EFFECTS OF MONOMER POLARITY ON MMA BA/NAMA EMULSIFIER-FREE EMULSION COPOLYMERIZATION/

The emulsifier-free emulsion copolymerizations of methyl methacrylate (MMA) and n-butyl acrylate (BA) in the presence of a small amount of s odium methacrylate (NaMA) with potassium persulfate as initiator at 70 degrees C were investigated. Increasing BA feed fraction causes the d ecrease of particle diameter, surface tension and viscosity of the lat ices, and the increase of particle number, polymerization rate, surfac e charge density of the latices and average molecular weight of copoly mers. The DSC thermograms of MMA/NaMA emulsifier-free latex copolymer (EFLC) shows one glass transition temperature (T-g), that of BA/NaMA E FLC shows two T(g)s, and those of MMA/BA NaMA EFLCs with the weight ra tio of MMA to BA within 2:1-1:2 show 4 T(g)s. The heterogeneity of cop olymer composition for multiple T(g)s is ascribed to the composition d ifference and phase separation, since the dissolved water in the subla yer surrounding the particle, enriched with -OSO3- and -COO- groups, c auses the diffusion of BA toward the particle core and that of MMA out ward the core. (C) 1998 Elsevier Science Ltd. All rights reserved.