Department of Chemistry, Texas A&M University , P.O. Box 30012, College Station, Texas 77842-3012, USA.
Biomacromolecules. 2011 Jul 11;12(7):2512-7. doi: 10.1021/bm2003048. Epub 2011 Jun 6.
Strategies for the preparation of polycarbonates, derived from natural polyhydroxy monomeric repeat units, were developed for biosourced polycarbonates based on quinic acid. The design and synthesis of regioselectively tert-butyldimethylsilyloxy (TBS)-protected 1,4- and 1,5-diol monomers of quinic acid were followed by optimization of their copolymerizations with phosgene, generated in situ from trichloromethyl chloroformate, to yield protected poly(1,4-quinic acid carbonate) and poly(1,5-quinic acid carbonate). The molecular weights reached ca. 7.6 kDa, corresponding to degrees of polymerization of ca. 24, with polydispersities ranging from 2.0 to 3.5, as measured by SEC using tetrahydrofuran as the eluent and with polystyrene calibration standards. Partially because of the presence of the bicyclic backbone, each regioisomeric poly(quinic acid carbonate) exhibited relatively high glass-transition temperatures, 209 °C for poly(1,4-quinic acid carbonate) and 229 °C for poly(1,5-quinic acid carbonate). Removal of the TBS-protecting groups was studied under mild conditions to achieve control over potential competing reactions involving polymer degradation, which could include cleavage of lactones within the repeat units, carbonate linkages, or both between the repeat units. Full deprotection was not achieved without some degree of polymer degradation. The regiochemistry of the monomer showed significant impact on the reactivity during deprotection and also on the thermal properties, with the 1,5-regioisomeric polymer having lower reactivity and giving higher T(g) values, in comparison with the 1,4-regioisomer. Each regioisomer underwent a 10-20 °C increase in T(g) upon partial removal of the TBS-protecting groups. As the extent of deprotection increased, the solubility decreased. Ultimately, at long deprotection reaction times, the solubility increased and the T(g) decreased because of significant degradation of the polymers.
基于奎尼酸的生物源聚碳酸酯的策略是为天然多羟基单体重复单元衍生的聚碳酸酯而开发的。对奎尼酸的 1,4-和 1,5-二醇单体进行了区域选择性叔丁基二甲基甲硅氧基（TBS）保护的设计和合成，然后优化了它们与光气的共聚反应，光气是由三氯甲基氯甲酸酯原位生成的，得到了保护的聚（1,4-奎尼酸碳酸酯）和聚（1,5-奎尼酸碳酸酯）。分子量达到约 7.6 kDa，对应的聚合度约为 24，使用四氢呋喃作为洗脱剂的 SEC 测量的多分散性范围为 2.0 至 3.5，使用聚苯乙烯校准标准。部分由于双环骨架的存在，每种区域异构体的聚（奎尼酸碳酸酯）都表现出相对较高的玻璃化转变温度，聚（1,4-奎尼酸碳酸酯）为 209°C，聚（1,5-奎尼酸碳酸酯）为 229°C。在温和条件下研究了 TBS 保护基团的脱保护，以实现对潜在竞争反应的控制，这些反应可能包括重复单元内内酯的裂解、碳酸酯键或两者之间的裂解，从而导致聚合物降解。如果不进行一定程度的聚合物降解，就无法完全脱保护。单体的区域化学对脱保护过程中的反应性以及热性能有显著影响，与 1,4-区域异构体相比，1,5-区域异构体的反应性较低，T(g)值较高。每种区域异构体在部分去除 TBS 保护基团后 T(g)值增加了 10-20°C。随着脱保护程度的增加，溶解度降低。最终，在长时间的脱保护反应时间后，由于聚合物的严重降解，溶解度增加，T(g)降低。
