丙烯酰胺/丙烯酸/甲基丙烯酸甲酯双水相共聚过程的临界分相

Critical phase separation of acrylamide/acrylic acid/methyl methacrylate aqueous two-phase copolymerization

采用偶氮二异丙基咪唑啉盐酸盐(VA-044)引发丙烯酰胺(AM)/丙烯酸(AA)/甲基丙烯酸甲酯(MMA)在含一定量聚丙烯酸钠(PAANa)的硫酸铵(AS)水溶液中进行双水相共聚合。用分光光度计对聚合体系分相进行在线确定,采用溴化法测定了聚合体系临界分相时的转化率,用凝胶渗透色谱(GPC)对聚合体系临界分相时聚合物链的分子量进行了研究。随着MMA用量的增加,临界分相转化率和临界分相分子量逐渐减少;AM与AA单体总量增加,临界分相转化率逐渐降低,临界分相分子量逐渐变大;AA质量比增加,临界分相转化率和临界分相分子量下降幅度减小;盐浓度增加,临界分相转化率几乎不变,临界分相分子量逐渐减小;温度升高,体系临界分相转化率逐渐上升,临界分相分子量几乎不变;稳定剂用量增加,临界分相转化率几乎不变,临界分相分子量增加幅度变大。

A latex of anionic polyacrylamide dispersed in an aqueous solution was prepared through aqueous two-phase copolymerization of acrylamide（AM）/acrylic acid（AA）/methyl methacrylate（MMA）with the stabilizer poly（acrylic acid sodium）in ammonium sulfate solution and 2,2′-azobis[2-（2-imidazolin-2-yl）propane]-dihydrochloride as initiator.By using spectrophotometer,the phase separation point was determined online where the transparence of reaction solution declined suddenly.The effect of various parameters on the critical conversion and critical molecular weight at phase separation was measured by the bromating method and gel permeation chromatography respectively.The experimental results showed that the addition of MMA could introduce hydrophobicity to the polymer chain and increase the interfacial tension of the two phases,as a result it was easier for the polymer chain to precipitate,which in accordance made the critical conversion and critical molecular weight at phase separation decrease.The total concentration of AM and AA was also related to the relative amount of MMA segment in the polymer chain.As the total concentration of AM and AA increased,the relative amount of MMA chain segment decreased.Thus the critical conversion at phase separation decreased while the critical molecular weight at phase separation increased.AA introduced electrostatic repulsion to the polymer chain and as the mass feed ratio of AA to AM decreased,the polymer chain was easier to coalesce because of the decrease of electrostatic repulsion.Salt concentration and stabilizer concentration had similar effects on the critical conversion at phase separation,but different effects on the critical molecular weight at phase separation.In addition,the increase of temperature was unfavorable for phase separation.It enhanced the solubility of the polymer chain and accelerated the growth of the polymer chain.