SiO2交联剂交联MMA聚合制备PMMA/SiO2纳米复合材料

用SiO2交联剂(SiO2HPA)交联甲基丙烯酸甲酯(MMA)自由基聚合制备PMMA SiO2纳米复合材料。采用两步法将可聚合乙烯基单体以化学键的形式键接到SiO2表面合成SiO2交联剂,首先利用过量的甲苯2,4二异氰酸酯(TDI)对SiO2纳米粒子表面进行化学修饰合成出表面带有高反应活性NCO基团的功能化SiO2粒子(SiO2TDI),SiO2TDI与丙烯酸羟丙酯(HPA)反应合成SiO2交联剂。系统研究了MMA单体与SiO2交联剂投料比及聚合时间对聚合反应的影响。此外,利用红外光谱(FT IR)、DSC、TGA、可见光光谱仪等实验手段对纳米复合材料进行了表征分析。结果表明,纳米SiO2粒子在复合材料中起着物理交联点和化学交联点作用,复合材料玻璃化转变温度(Tg)明显地高于其纯PMMA的玻璃化转变温度,随着纳米SiO2粒子含量的增加,复合材料玻璃化温度升高,而透明度明显降低。

Preparation of PMMA/Silica Nanocomposites by MMA Polymerization in the Presence of Silica Crosslinking Agent

Polymethylmethacrylate(PMMA)/silica nanocomposites were prepared by conventional radical polymerization of methlymethacrylate(MMA) in the presence of silica crosslinking agent (SiO_2-HPA). Two-stage process has been developed to synthesize the silica crosslinking agent through surface-modification of silica with polymerizable vinyl groups. Firstly, the silica surface was treated with excess toluene-2,4-diisocynate (TDI), after which the residual isocyanate groups were converted into polymerizable vinyl groups by reaction with hydroxypropylacrylate (HPA). The main effecting factors on the polymerization, such as ratios of MMA to the SiO_2-HPA together with the polymerization time, were studied by determining the extent of crosslinked MMA. The FT-IR, TGA, DSC and Vis spectra were employed to characterize the nanocomposites. Experiment results revealed that the silica nanoparticles acted as crosslinking points in the PMMA matrix, and the glass transition temperatures(T_g) of the nanocomposites were higher than that of the corresponding pure PMMA. DSC results indicated that the T_g of nanocomposites increased with the increasing of silica contents. However, the transparence of PMMA/silica nanocomposites decreased, which was determined by Vis spectroscopy.