含pH敏感聚(4-乙烯基吡啶)的嵌段共聚物成核胶束化过程的NMR研究

利用NMR技术研究了聚乙二醇-b-聚(4-乙烯基吡啶)(PEG114-b-P4VP107)和聚(N-异丙烯基丙烯酰胺)-b-聚(4-乙烯基吡啶)(PNIPAM53-b-P4VP260)在逐步降低聚(4-乙烯基吡啶)链段质子化程度时嵌段共聚物的胶束化过程.在开始形成胶束时,吡啶环上氢原子的自旋-晶格弛豫时间(T1)急剧减小.结果表明,PEG114-b-P4VP107在质子化程度降为0.54时已有胶束生成;PNIPAM53-b-P4VP260在质子化程度降为0.58时也能观测到胶束生成的信号.将两个嵌段共聚物各自制得胶束的溶液相混合,观测到了发生在高分子链间的2DNOE信号,这表明所制得溶液中胶束与高分子链间有链交换的动态平衡.

INVESTIGATION OF THE MICELLIZATION PROCESS OF DIBLOCK COPOLYMERS CONTAINING pH SENSITIVE POLY(4-VINYLPYRIDINE) BY NMR

The micellization process of poly(ethylene glycol)-b-poly(4-vinylpyridine)(PEG_ 114-b-P4VP_ 107)and poly(N-isopropylacrylamide)-b-poly(4-vinylpyridine)(PNIPAM_ 53-b-P4VP_ 260)in acidic aqueous solutions with varying degree of protonation of P4VP was investigated by NMR.When the micelles began to form due to the hydrophobicity of P4VP was resulted from its deprotonated,the NMR signal of pyridyl stayed unchanged.The signal kept becoming weaker with the decrease of the degree of protonation until no NMR signal can be detected at the point that all the 4VP unites were deprotonated.At the mean time,the spin-lattice relaxation time(T_1)decreased significantly when the P4VP blocks began to transfer to aggregation from their unimer state.The results indicated that micelles of PEG_ 114-b-P4VP_ 107 were formed at the degree of protonation of 0.54,while the micelles of PNIPAM_ 53-b-P4VP_ 260 were achieved at the point of 0.58.The two-dimensional Nuclear Overhauser Effect(2D NOE)signal was also detected when the micelle solutions made separately from PEG_ 114-b-P4VP_ 107(at the degree of protonation of 0.54)and PNIPAM_ 53-b-P4VP_ 260(at the point of 0.58)were mixed,which indicated the exchanges of macromolecules between micelles and the diblock copolymer in solution.However,no corresponding 2D NOE signal appeared while the micelle solutions were achieved at lower degree of protonation.This fact might imply the different mobility of the P4VP blocks,which formed the micelles core,at different degree of protonation.