Effects of Ethyl Acetate on the Soap-Free Emulsion Polymerization of 4-Vinylpyridine adn Styrene

摘要

The properties and morphologies of poly(4-vinylpyridine-co-styrene) [P(4VP/St)] lattices, prepared by soap-free emulsion polymerization using the water- soluble initiator 2,2'-azobis(2-amidinopropane) .2HCI (V50), were greatly affected by the addition of ethyl acetate (EA). The properties and morphologies of the resultant lattices were characterized by measuring the zeta potential, viscosity average molecu- lar weight, particle size and distribution, glass-transition temperature (T g), and pho- tographs taken by SEM and TEM. The effects of two kinds of monomer feeding modes, that is, the batch and semicontinuous emulsion copolymerization, were also investi- gated. For batch emulsion copolymerization, by charging EA, the core-shell morphology resulting from the disparate reactivity ratios of the 4VP(1)/St(2) copolymerization system (rl = 1.04, r2 = -0.73) disappeared. Instead, first a bimodal particle size distribution, with an apparently asymmetric composition structure, and then spherical microspheres were obtained as the amount of EA charged increased from 2 to 10 wt %. The particle size increased twofold by the addition ofEA. The zeta potential of particles increased from +64.4 to more than +100 mV, and viscosity average molecular weight decreased from 9.70 to 0.97 x 105 g/mol, as EA increased from 0 to 8 wt %. With the semicontinuous copolymerization, raspberry-Iike particles were obtained by charging 10 wt % EA, whereas a sandwich-Iike morphology was obtained without EA. The 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.