AB型聚乙二醇单甲醚-聚(L-丙氨酸)嵌段共聚物自组装过程的核磁共振研究

利用核磁共振方法研究了AB型双嵌段共聚物(MPEG45-b-PA32)在选择性溶剂中的自组装行为及胶束化过程.嵌段共聚物在三氟乙酸中聚氨基酸和聚乙二醇链段均处于自由运动状态,聚丙氨酸链段为无规线团结构.在向该溶液中逐渐加入氘代水的过程中,聚丙氨酸链段又重新聚集形成规整的二级结构.结合1H-NMR和COSY谱分析,结果显示这一自组装过程伴随着聚(L-丙氨酸)链段由无规线团向α-螺旋结构的构象转变,同时嵌段共聚物逐渐形成核-壳型胶束结构.利用透射电镜观察了所形成胶束的形态,嵌段共聚物主要形成粒径150 nm到220 nm的球形胶束.

NMR STUDIES ON THE SELF-ASSEMBLE BEHAVIOR OF POLY(ETHYLENE GLYCOL) METHYL ETHER-b-POLY(L-ALANINE) DIBLOCK COPOLYMER

Poly(ethylene glycol) methyl ether-block-poly(L-alanine)(MPEG-b-PA) was synthesized with the initiation of MPEG-NH_2. While MPEG is the hydrophilic block and PA is the hydrophobic block. It is known that poly( L-amino acid)s like polypeptides have their special secondary structures such as α-helix and β-sheet. ~1H-NMR and COSY-NMR were used to monitor the micellization process of a poly(ethylene glycol) methyl ether-block-poly (L-alanine) copolymer ( MPEG_(45)- b-PA_(32)). MPEG_(45)- b-PA_(32) was dissolved in CF_3 COOD first, while poly(L-alanine)blocks were in random coil structure. When D_2O was added in this CF_3 COOD solution, MPEG_(45)-b-PA_(32)_ could selfassemble into micelles. In the micellization process, mobility of PA blocks decreased while MPEG blocks kept very high mobility.Based on the chemical shifts and COSY data analysis,it was concluded that poly(amino acid) tended trend to form α-helix structure from random coil while the copolymer assembled in water. At the same time,transmission electron microscopy (TEM) results revealed that the diblock copolymer formed spherical micelles with the size of 150～220 nm in an aqueous medium.