选择性打开碳氮键、碳氧键分层次降解废弃聚氨酯的研究

To cope with environment pollution problems and to meet with the more strict carbon emission regulations, it is of vital importance to develop green and economical strategies for the recycling of end-of-life polymeric materials. As one type of the popular polymers, polyurethane aterials are widely used as raw materials in the field of construction industry, electronic industry, and sport/entertainment products because of their excellent physical and chemical properties. Typically, polyurethane materials are constructed of polyether,isocyanate and the chain extender, forming the three-dimentional and cross-linked structure with strengthful building bonds including C-C, C-O, urethane bonds and urea linkages. The selective cleavage of specific C-heteroatom bond(s) is of fundamental interest and an essential process for the recovery of valuable units from end-of-life polyurethane materials. Our studies have been demonstrated that the incompletely coordinated metal ions in water enable the selective cleavage of urea linkages to produce linear polyether molecules with urethane bonds as terminal groups. These recycled linear polyether molecules can be degraded with high efficiency into monomeric compound with the absence of solvents. Systematic investigations will be carried out in this work to elucidate the catalytic processes of the cleavage of urea linkages and urethane bonds by incompletely coordinated metal ions and ether bonds by Brønsted acids without solvents. Spacifically, the migration behaviors of the active metal ions, the interactions of these metal ions with the heteroatoms in the polymers, the cleavage mechanisms of urea linkages, urethane and ether bonds, and the effect of acid strength on the cleavage of ether bonds will be systematically studied, by the combination of several characterizations including infrared spectroscopy (IR), nuclear magnetic resonance (NMR), elemental analysis (ICP), gel-filtration chromatograph analysis(GPC), scanning electron microscope (SEM), terminal isotope tracer methods, modification of terminal groups and quantum chemistry calculations.

经济、绿色地降解和回收废弃高分子对日益突出的环境问题和全球碳排放政策具有重要的意义。典型的聚醚型聚氨酯材料是由聚醚、异氰酸酯和扩链剂构成的高分子材料，分子中含有醚键、氨基甲酸酯键和脲键，分层次、高选择性地打开这些化学键是全成分降解回收其废料的关键。前期研究发现浓氯化锌水溶液中的配位不饱和锌离子可以高选择性打开聚氨酯分子中的脲键和氨基甲酸酯键，生成线性聚醚分子，而线性聚醚分子在无溶剂体系高效降解生成单体化合物。基于此，本项目拟研究配位不饱和锌离子催化氨基甲酸酯键和脲键断裂的催化作用机理及无溶剂体系中质子酸催化醚键断裂的反应机制：通过IR和NMR表征催化剂与杂原子的相互作用，结合量子化学计算研究催化反应机理；利用端基改性和IR等技术研究聚醚催化降解的反应规律；采用ICP、GPC和SEM等考察金属离子在材料中的扩散和反应降解动力学，揭示催化剂配位状态和酸强度对目标键断裂的催化作用本质。

经济、绿色地降解和回收废弃高分子对日益突出的环境问题和全球碳排放政策具有重要的意义。典型的聚氨酯材料是由聚醚或者聚酯、异氰酸酯和扩链剂构成的高分子材料，分子中含有醚键或酯键、氨基甲酸酯键和脲键，分层次、高选择性地打开这些化学键是全成分降解回收其废料的关键。本项目针对当前大宗典型聚氨酯材料如聚氨酯弹性体、高交联聚氨酯发泡材料、氨纶以及聚碳酸酯聚氨酯材料的结构，设计不同的催化体系，将其高效、绿色、经济地降解为高附加值化学，深入研究了催化降解过程中溶剂效应、催化反应机理、产物的分离以及降解体系的循环等基本科学问题。系统深入研究了浓氯化锌水溶液中的配位不饱和锌离子高选择性打开聚氨酯分子中的脲键和氨基甲酸酯键和生成线性聚醚分子的催化作用机制，发现金属离子与氨基甲酸酯键上的羰基的作用是催化反应的关键过程；阐明了线性聚四氢呋喃高效降解生成四氢呋喃的催化机理，发现高溶解度的质子酸对于反应的关键作用。设计了尿素-氯化胆碱的DES催化降解反应体系，选择性打开高分子链中的氨基甲酸酯键而可以保留同样的弱键碳酸酯键，保留了高附加值的聚碳酸酯结构，实现了多弱键高分子链中特定化学键的选择性打开，机理研究发现氯化胆碱和尿素对氨基甲酸酯键的电子推拉作用是其选择性降解的催化本质原因；设计并开发了尿素-醇/水体系，将高交联聚氨酯泡沫材料降解为芳香二胺及聚醚多元醇类化合物，研究发现尿素不但可以在水相体系中进入材料的本体，而且其绿色、经济的化学特性，有利于技术的推广和应用；另外本项目还进行了多种聚氨酯材料的公斤级催化降解实验和聚醚多元醇及芳香二胺类化合物的公斤级分离实验，为相关技术的推广和产业化提供了技术保障。本项目相关技术不但将聚氨酯废弃物资源化为高附加值的化学品，而且实施过程中全流程考虑了工业推广可能遇到的科学技术问题，这些都为技术的进一步推广和升级提供了理论依据和保障。