Polymers functionalized with inorganic silane groups have been used in a wide range of applications due to the silane reactivity enabling the generation of covalently-bonded coatings, micelles, and hydrogels, and even bulk structural materials via the sol-gel process. Utilizing stimuli-responsive polymers in these hybrid systems can lead to smart and tunable behavior for sensing, drug delivery, and optical coatings. Of particular interest is the thermo-responsive polymer poly(<i>N</i>-isopropyl acrylamide) (PNIPAM) functionalized with 3-(trimethoxysilyl)propyl methacrylate (TMA), which has been used in micelles, coatings, and gels and has demonstrated unique aqueous thermal responses. Our prior work showed that introducing blocky TMA functionalization into NIPAM, where the NIPAM/TMA copolymer is localized to a smaller portion of the chains, can lead to controlled structure formation and highly cyclable optical responses. Here, we aim to connect silane hydrolysis and condensation of PNIPAM-co-TMA to polymer content, configuration, and molecular weight in binary solution systems. Mixtures of solvents can introduce additional phase transitions compared to purely aqueous systems, allowing for one- or two-phase behavior to be accessed over a wide range of temperatures depending on the solution composition. Utilizing nuclear magnetic resonance spectroscopy, the rate and extent of hydrolysis and the decrease in polymer mobility are quantified. Changes in solution viscosity due to silane coupling are investigated via shear rheology to connect polymer structure in solution to flow properties and processability. Binary solvent systems are advantageous for processing, as the systems have lower viscosity and increased volatility compared to aqueous systems, providing a pathway to process the responsive polymers in different conformations that is less variant with temperature. These findings can improve the scalability and versatility of responsive polymer coatings where the surface function is largely influenced by the polymer structure in solution, leading to potential advancements in energy efficiency, sensing, and antibiofouling.

Role of polymer configuration on silane coupling and processability of PNIPAM/silyl methacrylate copolymers in aqueous/organic binary solvent systems

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ACS Fall 2022

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