(16b) Role of Chain Architecture on the Solution Phase Assembly and Thermoreversibility of Aqueous PNIPAM/Silyl Methacrylate Copolymers

Responsive polymers undergo drastic changes in conformation due to external stimuli, which can be harnessed in wide-ranging applications including sensing, separations, and drug delivery. Functionalizing these responsive polymers with reactive inorganic silane groups enables the generation of covalently-bonded macromolecular structures including hydrogels, coatings, and micelles. Responsive poly(N-isopropylacrylamide) (PNIPAM) functionalized with 3-(trimethoxysilyl)propyl methacrylate (TMA) has been used to form stabilized micelles and responsive coatings; however, these systems display reduced responsivity over multiple thermal cycles, reducing the relevance of the system in certain applications. Here, we connect polymer content and configuration to the aqueous self-assembly, optical responses, and thermal reversibility of copolymers containing PNIPAM and TMA. Two polymer configurations are studied: random copolymers of NIPAM and TMA (P(NIPAM-co-TMA)), and ‘blocky-functionalized’ copolymers, where the TMA is localized to a portion of the chain (P(NIPAM-b-NIPAM-co-TMA)). The thermal responses of aqueous polymer solutions depend strongly on the TMA content and configuration, as characterized by cloud point testing, dynamic light scattering, and variable-temperature nuclear magnetic resonance spectroscopy. Remarkably, blocky-functionalized copolymers assemble into small, well-ordered structures above the cloud point temperature and display distinct transmittance responses over multiple thermal cycles, even at low TMA incorporation (~2%mol). In contrast, random copolymers form disordered aggregates above the cloud point temperature and only display repeated thermal responsivity at negligible TMA content (0.5% mol). These findings of the architectural effects and assembly of aqueous P(NIPAM-co-TMA) could be used to improve the scalability of applications that require macromolecular structures to function over multiple cycles, including separations, sensors, and coatings.