MGA values of value of 24 nm and about 20.103 nm2 respectively (Fig. 4, Table 3). Given the much larger surface energies of the PS component, the depression are likely associated with PS rich surface domains. Further and less ambiguous evidence is found for the corresponding TEM data (Fig. 5). Here the differences between the F13e15 K and F7T-15 K are noticeable with the blend of the telechelic polymers being finer grained than the F13e15 K sample with ~0.8e1.5 nm wide and variable length PBMA lamellae that are not readily identified as the structure as the morphology is expected to be bi-continuous. The widths of the dark grey F7T-15 K PS nano-domains are not as readily identifiable but the lamellar widths seem to be comparable. Interestingly clusters consisting of tiny (~1e2 nm) black dots appear to be located in the PS domains. It is conceivable that these dots correspond to RF rich PS domains or possibly clustered RF micelles. The TEMs of the F13e15 K blend with approximately the same blend RF content show a similar but more coarsely grained disordered bi-continuous lamellar morphology with lamellar widths in the order of 3e6 nm. The TEM images of F7T-30 k (Fig. 5), like F7T-15 K and F13E-15 K indicate the presence of disordered submicron but somewhat larger lighter and darker grey lamellae with widths of approximately 20e40 nm. The much smaller differences in grey tone

Fig. 3. Transmittance Spectra of F13E and F7 T blend films of about 2 mm thick-ness prepared by drop casting a toluene solution of polymer blends 50/50 (wt%) on cover glass.

suggest the presence of PS/PBMA partial mixing. Although the sizes of the nanosized objects appear small compared with optical wavelengths, the optical transmission of the F7T-15 K blend is only about 80e85% indicating that larger scale heterogeneities are present than suggested by the TEM image. However the rather well defined apparent sub micron TEM morphologies of the F7T-30 K blend breaks down for the F13e30 K blend that shows irregularly shaped diffuse and much larger (1-1.5 m) dark grey (PS rich) domains dispersed in similarly sized lighter PBMA rich domains (Fig. 5). The low contrast of this TEM indicates more polymer mixing than in F13-30 k consistent with the DSC studies (below). Overall the AFM and TEM results are generally in reasonable agreement although the details of the AFM data remain to be elucidated. Thus the macro-phase separated bulk morphology of F13E-30 K was consistent with a very rough AFM surface topography. Similarly, samples showing TEMs with small domains generally gave smooth AFM surfaces. Furthermore the blends of the telechelic polymers at the roughly same RF content are finer grained both with respect to AFM and TEM, indicating a clear effect of RF topology rather than RF content.

3.3. DSC measurements The blends of F7T-15 k and F13E-15 k gave single broad transitions at: 331.7 K and 326.2 K respectively, consistent with the presence of nm sized domains as also supported by the TEM and OT data. It is interesting that the Tg values of the F7-T-15 blend are 5 K higher than the end functionalized F13e15 K blend particularly as the MWs of the 1/1 PS/PBMA blend are nearly identical for the PS (13.6 k and 13.1 k) and similar for the PBMA components (15.3 k and 13.5 k) respectively (Table 4). The miscibility in F13-15 k and F7T-15 k is driven in large part by the relatively large RF content (~5%), which complicates the evaluation of the role of the RF end groups. However we have recently determined that MW PS homopolymers (10e30 k) (not blends) appended with C13F27 end groups showed consistent decreases in Tg (~10e12 K) of the end functionalized PS relative to the isobaric PS homopolymer. These decreases were found to be much smaller for the corresponding C7F15 and C10F21end functionalized polymers [52]. Given the high degree of disorder in the blend with poorly defined phases the C13F27 end-group related effects are likely present in the blends as well and this would account for this seemingly anomalous effect. In contrast, the F7T-30 k blend showed two Tg's (297.2 K and 368.9 K). The first transition has a value that is four degrees higher to than of the PBMA homopolymer (293 K) while the second transition corresponding to the PS component is nearly 4 lower than the corresponding PS of the same MW indicating about equal

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Fig. 4. AFM topography of perfluorocarbon end-functionalized and telechelic polymer blends. For sample composition see Table 3 and text. Table 3 Morphology statistical coefficients for RF end-functionalized and telechelic polymer blends.

F13-15Kc F7T-15K a b c d

RMSR (nm)a

MGAb (x103 nm2)

RFd (wt.%)

PS-PBMA blend

RMSR (nm)a

MGAb (x103 nm2)

RFd (wt.%)

0.60 0.53

e e

5.0 4.7

F13-30Kc F7T-30K

24.4 1.5

19.6 6.3

2.1 2.4

Root mean square roughness. Mean grain area, the mean area of the spheres that have the same surface area as a given particle. From Ref. [22]. Calculated based on weight average MW.

Fig. 5. TEM image of morphology of F7-T and F13-E blends. For sample composition see text.

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Table 4 Glass Transition Temperatures of F7-T and F13-E polymer blends.a Blend

Tg (K)

DTg (K)b

Blendc

Tg (K)c

DTg (K)b,c

F7-T-15k F7-T-30k

332 297, 369

e 4, 4

F13-E15k F13-E30k

326 301, 366

e 8, 7

a b c

Sample composition see Table 3. Differences with the Tg of unmodified PBMA and PS respectively (see text). Data from Ref. [22].

domains of the T-30 k blend while the 30k-E blend shows a completely different morphology with ill defined micron sized domains. The AFMs of the 30k-E-blend showed similar large changes with 3e8 m sized domains while the 30 k-T blend showed domains in the 50e500 nm scale. at the seen for the 30 k-E type blend that were also more pronounced for the 30 k blends. These results are consistent with the optical transmissions and DSC data. References

mutual blending of the PBMA and PS domains. Larger increase (8 K) and decreases (7 K) in Tg for the PBMA and PS respectively are observed for the F13-30 k blend indicating more extensive blending consistent with the TEM data [22]. The large differences seen for both the TEM/AFM and DSC data for the F7-T-30 k and F13-30 k blends having nearly the same RF content (Table 1) indicate that chain topology also plays a role in mediating blend formation. This is also, illustrated by the smaller TEM domains of the blends of the telechelic compared with that of the end-functionalized polymers for both MW ranges. Our observations are in agreement with a theoretical model proposed by Elliott et al. [30] Thus, the improved compatibility in blends of the RF telechelic polymers is consistent with the presence of perfluorocarbon groups at the PS-PBMA interfaces and thus lower interfacial tension (Scheme 2). Clearly, at about the same RF content, blending of the telechelic polymers occurs more readily. A possible rationale is illustrated schematically in Scheme 2, where the formation of both types of blends is compared. Although the Scheme is oversimplified being two-dimensional, blends of the telechelic type polymers given the postulated stacking of RF groups, would be expected to have the advantage of being less susceptible to excluded volume interactions. 4. Conclusions Narrow MW distribution perfluorocarbon end-functionalized polystyrene of the (E) (C13F27) and telechelic (T) (C7F15) with molecular weights (MWs) of about 15 k and 30 k and the corresponding isobaric polybutylmethacrylate were synthesized by a combination of ATRP and Cu (I) catalyzed click-coupling reactions. Blends of the E and T-type PS/PBMA (1/1 w/w) with nearly identical MWs of 15 and 30 kDa and RF contents were compared using TEM, AFM, DSC and optical transmittance. The 15 k blends with the same RF contents were both homogeneous as indicated by DSC data and the similar TEM and AFM morphologies but somewhat smaller sized lamellar TEM domains for the T-type blends. Much larger differences are seen for the 30 k-T and eE blends, as indicated by the relatively well defined but disordered 50e100 nm

Scheme 2. Proposed association of end-functionalized and telechelic polymer chains in corresponding polymer blends.

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