Molecular design and degradation mechanism of biodegradable polymer

生物可降解聚羧酸型功能高分子的分子设计主要从以下两个方面进行研究。(1)将对微生物反应敏感的侧基官能团，如羟基、羧基甲氧基或磺酸酯基团引入到不可生物降解的聚合物链中。(2)将醚键或酯键引入功能聚合物的主链。发现通过丙烯酸与乙酸乙烯酯、甲基乙烯基醚、甲基乙烯基硫醚、乙烯基磺酸酯或乙烯氧基乙酸的共聚获得的带有侧羟基、甲氧基、磺酸酯或羧基甲氧基的聚羧酸酯显示出对活性污泥或土壤细菌更好的生物降解性，与不含这种侧基官能团的聚羧酸酯相比，利用富集培养技术从土壤中分离到了对聚乙烯醇（PVA）和乙烯氧基乙酸钠（PVOA）具有同化作用的蜡状芽孢杆菌（Bacilluscereus）和假单胞菌（Pseudomonassp.），并利用PVOA同化菌株对含羧基甲氧基的丙烯酸酯共聚物进行了降解。在水溶性高分子中引入易微生物降解的侧基可以改善其生物降解性能，通过环氧乙烷衍生物的开环聚合制备了含醚键的聚羧酸酯。含酯基的聚合物通过相应的丙二酸内酯的开环聚合、通过苹果酸的直接聚合或通过丙烯酰胺与2-亚甲基-1，3-二氧杂环庚烷的自由基共聚来制备。在聚合物主链上引入醚或酯键可以提高其生物降解性，并且主链上含有酯基的聚合物，如聚苹果酸，很容易被活性污泥或土壤细菌生物降解。

Molecular design of biodegradable polycarboxylate-type functional polymers was studied on the following two approaches.(1) Introduction of pendant functional groups susceptible to microbial reaction,such as hydroxyl, carboxymethoxyl or sulfonate groups, to non-biodegradable polymer chain.(2) Introduction of ether or ester linkages to the main chain of functional polymer. polycarboxylates bearing pendant hydroxyl, methoxyl, sulfonate or carboxymethoxyl groups, obtained by the copolymerization of acrylic acid with vinyl acetate, methyl vinyl ether, methyl vinyl sulfide, vinyl sulfonate or vinyloxyacetic acid, were found to show better biodegradability with activated sludge or soil bacteria, comparing to those of polycarboxylates without such pendant functional groups.Several kinds of poly(sodium vinyloxyacetate) (PVOA) and poly(vinyl alcohol) assimilable microbial strains, such as Bacillus cereus and Pseudomonas sp. were isolated from soil by the enrichment culture technique.Also acrylate copolymers bearing carboxymethoxyl groups were subjected to microbial degradation by PVOA assimilable strains. It was suggested that the introduction of pendant groups susceptible to microbial degradation to non-biodegradable water soluble polymers was improved their biodegradability.Polycarboxylates containing ether linkages were prepared by the ring-opening polymerization of the corresponding oxirane derivatives. Polymers containing ester groups were prepared by the ring-opening polymerization of corresponding malolactonate, by direct polymerization of malic acid, or by the radical copolymerization of acrylamide with 2-methylene-1,3-dioxepane. Introduction of ether or ester linkages to the main chain of the polymer was found to improve their biodegradability, and polymers containing ester groups on the main chain, such as poly(malic acid) were readily biodegraded by activated sludge or soil bacteria.