Synthesis and Properties of Charge-Shifting Polycations: Poly[3-amino­propyl­methacrylamide-co-2-(dimethyl­amino)ethyl acrylate]

Charge-shifting copolymers of N-(3-aminopropyl)­methacrylamide (APM) and 2-(dimethyl­amino)­ethyl acrylate (DMAEA) were prepared and investigated as potential replacements for conventional polycations like poly­(l-lysine) (PLL) in biomaterial applications. 1H NMR was used to determine the reactivity ratios of APM and DMAEA to be 0.89 and 0.37, respectively, at pH 3–4 where both monomers were protonated and DMAEA was hydrolytically stable. Conventional free radical and reversible addition–fragmentation chain transfer (RAFT) copolymerization were used to prepare a series of P­(APM-co-DMAEA) (PAD) copolymers with different MWs and compositions. Charge shifting from cationic toward neutral and anionic net charges by hydrolysis of DMAEA units was determined by 1H NMR to depend on both composition and pH (pH 9 > 7 > 5). PAD copolymers bound strongly to anionic polymer particles and calcium alginate beads. For calcium alginate, the amount of PAD bound and the shell thickness depended on copolymer composition and MW. The PAD coating underwent hydrolysis and was released from the anionic surfaces as shown by microscopy and electrophoretic mobility measurements. PAD coatings that were cross-linked with tetrakis­(hydroxy­methyl)­phosphonium chloride (THPC) remained on the capsule surface after hydrolysis to form amphiphilic or anionic cross-linked surfaces.