Combining Ring-Opening Multibranching and RAFT Polymerization: Multifunctional Linear–Hyperbranched Block Copolymers via Hyperbranched Macro-Chain-Transfer Agents

Abstract

The synthesis of a hyperbranched macro-chain-transfer agent for RAFT polymerization of functional methacrylate or methacrylamide monomers was achieved by selectively attaching one single CTA onto hyperbranched polyglycerol dendron analogues. The combination of ring-opening multibranching polymerization of glycidol and subsequent RAFT polymerization of the hyperbranched macro-chain-transfer agents created a new route to a variety of multifunctional linear–hyperbranched block topologies. All linear–hyperbranched block copolymers could be synthesized with controlled molecular weight (Mn = 3.2–43.7 kg/mol) and low polydispersity (PDI = 1.15–1.34). As first examples for this universal approach, we present block copolymer syntheses with thermoresponsive methacrylate (tri(ethylene glycol) methyl ether methacrylate) and biocompatible methacrylamide (2-hydroxypropylmethacrylamide). Because of the presence of dithiobenzoate esters at the end of each linear polymer chain end, selective end-group modification with functional methanethiosulfonates for bioconjugation to proteins (via the biotin–avidin interaction) or drugs (and dyes as model compounds, respectively) could be achieved. This expands the scope of this class of polymer architectures and renders the obtained multifunctional linear–hyperbranched block copolymers applicable as topologically advanced polymeric drug delivery systems.