AB_g型单体超支化聚合反应的理论模型

Theoretical Model of Hyperbranched Polymerization with AB_g Type Monomer

超支化聚合物的可控制备与分子设计对其工业化应用是十分重要的,这有待于弄清超支化聚合物的形成机理.本文回顾了早期关于超支化聚合物的Flory-Stockmayer理论,重点介绍与ABg型单体相关的超支化聚合反应的动力学原理,这是我国科学家在这一领域的工作亮点,在国际上受到了广泛的关注.相比其它一些理论方法,聚合反应动力学理论原理清晰,可通过解动力学微分方程导出反应产物的平均支化度和聚合度分布函数的解析式,由此可以计算各种分子参数,为超支化聚合物的分子设计和可控制备提供了理论基础.

Molecular design and controllable preparation of hyperbranched polymers are of great significance for their industrialized application, which depends on the understanding for their formation mechanism. At the end of 1980＇s, Kim et al. successfully prepared hyperbranched polyphenylenes. Since then, the hyperbranched polymers have been a hot topic in polymer science and great progress has been made in both experiments and theory. The topological structure and molecular parameters can be estimated by the theory of hyperbranched polymers, which provided a great help to the molecular design and controllable preparation of hyperbranched polymers. Among the various theoretical models, kinetics of hyperbranched polymerization is the most perfect due to the clear principle and rigorous derivation, by which the analytical expressions of the molecular weight distribution functions and the various molecular parameters of the products can be derived. It is one of highlights of scientists working in China. The polymerization of ABg type monomer is one of the most important technologies to prepare the hyperbranched polymers. However, the molecular weight distribution is extremely wide for the products of the polycondensation with pure ABg type monomer. The presence of a little of multifunctional group can narrow the molecular weight distribution. Moreover, the polydispersity of hyperbranched polymers obtained can drastically decrease when the monomers are slowly added to the reaction system. Another deficiency of the hyperbranched polymers resulted from the polycondensation with pure ABg type monomer is the poor mechanical properties. One of the improved approaches is the copolymerization of AB and ABg monomers, in which some linear segments can be incorporated into the hyperbranched polymer obtained. Thus, the degree of branching and the mechanical properties of the polymer can be designed by suitable monomer feed ratio. Taking account of the substitution effect, various degree of branching of the products also can be understood. Yan et al. developed kinetic model for a large variety of hyperbranched polymerizations and successfully explained these phenomena mentioned above. In this work, the early Flory-Stockmayer theory for hyperbranched polymers is reviewed and, specially, the kinetic theory of hyperbranched polymerization with ABg type monomer is introduced.