Synthesis of Degradable PolyMMA via Copolymerization with Cyclic Ketene Acetals

Polyesters play a very important part in the development of (bio)degradable materials, due to the hydrolizable ester-groups. However, it usually requires stringent conditions and removal of condensates in order to reach high molecular weights in classical polyester step-growth polymerizations. This is in contrast with free radical polymerization, where high molecular weights are reached within seconds without the need for stringent conditions, drastically lowering the cost. Combining the simple procedures for free radical polymerization with the hydrolizability of polyesters has long been a focus in research. With the introduction of radical ring-opening polymerization by Bailey et al. In 1979^[1] it became feasible to incorporate ester-groups into polymer backbone by copolymerizing cyclic ketene acetals (CKAs). This method, however, did not immediately generate broad interest probably owing to the relatively complicated reaction mechanism and tedious synthesis procedures for CKAs. However, since the early 2000’s more research has been performed, mainly on the synthesis of copolymers of CKAs and vinyl monomers.^[2] The development of controlled radical polymerizations also proved to be an accelerator for RROP research. In this contribution, the synthesis of degradable linear and four-arm star copolymers of 5,6-benzo-2-methylene-1,3-dioxepane and methyl methacrylate via RAFT polymerization is presented.^[3] To determine exact copolymer composition, the reactivity ratios of both monomers have been determined and are thoroughly discussed.  ^[1] W. J. Bailey, P. Y. Chen, W. B. Chiao, T. Endo, L. Sidney, N. Yamamoto, N. Yamazaki and K. Yonezawa, Contemporary Topics Polym. Sci., 1979, 3, 29. ^[2] S. Agarwal, Polym. Chem., 2010, 1, 953 ^[3] S. Kobben, A. Ethirajan, T. Junkers, J. Polym. Sci.. A: Polym. Chem., 2014