Polymer 45 (2004) 5013–5020 www.elsevier.com/locate/polymer Block copolymer grafted-silica particles: a core/double shell hybrid inorganic/organic material G. Laruelle, J. Parvole, J. Francois, L. Billon* ` ´ ´ ´ ´ Laboratoire de Physico-Chimie des Polymeres, UMR 5067 CNRS, Universite de Pau et Pays de l’Adour Helioparc Pau-Pyrenees, 2 Av. P. Angot, 64053 Pau Cedex 09, France Received 19 December 2003; received in revised form 7 May 2004; accepted 13 May 2004 Available online 2 June 2004 Abstract Hybrid inorganic/organic materials consisting of a poly(n-butyl acrylate)-b-poly(styrene) diblock copolymer anchored to silica particles were synthesized via ‘grafting from’ technique using a controlled/living free radical polymerization named stable free radical polymerization. XPS and FTIR analysis were used to control the effectiveness of the chemical modiﬁcation of the silica particles. Thermal characterizations were performed by thermal gravimetric analysis (TGA) and by differential scattering calorimetry (DSC). The TGA permitted the determination of the quantity of grafted polymer and thus the grafting density; DSC was used to study the inﬂuence of the silica and blocks of the copolymer on their thermal behaviors. The glass transition temperature of the grafted copolymers was compared to these of free polymers or copolymers homologues. q 2004 Elsevier Ltd. All rights reserved. Keywords: Block copolymers; Stable free radical polymerization; Inorganic/organic materials 1. Introduction used. However these polymerizations require speciﬁc experimental conditions thus making their application The synthesis of dense ﬁlm of polymer chains covalently difﬁcult, while recent advances in controlled/’living’ free bound to surfaces is an important ﬁeld of research for its radical polymerization (suppression of terminations and ability to control and tune the properties of surfaces [1 – 3]. chain transfer reactions), a less constraining technique, have The ﬁrst approach used, named ‘grafting to’ , consists in made it viable for the synthesis of well deﬁned and narrow the condensation of functionalized polymers with reactive polydispersity polymers. Atom transfer radical polymeriz- groups of a solid substrate. This method does not give ation (ATRP) [9 –11] and stable free radical polymerization highly dense polymer brushes because chemi-sorption of the (SFRP) [12 –15] belong to the controlled/‘living’ radical ﬁrst fraction of chains hinders the diffusion of the following polymerization. These polymerizations are based on the chains to the surface for further attachments . Another reversible activation and deactivation of growing radicals. A approach, named ‘grafting from’, has been considered to very low concentration of propagating radicals is produced obtain better densities. In this technique, a mono-layer of suppressing termination reactions and giving polymers with initiator molecules is covalently attached to a solid surface narrow polydispersity. Another advantage with these two [4 – 6]. After activation the chains grow from the interface techniques is that the chains formed are end-capped by a then the only limit to propagation is the diffusion of dormant function that can be further thermo-activated to monomers to the active species. prepare block copolymers [15b]. Matyjaszewski et al. have used the ATRP technique to generate PS-b-PBzA from the To have a good control of the polymer mono-layer polysilsesquioxane nanoparticles, spending a lot of space thickness and polymer structure, living polymerization, for for the characterization of the particles and their nanoscale example anionic  or cationic  polymerizations, can be morphology on surfaces [9b]. Moreover, Hawker et al. have * Corresponding author. Tel.: þ 33-5-59-40-76-09; fax: þ33-5-59-40-76- described that tethering alkoxyamine initiators to a solid 23. support (as silicon wafer) can form PS brushes and that E-mail address: email@example.com (L. Billon). well-deﬁned PS-b-PMMA block copolymer brushes can be 0032-3861/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2004.05.030 5014 G. Laruelle et al. / Polymer 45 (2004) 5013–5020 prepared . But in the two previous studies [2,9b], the Refractive index detector and a 996 Waters Photodiode block copolymers were formed by sequences with high or array detector. A calibration curve established with low ambient glass transition temperatures and there is no polydispersity polystyrene standards was used for the characterization on the thermal properties of the grafted determination of the polyacrylate molecular weights. macromolecular chains. Thermal Gravimetric Analysis (TGA) was performed on In this paper, we present the preparation of polymer a TA Instruments TGA 2950 at a scan rate of 10 8C min21 brushes on silica particles via ‘grafting from’ approach. The under air. DSC was carried out using a DSC Q 100 polymer chosen was poly(n-butyl acrylate) (PBA) and was apparatus from TA Instruments at a scan rate of 20 8C/min prepared by stable free radical polymerization. In a second for both heating and cooling. The reported glass transition step, we have activated the chain end functions of PBA end temperatures were determined from the second heating run thus we have made a copolymer with polystyrene (PS), and were taken as the middle point of the DH=dt step in the verifying the control of chain terminal functionality DSC spectra. obtained during the stable free radical polymerization of butyl acrylate. The aim of this study was to generate hybrid 2.3. Mono-layer self assembly and polymerizations inorganic/organic particles by nitroxide-mediated polymer- ization (NMP), in order to elaborate a core-shell nano- The elaboration and the synthesis of the polyfunctional composite with a hard core of silica coated by a double shell coupling agent are based on a molecular engineering of a rubbery inner shell (PBA T g < 2 50 8C) and a glassy involving a multi-step reaction. Indeed, this coupling thermoplastic outer shell (PS T g < 100 8C). agent has to be constituted in its molecular structure of three functional groups. 2. Experimental part 2.4. Allyl 2-bromopropionate 2.1. Materials To a solution of 6.15 g (106 mmol) of 2-propen-1-ol in 400 ml of dichloromethane was added 14.8 ml of triethyl- Fumed Silica particles with an average elemental amine (110 mmol) and the solution was cooled to 0 8C in diameter of 13 nm and a speciﬁc surface area of an ice bath. Using an addition funnel, 16.4 ml (157 mmol) 255 m2 g21 (Aldrich) were dried overnight at 120 8C of 2-bromopropionyl bromide were added dropwise and the under vacuum before used. Toluene was distilled under temperature was kept on to 0 8C. Upon complete addition, nitrogen atmosphere from over molten sodium. MONAMS the mixture was brought to room temperature and allowed to alkoxyamine and SG1 counter-radical have been used as stir overnight. The product was washed with 3 £ 100 ml of received from ATOFINA. All other solvents and chemical H2O, dried over anhydrous MgSO4 and the solvent was products were purchased and used without further evaporated. The remaining pale yellow oil was distilled puriﬁcation. under reduced pressure (60 mtorr) at 60 –70 8C, and 15.38 g (75%) of the product was collected. 2.2. Characterizations and measurements 2.5. Allyl alkoxyamine synthesis X-ray photoelectron spectroscopy analyses were per- formed with a Surface Science Instrument (SSI) spectro- To a round bottom ﬂask containing 1.5 g (7.8 mmol) of meter at room temperature, using a monochromatic and allyl 2-bromopropionate, 2.6 g (7 mmol) of N-tert-butyl-N- focused (spot diameter of 600 mm, 100 W) Al Ka radiation (1-diethylphosphono-2, 2-dimethyl) propyl nitroxide at (1486.6 eV) under a residual pressure of 5 £ 1028 Pa. The 80% of purity (also referred to as DEPN or SG1), hemispherical analyzer worked under constant pass energy 0.5625 g (3.9 mmol) CuBr, 0.495 g (7.8 mmol) Cu and mode, 50 eV for high resolution spectra and 150 eV for 0.675 g (3.9 mmol) de PMDETA was added 15 ml of quantitative analysis. The binding energy scale was freshly distilled toluene. The mixture was stirred for 4 h at calibrated from the carbon contamination using the C1S room temperature in order to complete an Atom Transfer line (284.6 eV) (a mean atomic percentage of 8% was Radical Addition (ATRA). The green solution was ﬁltered determined). under celite in order to eliminate the copper. After ﬁltration, The Fourier transform infrared (FTIR) spectra were the yellow solution was washed with 2 £ 25 ml of 40% recorded using a Bruker IFS 66/S spectrometer at a aqueous solution of ammonium formate and 25 ml of resolution of 4 cm21 in absorption mode. 100 to 1000 aqueous solution saturated with sodium hydrogenocar- scans were accumulated. bonate. The remaining yellow oil was distilled under Size Exclusion Chromatography (SEC) characterization reduced pressure and 0.894 g (30%) of a orange oil was was performed using a 2690 Waters Alliance System with collected. This solution in toluene was directly used for the THF as eluent. It was equipped with four Styragel columns immobilization of the alkoxyamine initiator to silica HR 0.5, 2, 4 and 6 working in series at 40 8C, a 2410 Waters particle. G. Laruelle et al. / Polymer 45 (2004) 5013–5020 5015 2.6. Immobilization of the allyl alkoxyamine initiator to 3. Results and discussion silica 3.1. Synthesis of hybrid particles The surface modiﬁcation reaction has been realized using glass apparatus ﬂamed under vacuum. To a round bottom The silica used to synthesize the polymer brushes was ﬂask, 1.04 mmol of allyl alkoxyamine previously synthe- previously grafted by an alkoxyamine initiator, called sized and 0.9 g of silica were introduced with 5 ml of freshly coupling agent, derivated from DEPN  and composed distilled toluene (Silica was dried overnight at 180 8C under ¨ by three functions as described by Ruhe [5,6] and us  vacuum). Under N2 atmosphere, 0.5 ml of triethylamine was (Fig. 1) (a grafting function, an initiating function and a added dropwise and the mixture was stirred overnight at cleavable function). The synthesis of this coupling agent room temperature. The particles were washed free of any and these nano-particles are described in the experimental part of a previous article . From these modiﬁed adsorbed initiator with ﬁve cycles of centrifugation and re- particles, we initiated the bulk polymerization of n-butyl suspension in methanol and dichloromethane, and then acrylate. Free alkoxyamine initiator (MONAMS ) and a volatile products were removed under vacuum. slight excess of counter radical nitroxide (DEPN) ([DEPN]/ [MONAMS] ¼ 0.05) were added to the solution. The 2.7. Polymerizations additional initiator permits the polymerization of free chains, which can be later compared with the de-grafted chains thanks to the cleavable function of the coupling Under inert atmosphere, 1 g of modiﬁed silica particles agent, while the nitroxide permits a better control on the was suspended in a mixture of 20 ml of n-butyl acrylate, free polymerization of the grafted and free chains. The ﬁrst alkoxyamine MONAMS ([n-BA]/[MONAMS] ¼ 390) and monomer used was n-butyl acrylate, three PBA samples of SG1 ([SG1]/ [MONAMS] ¼ 0.05) using the schlenk different molecular weights were prepared by varying the process. This mixture was thoroughly degassed for 30 min polymerization time but keeping the same ratio [BA]/ and heated to 120 8C for 1 – 8 h. The nano-composites were [MONAMS]. The experimental conditions are resumed in washed and centrifuged in toluene (ﬁve cycles) to remove Table 1. The macromolecular dimensions (M n, M w, Ip) non-attached polymer. The removal of adsorbed polymer on of the free PBA (untethered) were determined by SEC these hybrid inorganic/organic silica-particles was moni- (Table 1). At this point, the PBA chains were not degrafted tored by FTIR up to no signiﬁcant variation of the because we wanted to synthesize block copolymer with absorbance of the characteristic peak of carbonyl function styrene. The polydispersity decreases with the polymeriz- (acrylic polymer). ation time and the values obtained for the three PBA are comprised between 1.4 and 1.2 signiﬁcant of a controlled free radical polymerization. 2.8. Copolymerizations The grafted PBA chains obtained by NMP are terminated by an alkoxyamine function thus permitting an initiation of Under inert atmosphere, 1 g of poly(n-butyl acrylate) a new NMP. We decided to re-initiate NMP from the PBA modiﬁed silica particles was suspended in a mixture grafted silica in presence of styrene in order to obtain a core- of styrene, free alkoxyamine MONAMS ([St]/ shell hybrid-composite with a hard core of silica and by a [MONAMS] ¼ 200) and SG1 ([SG1]/[MONAMS] ¼ 0.05) double shell of a soft material and a hard material (Fig. 2). using the schlenk process. This mixture was thoroughly We used the three different PBA grafted silicas and choose degassed for 30 min and heated to 120 8C for 3 h. The to have the same molecular mass of the polystyrene block hybrid-composites were washed and centrifuged in toluene for the three samples. So, the same procedure was used: bulk (ﬁve cycles) to remove non-attached polymer. polymerization in the presence of the PBA grafted silica, free initiator (MONAMS) and nitroxide (DEPN). The conditions are resumed in Table 1. The free PS obtained 2.9. Degrafting procedure in the three experiments have a similar molecular weight A total of 500 mg of inorganic/organic silica-particles was suspended in 100 ml of toluene in which 10 ml of MeOH and 50 mg of p-toluene sulfonic acid were added. The mixture was heated to reﬂux overnight. A study by 1H NMR and SEC do not show any modiﬁcation of the poly(n- butyl acrylate) structure under this trans-esteriﬁcation conditions . After freeze-drying of the degrafted Fig. 1. Coupling agent composed of three functions: grafting function (I), polymers, the molecular weights were determined by GPC cleavable function (II) and initiating function for nitroxide-mediated measurements and compared to the free chains. polymerization (III). 5016 G. Laruelle et al. / Polymer 45 (2004) 5013–5020 Table 1 Polymerization conditions of PBA and macromolecular parameters of the free chains as determined by SEC Free PBA chains Free PS chains 21 [BA]/[I]a Time (h) M n (g mol ) Ipb [St]/[I] Time (h) M n (g mol21) Ipb Si 1 390 1 13700 1.38 200 3 11300 1.15 Si 2 390 4 32600 1.25 200 3 11200 1.14 Si 3 390 8 39700 1.21 200 3 10800 1.15 a I: MONAMS b Mw =Mn (10; 800 , Mn , 11; 300Þ: This result will permit the study closely to the polydispersity of each free polymer, of the inﬂuence of the PBA block on the PS block and conﬁrming the control of the block copolymer formation conversely. By the presence of the ester function in the by Surface-Initiated Nitroxide Mediated polymerization grafted initiator, the copolymers chains can be cleaved from (Fig. 3), as also described from silicon wafer by Hawker . the silica and characterized by GPC. These characteristics cannot be directly compared with those of the untethered 3.2. Structural characterizations chains generated by the free initiator during the polymeriz- ation. However, if the reaction mechanism is analogous in The modiﬁed silicas have been characterized by FTIR bulk and at the surface, the number average molecular (Fig. 4) to determine the effectiveness of the modiﬁcations. weight of the grafted copolymers is expected by equal to the Fig. 4 shows the spectra of the three silicas, normalized with same of those of the two homopolymers obtained succes- the peaks of Si-O. Above, the top spectrum corresponds to sively in bulk (PBA then PS). In the particular of the Si3 the silica modiﬁed by an alkoxyamine initiator which was sample, this assumption is well veriﬁed (Table 1 and Fig. 3). used for the polymerization of butyl acrylate BA. The Indeed, if we compare the number average molar mass of intermediate spectrum were registered for puriﬁed silica the degrafted chains (M n Si3 ¼ 51,200 g mol21; Ip ¼ 1.20) obtained after BA polymerization and the spectrum below with the number average molar mass of both free PBA and corresponds to the puriﬁed silica obtained after copolymer- free PS synthesized during the same experiments ization of Styrene in order to synthesize PBA-b-PS. On the (M n ¼ 10,800 þ 39,700 ¼ 50,500 g mol21) we observe a right part of the spectrum (b), the peak at 1725 cm21 similar result knowing that the calibration curve was corresponds to the stretching vibration of the carbonyl established with PS standards. Moreover, the polydispersity groups of the poly(butyl acrylate), that well conﬁrms the value of the cleaved block copolymer PBA-b-PS is very presence of poly(butyl acrylate) on the silica particles. On Fig. 2. Schematization of the preparation of a core/soft-hard double shell. G. Laruelle et al. / Polymer 45 (2004) 5013–5020 5017 Fig. 3. Size Exclusion Chromatograms of degrafted PBA-b-PS (a), free PBA (b) and free PS (c). the spectrum (c), this peak is less marked but still present to the presence of silicon (152 eV, Si(2s); 103 eV, Si(2p)) and at 3000 – 3100 cm21 (left part) the new peaks and oxygen atoms (533 eV, O(1s)). After the immobiliz- characteristic of CH aromatic vibrations can be observed. ation of the coupling agent (b), three new signals appear due This indicates the presence of the poly(butyl acrylate)-b- to the phosphorus (133.8 eV, P(2p)), the carbon (285 eV, polystryrene copolymer at the silica’ surface. These C(1s)) and nitrogen atoms (400.7 eV, N(1s)) of the grafted qualitative characterizations show the formation of hybrid alkoxyamine compound characteristic of the presence of the composites, ﬁrst a poly(butyl acrylate) brush on silica and in SG1 nitroxide. Further more, comparison of the XPS spectra a second step after re-initiation, the synthesis of a poly(butyl of the coupling agent mono-layer (b) and the graft PBA (c) acrylate)-b-polystyrene copolymer brushes on silica. shows a strong enhancement of the carbon signal at 285 eV In order to conﬁrm the effective formation of polymer (C(1s)) due to the acrylic part. Additionally, in the (c) brushes, already seen by FTIR, a study by XPS was made. spectra the signals of Si(2p) are attenuated and the C(1s)/ Fig. 5 presents the results of XPS measurements. The O(1s) signals ratio is clearly enhanced demonstrating the spectrum of the bare substrate (Fig. 5(a)) shows signals due presence of organic polymer on the surface of the hybrid Fig. 4. FTIR spectra of initiator grafted silica (a), PBA grafted silica (b) and PBA-b-PS grafted silica (c). 5018 G. Laruelle et al. / Polymer 45 (2004) 5013–5020 Fig. 5. Surface analysis by XPS of silica particles (a), initiator grafted silica (b), PBA grafted silica (c) and silica (d). inorganic/organic particle. Moreover, it was very interesting performed by themogravimetric analysis. An analysis of the to note that the phosphorus and nitrogen atoms of SG1 pure silica used in this work shows no thermal degradation, nitroxide are still remaining at the end chain of macro- no weight loss was encountered in the temperature range molecules after polymerization. The presence of the used (30 – 650 8C). On the thermograms of polymer-grafted nitroxide SG1 gives us the opportunity to elaborate some silicas (Fig. 6), we can see a signiﬁcant weight loss due to block copolymers at the surface of the silica-particles with the degradation of the grafted organic compound. The antagonist properties such as copolymer PBA-b-PS. The weight loss is more important for the copolymer-grafted XPS spectra of the silica particles obtained after re-initiation silica than for the PBA-grafted silica proving that the in-situ of the SG1 end-capped PBA in presence of styrene is shown copolymerization is effective. The thermal behavior differ- Fig. 5. Indeed the C(1s)/O(1s) and C(1s)/Si(2p) signals ratio ence between the bare silica and grafted silicas permits the increase from 0.23/0.15 to 0.62/0.36, respectively, for estimation of the grafting densities for the initiator, the PBA grafted PBA/PBA-PS silica particles. and the copolymer PBA-b-PS. Indeed, if we make the approximation that at 650 8C all the organic material is 3.3. Grafting density degraded and that only the inorganic material remains we can calculate the grafting density (Table 2). For grafted A thermal study of the different grafted silicas was polymers the density decreases when M n increases (the G. Laruelle et al. / Polymer 45 (2004) 5013–5020 5019 Fig. 6. Thermograms of PBA (a), PBA-b-PS (b) grafted-silicas (Si3) and (c) pure silica. Fig. 7. DSC thermograms of PBA (Mn ¼ 130; 000 g mol21) (a), PBA-b-PS grafted-silica (b), PS ðMn ¼ 10; 000 g mol21) (c) and tri-block copolymer PBA-b-PS-b-PBA (d). density rises from 0.026 PBA chains by nm2 to 0.008 PBA chains by nm2 when M n increases from 14,000 g mol21 to temperature relative to the PBA block (elastomer phase) and 40,000 g mol21). The grafting density for a grafted PBA another relative to the PS block (thermoplastic phase), and the corresponding copolymer PBA-b-PS is nearly characteristic of a phase separation. For the PBA blocks the similar, showing that the re-initiation of the end-capped T g obtained is around 2 20 8C and this of the glassy state SG1 for the copolymerization has a good efﬁciency. block PS is closed to 80 8C. To compare, we have performed However all these values are far from the grafting density a DSC on homopolymers PBA of different molar mass and of the coupling agent (0.52 molecule nm22) so only small for PBA grafted on silica. For free PBA, T g was comprised amounts of the grafted coupling agent initiate the in situ between 2 53 8C for M n¼ 25; 000g mol21 and 2 47 8C for polymerization due the crowding effect of grafted chains or M n¼ 130; 000g mol21 ; respectively. In case of PBA to a degrafting process at high temperature as we will grafted-silica, T g was equal to 2 35 8C. The PS block and describe in a forthcoming paper. the silica have an important inﬂuence on the T g of the PBA. Indeed the T g of the PS is very high in comparison with PBA 3.4. Thermal properties of polymer grafted silica particles so when the glass transition of the PBA occurs, the two extremities of the copolymer chain are ﬁxed, one by the A second thermal study was made by DSC in order to rigidity of the PS the other by the presence of the silica estimate the inﬂuence of the silica on the grafted polymers particle. Then the motion of the PBA block is hindered and and the inﬂuence of one block on the other for grafted block more energy is needed to pass from a glassy state to a copolymers (Fig. 7 and Table 3). Indeed, in a DSC study, caoutchoutic state thereby increasing the temperature of the Patterson et al. have demonstrated the effects of tethering glass transition of the PBA. The silica has no signiﬁcant and chain immobilization on the glass transition tempera- direct inﬂuence on the PS block because the presence of the ture of PS (thermoplastic polymer). The measured T g of PBA between those two parts. On the other hand the PBA annealed bulk ﬁlms of hybrid nanoparticles was elevated has an inﬂuence on T g of the PS. For the PS block, T g varies with respect to the value of pure bulk PS because of the from 83 8C to 85 8C while for a PS with the same M n chain grafting or immobilization and to the chain extension (10 000 g mol21) T g is 97 8C. This time, the effect is the [9c], phenomena brieﬂy reported by Carrot et al. on PS opposite than the one described before for PBA. When the grafted silica particles also synthesized by ATRP . glass transition of the PS occurs, the PBA block is ﬂexible In our case, DSC spectra of copolymer PS-b-PBA grafted and in movement leading the PS block to be more ﬂexible on the silica (Fig. 7(b)) shows two T g; one under room than if it where alone so the PS block need less energy to Table 2 Determination of the PBA and PBA-b-PS grafting densities by TGA PBA grafting density PBA-b-PS grafting density Weight loss (%)a mmol g21 molecule nm22 mmol m22 Weight loss(%)a mmol g21 molecule nm22 mmol m22 Efﬁciency (%) Si 1 13.3 16.2 0.040 0.064 26.2 13.8 0.033 0.054 83 –85 Si 2 17.7 9.5 0.022 0.038 18.8 6.8 0.016 0.027 71 –73 Si 3 11.1 4.6 0.011 0.018 15.4 3.6 0.008 0.014 73 –78 a Weight loss by TGA. 5020 G. Laruelle et al. / Polymer 45 (2004) 5013–5020 Table 3 grafted to silica particles was shown, leading to a core/ Glass transition temperatures of core/shell PBA and PBA-b-PS grafted double shell hybrid inorganic/organic material (a double particles by DSC shell constituted by a rubbery inner layer and glassy PBA PS thermoplastic outer layer). The materials obtained have different thermal behaviors, function of the ratio PBA/PS. Tonset (8C) T g (8C) Tonset (8C) T g (8C) So, it is possible to tune the surface properties (for instance the adherence, wetability…) of the inorganic material by Si -PBA 247/240 235/230 – – Si -PBA-b-PS 230/225 222/216 74 83/85 choosing the nature (elastomeric, thermoplastic, hydro- Free PBA 260/255 253/247 – – philic…) and the dimension of an adequate grafted polymer. Free PS – – 90 97 Free PBA-b-PS 240 230 76 83 Free PS-b-PBA-b-PS 245 237 74 82 Acknowledgements pass from a glassy state to a caoutchoutic state thereby The authors are pleased to acknowledge O. Guerret from decreasing is glass transition temperature. In order to ATOFINA for supplying SG1 and MONAMS, and estimate the real inﬂuence of the silica particle over the PBA C. Guimon for the XPS measurements. block on the T g of the PBA, we have made a tri-block copolymer PS-b-PBA-b-PS, thanks to a di-alkoxyamine [15b], with two blocks of PS with a M n of 15 000 g mol21 and PBA block with a M n of 50 000 g mol21. The T g for the References PS of the tri-block and for the PS of the PBA-b-PS grafted  Mansky P, Liu Y, Huang E, Russel TP, Hawker CJ. Science 1997;119: are very similar conﬁrming the weak and important, 1619. respectively inﬂuence of the silica and PBA on this block. ¨  Husseman M, Malmstrom EE, McNamara M, Mate M, Mecerreyes D, The major difference between the tri-block and a grafted di- Benoit D, Hedrick JL, Mansky P, Huang E, Russel TP, Hawker CJ. block copolymer is on the T g of the PBA since its T g for the Macromolecules 1999;32:1424. tri-block is lower (2 42 8C) than for the grafted copolymers  Halperin A, Tirell M, Lodge TP. Adv Polym Sci 1991;100:31. (2 22 8C to 2 16 8C) meaning that the silica particles have a  Ulman A. Chem Rev 1996;96:1533. ¨  Prucker O, Ruhe JJ. 1998; 31: 592. higher impact than the PS block on the thermal behavior of ¨  Prucker O, Ruhe J. Macromolecules 1998;31:602. the PBA, as a tough and hard matter due to their inorganic  Jordan R, Ulman A. J Am Chem Soc 1998;120:243. character.  Jordan R, Ulman A, Kang JF, Rafailovich MH, Sokolov J. J Am Chem Soc 1999;121:1016.  (a) Luokala B, Siclovan T, Kickelbick G, Vallant T, Hoffmann H, Pakula T. Macromolecules 1999;32:8716. (b) Pyun J, Matyjaszewski 4. Conclusion K, Kowalewski T, Savin D, Patterson G, Kickelbick G, Huesing N. J Am Chem Soc 2001;123:9445. (c) Savin D, Pyun J, Patterson G, Formation of hybrid inorganic/organic materials, by in- Kowalewski T, Matyjaszewski K. J Polym Sci Part B 2002;40:2667. situ polymerization thanks to an alkoxyamine type coupling  Chen X, Randall D, Perruchot C, Watts J, Patten T, Von Werne T, agent previously grafted to the inorganic material, was Armes S. J Colloid Interface Sci 2003;257:56.  Von Werne T, Patten TE. J Am Chem Soc 2001;123:7497. conﬁrmed by both FTIR and XPS. This ‘grafting from’  Hedrick JL, Mansky P, Huang E, Russell TP, Hawker CJ. approach has given good polymer grafting densities giving Macromolecules 1999;32:1424. us hope to achieve formation of polymer brushes onto silica.  (a) Beyou E, Humbert J, Chaumont P. E-Polymers 2003;020. (b) The use of a stable free radical polymerization (also called Bartholome C, Beyou E, Bourgeat-Lami E, Chaumont P, Zydowicz N. nitroxide-mediated polymerization) permits a control of the Macromolecules 2003;36:7946.  Benoit D, Grimaldi S, Finet JP, Tordo P, Fontanille M, Gnanou Y. Am dimension and the structure of the grafted polymers. Indeed, Chem Soc, Polym Div 1997;38:651. we have shown that the molar mass and the polydispersity of  (a) Robin S, Guerret O, Coututrier JL, Pirri R, Gnanou Y. the grafted polymer were very similar with a free polymer Macromolecules 2002;35:3844–8. (b) Robin S, Gnanou Y. Macromol made in the same conditions. Another advantage of the Symp. 2001;165:43– 53. (c) Gnanou Y, Robin S, Guerret O, Couturier nitroxide-mediated polymerization is the ability to poly- JL. Polym Prepr 2000;41:1352.  Parvole J, Billon L, Montfort JP. Polym Int 2002;51:1111. merize a large range of monomers (styrenic, acrylic,  Parvole J, Laruelle G, Guimon C, Francois J, Billon L. Macromol methacrylic) and to make blocks copolymers. For example Rapid Commun 2003;24:1074. in this article the formation of a diblock poly(n-butyl  Carrot G, Diamanti S, Manuszak M, Charleux B, Vairon J-P. Polym acrylate)-b-poly(styrene), with narrow polydispersity, Sci Polym Chem 2001;39:4244.