High T_g microspheres by dispersion copolymerization of N-phenylmaleimide with styrenic or alkyl vinyl ether monomers

Solution and dispersion copolymerizations of N-phenylmaleimide (PMI) with either styrenics or alkyl vinyl ethers (AVEs), systems with a tendency to give alternating polymers, were investigated with the goal of producing high glass transition particles. Equimolar solution copolymerization of PMI with styrenics gave alternating copolymers, whereas AVEs gave PMI-rich copolymers (∼65:35) except for t-butyl vinyl ether, which gave copolymers with only a slight excess of PMI. These copolymers had glass transition temperatures (T_gs) ranging from 115 to 225 °C depending on comonomer(s). Dispersion copolymerization in ethanol-based solvents in the presence of poly(vinylpyrrolidone) as steric stabilizer led to narrow-disperse microspheres for many copolymers studied. Dispersion copolymeriations of PMI with styrenics required good cosolvents such as acetonitrile or methyl ethyl ketone as plasticizers during particle initiation and growth. Dispersion copolymerizations generally resulted in copolymer particles with compositions and T_gs very similar to those of the corresponding copolymers formed by solution polymerization, with the exception of t-butyl vinyl ether (tBVE), which now behaved like the other AVEs. Dispersion terpolymerizations of PMI (50 mol %) with different ratios of either n-butylstyrene and t-butylstyrene or n-butyl vinyl ether and tBVE led to polymer particles with T_gs that depended on the ratio of the two butyl monomers.