Controlled synthesis and pH-sensitive complexation of poly(methacrylic acid) polyampholytes†

Abstract

Studies of intra- and intermolecular interactions in pH-responsive polyampholyte solutions are essential for understanding protein molecule solution behavior and cell organelle organization. Understanding and controlling the formation of intra/intermolecular complexes of synthetic polyampholytes can broaden their applications in industry and the biomedical field. Studies of poly(cation-co-anion) statistical copolymer solutions with a predominant content of the same-charge groups in the polymer chain are present in the theory when the factual experimental data are underrepresented. Herein, we explored the controlled synthesis of poly(methacrylic acid) copolymers containing primary amine groups and studied the copolymer solution aggregation under various pH and salt conditions. Well-defined poly(methacrylic acid-co-3-(aminopropyl)-methacryl amide) copolymers (M_w of 45 kDa and 80 kDa, Đ < 1.36) with a varied content of the amine group (PMAA–NH₂ from 2 to 6 mol%) were synthesized via reversible addition–fragmentation chain transfer (RAFT) copolymerization. Both computational and experimental studies proved the copolymerization of tert-butyl methacrylate with N-(tert-butoxycarbonyl-aminopropyl)methacrylamide where the second monomer is less active in copolymerization due to strong interaction with a chain-transfer agent (CTA). We found that the resulting PMAA–NH₂ copolymers with more than 4 mol% of amine groups form polyampholyte complexes (PACs) in solution in the pH range from 3.1 to 4.8 due to charge compensation. Given the ability of this PMAA–NH₂ to undergo multilayer assembly at surfaces and controlled crosslinking, our findings can be further expanded to develop advanced and tunable PMAA thin multilayer hydrogels. The synthesis of PMAA–NH₂ copolymers via controlled copolymerization can also lead to facile alternatives for PAC synthesis without using cell-toxic cationic polyelectrolytes such as polyvinylpyridines or polyamines. The copolymers can help develop synthetic routes to novel copolymers and new hydrogel materials with controlled nanostructured architectures, environmentally adaptable microcontinents, PAC-based saloplastics, absorbents, anisotropically structured nanocoatings, and biomedical coatings.