Effects of ethyl acetate on the soap-free emulsion polymerization of 4-vinylpyridine and styrene

The properties and morphologies of poly(4-vinylpyridine-co-styrene) [P(4VP/ St)] lattices, prepared by soap-free emulsion polymerization using the wate r-soluble initiator 2,2'-azobis(2-amidinopropane) 2HCl (V50), were greatly affected by the addition of ethyl acetate (EA). The properties and morpholo gies of the resultant lattices were characterized by measuring the zeta pot ential, viscosity average molecular weight, particle size and distribution, glass-transition temperature (T-g), and photographs taken by SEM and TEM. The effects of two kinds of monomer feeding modes, that is, the batch and s emicontinuous emulsion copolymerization, were also investigated. For batch emulsion copolymerization, by charging EA, the core-shell morphology result ing from the disparate reactivity ratios of the 4VP(1)St(2) copolymerizatio n system (r(1) = 1.04, r(2) = -0.73) disappeared. Instead, first a bimodal particle size distribution, with an apparently asymmetric composition struc ture, and then spherical microspheres were obtained as the amount of EA cha rged increased from 2 to 10 wt %. The particle size increased twofold by th e addition of EA. The zeta potential of particles increased from +64.4 to m ore than +100 mV, and viscosity average molecular weight decreased from 9.7 0 to 0.97 x 10(5) g/mol, as EA increased from 0 to 8 wt %. With the semicon tinuous copolymerization, raspberry-like particles were obtained by chargin g 10 wt % EA, whereas a sandwich-like morphology was obtained without EA. T he DSC curves showed one T-g for all the lattices prepared with charging EA , but two T-g's for the latex prepared without using EA, regardless of the monomer feeding modes. (C) 2001 John Wiley & Sons, Inc.