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(<i>N</i>-isopropyl acrylamide) (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.

Role of chain architecture on the solution phase assembly and thermoreversibility of aqueous PNIPAM/silyl methacrylate copolymers

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