Stereospecific Synthesis of Biodegradable Segment for Design of Biodegradable Polymer and Chemistry of Biodegradation

聚（乙烯醇）（PVA）是聚乙烯类合成聚合物中唯一被证实可生物降解的物质。通过官能乙烯基单体的共聚，乙烯醇嵌段可以容易地作为可生物降解的链段并入官能聚合物链中。但与PVA降解酶反应所需的乙烯醇嵌段的最小结构尚未明确估计。在这份报告中，乙烯醇嵌段的制备和分析方面的嵌段长度和其立体化学构型，预计反应作为一个可生物降解的功能性聚合物链段。即，制备三种乙烯醇低聚物，全同立构型三聚体（i-3VA）、无规立构型三聚体（a-3VA）和全同立构型五聚体（i-5VA）。利用PVA降解共生菌（PVA-IMX）、PVA同化菌和PVA降解菌，通过测定生物需氧量（BOD），比较了这些化合物的生物降解性（粪产碱菌KK 314和假单胞菌113 P3）。发现链长大于3-5个单体单元并具有全同立构结构的乙烯醇嵌段，其中所有的羟基都位于Z字形平面的同一侧，以便被接受为PVA同化微生物和酶的底物。从粪产碱杆菌KK 314和假单胞菌113 P3中获得的PVA-脱氢酶的底物特异性非常相似。对于大于约3的乙烯醇嵌段长度，观察到含有乙烯醇嵌段的聚（羧酸钠）的酶促生物降解性的显著增加。总之，发现具有大于3-5的乙烯醇链长的全同立构PVA需要被PVA降解微生物裂解为可生物降解的片段。

Poly (vinyl alcohol) (PVA) is the only substance which is confirmed to be biodegradable in the class of polyvinyl-type synthetic polymers. Vinyl alcohol blocks may be readily incorporated as biodegradable segments into a functional polymer chain by the copolymerization of functional vinyl monomers. But the minimum struture of vinyl alcohol block necessary to react with PVA-degrading enzyme has not yet been clearly estimated. In this report, vinyl alcohol blocks were prepared and analyzed with respect to the block length and its stereochemical configuration which is expected to react as a biodegradable segment in the functional polymer chain. That is, three vinyl alcohol oligomers, isotactic-type trimer (i-3VA) , atactic-type trimer (a-3VA) and isotactic-type pentamer (i-5VA) were prepared. The biodegradability of these compounds was compared by measuring biologycal oxygen demand (BOD) using symbiotic PVA degrading microbes (PVA-IMX) , isolated PVA-assimilating strain (Alcaligenes faecalis KK314 and Pseudomonas sp.113 P3) .It was found that the vinyl alcohol block having a chain length of more than 3-5 monomer units and having an isotactic structure, in which all hydroxyl groups are lacated on the same side of the zig-zag plane, is needed in order to be accepted as a substrate for PVA-assimilating microbes and enzyme. It was also found that substrate specificity of PVA-dehydrogenase obtained from both Alcaligenes faecalis KK314 and Pseudomonas sp. 113 P3 was quite similar. A significant increase in enzymatic biodegradability of poly (sodium carboxylate) containing vinyl alcohol blocks was observed for a vinyl alcohol block length of more than about 3. In conclusion, it is found that the isotactic PVA having a vinyl alcohol chain length of more than 3-5 is needed to be cleaved by PVA-degrading microbes as a biodegradable segment.