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									                                                             Polymer 45 (2004) 5013–5020

     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

   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’ [1], 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 [2]. 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 [7] or cationic [8] 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: (L. Billon).                    well-defined PS-b-PMMA block copolymer brushes can be
0032-3861/$ - see front matter q 2004 Elsevier Ltd. All rights reserved.
5014                                       G. Laruelle et al. / Polymer 45 (2004) 5013–5020

prepared [2]. 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
                                                                       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 [14] and composed
distilled toluene (Silica was dried overnight at 180 8C under                                                   ¨
                                                                       by three functions as described by Ruhe [5,6] and us [16]
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 [17]. 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 [15]) 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 [16]. 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
                               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
     I: MONAMS
     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 [2].
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 [18].                             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
     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
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
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    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                 [10] 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.
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confirmed by both FTIR and XPS. This ‘grafting from’                        [12] 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.               [13] (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.
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dimension and the structure of the grafted polymers. Indeed,
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we have shown that the molar mass and the polydispersity of                [15] (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.
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merize a large range of monomers (styrenic, acrylic,
                                                                           [17] 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                    [18] 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.

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