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

在本研究中，利用环境友好的催化剂，如酶和固体酸，开发了可生物降解的聚乳酸和生物基聚合物的可持续化学循环利用。此外，还对生物多硫酯的酶催化合成和化学回收进行了研究。主要研究结果如下：(1)生物基聚合物向可再聚合环状低聚物的转化研究了酶催化的聚己二酸丁二醇酯的环状齐聚反应。研究发现，在某些有机溶剂中，脂肪酶能迅速发生环状齐聚反应。环状低聚物的大小对脂肪酶的亲和力和共聚产物的相对分子质量有显著影响。(2)开发了固体酸化学循环利用聚L-乳酸的新方法，发现蒙脱土能有效地将聚L-乳酸降解为低聚物。得到的乳酸低聚物可以很容易地通过固相聚合重新聚合，从而再生出相对分子质量大于10万的聚乳酸。在此基础上，提出了生物质聚合物的可持续化学循环利用。(3)新型酶法合成及性质首次发现，硫代羧酸很容易被酶聚合，生成相对分子质量达数万的聚硫酸酯。与相应的聚氧酯相比，所制得的聚硫酸酯具有更高的熔融温度和耐有机溶剂性能。同时，通过烷基二硫醇与烷基二元酸的缩聚反应合成了一系列多硫酯，并利用酶建立了它们的化学循环。

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.