Polymer Microstructure Directs the Solvent-Selective Swelling Response of Polymer Brushes

To exploit polymer brushes' solvent-responsive properties for applications in nanoparticle transport and sensing, we must elucidate how polymer composition and polymer microstructure shape brush swelling in varied solvent environments. We compared the solvent-selective response of block and statistical copolymer brushes of varied solvophobic-to-solvophilic ratios by measuring brush swelling in two solvents of varying polarity. We first copolymerized 2-(dimethylamino)ethyl methacrylate (DMA) and 2-(diisopropylamino)ethyl methacrylate (DiPA) and tuned DMA/DiPA ratios in block and statistical copolymer brushes. Then, we selectively quaternized DMA to enlarge solvophilicity differences between DMA and DiPA:water but not isopropanol is a good solvent for qDMA whereas DiPA exhibits the opposite solvation preference. In water, increasing DiPA incorporation depressed brush swelling for both block and statistical copolymer brushes. However, in isopropanol, swelling responses diverged; block copolymer brushes swelled between 9 and 37% less than compositionally equivalent statistical copolymer brushes. Additionally, we investigated the feasibility of deploying our polymer brushes in cell-interfacing applications by evaluating cytocompatibility. We established that the spatial distribution-and not just the relative abundance of solvophobic and solvophilic repeat units-governs polymer brushes' solvent responsivity.