发泡剂存在下甲基丙烯酸甲酯悬浮聚合制备热膨胀微球

摘要

通过戊烷发泡剂存在下的甲基丙烯酸甲酯(MMA)悬浮聚合方法制备热膨胀聚甲基丙烯酸甲酯(PMMA)微球，利用在线激光粒度分析仪和光学显微镜观察聚合过程中PMMA微球粒径和形貌的变化，并对微球的热膨胀性能进行分析。结果表明，存在戊烷发泡剂时，聚合温度对微球粒径及形貌变化的影响显著，当聚合温度(70℃)远高于戊烷沸点时，微球粒径变化存在悬浮聚合成粒的典型特征阶段(转变、准稳态、增长和恒定阶段)，但最终微粒形貌较差，核-壳结构不完善，导致微球热膨胀性能不佳。当聚合温度(50℃)接近戊烷沸点时，聚合过程微球粒径增长阶段不明显，粒子表面光滑且核-壳结构完善，微球的热膨胀性能良好，稳泡温程为60℃(起始发泡温度为95℃，收缩温度为155℃)，体积膨胀率达56倍。%Poly(methyl methacrylate) (PMMA) thermally expandable microspheres were prepared by methyl methacrylate suspension polymerization using pentane as a foaming agent. The evolution of average size and morphology of PMMA microspheres during suspension polymerization were monitored with an on-line laser particle size analyzer and an optical microscope, respectively. The thermal expansion performance of the microspheres was also characterized. The results show that polymerization temperature has a great influence on the evolution of average size and microsphere morphology in the presence of pentane. When the polymerization temperature (70℃) is much higher than the boiling point of pentane, the variation of average size exhibits typical feature of suspension polymerization with transition, quasi-steady state, growth and identification stages as polymerization time (conversion) increases, but the morphology and thermal expansion property of the microsphere are poor due to the imperfect core-shell structure. When the polymerization temperature (50℃) is closed to the boiling point of pentane, the particle growth stage is not obvious. The obtained microspheres exhibits proper core-shell structure and excellent thermal-expansion performance with an expandable temperature range of 60℃ (the onset expansion temperature is 95℃ and the onset shrinkage temperature is 155℃) and a volume expansion ratio of 56.