Synthesis of Model Primary Amine-Based Branched Copolymers by Pseudo-Living Radical Copolymerization and Post-polymerization Coupling of Homopolymers

Abstract

Two synthetic routes to highly branched primary amine-based methacrylic copolymers are described. One route involves statistical copolymerization of 2-aminoethyl methacrylate (AMA) monomer in its hydrochloride salt form with a disulfide-based dimethacrylate (DSDMA) comonomer via RAFT copolymerization, while the other route involves statistical coupling of near-monodisperse PAMA homopolymer chains using bifunctional reagents that react with primary amines. Both intermolecular branching and intramolecular cyclization occur in each route, with the former being favored at high PAMA concentration and the latter being favored at low PAMA concentration, as expected. In the former case, cleavage of the disulfide bonds in the DSDMA branch points confirms that the highly branched, polydisperse copolymers simply comprise randomly linked, near-monodisperse primary chains. In the latter case, the final product is highly dependent on the type of branching reagent that is used. In the case of divinyl sulfone (DVS), the coupling chemistry is both fast and irreversible, leading to permanently branched copolymer chains. On the other hand, using poly(ethylene glycol) diacrylate (PEGDA) initially leads to branched copolymer chains, but the remaining primary amine groups subsequently catalyze hydrolysis of the β-aminoester bonds in the PEGDA branch points, leading to slow regeneration of linear chains. No hydrolytic degradation occurs if N,N′-methylenebis(acrylamide) is used as a brancher, but this reagent is significantly less reactive than DVS.