The effect of monomer polarity on MMA/BA sodium methacrylate emulsifier-free emulsion copolymerization

The soapless emulsion copolymerization of methyl methacrylate (MMA) and n-butyl acrylate (BA) with various ratios of MMA to BA in the presence of small amount of sodium methacrylate (NaMA) was studied. Increasing BA feed fraction results in a decrease of particle diameter, surface tension and viscosity of the latexes, and an increase of particle number, polymerization rate, surface charge density of the latexes and molecular weight of copolymer. The DSC thermogram of MMA/NaMA soapless latex copolymer (SLC) shows one glass transition temperature (T-g), while that of BA/NaMA SLC shows two T-g, and those of MMA/BA/NaMA SLCs with the ratio of MMA to BA within 2:1 similar to 1:2 show 4 T-g. The heterogeneity of copolymer composition for multiple T-g is ascribed to the assumption that the dissolved water in the sublayer surrounding the particle, enriched with -OSO3- and -COO- groups, will cause the concentration gradients of MMA and BA monomers and phase separation.