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

聚乙烯醇(PVA)是聚乙烯醇类合成聚合物中唯一被证实可生物降解的物质。通过功能性乙烯基单体的共聚，乙烯醇嵌段可以容易地作为可生物降解的链段并入到功能聚合链中。但乙烯醇嵌段与PVA降解酶反应所需的最小结构还没有得到明确的估计。在本报告中，制备了乙烯醇嵌段，并对其嵌段长度及其立体化学构型进行了分析，预计其将作为功能聚合物链中可生物降解的链段进行反应。即制备了三种乙烯醇齐聚物，即等规三聚体(I-3VA)、无规三聚体(a-3VA)和等规五聚体(I-5VA)。通过测定共生PVA降解微生物(PVA-IMX)和分离的PVA同化菌株(粪产碱菌K314和假单胞菌113P3)的生物需氧量(BOD)，比较了这些化合物的生物降解性。结果表明，要被接受为PVA同化微生物和酶的底物，需要具有3-5个单体单元以上的链长和具有等规结构的乙烯醇嵌段，其中所有羟基都在之字形平面的同一侧被内切。粪产碱菌KK314和假单胞菌KK314的PVA脱氢酶具有底物专一性。113P3非常相似。当乙烯醇嵌段长度大于3时，含有乙烯醇嵌段的聚羧酸钠的酶生物降解性显著提高。综上所述，乙烯醇链长大于3~5的全同立构PVA需要被PVA降解菌切割为可生物降解的链段。

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.