微波聚合PMMA立体规整性的光谱研究

THE FT-IR AND ^(13)C-NMR STUDY OF STEREOSTURCTURE OF PMMA PREPARED BY MICROWAVE EMULSIFIER- FREE EMULSION POLYMERIZATION

用 FT- IR、13 C- NMR研究了微波无乳化剂聚合得到的聚甲基丙烯酸甲酯的立体规整性 ,聚合物中单体链节多元组含量从季碳和羰碳的核磁共振信号测得 ,实验测得的三元组、五元组分数与按 Bernolli和 First order Makov模型的计算值相符。与热聚合的对比研究说明 ,微波辐照会降低 PMMA中间同立构含量、增加全同和无规立构含量 ,原因是微波加速极性分子运动 ,有利于克服链增长过程中的空间位阻。反应体系中引入乳化剂 ,会增加 PMMA中间同立构的含量。

PMMA prepared by microwave irradiation with KPS catalyst at 70 ℃ was confirmed to be atactic structure. The difference of syndiotactic content reveals the influence of microwave emulsifier free polymerization on the stereostructure of PMMA. The FT IR and 13 C NMR results reveal that polymerization accomplished by microwave will decrease the syndiotactic structure content in prepared PMMA, and so do the emulsifier free polymerization. Further calculation based on 13 C NMR data indicates that for emulsifier free polymerization, the continuous ratio( ρ ) is about 0.90 and the N (ad) probability values are closed to the predictive values by first order Makov model. We believe that such kind of results are ascribed to two facts: the agitating to monomer by microwave irradiation and the change of polymerizing environment. For microwave polymerization, microwave can agitate and accelerate the movement of high polarity monomer MMA, help it overcome the steric hindrance. This will promote the formation of more isotactic structure than traditional convection heating polymerization. In emulsifier free polymerization, the chain growth is accomplished directly in water not in micelle. The hydrogen bond interaction among H 2O, MMA and the end of growing chain can partially counteract the steric effect, leads to more formation of isotactic structure.