单体极性对甲基丙烯酸甲酯/丙烯酸丁酯/甲基丙烯酸钠无皂乳液共聚合的影响

研究了少量甲基丙烯酸钠（ＮａＭＡ）存在下单体极性对甲基丙烯酸甲酯（ＭＭＡ）／丙烯酸丁酯（ＢＡ）无皂乳液共聚合的影响．单体极性降低，使粒径减小、聚合速率提高、乳液表面张力和粘度降低、粒子表面电荷密度增大、聚合物分子量提高．ＭＭＡ／ＮａＭＡ无皂乳液聚合物只呈现一个玻璃化温度Ｔｇ，ＢＡ／ＮａＭＡ无皂乳液聚合物呈现两个Ｔｇ，ＭＭＡ／ＢＡ比为２∶１～１∶２的ＭＭＡ／ＢＡ／ＮａＭＡ无皂乳液聚合物呈现四个Ｔｇ，这是由于粒子外面相对富含ＯＳＯ－３和ＣＯＯ－基聚合物的亚层溶解了较多的水，使ＢＡ向粒子中心扩散，ＭＭＡ向外扩散，造成组成差异和相分离而引起的．

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∶1～1∶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 —OSO_3~- and —COO~- groups,will cause the concentration gradients of MMA and BA monomers and phase separation.