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Polymer 45 (2004) 5013–5020 www.elsevier.com/locate/polymer Block copolymer grafted-silica particles: a core/double shell hybrid inorganic/organic ma...

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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 Polyme`res, UMR 5067 CNRS, Universite´ de Pau et Pays de l’Adour He´lioparc Pau-Pyre´ne´es, 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 The synthesis of dense film of polymer chains covalently bound to surfaces is an important field of research for its ability to control and tune the properties of surfaces [1 – 3]. The first approach used, named ‘grafting to’ [1], consists in the condensation of functionalized polymers with reactive groups of a solid substrate. This method does not give highly dense polymer brushes because chemi-sorption of the first fraction of chains hinders the diffusion of the following chains to the surface for further attachments [2]. Another approach, named ‘grafting from’, has been considered to obtain better densities. In this technique, a mono-layer of initiator molecules is covalently attached to a solid surface [4 – 6]. After activation the chains grow from the interface then the only limit to propagation is the diffusion of monomers to the active species. To have a good control of the polymer mono-layer thickness and polymer structure, living polymerization, for example anionic [7] or cationic [8] polymerizations, can be * Corresponding author. Tel.: þ 33-5-59-40-76-09; fax: þ33-5-59-40-7623. E-mail address: [email protected] (L. Billon). 0032-3861/$ - see front matter q 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2004.05.030

used. However these polymerizations require specific experimental conditions thus making their application difficult, while recent advances in controlled/’living’ free radical polymerization (suppression of terminations and chain transfer reactions), a less constraining technique, have made it viable for the synthesis of well defined and narrow polydispersity polymers. Atom transfer radical polymerization (ATRP) [9 –11] and stable free radical polymerization (SFRP) [12 –15] belong to the controlled/‘living’ radical polymerization. These polymerizations are based on the reversible activation and deactivation of growing radicals. A very low concentration of propagating radicals is produced suppressing termination reactions and giving polymers with narrow polydispersity. Another advantage with these two techniques is that the chains formed are end-capped by a dormant function that can be further thermo-activated to prepare block copolymers [15b]. Matyjaszewski et al. have used the ATRP technique to generate PS-b-PBzA from the polysilsesquioxane nanoparticles, spending a lot of space for the characterization of the particles and their nanoscale morphology on surfaces [9b]. Moreover, Hawker et al. have described that tethering alkoxyamine initiators to a solid support (as silicon wafer) can form PS brushes and that well-defined PS-b-PMMA block copolymer brushes can be

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prepared [2]. But in the two previous studies [2,9b], the block copolymers were formed by sequences with high or ambient glass transition temperatures and there is no characterization on the thermal properties of the grafted macromolecular chains. In this paper, we present the preparation of polymer brushes on silica particles via ‘grafting from’ approach. The polymer chosen was poly(n-butyl acrylate) (PBA) and was prepared by stable free radical polymerization. In a second step, we have activated the chain end functions of PBA end thus we have made a copolymer with polystyrene (PS), verifying the control of chain terminal functionality obtained during the stable free radical polymerization of butyl acrylate. The aim of this study was to generate hybrid inorganic/organic particles by nitroxide-mediated polymerization (NMP), in order to elaborate a core-shell nanocomposite with a hard core of silica coated by a double shell of a rubbery inner shell (PBA T g < 2 50 8C) and a glassy thermoplastic outer shell (PS T g < 100 8C).

Refractive index detector and a 996 Waters Photodiode array detector. A calibration curve established with low polydispersity polystyrene standards was used for the determination of the polyacrylate molecular weights. Thermal Gravimetric Analysis (TGA) was performed on a TA Instruments TGA 2950 at a scan rate of 10 8C min21 under air. DSC was carried out using a DSC Q 100 apparatus from TA Instruments at a scan rate of 20 8C/min for both heating and cooling. The reported glass transition temperatures were determined from the second heating run and were taken as the middle point of the DH=dt step in the DSC spectra.

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 triethylamine (110 mmol) and the solution was cooled to 0 8C in an ice bath. Using an addition funnel, 16.4 ml (157 mmol) of 2-bromopropionyl bromide were added dropwise and the temperature was kept on to 0 8C. Upon complete addition, the mixture was brought to room temperature and allowed to stir overnight. The product was washed with 3 £ 100 ml of H2O, dried over anhydrous MgSO4 and the solvent was evaporated. The remaining pale yellow oil was distilled under reduced pressure (60 mtorr) at 60 –70 8C, and 15.38 g (75%) of the product was collected.

Fumed Silica particles with an average elemental diameter of 13 nm and a specific surface area of 255 m2 g21 (Aldrich) were dried overnight at 120 8C under vacuum before used. Toluene was distilled under nitrogen atmosphere from over molten sodium. MONAMS alkoxyamine and SG1 counter-radical have been used as received from ATOFINA. All other solvents and chemical products were purchased and used without further purification.

2.3. Mono-layer self assembly and polymerizations The elaboration and the synthesis of the polyfunctional coupling agent are based on a molecular engineering involving a multi-step reaction. Indeed, this coupling agent has to be constituted in its molecular structure of three functional groups.

2.2. Characterizations and measurements 2.5. Allyl alkoxyamine synthesis X-ray photoelectron spectroscopy analyses were performed with a Surface Science Instrument (SSI) spectrometer at room temperature, using a monochromatic and focused (spot diameter of 600 mm, 100 W) Al Ka radiation (1486.6 eV) under a residual pressure of 5 £ 1028 Pa. The hemispherical analyzer worked under constant pass energy mode, 50 eV for high resolution spectra and 150 eV for quantitative analysis. The binding energy scale was calibrated from the carbon contamination using the C1S line (284.6 eV) (a mean atomic percentage of 8% was determined). The Fourier transform infrared (FTIR) spectra were recorded using a Bruker IFS 66/S spectrometer at a resolution of 4 cm21 in absorption mode. 100 to 1000 scans were accumulated. Size Exclusion Chromatography (SEC) characterization was performed using a 2690 Waters Alliance System with THF as eluent. It was equipped with four Styragel columns HR 0.5, 2, 4 and 6 working in series at 40 8C, a 2410 Waters

To a round bottom flask containing 1.5 g (7.8 mmol) of allyl 2-bromopropionate, 2.6 g (7 mmol) of N-tert-butyl-N(1-diethylphosphono-2, 2-dimethyl) propyl nitroxide at 80% of purity (also referred to as DEPN or SG1), 0.5625 g (3.9 mmol) CuBr, 0.495 g (7.8 mmol) Cu and 0.675 g (3.9 mmol) de PMDETA was added 15 ml of freshly distilled toluene. The mixture was stirred for 4 h at room temperature in order to complete an Atom Transfer Radical Addition (ATRA). The green solution was filtered under celite in order to eliminate the copper. After filtration, the yellow solution was washed with 2 £ 25 ml of 40% aqueous solution of ammonium formate and 25 ml of aqueous solution saturated with sodium hydrogenocarbonate. The remaining yellow oil was distilled under reduced pressure and 0.894 g (30%) of a orange oil was collected. This solution in toluene was directly used for the immobilization of the alkoxyamine initiator to silica particle.

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2.6. Immobilization of the allyl alkoxyamine initiator to silica

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3. Results and discussion 3.1. Synthesis of hybrid particles

The surface modification reaction has been realized using glass apparatus flamed under vacuum. To a round bottom flask, 1.04 mmol of allyl alkoxyamine previously synthesized and 0.9 g of silica were introduced with 5 ml of freshly distilled toluene (Silica was dried overnight at 180 8C under vacuum). Under N2 atmosphere, 0.5 ml of triethylamine was added dropwise and the mixture was stirred overnight at room temperature. The particles were washed free of any adsorbed initiator with five cycles of centrifugation and resuspension in methanol and dichloromethane, and then volatile products were removed under vacuum. 2.7. Polymerizations Under inert atmosphere, 1 g of modified silica particles was suspended in a mixture of 20 ml of n-butyl acrylate, free alkoxyamine MONAMS ([n-BA]/[MONAMS] ¼ 390) and SG1 ([SG1]/ [MONAMS] ¼ 0.05) using the schlenk process. This mixture was thoroughly degassed for 30 min and heated to 120 8C for 1 – 8 h. The nano-composites were washed and centrifuged in toluene (five cycles) to remove non-attached polymer. The removal of adsorbed polymer on these hybrid inorganic/organic silica-particles was monitored by FTIR up to no significant variation of the absorbance of the characteristic peak of carbonyl function (acrylic polymer). 2.8. Copolymerizations Under inert atmosphere, 1 g of poly(n-butyl acrylate) modified silica particles was suspended in a mixture of styrene, free alkoxyamine MONAMS ([St]/ [MONAMS] ¼ 200) and SG1 ([SG1]/[MONAMS] ¼ 0.05) using the schlenk process. This mixture was thoroughly degassed for 30 min and heated to 120 8C for 3 h. The hybrid-composites were washed and centrifuged in toluene (five cycles) to remove non-attached polymer. 2.9. Degrafting procedure 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(nbutyl acrylate) structure under this trans-esterification conditions [16]. After freeze-drying of the degrafted polymers, the molecular weights were determined by GPC measurements and compared to the free chains.

The silica used to synthesize the polymer brushes was previously grafted by an alkoxyamine initiator, called coupling agent, derivated from DEPN [14] and composed by three functions as described by Ru¨he [5,6] and us [16] (Fig. 1) (a grafting function, an initiating function and a cleavable function). The synthesis of this coupling agent and these nano-particles are described in the experimental part of a previous article [17]. From these modified particles, we initiated the bulk polymerization of n-butyl acrylate. Free alkoxyamine initiator (MONAMS [15]) and a slight excess of counter radical nitroxide (DEPN) ([DEPN]/ [MONAMS] ¼ 0.05) were added to the solution. The 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 agent, while the nitroxide permits a better control on the polymerization of the grafted and free chains. The first monomer used was n-butyl acrylate, three PBA samples of different molecular weights were prepared by varying the polymerization time but keeping the same ratio [BA]/ [MONAMS]. The experimental conditions are resumed in Table 1. The macromolecular dimensions (M n, M w, Ip) of the free PBA (untethered) were determined by SEC (Table 1). At this point, the PBA chains were not degrafted because we wanted to synthesize block copolymer with styrene. The polydispersity decreases with the polymerization time and the values obtained for the three PBA are comprised between 1.4 and 1.2 significant of a controlled free radical polymerization. The grafted PBA chains obtained by NMP are terminated by an alkoxyamine function thus permitting an initiation of a new NMP. We decided to re-initiate NMP from the PBA grafted silica in presence of styrene in order to obtain a coreshell hybrid-composite with a hard core of silica and by a double shell of a soft material and a hard material (Fig. 2). We used the three different PBA grafted silicas and choose to have the same molecular mass of the polystyrene block for the three samples. So, the same procedure was used: bulk 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 in the three experiments have a similar molecular weight

Fig. 1. Coupling agent composed of three functions: grafting function (I), cleavable function (II) and initiating function for nitroxide-mediated polymerization (III).

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Table 1 Polymerization conditions of PBA and macromolecular parameters of the free chains as determined by SEC Free PBA chains

Si 1 Si 2 Si 3 a b

Free PS chains

[BA]/[I]

Time (h)

M n (g mol )

Ip

[St]/[I]

Time (h)

M n (g mol21)

Ipb

390 390 390

1 4 8

13700 32600 39700

1.38 1.25 1.21

200 200 200

3 3 3

11300 11200 10800

1.15 1.14 1.15

a

21

b

I: MONAMS Mw =Mn

(10; 800 , Mn , 11; 300Þ: This result will permit the study of the influence of the PBA block on the PS block and conversely. By the presence of the ester function in the grafted initiator, the copolymers chains can be cleaved from the silica and characterized by GPC. These characteristics cannot be directly compared with those of the untethered chains generated by the free initiator during the polymerization. However, if the reaction mechanism is analogous in bulk and at the surface, the number average molecular weight of the grafted copolymers is expected by equal to the same of those of the two homopolymers obtained successively in bulk (PBA then PS). In the particular of the Si3 sample, this assumption is well verified (Table 1 and Fig. 3). Indeed, if we compare the number average molar mass of the degrafted chains (M n Si3 ¼ 51,200 g mol21; Ip ¼ 1.20) with the number average molar mass of both free PBA and free PS synthesized during the same experiments (M n ¼ 10,800 þ 39,700 ¼ 50,500 g mol21) we observe a similar result knowing that the calibration curve was established with PS standards. Moreover, the polydispersity value of the cleaved block copolymer PBA-b-PS is very

closely to the polydispersity of each free polymer, confirming the control of the block copolymer formation by Surface-Initiated Nitroxide Mediated polymerization (Fig. 3), as also described from silicon wafer by Hawker [2]. 3.2. Structural characterizations The modified silicas have been characterized by FTIR (Fig. 4) to determine the effectiveness of the modifications. Fig. 4 shows the spectra of the three silicas, normalized with the peaks of Si-O. Above, the top spectrum corresponds to the silica modified by an alkoxyamine initiator which was used for the polymerization of butyl acrylate BA. The intermediate spectrum were registered for purified silica obtained after BA polymerization and the spectrum below corresponds to the purified silica obtained after copolymerization of Styrene in order to synthesize PBA-b-PS. On the right part of the spectrum (b), the peak at 1725 cm21 corresponds to the stretching vibration of the carbonyl groups of the poly(butyl acrylate), that well confirms the 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

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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 and at 3000 – 3100 cm21 (left part) the new peaks characteristic of CH aromatic vibrations can be observed. This indicates the presence of the poly(butyl acrylate)-bpolystryrene copolymer at the silica’ surface. These qualitative characterizations show the formation of hybrid composites, first a poly(butyl acrylate) brush on silica and in a second step after re-initiation, the synthesis of a poly(butyl acrylate)-b-polystyrene copolymer brushes on silica. In order to confirm the effective formation of polymer brushes, already seen by FTIR, a study by XPS was made. Fig. 5 presents the results of XPS measurements. The spectrum of the bare substrate (Fig. 5(a)) shows signals due

to the presence of silicon (152 eV, Si(2s); 103 eV, Si(2p)) and oxygen atoms (533 eV, O(1s)). After the immobilization of the coupling agent (b), three new signals appear due to the phosphorus (133.8 eV, P(2p)), the carbon (285 eV, C(1s)) and nitrogen atoms (400.7 eV, N(1s)) of the grafted alkoxyamine compound characteristic of the presence of the SG1 nitroxide. Further more, comparison of the XPS spectra of the coupling agent mono-layer (b) and the graft PBA (c) shows a strong enhancement of the carbon signal at 285 eV (C(1s)) due to the acrylic part. Additionally, in the (c) spectra the signals of Si(2p) are attenuated and the C(1s)/ O(1s) signals ratio is clearly enhanced demonstrating the 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).

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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 to note that the phosphorus and nitrogen atoms of SG1 nitroxide are still remaining at the end chain of macromolecules after polymerization. The presence of the nitroxide SG1 gives us the opportunity to elaborate some block copolymers at the surface of the silica-particles with antagonist properties such as copolymer PBA-b-PS. The XPS spectra of the silica particles obtained after re-initiation of the SG1 end-capped PBA in presence of styrene is shown Fig. 5. Indeed the C(1s)/O(1s) and C(1s)/Si(2p) signals ratio increase from 0.23/0.15 to 0.62/0.36, respectively, for grafted PBA/PBA-PS silica particles. 3.3. Grafting density A thermal study of the different grafted silicas was

performed by themogravimetric analysis. An analysis of the pure silica used in this work shows no thermal degradation, no weight loss was encountered in the temperature range used (30 – 650 8C). On the thermograms of polymer-grafted silicas (Fig. 6), we can see a significant weight loss due to the degradation of the grafted organic compound. The weight loss is more important for the copolymer-grafted silica than for the PBA-grafted silica proving that the in-situ copolymerization is effective. The thermal behavior difference between the bare silica and grafted silicas permits the estimation of the grafting densities for the initiator, the PBA and the copolymer PBA-b-PS. Indeed, if we make the approximation that at 650 8C all the organic material is degraded and that only the inorganic material remains we can calculate the grafting density (Table 2). For grafted polymers the density decreases when M n increases (the

G. Laruelle et al. / Polymer 45 (2004) 5013–5020

Fig. 6. Thermograms of PBA (a), PBA-b-PS (b) grafted-silicas (Si3) and (c) pure silica.

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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 40,000 g mol21). The grafting density for a grafted PBA and the corresponding copolymer PBA-b-PS is nearly similar, showing that the re-initiation of the end-capped SG1 for the copolymerization has a good efficiency. However all these values are far from the grafting density of the coupling agent (0.52 molecule nm22) so only small amounts of the grafted coupling agent initiate the in situ polymerization due the crowding effect of grafted chains or to a degrafting process at high temperature as we will describe in a forthcoming paper.

temperature relative to the PBA block (elastomer phase) and another relative to the PS block (thermoplastic phase), characteristic of a phase separation. For the PBA blocks the T g obtained is around 2 20 8C and this of the glassy state block PS is closed to 80 8C. To compare, we have performed a DSC on homopolymers PBA of different molar mass and for PBA grafted on silica. For free PBA, T g was comprised between 2 53 8C for M n¼ 25; 000g mol21 and 2 47 8C for M n¼ 130; 000g mol21 ; respectively. In case of PBA grafted-silica, T g was equal to 2 35 8C. The PS block and 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 so when the glass transition of the PBA occurs, the two extremities of the copolymer chain are fixed, one by the rigidity of the PS the other by the presence of the silica particle. Then the motion of the PBA block is hindered and more energy is needed to pass from a glassy state to a caoutchoutic state thereby increasing the temperature of the glass transition of the PBA. The silica has no significant direct influence on the PS block because the presence of the PBA between those two parts. On the other hand the PBA has an influence on T g of the PS. For the PS block, T g varies from 83 8C to 85 8C while for a PS with the same M n (10 000 g mol21) T g is 97 8C. This time, the effect is the opposite than the one described before for PBA. When the glass transition of the PS occurs, the PBA block is flexible and in movement leading the PS block to be more flexible than if it where alone so the PS block need less energy to

3.4. Thermal properties of polymer grafted silica particles A second thermal study was made by DSC in order to estimate the influence of the silica on the grafted polymers and the influence of one block on the other for grafted block copolymers (Fig. 7 and Table 3). Indeed, in a DSC study, Patterson et al. have demonstrated the effects of tethering and chain immobilization on the glass transition temperature of PS (thermoplastic polymer). The measured T g of annealed bulk films of hybrid nanoparticles was elevated with respect to the value of pure bulk PS because of the chain grafting or immobilization and to the chain extension [9c], phenomena briefly reported by Carrot et al. on PS grafted silica particles also synthesized by ATRP [18]. In our case, DSC spectra of copolymer PS-b-PBA grafted on the silica (Fig. 7(b)) shows two T g; one under room Table 2 Determination of the PBA and PBA-b-PS grafting densities by TGA PBA grafting density

Si 1 Si 2 Si 3 a

PBA-b-PS grafting density

Weight loss (%)a

mmol g21

molecule nm22

mmol m22

Weight loss(%)a

mmol g21

molecule nm22

mmol m22

Efficiency (%)

13.3 17.7 11.1

16.2 9.5 4.6

0.040 0.022 0.011

0.064 0.038 0.018

26.2 18.8 15.4

13.8 6.8 3.6

0.033 0.016 0.008

0.054 0.027 0.014

83 –85 71 –73 73 –78

Weight loss by TGA.

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Table 3 Glass transition temperatures of core/shell PBA and PBA-b-PS grafted particles by DSC PBA

Si -PBA Si -PBA-b-PS Free PBA Free PS Free PBA-b-PS Free PS-b-PBA-b-PS

PS

Tonset (8C)

T g (8C)

Tonset (8C)

T g (8C)

247/240 230/225 260/255 – 240 245

235/230 222/216 253/247 – 230 237

– 74 – 90 76 74

– 83/85 – 97 83 82

pass from a glassy state to a caoutchoutic state thereby decreasing is glass transition temperature. In order to estimate the real influence of the silica particle over the PBA 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 PS of the tri-block and for the PS of the PBA-b-PS grafted are very similar confirming the weak and important, respectively influence of the silica and PBA on this block. The major difference between the tri-block and a grafted diblock copolymer is on the T g of the PBA since its T g for the tri-block is lower (2 42 8C) than for the grafted copolymers (2 22 8C to 2 16 8C) meaning that the silica particles have a higher impact than the PS block on the thermal behavior of the PBA, as a tough and hard matter due to their inorganic character.

4. Conclusion Formation of hybrid inorganic/organic materials, by insitu polymerization thanks to an alkoxyamine type coupling agent previously grafted to the inorganic material, was confirmed by both FTIR and XPS. This ‘grafting from’ approach has given good polymer grafting densities giving us hope to achieve formation of polymer brushes onto silica. The use of a stable free radical polymerization (also called nitroxide-mediated polymerization) permits a control of the dimension and the structure of the grafted polymers. Indeed, we have shown that the molar mass and the polydispersity of the grafted polymer were very similar with a free polymer made in the same conditions. Another advantage of the nitroxide-mediated polymerization is the ability to polymerize a large range of monomers (styrenic, acrylic, methacrylic) and to make blocks copolymers. For example in this article the formation of a diblock poly(n-butyl acrylate)-b-poly(styrene), with narrow polydispersity,

grafted to silica particles was shown, leading to a core/ double shell hybrid inorganic/organic material (a double shell constituted by a rubbery inner layer and glassy thermoplastic outer layer). The materials obtained have different thermal behaviors, function of the ratio PBA/PS. So, it is possible to tune the surface properties (for instance the adherence, wetability…) of the inorganic material by choosing the nature (elastomeric, thermoplastic, hydrophilic…) and the dimension of an adequate grafted polymer.

Acknowledgements The authors are pleased to acknowledge O. Guerret from ATOFINA for supplying SG1 and MONAMS, and C. Guimon for the XPS measurements.

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