Synthesis of degradable poly(methyl methacrylate) star polymers via RAFT copolymerization with cyclic ketene acetals

Abstract

Copolymerization of the cyclic ketene acetal 5,6-benzo-2-methylene-1,3- dioxepane (BMDO) with methyl methacrylate (MMA) is studied with respect to its copolymerization parameters and the suitability to control BMDO/MMA copolymerizations via the reversible addition-fragmentation chain transfer (RAFT) technique to obtain linear and 4-arm star polymers. BMDO shows disparate copolymerization behavior with MMA and r1 = 0.33 ± 0.06 and r2 = 6.0 ± 0.8 have been determined for polymerization at 110 °C in anisole from fitting copolymer composition vs. comonomer feed data to the Lewis-Mayo equation. Copolymerization of the two monomers is successful in RAFT polymerization employing a trithiocarbonate control agent. As desired, polymers contain only little amount of polyester units stemming from BMDO units and preliminary degradation experiment show that the polymer degrades slowly, but steadily in aqueous 1 M NaOH dispersion. Within ten days, the polymers are broken down to low molecular weight segments from an initial molecular weight of Mn = 6000 g mol-1. Star (co)polymerization with an erythritol-based tetra-functional RAFT agent following the Z-group approach proceeds efficiently and polymers with a number-average molecular weight of 10,000 g mol-1 are readily obtained that degrade in similar manner as the linear copolymer counterparts. © 2014 Wiley Periodicals, Inc.