EMULSIFIER-FREE EMULSION COPOLYMERIZATION OF STYRENE WITH 2 DIFFERENTAMINO-CONTAINING CATIONIC MONOMERS .1. KINETIC-STUDIES

The kinetics of emulsifier-free emulsion copolymerization of styrene w ere investigated in the presence of two amino-containing monomers, ami noethyl methacrylate hydrochloride (AEMH) and vinyl benzyl amine hydro chloride (VBAH), using 2,2'-azobis (2-amidinopropane) dihydrochloride (V50) as a cationic initiator. At first the partition coefficient of A EMH and VBAH in a water-styrene mixture were measured, indicating a st rong hydrophilicity for both monomers; kinetics of solution homopolyme rization, as followed by H-1-NMR, in water provided high k(p)/k(t)(1/2 ) values at 4.0 and 1.75 (L mol(-1) s(-1))(1/2) for AEMH and VBAH, res pectively. The two monomers were found to similarly affect the kinetic s of emulsion copolymerization of styrene: the overall polymerization rate and particle number increased dramatically upon increasing the fu nctional monomer concentration; the average number of radicals per par ticle ((n) over bar) was dependent upon the particle size, reaching a 0.5 value for particle size below 100 nm; and the molecular weight of polymer samples decreased with the functional monomer concentration, r evealing the strong activity of VBAH and AEMH in the chain transfer. T he polymerization mechanism in the presence of VBAH and AEMH was discu ssed, referring to the coagulation nucleation mechanism to explain the formation of a large particle number. Using the method proposed by Gi lbert et al., transfer rate constants were determined for each monomer (around 10 L mol(-1) s(-1)) and styrene (4.5 10(-2) L mol(-1) s(-1)). (C) 1997 John Wiley & Sons, Inc.