Effect of Micellization on the Thermoresponsive Behavior of Polymeric Assemblies

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• 作者：Lewis D. Blackman ; Daniel B. Wright ; Mathew P. Robin ; Matthew I. Gibson ; Rachel K. O鈥橰eilly
• 刊名：ACS Macro Letters
• 出版年：2015
• 出版时间：November 17, 2015
• 年：2015
• 卷：4
• 期：11
• 页码：1210-1214
• 全文大小：338K
• ISSN：2161-1653

文摘

The chain density of polymer micelles, dictated by their aggregation number (N_agg), 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(N-isopropylacrylamide) (pNIPAM) corona chains at lower temperatures than the cloud point were found to be largely independent of the micelle鈥檚 N_agg. 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 N_agg values, composed of a thermoresponsive corona (pNIPAM) and a nonresponsive core block poly(n-butyl acrylate-co-N,N-dimethylacrylamide) (p(nBA-co-DMA)), which were synthesized using reversible addition鈥揻ragmentation 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.