Development of Biodegradable Engineering Plastics

可生物降解的无组织聚酯可用于生物医学和一般用途。然而，与芳香族聚酯相比，它们的机械性能和热性能不足。众所周知，在聚合物骨架中引入刚性环可以提高热性能和机械性能，尽管这种材料水解产生的小芳香族化合物可能是有害的。因此，为了改善脂肪族聚酯的热性能，以天冬氨酸为原料合成了具有刚性六元环的二甲基3,6 -二酮哌嗪- 2,5 -二乙酸酯（DDK），并将其作为脂肪族聚酯的二羧酸组分。首先，以DDK和四乙二醇（TEG）为原料制备了均聚物P（DDK-TEG）。P（DDK- teg）的分子量低是因为DDK的溶解度低以及所得均聚物的热稳定性低。接下来，DDK通过与琥珀酸二甲酯和1,4 -丁二醇的共聚引入PBS。当DDK含量不超过10 mol%时，产品可溶于氯仿。该共聚物表现出较好的热稳定性，在氮气条件下，其5%失重温度为341℃，而PBS的失重温度为307℃。在共聚物主链中引入刚性单元降低了熔点以上链的迁移率，这被认为可以延缓其热分解。该共聚物的DDK含量为6.8 mol%，分子量为10万Mw。该样品被脂肪酶PS^【〇R】成功水解，但降解率低于PBS。共聚物的非酶降解比PBS快得多，这可以用DDK单元的高极性性质来解释：它是如此亲水，以至于它有助于水渗透到样品中，从而加速非酶水解。

Biodegradable ahphatic polyesters are used for both biomedical and general purposes. However, their mechanical and thermal properties are insufficient in comparison with aromatic polyesters. It is well known that the introduction of rigid rings into the polymer backbone improves both thermal and mechanical properties, although small aromatic compounds produced by the hydrolysis of such a material can be harmful. Therefore, to improve thermal properties of ahphatic polyesters, dimethyl 3, 6-diketopiperazine-2, 5-diacetate (DDK), which has a rigid 6-membered ring, was synthesized from aspartic acid and used as the dicarboxylic acid component for aliphatic polyesters.First, a homopolymer (P(DDK-TEG)) was prepared from DDK and tetraethylene glycol (TEG). The molecular weight of P(DDK-TEG) was low because of the low solubility of DDK as well as the low thermal stability of the resulting homopolymer.Next, DDK was introduced to PBS by the copolycondensation with dimethyl succinate and 1, 4-butanediol. The products were soluble in chloroform as far as their DDK content did not exceed 10 mol%. The copolymer showed improved thermal stability: its 5% weight loss temperature was found to be 341℃ under nitrogen, while that of PBS was 307℃. The introduction of the rigid unit into the copolymer backbone reduces the mobility of the chain above the melting point, which is considered to retard its thermal decomposition. A film was prepared from a copolymer, whose DDK content was 6.8 mol% and Mw was 100, 000. This sample was successfully hydrolyzed by Lipase PS^【○R】, although the degradation rate was lower than that of PBS. The non-enzymatic degradation of the copolymer proceeded much faster than that of PBS did, which is explained by the highly polar nature of the DDK unit: it is so hydrophilic that it assists the penetration of water into the sample which results in the acceleration of non-enzymatic hydrolysis.