乳液聚合共聚物玻璃化转变温度及其理论计算

从共聚单体的竞聚率、油相水相分布系数出发,通过动力学模拟计算了丙烯酸丁酯与醋酸乙烯酯乳液共聚物的链结构,并用Johnson公式对其玻璃化转变温度(T_g)进行了理论计算,给出了共聚物T_g及其对应聚合物的重量分布图。发现半连续共聚物有1个T_g,其值随共聚物组成而变化;但一步法共聚物有两个T_g:低温区T_g代表富丙烯酸丁酯共聚物,高温区T_g则代表PVA均聚物。计算结果与实验十分吻合。

Glass Transition Temperature of Emulsion Copolymer and Its Theoretical Simulation

Based on monomer reactivity ratios and monomer partition coefficient, the glass transition temperature (Tg) of emulsion eopolymers of butyl acrylate (BA) and vinyl acetate (VA) was simulated using Johnson' s equation, and T8 diagrams versus polymer weight fraction distribution was given. The simulation results, as well as experiments, showed that one Tg was observed for semi-continuous eopolymers, and two well separated Tg's for batch process eopolymers. In semi-continuous eopolymers , Tg's values constantly increase with VA content in the eopolymers, and by theoretical simulation of Tg's in batch eopolymers at different conversions, it is shown that the experimentally observed lower Tg, which is moving towards higher temperature zone with VA content in copolymerization, represents a BA-rich copolymer mainly formed in an early stage of the copolymerization, while the higher Tg, representing a nearly PVA homopolymer and unaffected by monomer ratio variation in copolymerization , is mainly produced at a later stage of the copolymerization after BA exhausted. The theoretical simulation agrees well with experimental results.