Synthesis and physico-chemical characterization of networks based on methacryloxypropyl-grafted nano-silica and methyl methacrylate

Model hybrid materials were prepared by using a well-known four-step procedure, including (a) preparation of spherical silica particles of nanometre size and narrow size-distribution, (b) grafting of 3-methacryloxypropyl units (MOPGS) at the surface of the particles, (c) formation of stable dispersions of the grafted particles in methyl methacrylate (MMA), and (d) copolymerization of MMA and MOPGS, initiated by UV irradiation, and then completed by thermal reaction. Progressive changes in network architecture were obtained by changing the particle diameter, d, the volume fraction of filler, phi, the number of MOP units grafted per surface unit of silica particle, n, and the nature of the grafting agent bearing the MOP unit. Materials of good transparency were obtained, even at high volume fractions of filler. This feature is the result of an excellent dispersion of the particles within the polymer matrix, as confirmed by transmission electron microscopy and atomic force microscopy. Swelling experiments were carried out to define the conditions, and function of d, phi, and n for preparing networks, in which the sol phase is almost lacking. The results were rationalized by defining a new parameter: xi(D) = 6phinl(1-phi)d. DSC plots were used as a first characterization of the materials. The presence of filler was accompanied by a slight increase in the glass transition onset temperature, T-go, and a marked broadening of the transition range, DeltaT(g). Both T-go and DeltaT(g) were shown to increase linearly as a function of xi(D). (C) 2004 Society of Chemical Industry.