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 temperrature(Tg)

while that of BA/NaMA SLC shows two Tg.and those of MMA/BA/NaMA SLCs with the ratio of MMA to BA within 2:1～1:2 show 4Tg.The heterogeneity of copoymer composition for multiple Tg is ascribed to the assumption that the dissolved water in the sublayer surrounding the particle

enriched with-OSO-3 and -COO- groups

will cause the concentration gradients of MMA and BA monomers and phase separation.