ORIGINAL PAPER

Synthesis and properties of cross-linkable block copolymerend-capped with 2, 2, 3, 4, 4, 4-hexafluorobutyl methacrylate

Yue Sun & Weiqu Liu

Received: 2 June 2011 /Accepted: 29 September 2011 /Published online: 16 December 2011# Springer Science+Business Media B.V. 2011

Abstract A series of novel cross-linkable copolymers 2,2, 3, 4, 4, 4-hexafluorobutyl methacrylate-poly (isobutylmethacrylate)-b-poly[3-(trimethoxysilyl)propyl methacrylate](HFMA-PIBMA-b-PTMSPMA) were synthesized via atomtransfer radical polymerization (ATRP). The synthesis andstructure of the polymers were characterized by gel perme-ation chromatography (GPC), Fourier transform infrartd(FTIR) and 1H nuclear magnetic resonance (NMR).The properties of HFMA-PIBMA-b-PTMSPMA and thecorresponding copolymers end-capped with nonfluorinatedacrylate were comparatively studied by contact angle,transmission electron micrograph (TEM), and dynamiclight scattering (DLS) measurement. The results indicated thatthe surface properties and self-assembly behaviors ofHFMA-PIBMA-b-PTMSPMA were changed greatly bythe introducing of only one fluorinated acrylate. Finally,the transparent solid materials with a slightly blue colorwere obtained based on the cross-linked behaviors of HFMA-PIBMA-b-PTMSPMA and fracture surfaces of the materialswere exhibited by scanning electron microscopy (SEM).

Keywords Cross-linkable copolymers . ATRP. Surfaceproperties . Self-assembly behaviors

Introduction

Block copolymers have unique microphase separation,which make them have broad application including disper-sants, compatibilizers, surfactants, emulsifiers, foam stabil-izers and templates for functional materials [1-5]. Besidesthe common properties of block copolymers, cross-linkableblock copolymers presented more advantages. As examples,the flexibility or stability can be improved by introducingthem into materials. Consequently, they have received manyconsiderations for their potential applications on abrasive-resistant coatings, adhesives, contact lens materials, chemi-cal/biomedical sensors, drug delivery system, etc. [6-9].

Many reactive and functional monomers can be used forcross-linkable copolymers. Such as 3-(trimethoxysilyl) propylmethacrylate (TMSPMA) [10], 4-methyl-[7-(methacryloyl)oxyethyloxy] coumarin (CMA) [11], glycidyl methacrylate(GMA) [12] and 4-vinyl pyridine [13] et al. Among them,TMSPMA has a reactive -Si(OCH3)3 group which canhydrolyze into -Si(OH)3 and turn into the cross-linkedpolysilsesquioxane by polycondensation [10]. The cross-linking of copolymers contained TMSPMA will introduceinorganic silica network structures into the organic polymerchains, thus special materials may be produced [14].Furthermore, TMSPMA is generally low cost, low tox-icity and more likely to be employed in commercialapplications [15]. Especially, the “silica-based” cross-linking of TMSPMA can be resulted from an acid- orbase-catalyzed process, which is easy to perform andthe purification is straightforward [16]. Many cross-linkable block copolymers containing TMSPMA havebeen prepared. For example, Zhou et al. synthesized brush-type amphiphilic copolymer of poly (stearyl methacrylate)-b-poly [3-(trimethoxysilyl) propyl methacrylate] (PSMA-b-PTMSPMA) [14]. Yu et al. synthesized the block copolymer

Y. Sun :W. Liu (*)Guangzhou Institute of Chemistry, Chinese Academy of Sciences,Guangzhou 510650, Chinae-mail: liuwq@gic.ac.cn

Y. SunSchool of Chemistry and Chemical Engineering, Liaoning NormalUniversity,Dalian 116029, China

Y. SunGraduate School of Chinese Academy of Sciences,Beijing 100049, China

J Polym Res (2012) 19:9768DOI 10.1007/s10965-011-9768-2

of ferrocene-poly (styrene)-b-poly [3-(trimethyoxysilyl)propyl methacrylate] (Fc-PS-b-PTMSPMA) and preparedthe organic/inorganic hybrid nanoparticles from self-assemblyaggregates of the copolymer [17]. Du et al. presented anorganic/inorganic hybrid vesicles based on poly(ethyleneoxide)-b-poly[3-(trimethoxysilyl) propyl methacrylate] (PEO-b-PTMSPMA) [18]. In short, TMSPMA has been one of themost widely monomers used for cross-linkable copolymers.

Fluorinated polymers are very interesting due to a numberof unique properties that include hydrophobicity and lowsurface energy, as well as high chemical and thermal resis-tance [19]. They have been broadly applied to high-performance paint and varnish in the textile, paper, leather,construction, automotive and aerospace industries, optics andmicroelectronics [20, 21]. 2, 2, 3, 4, 4, 4-Hexafluorobutylmethacrylate (HFMA) is one of fluorinated acrylate with highfluorine content. It has been widely used for the preparation ofvarious fluorinated copolymers. However, the studies aboutthe block copolymers containing HFMA and TMSPMA havebeen seldom reported.

Considering that the efficiency of fluorine could be max-imized by anchoring the fluorinated group at the end of themolecular chain [22], in this paper, the bromo-terminatedinitiator was prepared by the direct addition reaction ofHFMA with hydrobromic acid in acetic acid under mildconditions. Then the initiator (HFMA-Br) initiated the atomtransfer radical polymerization (ATRP) of isobutyl methac-rylate (IBMA) to synthesize the macroinitiator of HFMA-PIBMA-Br. Finally, a series of well-defined cross-linkablecopolymers end-capped with HFMA were synthesized viathe ATRP of TMSPMA. Gel permeation chromatography(GPC), Fourier transform infrartd (FTIR) and 1H nuclearmagnetic resonance (NMR) data obtained verified the syn-thesis and measured the structures of the polymers. In orderto demonstrate the effect of fluoroalkyl group on the prop-erties of HFMA-PIBMA-b-PTMSPMA the correspondingcopolymers end-capped with nonfluorinated acrylate wereprepared under the similar conditions. The properties of thetwo kinds of polymers were comparatively studied by con-tact angle, transmission electron microscopy (TEM) anddynamic light scattering (DLS) measurements. Finally, thecross-linked behaviors of HFMA-PIBMA-b-PTMSPMAwere studied by TEM and scanning electron microscopy(SEM).

Experimental

Materials

2, 2, 3, 4, 4, 4-Hexafluorobutyl methacrylate (HFMA) waspurchased from Xeogia Fluorine-Silicon Chemical Co. Ltd.(Harbin, China). 3-(Trimethoxysilyl)propyl methacrylate

(TMSPMA) was from WD Silicone Co., Ltd., China.Isobutyl methacrylate (IBMA) and butanone were obtainedfrom Kemiou Chemical Co. (Tianjin, China). Hydrobromicacid in acetic acid (44 wt.%) was supplied by King SuccessFine Chemical Co. Ltd. (Hubei, China). 2,2′-Bipyridine(Bpy), ethyl 2-bromoisobutyrate (EbiB, 98%) and copper(0) powder were from Alfa Aesar Chemical Co.. Copper(II)bromide was purchased from Zhenxin Chemical Co.(Shanghai, China).

All chemicals used were without further purification. Allsolvents were reagent grade.

Sample preparation

Preparation of HFMA-Br

HFMA (20.00 g) and hydrobromic acid in acetic acid(350 mL) were put into a 500-ml three-necked flask, whichwas fitted with a mechanical stirrer, a thermometer and anapparatus for dealing with tail gas (HBr). Then the reactionmixture was stirred at 0 °C for 12 h. The products wereextracted by NaHCO3 aqueous solution (saturation) anddichloromethane, until the pH of the oil liquid was 7.0.Residual solvent was removed by a rotary evaporator undervacuum. Because HFMA has strong electron-drawing sub-stitutes, the main products were those according to anti—Markovnikov’s rule. However, it was reported that the activ-ity of alkyl group for ATRP initiators followed the orderof 3°>2°>1° [23]. So the products according toMarkovnikov’srule were used as the ATRP initiators in this paper. Theisomers was separated by column chromatographic (ordinarycolumn; stationary phase: silica gel for column chromatogra-phy; mobile phase: petroleum ether) [24]. Finally, excesssolvent was thoroughly removed by a rotary evaporator undervacuum. The structure of the initiator was measured by FTIRand 1H NMR.

Synthesis of HFMA-PIBMA-Br by ATRP

HFMA-Br was firstly dissolved in butanone in a 100 mlthree-necked flask equipped with a mechanical stirrer, athermometer and an inlet system of nitrogen. Then, thereagent with molar ratio IBMA/CuBr2/Bpy0100/0.1/0.2was injected into the reaction flask. After the reaction mix-ture was thoroughly purged by vacuum and flushed withnitrogen three times, the flask was immersed in an oil bath at90 °C. Finally Cu (0) powder (with a molar ratio CuBr2/Cu(0)00.1/0.2) was added to initiate the polymerization, andthe reaction was conducted under nitrogen atmosphere allthe time. After 8 h, the reaction was stopped and quicklycooled down to room temperature. The product of HFMA-PIBMA-Br was obtained after precipitation in water,

Page 2 of 11 Y. Sun, W. Liu

filtration, washing with methanol, and drying under highvacuum to constant weight.

Synthesis of HFMA-PIBMA-b-PTMSPMA by ATRP

HFMA-PIBMA-Br was dissolved in butanone in a 100 mlthree-necked flask equipped with a thermometer, a mechan-ical stirrer and an inlet system of nitrogen. Then, the reagentwith molar ratio TMSPMA/CuBr2/Bpy0100/0.1/0.2 wasinjected into the flask. After the reaction mixture was thor-oughly purged by vacuum and flushed with nitrogen threetimes, the flask was immersed in an oil bath at 90 °C.Finally Cu (0) powder (with a molar ratio CuBr2/Cu (0)00.1/0.2) was added to initiate the polymerization ofTMSPMA, and the reaction was conducted under nitrogenatmosphere all the time. After 3 h, the reaction was stoppedand quickly cooled down to room temperature. The productsof HFMA-PIBMA-b-PTMSPMA were obtained afterprecipitation in petroleum ether, filtration, washing with meth-anol, and drying under high vacuum to constant weight.

Synthesis of copolymers end-capped with nonfluorinatedacrylate

The copolymers end-capped with nonfluorinated acrylatewas prepared under the similar condition with HFMA-PIBMA-b-PTMSPMA.

EBib was firstly dissolved in butanone in a 100 ml three-necked flask equipped with a mechanical stirrer, a thermom-eter and an inlet system of nitrogen. Then, the reagent withmolar ratio IBMA/CuBr2/Bpy0100/0.1/0.2 was injected intothe reaction flask. After the reaction mixture was thoroughlypurged by vacuum and flushed with nitrogen three times, theflask was immersed in an oil bath at 85 °C. Finally Cu (0)powder (with a molar ratio CuBr2/Cu (0)00.1/0.2) was addedto initiate the polymerization, and the reaction was conductedunder nitrogen atmosphere all the time. After 7 h, the reactionwas stopped and quickly cooled down to room temperature.The product of EBib-PIBMA-Br was obtained by the samemethod with the HFMA-PIBMA-Br.

The block copolymers of EBib-PIBMA-b-PTMSPMAwere obtained by the same method under the samecondition with HFMA-PIBMA-b-PTMSPMA except the themacroinitiator was replaced by EBib-PIBMA-Br.

The preparation of micelles solutions

The block copolymers were first dissolved in tetrahy-drofuran (THF), and then the water was added to thepolymer solution. The initial polymer concentration was2 wt.%.

Characterization

GPC analyses were run at 35 °C in THF (at a flow rate of1.0 mL/min) on a Waters 515 pump equipped with columnsof styragel HR 4 (M.W. 5,000–600,000) and styragel HR 3(M.W.500–30,000). A Waters 410 refractive index detectorwas used, and linear polystyrene standards were applied asthe calibration.

The FTIR spectra were recorded on a WQF 410Spectrophotometer made in Beijing, China. The films forFTIR were prepared by casting the polymer solution (20%w/w in butanone) onto KBr substrate. In order to remove theresidual solvent completely the films were placed in a vac-uum oven at 60 °C for 3 h.

1H NMR was performed on a 400 MHz Brüker NMRspectrometer (Model DRX-400) using CDCl3 as solvent andtetramethylsilane as an internal reference. Chemical shifts ofthe 1H NMR were related to the CDCl3 signal at 7.24 ppm.

Fluorine-element analysis was employed through theignition method [22], and the silicon-element analysiswas employed by Leeman Prodigy (USA).

The contact angle was measured on the air-side surface ofthe coating films with a contact goniometer (Erma ContactAnglemeter, Model G-I, 13-100-0, Japan) by the sessiledrop method with a micro-syringe at 30 °C. The samplewas prepared by casting the polymer onto a clean substratedisk of glass from 10% (w/w) solution of butanone. Thedisk was put into an oven at 40 °C for 3 h and 40 °C for 3 hunder vacuum. More than 10 readings were averaged to geta reliable value for each sample.

TEM images were obtained by JEM-100CXII at 200 kV.For the observation of the size and morphology of thecopolymer micelles, a small drop of sample which wasstained by phosphotungstic acid solution was deposited ontoa copper TEM grid covered with carbon thin film, and thenthe solution was dried at atmospheric pressure and roomtemperature.

DLS (Brookhaven Zeta Pals) determined the diameters ofthe aggregates in solution and the measurements were car-ried out at 25 °C at a scattering angle of 90o.

The fracture surfaces of the materials based on thecross-linked behaviors of HFMA-PIBMA-b-PTMSPMAwere observed with SEM (XL-30, Philips-FEI, Holland)with an accelerating voltage of 15 kV.

Results and discussion

The synthesis of initiators and block copolymers

HFMA transformed into initiators (HFMA-Br) by directaddition reaction with hydrobromic acid in acetic acid, andthen HFMA-Br initiated the polymerization of IBMA to

Synthesis and properties of cross-linkable block copolymer Page 3 of 11

prepare macroinitiator. Finally, well-defined cross-linkableblock copolymers end-capped with HFMAwere synthesizedvia ATRP, as shown in Scheme 1.

In order to demonstrate the effect of fluoroalkyl group onthe properties of HFMA-PIBMA-b-PTMSPMA, EBibwhich had been widely used in ATRP was as the intiatorto prepare the corresponding copolymers end-capped withnonfluorinated acrylate under the similar conditions. Themolecular weights, polydispersity index (PDI) and compo-sition of the polymers were shown in Table 1. The low PDIindicated that the reactions were well controlled.

The representative GPC traces of polymers were shownin Fig. 1. The elution time of HFMA-PIBMA-b-PTMSPMAwas shorter than that of HFMA-PIBMA-Br, showing that itsmolecular weight was larger than that of HFMA-PIBMA-Br. The monomodal GPC curve of the copolymer suggestedthe formation of block copolymer without homopolymeri-zation. No observable peak of the macroinitiator from theGPC curve of the block copolymer indicated the completeinitiation of the macroinitiator.

Characterization of initiators and block copolymers

Based on the FT-IR and 1 H NMR data the structures ofinitiators and block copolymers were analyzed. The FT-IRspectra of HFMA monomer (a), HFMA-Br initiator (b), themacroinitiator (HFMA-PIBMA-Br, c) and the block

copolymer (HFMA-PIBMA-b-PTMSPMA, d) were shownin Fig. 2. The peaks of trace a were very similar to that oftrace b, they both exhibited the characteristic peaks at 1,190and 690 cm−1, which were caused by the stretching vibrationand wagging vibrations of C–F [25, 26]. Comparing trace awith trace b, unambiguous disappearance of the characteristicpeak of C0C at 1,640 cm−1 (trace a) and the appearance of thecharacteristic peak of C-Br at 523 cm−1 (trace b) wereobserved, this indicated the completion of the additionreaction and the successful preparation of HFMA-Br.Trace c showed the spectrum of HFMA-b-PIBMA-Br.The characteristic peaks of C–F mentioned above becamefaintness, and the peak at 1,150 cm−1 can be seen, it wasascribed to the characteristic absorbance of -CH(CH3)2 inIBMA. Trace d showed the spectrum of HFMA-PIBMA-b-PTMSPMA, the peak at 1,090 cm−1 which was assigned to theasymmetric Si–O–C stretching in TMSPMA, showed thesuccessful ATRP of TMSPMA [6].

The 1H NMR spectra of initiators and block copoly-mers were shown in Fig. 3. Trace I showed the spectraof HFMA-Br. Peak at ~1.8 ppm was assigned as -CH3

(a), and peak at 4.4–4.5 ppm was corresponding to -OCH2 (b), while peak at ~4.8 ppm was designated tothe splitting of -CHF(c) which may result from thecoupling of proton with nuclei of fluorine atoms [27].Olefinic proton signals derived from unreacted HFMAcould not be detected in trace I. For HFMA-PIBMA-Br

Scheme 1 Synthesis of HFMA-Br, the macroinitiator of HFMA-PIBMA-Br and the block copolymer of HFMA-PIBMA-b-PTMSPMA

Page 4 of 11 Y. Sun, W. Liu

(trace II), some new peaks compared with trace Iappeared. Peaks at 3.6–3.8 ppm, 1.7–1.9 ppm and 1.3–1.4 ppm were assigned as -COOCH2 (f), -CH2 (e) and -CH (g) in the PIBMA segments, respectively. The peakof -CH3 (a) in HFMA overlaped with -CH3 (d) ofPIBMA at 0.7–1.0 ppm [28], while peak at ~0.9 ppmwas corresponding to -CH3 (h) of IBMA. TraceIIIshowed the spectra of HFMA-PIBMA-b-PTMSPMA(synthesized for 1H NMR, not listed in Table 1). Exceptthe peaks of HFMA and IBMA mentioned above, peaksat ~3.9 ppm, ~3.5 ppm, ~1.7 ppm and ~0.7 ppm wereassigned as -COOCH2 (j), -SiO(CH3)(i), -CH2 (k) and -CH2Si(l) in the PTMSPMA segments, respectively [10].

From FTIR and 1H NMR spectra the structures of initia-tors and block copolymers were verified.

Surface properties of the block copolymers

Low surface energy of organosilicon or fluorinated poly-mers was well known. In order to demonstrate the effect offluoroalkyl group on the surface properties, the similarpolymers end-capped with fluorinated or nonfluorinatedacrylate were comparatively evaluated by contact anglesmeasurement, and the data were shown in Table 2. Asexpected, although only one molecule of HFMA was intro-duced, the contact angles of HFMA-PIBMA-Br increasedgreatly comparing with EBib-PIBMA-Br, and they increasedwith the gradual increase of fluorine content in the macro-initiator. When organosilicon was introduced the contactangles of water increased furtherly, and the data ofHFMA-PIBMA-b-PTMSPMA was also higher than thatof corresponding EBib-PIBMA-b-PTMSPMA. For example,the molecular weights and the content of silicone were similarfor EBSi-1 and FBSi-1 in Table 2, while the contact angles ofwater on FBSi-1 was 2° higher than EBSi-1 by reason of onlyone HFMA molecule.

We obtained indirectly surface energy from the water contact

angle. An equation, 1þ cos θ ¼ 2 gS=gLð Þ1 2= exp �b gL � gSð Þ2h i

[29, 30] was applied to calculate the surface energy. βwas a constant with a value of 0.0001247 (m2/mJ)2

[30]; θ, γS and γL were the contact angle, the surfaceenergy of the solid and the surface energy of the testedliquid, respectively. The results in Table 2 showed that thesurface energies of polymers decreased with the increase offluorine or organosilicon content. Especially, when the HFMAand TMSPMA content were 0.74% and 21.48% (FBSi-2of Table 2), respectively, the surface energy of thepolymer film dropped to 21.1mN/m, which was muchlower than that of EB-2 (33.1 mN/m). All the results of

Table 1 The molecular weights, polydispersity index (PDI) and com-position of the polymers

Sample Mna PDIb Composition of the polymerc

EB-1 10150 1.14 Ebib-PIBMA70-Br

EB-2 35600 1.16 Ebib-PIBMA249-Br

EBSi-1 11640 1.19 Ebib-PIBMA70-b-PTMSPMA6

EBSi-2 45040 1.20 Ebib-PIBMA249-b-PTMSPMA38

FB-1 10100 1.20 HFMA-PIBMA69-Br

FB-2 35340 1.21 HFMA-PIBMA248-Br

FBSi-1 11300 1.21 HFMA-PIBMA69-b-PTMSPMA5

FBSi-2 45000 1.21 HFMA-PIBMA248-b-PTMSPMA38

aMn: the number-average molecular weight, determined by GPCb PDI: the polydispersity index, determined by GPCcDetermined by 1 H NMR combined with GPC results

Fig. 1 The representative GPC traces of HFMA-PIBMA-Br (a, Mn035340, PDI01.21) and HFMA-PIBMA-b-PTMSPMA (b, Mn045000,PDI01.21)

Fig. 2 FT-IR spectra of HFMA (a), HFMA-Br (b), HFMA-PIBMA-Br(c) and the block copolymer of HFMA-PIBMA-b-PTMSPMA (d)

Synthesis and properties of cross-linkable block copolymer Page 5 of 11

surface energy were agreeable with the contact anglemeasurements.

From the results above mentioned, small amount of fluo-rine content would have large influence on the surfaceproperties of the polymer. This may be explained in twoterms. Firstly, during the film formation process (for themeasurement of surface properties) the fluorinated segmentsin the systems were very easy to enrich on the surface of thecoated film. The enrichment of fluorine had been reported inour previous study [4], and similar conclusion had also beenmentioned in other literatures [31, 32].The second can bedue to the structure of the HFMA-PIBMA-b-PTMSPMA. Itwas found that the polymer end-capped fluorinated grouphad the special push-me/pull-you architectures, the low-energy functional groups in the polymer could be pulled tothe air-polymer interface and the high-energy functionalgroups could be pulled to the glass-polymer interface[22, 33].Thus, the efficiency of fluorine could be maximizedby anchoring the fluorinated group at the end of the molec-ular chain. No matter the enrichment of fluorine or the push-me/pull-you architectures of polymers would improve thesurface properties of HFMA-PIBMA-b-PTMSPMA.

Self-assembly behaviors of the block copolymers

It was reported that the solvent was one of important morpho-genic factors, since polymer-solvent interactions determinedthe coil dimensions of each block. Moreover, the role of the

solvent was very important on the aggregation since it had animpact on the free energy of micellization [34-36]. In order tochoose appropriate solvent for the aggregation many agentwere tentatively used as good solvents for the polymer blocks,THF was found to well solubilize HFMA, homo-IBMA andoligomer of TMSPMA. Furtherover, compared to pure sol-vents mixing solvents was expected to make possible theformation of a much broader range of morphologies, in thispaper, the morphologies self-assembled from FBSi-2 and

Fig. 3 1H NMR spectra ofHFMA-Br (I), macroinitiatorHFMA-PIBMA-Br (II) and theblock copolymer of HFMA-PIBMA-b-PTMSPMA (III)

Table 2 The content of fluorine or silicone, contact angle and surfaceenergy of the copolymers

Sample W[%]a Contact angle [o]b γSc [mN/m]

HFMA TMSPMA

EB-1 – – 84.0 33.0

EB-2 – – 83.8 33.1

FB-1 2.50 – 94.6 26.4

FB-2 0.77 – 89.1 29.8

EBSi-1 – 12.80 99.8 23.1

EBSi-2 – 21.49 102.6 21.5

FBSi-1 2.20 12.64 101.8 22.0

FBSi-2 0.74 21.48 103.2 21.1

a HFMA and TMSPMA content was obtained through element analysisb The contact angle of water on the air-side surface of the copolymersfilmsc Surface energy obtained indirectly from the water contact angle

Page 6 of 11 Y. Sun, W. Liu

EBSi-2 were demonstrated in THF/water with various watercontents.

As shown in Fig. 4, the copolymer architecture played arole on the resulting morphology. Comparing Fig. 4a and d,FBSi-2 and EBSi-2 had distinct microphase-separatedstructure, but both they had no clear morphologiesresulted from the self-assembly behaviors of blockcopolymers in THF/water when the water content wasonly 1.0 wt.%. After water was added to 50.0 wt.%, themorphology change could be observed when comparingthe copolymer end-caped fluoroalkyl or nonfluoroalkylgroup. Although in both cases the core-shell structurewere showed, the shell of micelles formed from FBSi-2had the explicit boundary (Fig. 4b) and the one fromEBSi-2 in the same solvent had blur boundary (Fig. 4e).In order to enhance the image contrast of TEM phos-photungstic acid (PTA) was used as a selective stainingagent in this paper. Li et al. reported that PTA could bea selective staining agent because of its solubility dif-ference in water and ester at different pH values [37].

From Fig. 4b, the core-shell structure had grey coresand shell with the clear colour bands against a lightbackground. Considing the nature of the blocks ofFBSi-2, PTA may have dissolved in ester under thiscondition and stained the blocks of PIBMA. It wassuggested that the hydrophobic blocks (HFMA andPTMSPMA block) associated to form the core and theloop of the PIBMA middle block formed the corona ofthe aggregates. Of cause, the reason for this may be notthat PIBMA blocks had good hydrophilicity but that thereactive -Si(OR)3 group of PTMSPMA block partlyhydrolyze into the -Si(OH)3 groups and turn into thecross-linked polysilsesquioxane by polycondensation,that is, when the PTMSPMA and HFMA block associatedto form a large core the PIBMA block would have to form thecorona of the aggregates. Since EBSi-2 had only one hydro-phobic block (PTMSPMA block) at PIBMA chain ends, thePIBMA chain stretched and surrounded the core formed fromthe PTMSPMA blocks (Fig. 4e). This may be the reason forthe blur boundary of the micelles formed from EBSi-2.

Fig. 4 TEM morphologies ofaggregates self-assembled fromFBSi-2 (first column) andEBSi-2 (second column) inTHF/water, water content:1.0 wt.% (a, d), 50.0 wt.%(b, e), 75.0 wt.% (c, f)

Synthesis and properties of cross-linkable block copolymer Page 7 of 11

When water content became 75.0 wt.%, the morphologychange was more evident when comparing copolymer end-caped fluoroalkyl or nonfluoroalkyl group. The core-shellstructures of FBSi-2 disappeared and large compoundmicelles (LCMs) were observed (Fig. 4c), while bowl-shaped structures were encountered from EBSi-2 under thesame conditions (Fig. 4f). It was reported [38] that com-pound micelles and bowl-shapes were somehow relatedregarding their mechanism of formation, and they mustbe related with the hydrolysis and polycondensation ofPTMSPMA block in this paper . LCMs was first reported in1996 and found to result from diblock copolymers of veryshort hydrophilic blocks [39]. The typical characteristics ofthe LCMs were their high polydispersity and very large sizes[34, 39]. A possible explanation for the features of LCMscould be given based on the work conducted by Esselink et al.[40]. They studied the process of reaching the equilibriummicellar size and structures of reverse micelles, they alsoreported that the larger the micelle equilibrium size, thebroader the size distribution than could be expected.

Figure 4f showed an unexpected morphology, resemblingthe shape of a bowl, which was one of the most interestingfinding on the present copolymer systems. The bowl-shaped

Fig. 5 DLS plot of micelles sizes distribution of FBSi-2 (first column) and EBSi-2 (second column) in THF/water, water content: 50.0 wt.% (a, c);75.0 wt.% (b, d). The data of micelles sizes and polydispersity were included in Table 3

Table 3 The comparative study of the micelles sizes from TEMimages and DLS measurement

Sample Water content inTHF/water [wt%]

Micelles sizes[μm] Polydispersityb

TEMimagesa

DLSmeasurement

FBSi-2 50.0 2.20 2.25 0.258

EBSi-2 50.0 2.45 2.54 0.308

FBSi-2 75.0 2.00 2.10 0.304

EBSi-2 75.0 – 1.30 0.321

a The average diameter was estimated from the outer diameter if themicelles with core-shell structure; most of the bowl-shapes of EBSi-2were in a collapsed form, the micelles sizes were measured only byDLSb The polydispersity was obtained from DLS measurement

Page 8 of 11 Y. Sun, W. Liu

aggregates had been encountered in the triblock copolymers indioxane and THF in previous paper [34, 38]. This novelmorphology was extensively described and a possible mech-anism of formation was proposed by Riegel and Eisenberg [38].

TEM results showed that small amount of fluorine con-tent had large influence in the morphology of polymer. Thismay be due to very high hydrophobicity of fluorinated seg-ments [41]. As it was known that fluorinated segments werequite hydrophobic and their tendency to separate from waterand hydrophilic groups was among the strongest [42, 43].Fluorinated segments of FBSi-2 would undergo rapid con-striction and move from the interface when the polymersurface contacts with water in order to minimize the inter-facial free energy [22], that was, FBSi-2 had two hydropho-bic blocks (HFMA and PTMSPMA block) while EBSi-2had only one (PTMSPMA block).

Figure 5 showed the micelles sizes distribution determinedby DLS measurement. From the images, the unimodal

distributions were observed for FBSi-2 and EBSi-2 indifferent water content of THF/water. The average micellessizes were also determined by the survey for 50 samples pickedup from the images of the TEM that were obtained [44, 45].The micelles sizes obtained by DLS and TEM were compar-atively studied in Table 3. It could be observed that the averagediameters measured by TEM were in reasonable accordancewith that measured by DLS, although the former was a littlesmaller than the latter because that the DLS measurementswere carried out in solution where the corona of the aggregateswould stretched out to some centent due to the solubility in thesolution, while the TEMmeasurements were made on the solidaggregates in which the corona were collapsed [46].

Cross-linked behaviors of the block copolymers

Figure 6 demonstrated the morphologies of cross-linkedbehavior from FBSi-2. Figure 6a showed the morphology

Fig. 6 The TEM micrographsof FBSi-2 in THF/water (a), thesamples were heated at 100 °Cfor 1 min (b), 5 min (c) and10 min (d)

Fig. 7 The SEM images offracture surfaces of materialsbased on the cross-linkedbehaviors of FBSi-2

Synthesis and properties of cross-linkable block copolymer Page 9 of 11

of copolymers in THF/water when the water content main-tained at 75.0 wt.%. After the samples were heated at 100 °Cfor 1 min, some spherical structures disappeared and fusedtogether to form an extended flaky structure with roundededges (Fig. 6b). Longer reaction times resulted in largerflakes with well-defined edges (Fig. 6c and d). The evidentchange of the morphologies must be related to PTMSPMAblocks of the polymers. The reactive -Si(OCH3)3 group ofPTMSPMA blocks could partly hydrolyze into the -Si(OH)3groups and turn into the cross-linked polysilsesquioxane bypolycondensation [9]. It was suggested that heat for thesamples greatly promoted the polycondensation.

In order to further characterize the cross-linkedbehaviors formed from FBSi-2, a drop of polymer solution(corresponding to Fig. 6a) was spread on a silica wafer andheated at 120 °C for 2 h. The products were transparent solidmaterials with a slightly blue color. Figure 7 exhibited thefracture surfaces of the materials, there were many smallparticles dispersing in the polymer matrix, as can be seen inFig. 7a and muchmore clearly in the magnified micrograph ofFig. 7b, which indicated that the cross-linked behaviors ofFBSi-2 had happened [47, 48] and the inorganic silica net-work structures had been introduced into the organic polymerchains.

Conclusion

A series of well-defined cross-linkable copolymers end-capped with HFMA (HFMA-PIBMA-b-PTMSPMA) weresynthesized via ATRP. GPC, FTIR and 1H NMR dataobtained verified the synthesis and measured the structuresof the copolymers. The properties of HFMA-PIBMA-b-PTMSPMA and the corresponding copolymers end-cappedwith nonfluorinated acrylate were comparatively studied.The contact angle measurement indicated that although onlyone molecule of fluorinated acrylate was introduced thesurface properties of polymers were improved greatly. ByTEM and DLS, some unexpected self-assembly behaviorswere showed for the two block copolymers in THF/water.After the cross-linked behaviors formed from HFMA-PIBMA-b-PTMSPMA, the transparent solid materials witha slightly blue color were obtained and exhibited by SEM.In summary, the fluoroalkyl group at the end of the poly-mers had great effect on their properties and the novel cross-linkable copolymers would lead to potential applications inspecial polymeric materials.

Acknowledgement Authors gratefully acknowledge the financialsupport from the Guangdong Natural Science Foundation, China(NO: 07006841) and the open project of key laboratory of celluloseand lignocellulosics chemistry, Chinese Academy of sciences (NO:LCLC-2010-11).

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