新型环境敏感嵌段聚合物在水溶液中的多重胶束化行为

"Schizophrenic" micellization behavior of a novel stimuli-responsive diblock copolymer in aqueous solution

采用三(2-二甲基氨乙基)胺/氯化亚铜作催化剂,通过原子转移自由基聚合方法,合成了聚(N-异丙基丙烯酰胺)-b-聚(2-羟乙基甲基丙烯酸酯)二嵌段聚合物.该聚合物和过量的丁二酸酐反应,得到了同时具有温度和pH敏感的嵌段聚合物聚(N-异丙基丙烯酰胺)-b-聚(2-琥珀酰氧乙基甲基丙烯酸酯)(PNIPAM-b-PSEMA).该聚合物在水溶液中具有环境敏感多重胶束化行为.在pH9时,当温度高于嵌段聚合物中PNIPAM的最低临界溶解温度,自组装形成以PNIPAM为核,PSEMA为壳的胶束;在20℃和pH<7时,PSEMA嵌段的溶解性逐渐下降,逐渐形成以PSEMA为核,PNIPAM为壳的胶束.在pH3,20℃和pH9,40℃时,PNIPAM-b-PSEMA的临界胶束化浓度分别为0.032 g/L和0.025 g/L.

Poly （ N-isopropylacrylamide）-b-poly （ 2-hydroxyethyl methacrylate） （PNIPAM-b-PHEMA） diblock copolymer was synthesized via atom transfer radical polymerization （ATRP） using tris [2- （dimethylamino）-ethyl]amine （Me6TREN） / CuCl as the catalysts. The pH- and thermo-responsive poly （ N-isopropylacrylamide ）-b-poly （ 2-succinyloxyethyl methacrylate ） （ PNIPAM-b-PSEMA ） diblock copolymer was obtained by reacting PNIPAM-b-PHEMA with excess succinic anhydride in pyridine under mild conditions. In aqueous solution, the ＂schizophrenic＂ micellization behavior of PNIPAM-b-PSEMA was studied by ^1 H NMR, temperature-dependent optical transmittance and laser light scattering （LLS）. PNIPAM-b-PSEMA was molecularly soluble in water at pH9 and 20 ℃. At pH9, it formed micelles ＂with PNIPAM cores and PSEMA coronas at elevated temperatures; whereas at 20 ℃, structurally ＂inverted＂ micelles with compact PSEMA cores and PNIPAM coronas were formed below pHT. The critical micellization concentrations （cmc） of PSEMA-core （pH3, 20℃） and PNIPAM-core （pH9, 40℃） micelles were estimated to be ca. 0. 032 g/L and 0. 025 g/L by surface tensiometry.