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ABSTRACT: We report in this paper an original and simple method for the grafting of polymer chains on colloidal silica particles. We first synthesize an alkoxyamine bi-functional initiator, by coupling 2-methyl-2-[N-tert-butyl-N-(dimethoxyphosphoryl-2,2-dimethylpropyl)aminoxy]propionic acid (MAMA) and an acrylate coupling agent, 3-(trimethoxysilyl)propyl acrylate (TPMA). Based on the fact that MAMA dissocs. at 25°, but activates polymn. of acrylates at only 110°, it is possible to stop the reaction after the insertion of only one C:C acrylate double bond, in the temp. range 25-80°. This synthetic methodol. is called "in situ thermo-dependant trapping of carbon radicals". The "new" initiator obtained at that stage is then grafted on Stoeber silica particles, by simple condensation of its alkoxysilane functions. We show that the initiator-grafting d. is twice as high as the value obtained by our first approach of "trapping of carbon radicals". The last step of the synthesis process is the grafting from polymn. of polybutylacrylate (PBA). Transmission electron microscopy (TEM) images and small-angle neutron scattering (SANS) spectra show that the PBA-grafted silica particles are spherical, with a narrow size distribution, and do not form aggregates. Moreover, by this versatile route, the grafted polymer d., the mol. wt. and therefore the polymer-layer morphol., can be easily controlled and tuned. It can also be extended to other monomers that work well with SG1 nitroxide. [on SciFinder(R)]
Soft Matter 01/2007; 3(Copyright (C) 2012 American Chemical Society (ACS). All Rights Reserved.):1014-1024. · 4.39 Impact Factor
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ABSTRACT: We investigate the nanostructure and the linear rheological properties of polybutylacrylate (PBA) filled with Stöber silica particles grafted with PBA chains. The silica volume fractions range from 1.8 to 4.7%. The nanostructure of these suspensions is investigated by small-angle neutron scattering (SANS), and we determine their spectromechanical behavior in the linear region. SANS measurements performed on low volume fraction composites show that the grafted silica particles are spherical, slightly polydisperse, and do not form aggregates during the synthesis process. These composites thus constitute model filled polymers. The rheological results show that introducing grafted silica particles in a polymer matrix results in the appearance of a secondary process at low frequency: for the lowest volume fractions, we observe a secondary relaxation that we attribute to the diffusion of the particles in the polymeric matrix. By increasing the silica volume fraction up to a critical value, we obtain gellike behavior at low frequency as well as the appearance of a structure factor on the scattering intensity curves obtained by SANS. Further increasing the silica particle concentration leads to composites exhibiting solidlike low-frequency behavior and to an enhanced structure peak on the SANS diagrams. This quantitative correlation between the progressive appearance of a solidlike rheological behavior, on one hand, and a structure factor, on the other hand, supports the idea that the viscoelastic behavior of filled polymers is governed by the spatial organization of the fillers in the matrix.
Langmuir 08/2006; 22(15):6683-9. · 4.19 Impact Factor
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ABSTRACT: We report in this paper an original method for the synthesis of polybutylacrylate grafted on silica particles. First, we use the Stoeber method to synthesize silica particles with a narrow size distribution. An initiator for radical-chain controlled polymerization is then grafted on the silica surface in two steps. Trimethoxysilylpropyl methacrylate (TPM) is first grafted on silica by simple condensation. Then, a alkoxyamine initiator N-tert-butyl-N-1-diethylphosphono2,2-dimethylpropyl-0,1-methoxycarbonyl ethylhydroxylamine (MONAMS) reacts with the CC double bond of the TPM to form the grafted initiator of radical polymerization. The last step is the grafting of butylacrylate. For this, we use living free radical polymerization that allows to control the molecular weight and the polydispersity of the polybutylacrylate chains. We show that this synthesis method makes it possible to obtain a colloidal suspension of silica particles having a mean size of about 88 nm, a weak polydispersity and an important grafting density of polybutylacrylate (PBA).
Polymer. 46(8):2486-2496.
