Direct Synthesis of Controlled-Structure Primary Amine-Based Methacrylic Polymers by Living Radical Polymerization

Abstract

We report the direct homopolymerization and copolymerization of a primary amine-based methacrylic monomer, 2-aminoethyl methacrylate (AMA), in its hydrochloride salt form by living radical polymerization. Linear PAMA homopolymer and AB diblock copolymers (where A = AMA and B = 2-(diisopropylamino)ethyl methacrylate, or DPA) were prepared with reasonably narrow polydispersities (Mw/Mn ∼ 1.2−1.3) in either DMSO or DMSO/1,4-dioxane mixtures at 70 °C using cumyl dithiobenzoate (CDB) as a reversible addition−fragmentation transfer (RAFT) chain transfer agent. AMA monomer is highly unstable in its nonprotonated form, undergoing rapid internal rearrangement to afford 2-hydroxyethyl methacrylamide. PAMA homopolymer proved to be significantly more stable than AMA monomer, but nevertheless slow chemical degradation occurred over long time scales (days) in alkaline solution. Initial 1H NMR studies confirm that (i) this PAMA degradation involves the elimination of 2-aminoethanol and (ii) at least some of its repeat u...