纳米SiO_2粒子表面静电吸附引发剂的活性研究

STUDY ON THE ACTIVITY OF ADSORBED INITIATOR ON NANOSILICA PARTICLES SURFACE

引发剂2,2′-偶氮二(2-脒基丙烷)二氢氯化物(AIBA)可通过静电作用而高效稳定地吸附到在弱碱性水相中均匀稳定分散的纳米SiO2粒子表面.对这些吸附引发剂的热分解行为、在纳米SiO2粒子表面原位引发甲基丙烯酸甲酯(MMA)乳液聚合的动力学和纳米SiO2粒子表面的聚合锚固情况进行了研究.发现非吸附和吸附引发剂的热分解活化能分别为148.5kJ/mol和124.5kJ/mol,70℃时半衰期分别为12.6h和5.2h,说明在相同状态下静电吸附引发剂具有比非吸附引发剂更高的活性,因而在原位乳液聚合中表现出比常规乳液聚合更短的诱导期和更高的聚合速率.更关键的是,具有较高活性的吸附引发剂高效稳定地吸附在SiO2粒子表面,可以使聚合反应总是优先发生于纳米SiO2粒子表面,从而可以更好地促进单体在纳米SiO2粒子表面的锚固,最终有效提高无机/有机相间的复合程度.

2,2＇-Azobis（2-amidinopropane）dihydrochloride （AIBA） initiator can be efficiently and stably adsorbed onto nanometer silica particles via electrostatic adsorption, and then it can initiate the in situ polymerization of acrylate monomer onto/from the silica particles surface. In order to investigate the activity of adsorbed initiator and the action of adsorbed initiator in the in situ polymerization, the thermal decomposition behaviors of pure AIBA, no- adsorbed AIBA and adsorbed AIBA were studied by differential scanning calorimetry （DSC）, and the polymerization kinetics of methyl methacrylate （MMA） in in situ emulsion polymerization and in conventional emulsion polymerization was compared by gravimetrie method. It was found the thermal decomposition energy of no-adsorbed AIBA and adsorbed AIBA was 148.5 kJ/mol and 124.5 kJ/mol,and their half-life time at 70℃ were 12.6 h and 5.2 h, respectively. All of them implied that the adsorbed AIBA was of higher activity, which finally brought the weakening of the induction period and the improvement of polymerization rate in in situ emulsion polymerization. The anchoring degree and anchoring efficiency of PMMA onto nanosilica particles during in situ emulsion polymerization were further studied by extraction treatment and elemental analysis. It was found that the anchoring of PMMA onto/ from silica particles was the dominant means in the early stage. Thus, it is the absorbed AIBA that facilitate the initiation of polymerization on silica surface, which would improve the anchoring of polymer onto/from silica particles and subsequently the composite degree between silica particles and polymer remarkably.