Synthesis of functional degradable polymers by radical ring-opening polymerization
Sammanfattning: The increased demand for understanding cell-material interactions and subsequently create personalized implants for tissue engineering has resulted in an increased interest in developing new monomers with functional groups. The focus of the work presented in this thesis has been on the synthesis of functional monomers and the polymerization of these into functional amorphous aliphatic polyesters. The cyclic ketene acetal 2-methylene-1,3,6-trioxocane (MTC) was synthesized in a two-step reaction and subsequently polymerized at different temperatures using either 2,2’-azoisobutyronitrile (AIBN) or dicumyl peroxide as initiator. It was shown that the polymerization mechanism was not temperature-dependent and the polymerization proceeded with 100% ring-opening at all evaluated temperatures. The polyester-ether was then successfully copolymerized with another cyclic ketene acetal 2-methylene-1,3-dioxepane (MDO) and a functional, hydrophilic and amorphous copolymer was obtained. The feed ratios were varied between 90 to 25 mol% of MTC and it was shown that the proportion of MTC in the copolymers was in general higher than the proportion of MTC in the feed, confirming that the reactivity ratio was higher for MTC. A number average molecular weight of 6500 g/mol was obtained after 2 days at 70 °C in bulk. The high polydispersity index as well as the glass transition temperatures indicated a significant amount of branching. MDO was also copolymerized with vinyl acetate (VAc). A series of copolymers with various combinations of MDO and VAc were synthesized by using AIBN as radical initiator. It was shown that the proportion of MDO in the copolymers was strictly controlled by the feed ratios and that the composition of the copolymers, the thermal properties and the molecular weights could be predetermined. The reactivity ratios for MDO and VAc were determined to be rMDO = 0.93 and rVAc = 1.71. The copolymerization resulted in a high degree of conversions and a high number average molecular weights, where both the molecular weight and the glass transition temperature increased with increased proportion of VAc in the feed. It was also confirmed that the copolymer were susceptible to both alkali and 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 molecular weights.
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