ABg型缩聚形成的超支化聚合物的支化度与分子形态

用聚合反应动力学模型, 详细分析了AB_g型缩聚体系中各种结构单元的演变, 对超支化聚合物支化度的各种定义作了比较, 并对AB_g型反应体系的支化度提出了一个改进的定义, 使得支化度随g的增加而增加, 当g从2增加到无穷大, 最大支化度相应地从0.5增加到1－e^－1. 对均方回转半径的数值计算表明, 在确定的A基团转化率(x), z-均均方回转半径几乎与g无关, 当x＝0.999时, 随着g从2增加到无穷大, z-均回转半径只增加0.1%. 但是, 同样的条件下, z-均聚合度增加到2倍. 这一现象表明在任何指定的A转化率, AB_g型缩聚中形成的超支化聚合物的分子轮廓与g无关, 随着g 增大而在超支化聚合物中增加的结构单元(或聚合度)必定分布在分子内部.

Degree of Branching and Molecular Configuration of the Hyperbranched Polymers Formed from ABg Type Polycondensation

The evolution of the various structural units incorporated in the hyperbranched polymers formed from ABg polycondensation was investigated by the kinetic model.The various definitions for the degree of branching(DB)of hyperbranched polymers were reviewed and an improved definition was presented for the general ABg polycondensation system.DB increased with increasing g at any specified conversion of A groups(x),and reached a maximum value of 1-e-1 at full conversion of A group and infinite g.The z-average mean-square radius of gyration was almost independent of the variation in the g at any specified x.It only increased 0.1% with the variation in the g from 2 to infinite at x=0.999.However,the z-average de-gree of polymerization became twice at the same condition.Such a phenomenon suggests that the outline of the hyperbranched polymers formed in the polycondensation of ABg type monomers is almost independent of the g at any specified conversion,since that the radius of gyration is decided by the shape and distribution.The added structural units(or degree of polymerization)with increasing g must be distributed over interior of the molecules.