Savoji Mohammad T, Strandman Satu, Zhu X X
Department of Chemistry, Université de Montréal, CP 6128, Succursale Centre-ville, Montreal, QC H3C 3J7, Canada.
Soft Matter. 2014 Aug 28;10(32):5886-93. doi: 10.1039/c4sm01049c.
Dually responsive diblock random copolymers poly(nPA0.8-co-DEAEMA0.2)-block-poly(nPA0.8-co-EA0.2) were made from N-n-propylacrylamide (nPA), 2-(diethylamino)ethyl methacrylate (DEAEMA) and N-ethylacrylamide (EA) via reversible addition-fragmentation chain transfer (RAFT) polymerization. Copolymers of different block length ratios, poly(nPA28-co-DEAEMA7)-block-poly(nPA29-co-EA7) (P1) and poly(nPA28-co-DEAEMA7)-block-poly(nPA70-co-EA18) (P2), self-assemble into vesicles and micelles, responding to external stimuli in aqueous solutions, and both show "schizophrenic" inversion behavior when the pH and temperature are varied. The relative lengths of the two blocks are shown to affect the self-assembly of amphiphilic diblock copolymers. P1 has a similar length for both blocks and forms spherical vesicles with the first block poly(nPA29-co-EA7) as the membrane inner layer at pH 7 and 37 °C (above the cloud point of the more hydrophobic block, CP1), while spherical micelle-like aggregates are obtained at pH 10 and 25 °C (above CP1) with the second block poly(nPA28-co-DEAEMA7) as the core. In comparison, P2 has a different block length ratio (1 : 3, thus a much longer second block) and forms spherical micelles above CP1 at both pH 7 (the second block as the core) and pH 10 (the first block as the core). Further aggregation was observed by heating the polymer solution above the cloud point of the more hydrophilic block (CP2). The variation of the length and chemical composition of the blocks allows the tuning of the responsiveness of the block copolymers toward both pH and temperature and determines the formation of either micelles or vesicles during the aggregation.
通过可逆加成-断裂链转移（RAFT）聚合反应，由N-正丙基丙烯酰胺（nPA）、甲基丙烯酸2-（二乙氨基）乙酯（DEAEMA）和N-乙基丙烯酰胺（EA）制备了双响应性二嵌段无规共聚物聚（nPA0.8-co-DEAEMA0.2）-嵌段-聚（nPA0.8-co-EA0.2）。不同嵌段长度比的共聚物，聚（nPA28-co-DEAEMA7）-嵌段-聚（nPA29-co-EA7）（P1）和聚（nPA28-co-DEAEMA7）-嵌段-聚（nPA70-co-EA18）（P2），在水溶液中响应外部刺激自组装成囊泡和胶束，并且当pH值和温度变化时都表现出“精神分裂症式”的反转行为。结果表明，两个嵌段的相对长度会影响两亲性二嵌段共聚物的自组装。P1的两个嵌段长度相似，在pH 7和37℃（高于疏水性更强的嵌段的浊点CP1）时，以第一个嵌段聚（nPA29-co-EA7）作为膜内层形成球形囊泡，而在pH 10和25℃（高于CP1）时，以第二个嵌段聚（nPA28-co-DEAEMA7）作为核心形成球形胶束状聚集体。相比之下，P2具有不同的嵌段长度比（1∶3，因此第二个嵌段长得多），在pH 7（第二个嵌段作为核心）和pH 10（第一个嵌段作为核心）时，在CP1以上均形成球形胶束。通过将聚合物溶液加热到亲水性更强的嵌段的浊点（CP2）以上，观察到了进一步的聚集现象。嵌段的长度和化学组成的变化使得可以调节嵌段共聚物对pH值和温度的响应性，并决定了聚集过程中胶束或囊泡的形成。
