Study of the incorporation of alkoxysilane monomers into model latex systems

A miniemulsion copolymerization technique was applied to incorporate vinylalkoxysilanes into acrylate latex systems by an one-step batch polymerization. The use of the miniemulsion approach yields lower coagulum amounts at high silane feed contents compared to the conventional emulsion polymerization. The reactivity ratio of vinyltriethoxysilane (VTES) (1) was found to be significantly lower than that of n-butyl acrylate (BA) (2) (r₁ = 0.044, r ₂ = 8.56); a direct incorporation of the silane by batch vinyl copolymerization is not effective.; Oil-soluble 2,2′-azobis(2-methyl-butyronitrile), is a suitable initiator for the study of silane incorporation into acrylate latexes, giving good silane incorporation with an acceptable rate of hydrolysis. Alkoxysilane hydrolysis in miniemulsions depends on the acrylate hydrophobicity; the best protection from hydrolysis is achieved using the least hydrophobic acrylate. The VTES/BA latex particle morphologies are pH-dependent; a lower pH induces a core/shell morphology. Phase separation and domain formation were found to occur in the VTES/acrylate latexes. Latex aging results in a lower solubles content and higher rigid polymer fraction in the latex (NMR spin diffusion). The rigid domains observed in films cast from aged latexes were found to be crystalline and were formed in the continuous phase.; The incorporation of vinylalkoxysilanes into acrylate latexes by miniemulsion polymerization involves: (a) vinyl copolymerization between the acrylate and the vinylalkoxysilane, (b) hydrolysis of the silane alkoxy groups, followed by the condensation of the resulting hydroxyl groups leading to the formation of a Si-O-Si network that is organized in rigid domains, and (c) chain transfer to the silane vinyl group, with the formation of chemical bonds between the crosslinked network and the poly(n-butyl acrylate) (PBA) chains. The observed features of the poly(VTES-co-BA) latex particle morphology are: (1) rigid domains of Si-O-Si crosslinked VTES/BA copolymer moieties, (2) a soft matrix of non-extractable PBA chains, and (3) solvent-extractable silane moieties containing double bonds. At low silane contents (2–4 mole %), the tensile strength of silane/acrylate latex films can be dramatically modified by small changes in the process parameters, such as polymerization procedure (conventional emulsion vs. miniemulsion), initiator (oil-soluble vs. water-soluble), and use of prepolymerized VTES vs. neat VTES.