Kinetics and particle nucleation mechanism of St/BA/qBVPBr emulsifier‐free cationic emulsion polymerization

Stable functional cationic latices were prepared by emulsifier‐free emulsion copolymerization of styrene (St) and butyl‐acrylate (BA) with 1‐butyl‐4‐vinylpyridinium bromide (qBVPBr) as functional comonomer and azobis(isobutyramidine hydrochloride) (AIBA) as initiator at (70 ± 1)°C. The influences of the reaction temperature, the initiator concentration, and comonomer concentration on the polymerization conversion (x %), polymerization rate (R_p) of poly(St/BA/qBVPBr) emulsions were investigated. The results indicated that x % and R_p increase with increasing qBVPBr or AIBA concentration and temperature, and R_p can be expressed as R_p = K_p[AIBA]^0.73[qBVPBr]^0.08 (r_AIBA = 0.9968; r_qBVPBr = 0.9946, both r_AIBA and r_qBVPBr are linear correlation coefficient) and the apparent activation energy (E_a) is 47.89 kJ mol^?1. In the absence of emulsifier condition, curves of R_p versus reaction time obeyed the typical behavior characterized by Intervals I, II, and III as similar conventional emulsion polymerization. The formation and growth of poly(St/BA/qBVPBr) latex particles has been studied at different reaction times. The results indicate that N_p decrease gradually with time at the early polymerization stages and then reach a constant value after about 20% conversion, but D_p by photon correlation spectroscopy grow continuously as all polymerization proceed. Both the particle size distribution and molecular weight distribution curves are of bimodal size distribution and indicate the participation of at least two mechanisms of particle formation, namely, homogeneous nucleation in the aqueous phase and micellar nucleation. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009