Random introduction of degradable linkages into functional vinyl polymers by radical ring-opening polymerization, tailored for soft tissue engineering

Vinyl polymers, e.g. polyvinyl acetate and polyvinyl alcohol, have properties which suit tissue engineering in many perspectives. A copolymer of 2-methylene-1,3-dioxepane (MDO) with vinyl acetate (VAc) should combine the desirable properties of vinyl polymers with the degradability of aliphatic polyesters. Our results and detailed kinetics information show that it is possible to vary the amount of MDO widely in the copolymer. Between 1 and 70% MDO was incorporated into the polymer when copolymerized with VAc at 60 °C using 2,2-azobisisobutyronitrile (AIBN) as an initiator. The amount of MDO in the copolymer was strictly controlled by the feed ratio, the copolymerization resulted in a high conversion, and the copolymers had high number average molar masses. The polymerization kinetics indicated that the ester units were added in a randomized manner to the vinyl backbone. This was a crucial point since the distribution of degradable bonds provides the opportunity to design the degradation profile of the polymer. The reactivity ratios for MDO and VAc were determined to be rMDO = 0.93 and rVAc = 1.71. The glass transition temperature and the number average molar masses increased with increasing amount of VAc in the feed. We confirmed that the copolymer degraded rapidly in alkali hydrolysis and less in enzymatic hydrolysis and it was apparent that it is possible to synthesize various degradable materials based on VAc and MDO with predetermined polymer compositions and high number average molar masses.