八甲基环四硅氧烷/正硅酸乙酯乳液开环聚合反应动力学

Kinetics of Emulsion Polymerization of Octamethylcyclotetrasiloxane/Tetraethylorthosilicate

以八甲基环四硅氧烷(D4)和正硅酸乙酯(TEOS)为单体,采用乳液开环聚合法合成了交联型聚硅氧烷乳液。考察了预乳化时间、硫酸催化剂浓度和十二烷基苯磺酸钠(SDBS)乳化剂浓度、反应温度和TEOS含量对聚合反应动力学的影响。实验结果表明,乳液进行预乳化(较佳预乳化时间5min)可加快单体的聚合反应速率,且可提高单体的最终转化率;升高反应温度(较佳温度为80℃)、增加硫酸浓度(较佳浓度125.2mmol/L)和SDBS浓度(较佳浓度77.3mmol/L)有利于加快聚合反应速率;随TEOS含量的增加,聚合反应速率加快,反应达到平衡的时间缩短。该反应的聚合反应速率与硫酸浓度0.42次方、SDBS浓度0.38次方、TEOS质量分数(基于D4质量)0.27次方成正比,该反应的表观活化能为14.67kJ/mol。

Cured polysiloxane was prepared through emulsion copolymerization of octamethylcyclotetrasiloxane （ D4 ） and tetraethylorthosilicate （ TEOS ）. The influences of preemulsification time, sulfuric acid catalyst concentration, sodium dodecylbenzene sulfonate emulsifier concentration, reaction temperature and mass ratio of TEOS to D4 on the copolymerization kinetics were investigated. Results showed that the final conversion of D4/TEOS increased when preemulsification time increased, and the copolymerization rate was promoted when reaction temperature rose and the concentrations of the catalyst and emulsifier increased. Optimal reaction conditions were pre-emulsification time 5 min, copolymerization temperature 80 0（2, catalyst concentration 125.2 mmol/L and emulsifier concentration 77.3 mmol/L. The copolymerization accelerated when TEOS content increased. Reaction orders of sulfuric acid concentration, emulsifier concentration and TEOS mass fraction（ based on D4 mass） were 0.42, 0.38 and 0.27, respectively. Apparent activation energy of the copolymerization was 14.67 kJ/mol .