Effects of monomer polarity on MMA/BA/NaMA emulsifier-free emulsion copolymerization

摘要

The emulsifier-free emulsion copolymerizations of methyl methacrylate (MMA) and n-butyl acrylate (BA) in the presence of a small amount of sodium methacrylate (NaMA) with potassium persulfate as initiator at 70 degrees C were investigated. Increasing BA feed fraction causes the decrease of particle diameter, surface tension and viscosity of the latices, and the increase of particle number, polymerization rate, surface charge density of the latices and average molecular weight of copolymers. The DSC thermograms of MMA/NaMA emulsifier-free latex copolymer (EFLC) shows one glass transition temperature (T-g), that of BA/NaMA EFLC shows two T(g)s, and those of MMA/BA NaMA EFLCs with the weight ratio of MMA to BA within 2:1-1:2 show 4 T(g)s. The heterogeneity of copolymer composition for multiple T(g)s is ascribed to the composition difference and phase separation, since the dissolved water in the sublayer surrounding the particle, enriched with -OSO3- and -COO- groups, causes the diffusion of BA toward the particle core and that of MMA outward the core. (C) 1998 Elsevier Science Ltd. All rights reserved. [References: 15]