Institute of Materials Research and Engineering, Agency for Science, Technology and Research, 3 Research Link, Singapore 117602.
Langmuir. 2010 Jul 20;26(14):11763-73. doi: 10.1021/la101686q.
A series of well-defined amphiphilic di- and triblock copolymers have been synthesized, using atom transfer radical polymerization, with poly(ethylene glycol) (PEG) and poly(methacrylisobutyl polyhedral oligomeric silsesquioxane) P(MA-POSS) as the hydrophilic and hydrophobic blocks, respectively. The detailed self-assembly behavior of the amphiphilic macromolecules in aqueous media was studied using both static and dynamic light scattering (SLS and DLS) techniques. The evolution of block copolymer micelle formation in THF/water mixture (20/80 v/v) was monitored as the THF evaporated from the solvent mixture. Initially the block copolymer chains existed as unimers in solution, followed by the formation of smaller aggregates (R(h) < 2 nm) after 30 min, eventually growing in size to reach an equilibrium size when all the THF evaporated within 24 h. The micelles formed by the block copolymers were found to be kinetically unstable (not frozen); i.e., they tended to revert to individual copolymer chains on dilution. The hydrodynamic radii, R(h), of the micelles varied with the degree of polymerization (DP) of the hydrophobic P(MA-POSS); for example, for PEG(5K)-b-P(MA-POSS), an increase from R(h) approximately 13.3 +/- 1.1 nm to R(h) approximately 17.5 +/- 1.4 nm was observed with a nominal change in the DP of P(MA-POSS) from 4 to 6. The micelles formed by the triblock copolymers (P(MA-POSS)-b-PEG(10K)-b-P(MA-POSS)) were comparable in size to the diblock copolymer micelles; e.g., R(h) approximately 14.0 +/- 1.3 nm was found for P(MA-POSS)(4)-b-PEG(10K)-b-P(MA-POSS)(4). The micellar structures created by the triblocks in aqueous media were "flowerlike", where the PEG middle block adopted a loop conformation in the micelle corona. In addition to micelles, larger aggregates formed by P(MA-POSS)-b-PEG(10K)-b-P(MA-POSS) were also detected in solution. The larger aggregates may suggest a contribution from some PEG blocks adopting an extended conformation with one end dangling in solution, causing gelation at higher copolymer concentrations via intermicellar interactions. The P(MA-POSS)(4)-b-PEG(10K)-b- P(MA-POSS)(4) formed a gel in water at approximately 8.8 wt % copolymer concentration. No gel formation by diblock copolymers was observed; however, the addition of a small amount of triblock copolymer to an aqueous solution of diblock copolymer results in gel formation. Finally, rheological behavior of the obtained gels was also investigated.
已经使用原子转移自由基聚合合成了一系列定义明确的两亲性二嵌段和三嵌段共聚物，其中聚（乙二醇）（PEG）和聚（甲基丙烯酰亚基聚倍半硅氧烷）P（MA-POSS）分别作为亲水性和疏水性嵌段。使用静态和动态光散射（SLS 和 DLS）技术研究了两亲性大分子在水介质中的详细自组装行为。监测了在 THF/水混合物（20/80 v/v）中嵌段共聚物胶束形成的演变，随着溶剂混合物中 THF 的蒸发。最初，嵌段共聚物链在溶液中以单体形式存在，30 分钟后形成较小的聚集体（R(h) < 2nm），最终在 24 小时内所有 THF 蒸发时生长到达到平衡尺寸。发现由嵌段共聚物形成的胶束是动力学不稳定的（未冻结）；也就是说，它们在稀释时倾向于恢复为单个共聚物链。胶束的流体力学半径，R(h)，随疏水 P(MA-POSS)的聚合度（DP）而变化；例如，对于 PEG(5K)-b-P(MA-POSS)，观察到 R(h) 从约 13.3 +/- 1.1nm 增加到 R(h) 约 17.5 +/- 1.4nm，而 P(MA-POSS)的 DP 名义上从 4 增加到 6。三嵌段共聚物（P(MA-POSS)-b-PEG(10K)-b-P(MA-POSS)）形成的胶束的尺寸与二嵌段共聚物胶束相当；例如，对于 P(MA-POSS)(4)-b-PEG(10K)-b-P(MA-POSS)(4)，发现 R(h) 约为 14.0 +/- 1.3nm。在水介质中，三嵌段形成的胶束结构为“花状”，其中 PEG 中间嵌段在胶束冠中采用环构象。除了胶束之外，还在溶液中检测到由 P(MA-POSS)-b-PEG(10K)-b-P(MA-POSS)形成的较大聚集体。较大的聚集体可能表明一些 PEG 块采用伸展构象，一端在溶液中悬垂，导致在较高共聚物浓度下通过胶束间相互作用凝胶化。P(MA-POSS)(4)-b-PEG(10K)-b-P(MA-POSS)(4)在约 8.8wt%共聚物浓度的水中形成凝胶。没有观察到二嵌段共聚物的凝胶形成；然而，将少量三嵌段共聚物添加到二嵌段共聚物的水溶液中会导致凝胶形成。最后，还研究了所得凝胶的流变行为。
