Design, Synthesis and Application of Novel Degradable Materials Based on Polyesters by Radical Ring-Opening Polymerization
Design, synthesis and application of novel degradable material based on polyesters by radical ring-opening polymerization (RROP) were described in this thesis. Herein, we studied a rare example of the formation of polystyrene-grafted aliphatic polyester in one-pot by radical polymerization including the reaction mechanism, designed enzymatically degradable amphiphilic conetworks by RROP, developed enzymatically degradable DOPA-containing polyester based adhesives by radical polymerization, and prepared and characterized novel thermally stable optically transparent copolymers with degradable ester linkages. In the case of formation of a graft copolymer in one-pot by radical polymerization, the cyclic ester β-propiolactone (β-PL) and styrene (St) were copolymerized at 120 °C with various monomer ratios. It is a rare example of a system providing graft copolymers (PSt-g-β-PL) with a complete range of monomer ratios in one pot. The structure of the resulting β-PL-St copolymers was proved by using a combination of different characterization techniques, such as 1D and 2D NMR spectroscopy and gel permeation chromatography (GPC), and also the analysis before and after alkaline hydrolysis of polymers. A significant difference in the reactivity of St and β-PL and radical chain transfer reactions at the polystyrene (PSt) backbone, followed by combination with the active growing poly(β-PL) chains, led to the formation of graft copolymers by a grafting-onto mechanism. We designed a different route for the preparation of enzymatically degradable amphiphilic conetworks (APCNs) based on unsaturated polyesters by RROP of vinylcyclopropane (VCP) with cyclic ketene acetal (CKA). In the first step, the unsaturated degradable polyesters with random distribution of cross-linkable double bonds and degradable ester units were prepared by radical ring-opening copolymerization of VCP and 2-methylene-4-phenyl-1,3-dioxolane (MPDO). Very similar reactivity ratios, unimodal GPC curves and 2D NMR technique (heteronuclear multiple bond correlation, HMBC) showed the formation of random copolymers with unsaturation and ester units. The unsaturated units were used for cross-linking with hydrophilic macromonomer (oligo(ethylene glycol) methacrylate, OEGMA) by radical polymerization in a second step for the formation of enzymatically degradable APCNs. Enzymatic degradability was studied using Lipase from Pseudomonas cepacia. Due to the hydrophilic (HI) and hydrophobic (HO) microphase separation, the APCNs showed swelling in both water and organic solvents with different optical properties. This method provides an interesting route for making functional degradable APCNs using radical chemistry in the future. We developed a 3,4-dihydroxyphenylalanine (DOPA) containing enzymatic degradable non-toxic synthetic adhesive with good adhesion to soft tissue and metals by a simple two-step reaction. This adhesive had degradable polycaprolactone- type repeating units together with glycidyl methacrylate (GMA) and OEGMA in the polymer backbone. Radical initiated copolymerization of 2-methylene-1,3-dioxepane (MDO), GMA and OEGMA followed by immobilization of DOPA on epoxy rings of GMA provided the adhesive material. Fe(acac)3 was proved to be the most effective cross-linking agent with lap shear strength on soft tissue (porcine skin) and metal (aluminum). The cross-linked adhesive showed good adhesion stability in pH 7 PBS buffer at 37 °C for at least one week. Due to the high adhesive strength, enzymatic degradability and low toxicity, the material is a promising candidate for future studies as medical glue. Finally, copolymers with high thermal stability, glass transition temperature and optical transparency were produced by radical polymerization of MDO and N-phenyl maleimide (NPM). The polymers made under specific reaction conditions, i.e. 120 oC and high amounts of MDO had degradable ester units, which were formed via radical ring-opening polymerization of MDO. Formation of charge-transfer complex between MDO and NPM also led to the formation of high molar mass copolymers by simple mixing and heating of monomers without use of any initiator. The structural characterization of copolymers including mechanistic studies was studied in details.
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