用NMR分析可生物降解的两亲性嵌段共聚物的相对分子质量和组成

Determination of the Relative Molecular Mass and Composition of Biodegradable Amphiphilic Diblock Copolymer by NMR

分别采用1H NMR和凝胶渗透色谱(GPC)法分析两亲性嵌段共聚物单甲氧基聚乙二醇-聚己内酯(M eOPEG-PCL)和单甲氧基聚乙二醇-聚(己内酯/乳酸)(M eOPEG-P(CL-co-LA))的相对分子质量(以下简称分子量),并用NMR测得M eOPEG-P(CL-co-LA)中共聚单元的组成比。在不同氘代溶剂中利用NMR测得的M eOPEG-PCL的分子量基本相同,且与根据投料比计算的理论值非常接近。相比之下,GPC测定结果普遍低于理论值,且随着两亲性嵌段共聚物中亲油链段分子量的增加,两者相差越来越大。这是由于两亲性嵌段共聚物分子链中亲水链段和亲油链段的构象几乎在任何溶剂中都不相同,因此用GPC法很难准确测定它们的分子量,而1H NMR法测两亲性嵌段共聚物的分子量与其链段的构象无关,只与质子的化学环境有关。

The relative molecular masses of the amphiphilic diblock copolymers （ methoxy poly （ ethylene glycol） ） - poly （ e-caprolactone ） （ MeOPEG - PCL） and （ methoxy poly （ ethylene glycol ） ） - poly （e-caprolactone-co-d, 1-1actide）（ MeOPEG- P（CL-co-LA）） were determined by ^1H NMR and GPC, respectively, and the ratios of LA units to CL units in MeOPEG - P（CL-co-LA） copolymer were also determined by ^1H NMR. The relative molecular masses obtained by I H NMR in different deuterated solvents were nearly identical, and were close to the theoretical values calculated from the feed ratios. On the contrary, the relative molecular masses obtained by GPC were all lower than the theoretical values, and their difference became more significant with the increase of the relative molecular masses of the hydrophobic blocks in the amphiphilic diblock copolymers. Since the conformations of hydrophilic blocks and hydrophobic blocks in amphiphilic block copolymers are different almost in any types of solvents, it is difficult to measure accurately their relative molecular masses by GPC; whereas their relative molecular masses obtained by ^1H NMR are not related to the conformations of the blocks in amphiphilic block copolymers, but only related to the chemical environments of their proton.