Polymer Grafting to Polydopamine Free Radicals for Universal Surface Functionalization.

Modifying surfaces using free radical polymerization (FRP) offers a means to incorporate the diverse physicochemical properties of vinyl polymers onto new materials. Here, we harness the universal surface attachment of polydopamine (PDA) to "prime" a range of different surfaces for free radical polymer attachment, including glass, cotton, paper, sponge, and stainless steel. We show that the intrinsic free radical species present in PDA can serve as an anchor point for subsequent attachment of propagating vinyl polymer macroradicals through radical-radical coupling. Leveraging a straightforward, twofold soak-wash protocol, FRP over the PDA-functionalized surfaces results in covalent polymer attachment on both porous and nonporous substrates, imparting new properties to the functionalized materials, including enhanced hydrophobicity, fluorescence, or temperature responsiveness. Our strategy is then extended to covalently incorporate PDA nanoparticles into organo-/hydrogels via radical cross-linking, yielding tunable PDA-polymer composite networks. The propensity of PDA free radicals to quench FRP is studied using in situ 1H nuclear magnetic resonance and electron paramagnetic resonance spectroscopy, revealing a surface area-dependent macroradical scavenging mechanism that underpins PDA-polymer conjugation. By combining the arbitrary surface attachment of PDA with the broad physicochemical properties of vinyl polymers, our strategy provides a straightforward route for imparting unlimited new functionality to practically any surface.

Rapid Online Analysis of Photopolymerization Kinetics and Molecular Weight Using Diffusion NMR.

Online, high-throughput molecular weight analysis of polymerizations is rare, with most studies relying on tedious sampling techniques and batchwise postanalysis. The ability to track both monomer conversion and molecular weight evolution in real time could underpin precision polymer development and facilitate study of rapid polymerization reactions. Here, we use a single time-resolved diffusion nuclear magnetic resonance (NMR) experiment to simultaneously study the kinetics and molecular weight evolution during a photopolymerization, with in situ irradiation inside the NMR instrument. As a model system, we used a photoinduced electron transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization. The data allow diffusion coefficients and intensities to be calculated every 14 s from which the polymer size and monomer conversion can be extracted. Key to this approach is (1) the use of shuffled gradient amplitudes in the diffusion NMR experiment to access reactions of any rate, (2) the addition of a relaxation agent to increase achievable time resolution and, (3) a sliding correction that accounts for viscosity changes during polymerization. Diffusion NMR offers a uniquely simple, translatable handle for online monitoring of polymerization reactions.