Novel Sustainable chemical recycling of green polymers using environmentally benign catalytic process

本研究利用酶和固体酸等环境友好型催化剂，开发了可再生资源生产的可生物降解聚乳酸和生物基聚合物的可持续化学回收。此外，还研究了酶催化生物聚硫酯的合成和化学回收。结果总结如下。(1)根据基本反应参数，研究了生物基聚合物转化为可再聚合环低聚物的酶催化聚己二酸丁烯环低聚反应。研究发现，在某些有机溶剂中，脂肪酶能迅速发生环寡聚反应。环寡聚物的大小对再聚合产物的分子量和对脂肪酶的亲和力有显著影响。(2)利用固体酸化学回收聚l -乳酸的新进展。研究发现，聚l -乳酸在蒙脱土的催化下可有效降解为低聚物。所得的乳酸低聚物很容易通过固态聚合重新聚合，再生分子量大于100,000的聚乳酸。基于这些结果，提出了生物基聚合物的可持续化学回收。(3)新型酶法合成聚硫酯及其性质首次发现巯基羧酸可通过酶聚合制备分子量数万的聚硫酯。由此制备的聚硫酯比相应的聚氧酯具有更高的熔融温度和耐有机溶剂性。以烷烃二硫醇与烷烃二羧酸缩聚为原料，制备了一系列聚硫酯，并建立了酶法对其进行化学回收的方法。

In this study, sustainable chemical recycling of biodegradable poly(lactic acid) and bio-based polymers, which were produced from renewable resources, were developed using environmentally benign catalysts, such as enzymes and solid acids. Also, enzyme-catalyzed synthesis and chemical recycling of biopolythioesters were also studied. Summaries of the results are as follows.(1)Transformation of bio-based polymers into repolymerizable cyclic oligomersEnzyme-catalyzed cyclic oligomerization of poly(butylene adipate) was studied with respect to the basic reaction parameters. It was found that in certain organic solvents cyclic oligomerization was quickly occurred by lipase. The affinities toward lipase as well as the molecular weight of the repolymerization products were significantly influenced by the cyclic oligomer size.(2)Developing of novel chemical recycling of poly(L-lactic acid) using solid acidIt was found that poly(L-lactic acid) was efficiently degraded into oligomers by montmorillonite. The obtained lactic acid oligomer was readily repolymerized by solid state polymerization to regenerate the polylactic acid with a molecular weight of greater than 100,000. Based on these results, sustainable chemical recycling of bio-based polymers was proposed.(3)Novel enzymatic synthesis and properties of polythioestersIt was first found that mercaptocarboxylic acid was readily polymerized by enzyme to produce polythioester with a molecular weight of several ten thousands. Thus produced polythioester showed a higher melting temperature and resistance against organic solvents comparing to those of the corresponding polyoxyesters. Also, a series of polythioesters were produced by the polycondensation of alkanedithiol with alkanedicarobxylic acid, and their chemical recycling was established using an enzyme.