聚对苯二甲酸乙二醇酯的结晶成核改性研究进展

摘要

聚对苯二甲酸乙二醇酯（PET）因其重复结构单元中含有刚性苯环而成核慢、结晶度低，从而导致综合力学性能与耐热性较差，限制了其工程化应用，故对PET进行成核改性以提高结晶速率与结晶度成为亟待解决的问题。综述了PET的4大类成核剂：无机填料、有机小分子、有机高分子及复合型成核剂；在此基础上，提出机理上不同于异相成核的“离子簇集诱导成核”的概念，即与离子共价相连的聚合物链段因离子簇集而在离子簇近围紧密堆砌，从而诱导“拥挤”链段结晶成核。无机填料类成核剂包括粘土、氧化物与氢氧化物、无机盐、Si3 N4及碳纳米管／石墨等，其成核机理均为异相成核。有机小分子类成核剂涉及羧酸盐、二胺、双酰胺及改性山梨醇等，其中羧酸盐成核机理为离子簇集诱导成核，而其它均属于异相成核。有机高分子类成核剂分为结晶性聚合物、液晶高分子、嵌段共聚物及离子交联型聚合物等；其中前三者属异相成核，后者为离子簇集诱导成核。复合型成核剂为两种以上成核剂（或成核机理）配合使用协同促进PET结晶成核。对比发现，有机高分子与复合型成核剂效果较好，且不会引起PET的降解，为PET优良成核剂。异相与离子簇集诱导耦合高分子成核剂为PET结晶成核改性未来的重点发展方向之一。%Owing to the inclusion of a rigid phenylene group in its constitutional repeating unit,poly(ethylene terephthalate)(PET)is of slow nucleation and thus low degree of crystallinity,which results in relatively deteriorated overall mechanical properties as well as poor heat resistance that limit its engineering applications.Therefore,it is im-perative that the nucleation of PET be so modified as to improve its crystallization rate and degree of crystallinity. Herein,the four types of nucleating agents reported in the literatures for PET crystallization have been reviewed, i.e.,inorganic fillers (IFs),organic small-molecules (OSMs),organic polymers (OPs),and composite nucleating agents (CNAs),on the basis of which a concept of “ion-aggregation induced nucleation”(IAIN)different in mecha-nism from heterogeneous nucleation (HN)has been proposed,that is the polymer chain-segments covalently attached to ion pairs,upon ion aggregation,are closely packed in the coronas of the ionic aggregates,which induces crystalline nucleation of the“crowding”chain segments.The IF nucleating agents include clays,oxides and hydroxides,mineral salts,Si3 N4 ,carbon nanotubes/graphite,etc,all of which assume the HN mechanism.The OSM nucleating agents involve carboxylate salts,diamines,bisamides,modified sorbitols,etc,among which carboxylate salts belong to the IAIN mechanism while all others the HN.Crystalline polymers,liquid-crystalline polymers,block copolymers,iono-mers,etc,constitute the OP nucleating agents of PET,where the former three are of the HN mechanism while the latter the IAIN.The CNAs comprise two or above nucleating agents or mechanisms that synergistically promote the crystalline nucleation of PET.By comparison,the OPs and CNAs are excellent nucleating agents for PET in that they have the best nucleation effectiveness and at the same time do not give rise to PET-degradation.HN and IAIN coupled OP nucleating agents are one of the most important and promising R&D approaches to the effective modification of PET crystalline nucleation.