端基对大单体共聚活性及聚羧酸减水剂侧链分布的影响

Effects of end groups on copolymerization activity of polyether macromers and consequent copolymer structure

为研究大单体端基对其共聚活性及形成共聚物结构的影响,测定了甲基烯丙基聚乙二醇醚(MAPEG)、异戊烯基聚乙二醇醚(IPEG)、乙氧基乙烯基聚乙二醇醚(VEPEG)与丙烯酸(AA)进行自由基水溶液共聚反应时的单体竞聚率,通过核磁共振氢谱(1H NMR)和前线轨道理论分析3种大单体共聚活性,对比了3组共聚合过程及共聚物微观结构的差异。结果表明:MAPEG和IPEG单体的化学结构及共聚合活性十分相似,而具有不同端基的VEPEG大单体有不同的共聚合活性;VEPEG-AA共聚体系的大单体转化率与MAPEG-AA和IPEG-AA共聚体系变化趋势相反。MAPEG-co-AA与IPEG-co-AA共聚物的侧链密度及侧链分布基本相同,VEPEG-co-AA共聚物侧链密度始终较低;但随着大单体加料量增加,大单体活性和共聚过程的差异使3种共聚物侧链密度差异变小。

In order to study the effect of end groups on copolymerization activity of polyether macromers and consequent copolymer structure,methyl allyl poly(ethylene glycol)ether(MAPEG),isoprenyl oxy poly(ethylene glycol)ether(IPEG)and vinyloxyethyl ether poly(ethylene glycol)ether(VEPEG)were copolymerized with acrylic acid(AA)via aqueous free radical copolymerization.The monomer reactivity was obtained and explained through 1 H NMR spectra and Frontier Molecular Orbital Theory,and three copolymerization processes and consequent copolymer microstructure were compared.The results show that the chemical structure and copolymerization activity of MAPEG and IPEG monomers are similar but significantly different from VEPEG monomers as VEPEG monomers has different end groups.The macromonomer conversion trendency of the VEPEG-AA copolymerization system was opposite to that of the MAPEG-AA and IPEG-AA copolymerization systems.The side chain density and side chain distribution of MAPEG-co-AA and IPEG-co-AA copolymers were similar,while the side chain density of VEPEG-co-AA copolymers was low.As the feeding amount of macromonomer increased,the difference in macromonomer activity and copolymerization process resulted in less difference in side chain density of the three copolymers.