Poly(vinyl acetate)-Based Block Copolymer/Clay Nanocomposites Prepared by In Situ Atom Transfer Radical Polymerization
Atom transfer radical polymerization of styrene (St) and methyl methacrylate (MMA) was performed at 90oC in the absence and presence of nanoclay (Cloisite 30B). Trichloromethyl-terminated poly(vinyl acetate) telomer and CuCl/ PMDETA were used as a macroinitiator and catalyst system, respectively. The experimental results showed that the atom transfer radical polymerization of St and MMA in the absence or presence of nanoclay proceeds via a controlled/living mode. It was observed that nanoclay significantly enhances the homopolymerization rate of MMA, which was attributed to the activated conjugated C=C bond of MMA monomer via interaction between the carbonyl group of MMA monomer and the hydroxyl moiety (Al-O-H) of nanoclay as well as the effect of nanoclay on the dynamic equilibrium between the active (macro) radicals and dormant species. Homopolymerization rate of St (a non-coordinative monomer with nanoclay) decreased slightly in the presence of nanoclay. This could be explained by insertion of a portion of macroinitiator into the clay galleries, where no sufficient St monomer exists due to the low compatibility or interaction of St monomer with nanoclay to react with the macroinitiator. The results obtained from XRD, TEM and TGA analyses were fully in agreement with the kinetic data. Structure of the poly(vinyl acetate)-bpolystyrene nanocomposite was found to be a combination of stacking layers and exfoliated structures while poly(vinyl acetate)-b-poly(methyl methacryale) nanocomposite had an exfoliated structure. This difference in the structure of nanocomposites was attributed to the different capability of the monomers (styrene and methyl methacrylate) to react with the hydroxyl moiety (Al-O-H) of nanoclay.
کلیدواژه ها [English]
In situ atom transfer radical polymerization, methyl methacrylate, poly(vinyl acetate), nanocomposite, polymerization kinetics