Blackman Lewis D, Wright Daniel B, Robin Mathew P, Gibson Matthew I, O'Reilly Rachel K
University of Warwick, Gibbet Hill Road, Coventry CV4 7AL, U.K.
ACS Macro Lett. 2015 Nov 17;4(11):1210-1214. doi: 10.1021/acsmacrolett.5b00551. Epub 2015 Oct 19.
The chain density of polymer micelles, dictated by their aggregation number (), is an often overlooked parameter that governs the macroscopic behavior of responsive assemblies. Using a combination of variable-temperature light scattering, turbidimetry, and microcalorimetry experiments, the cloud point and thermal collapse of micellar poly(-isopropylacrylamide) (pNIPAM) corona chains at lower temperatures than the cloud point were found to be largely independent of the micelle's . By controlling the core composition, the degree of hysteresis associated with the thermal transition was found to increase as a function of core hydrophobicity. We performed this study on well-characterized micelles with tunable values, composed of a thermoresponsive corona (pNIPAM) and a nonresponsive core block poly(-butyl acrylate--,-dimethylacrylamide) (p(BA--DMA)), which were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization. This allowed for a distinction to be made between thermoresponsive behavior at both the molecular and macroscopic level. The study of the subtle differences between these behaviors was made possible using a combination of complementary techniques. These results highlight the critical need for consideration of the effect that self-assembly plays on the responsive behavior of polymer chains when compared with free unimers in solution.
聚合物胶束的链密度由其聚集数（）决定，是一个常常被忽视的参数，它控制着响应性组装体的宏观行为。通过结合变温光散射、比浊法和微量量热法实验，发现胶束状聚（N-异丙基丙烯酰胺）（pNIPAM）冠链在低于浊点的温度下的浊点和热塌缩在很大程度上与胶束的聚集数无关。通过控制核组成，发现与热转变相关的滞后程度随着核疏水性的增加而增加。我们对具有可调聚集数的、表征良好的胶束进行了这项研究，这些胶束由热响应性冠层（pNIPAM）和非响应性核嵌段聚（丙烯酸丁酯-共-2,2-二甲基丙烯酰胺）（p(BA-co-DMA)）组成，采用可逆加成-断裂链转移（RAFT）聚合反应合成。这使得能够区分分子水平和宏观水平上热响应行为的差异。使用互补技术组合使得对这些行为之间细微差异的研究成为可能。这些结果突出表明，与溶液中的游离单聚物相比，在考虑自组装对聚合物链响应行为的影响时，迫切需要加以考虑。
