双酚A型聚碳酸酯的结晶增速改性研究进展

Modification of Bisphenol-A Polycarbonate for Crystallization-rate Enhancement:A State-of-the-art Review

双酚A型聚碳酸酯(BAPC)因重复结构单元中含有两个苯撑而使分子链过于刚硬,导致其结晶极其缓慢。本文评述了BAPC的三类结晶增速改性剂,即成核剂(NAs)、晶体生长促进剂(CGAs)及成核-晶体生长耦合改性剂(NA-CGAs);提出机理上不同于异相成核(HN)的"离子簇集诱导成核(IAIN)"的概念,即NA所含离子(对)经交换反应转移至BAPC链端,而后经(单)遥爪离子静电簇集引发与之共价相连的链段在离子簇近围紧密堆砌从而诱导结晶成核的过程。NAs包括无机填料、有机小分子及有机高分子等;前者属于HN,而后两者属于HN或IAIN,取决于其中是否含有可交换离子对。CGAs包括有机溶剂、超临界CO2、酯类增塑剂、液晶小分子及柔性聚合物等;其均通过降低BAPC链段间作用力而加速晶体生长。NA-CGAs为将NA与CGA配合使用、协同促进BAPC结晶的混合物。然而,在实际熔融加工时间尺度内BAPC的结晶增速仍显不足;HN-IAIN-CGAs三元耦合改性剂有望成为今后的重点发展方向。

Owing to the presence of two phenylene groups in the constitutional repeating unit, bisphenol-A polycarbonate （BAPC） has too rigid chain-segments, which result in its extremely slow crystallization. In this work, three types of crystallization-rate enhancers reported in the literature have been reviewed and commented for BAPC, including nucleating agents （NAs）, crystal-growth accelerators （CGAs）, and nucleation-crystal-growth coupled modifiers （NACGAs）, and a new concept of ＂ion-aggregation induced nucleation （IAIN）＇, which is distinct in mechanism from heterogeneous nucleation （HN）, has been proposed, i. e. , a process of translocation of an NA＇s ion pairs via exchange reaction to BAPC chain ends, followed by monochelic or telechelic ion-aggregation, due to electrostatic attractions, to trigger close packing of covalently attached chain-segments in the coronas of the ionic aggregates, thus inducing crystalline nucleation of the BAPC. The NAs for BAPC include inorganic fillers, organic small-molecules, organic polymers, etc. , the former of which belongs to HN, and the latter two of which assume either HN or IAIN, contingent upon whether there are exchangeable ion pairs. The CGAs comprise organic solvents, supercritical COz, ester plasticizers, liquid-crystalline small- molecules, flexible polymers, etc. , all of which accelerate the crystal growth invariably through decreasing the chain inter- segmental interactions of BAPC. The NA-CGAs are mixtures of NA and CGA that accelerate jointly the crystallization of BAPC. Nevertheless, the crystallization-rate enhancement for BAPC has still been insufficient within a time scale of practical melt-processing; to address this issue, HN-IAIN-CGA coupled ternary modifiers are becoming one of the most promising approaches to the maximal improvement in BAPC crystallization.