White Joanna M, Crabtree Adelyn A, Bates Frank S, Calabrese Michelle A
Department of Chemical Engineering and Materials Science, University of Minnesota, 421 Washington Ave. SE, Minneapolis, MN, 55455.
Macromolecules. 2023 Sep 12;56(17):6834-6847. doi: 10.1021/acs.macromol.3c01107. Epub 2023 Aug 23.
Poloxamers, ABA triblock polymers composed of a poly(propylene oxide) (PPO) midblock (B) and poly(ethylene oxide) (PEO) endblocks (A), are widely studied for biomedical applications. Aqueous poloxamer 407 (P407; also referred to as F127) undergoes a solution-to-gel transition with increasing temperature, driven by the formation and ordering of micelles onto periodic lattices; however, the gel temperature and resulting modulus has limited tunability. Here, reverse P407 (RP407), a BAB polymer of the same composition and molar mass but the inverted architecture, is synthesized via anionic polymerization. The micellization and gelation temperatures of RP407 are higher than that of P407 and the PPO endblocks allow for intermicelle bridging; however, both single-component solutions favor body-centered cubic (BCC) packings. Further, aqueous RP407 displays a "soft gel" region with interesting rheological behavior, including viscoelastic aging and thermal hysteresis. Combining P407 and RP407 yields solutions with intermediate transition temperatures and alters the size and micelle packing. While the single-component solutions produce BCC packings, the blends form close-packed structures and larger micelles of higher aggregation numbers. Blends of P407 with an analogous AB diblock (EP) display similar behavior, whereas RP407/diblock blends form intermediate-sized BCC-packed micelles. These differences in packing and aggregation alter the local environments within the gels, which could have implications for applications such as drug delivery and protein stabilization.
泊洛沙姆是由聚环氧丙烷（PPO）中间嵌段（B）和聚环氧乙烷（PEO）末端嵌段（A）组成的ABA三嵌段聚合物，在生物医学应用方面受到广泛研究。泊洛沙姆407（P407；也称为F127）水溶液随着温度升高会发生溶液到凝胶的转变，这是由胶束在周期性晶格上的形成和排列驱动的；然而，凝胶温度和由此产生的模量的可调性有限。在这里，通过阴离子聚合合成了反向P407（RP407），它是一种组成和摩尔质量相同但结构相反的BAB聚合物。RP407的胶束化和凝胶化温度高于P407，并且PPO末端嵌段允许胶束间桥连；然而，两种单组分溶液都倾向于体心立方（BCC）堆积。此外，RP407水溶液显示出一个具有有趣流变行为的“软凝胶”区域，包括粘弹性老化和热滞后。将P407和RP407混合可得到具有中间转变温度的溶液，并改变胶束的大小和堆积方式。虽然单组分溶液产生BCC堆积，但混合物形成紧密堆积结构和更高聚集数的更大胶束。P407与类似的AB二嵌段（EP）的混合物表现出类似的行为，而RP407/二嵌段混合物形成中等大小的BCC堆积胶束。这些堆积和聚集的差异改变了凝胶内的局部环境，这可能对药物递送和蛋白质稳定等应用产生影响。
