Defence of doctoral thesis: Maryam Mousa – Exploring bio-based and biodegradable polymers: free-radical polymerization, hydrolysis and applications

Increasing concerns regarding the depletion of fossil-based resources and the accumulation of plastic waste in the environment have resulted in extensive research aimed at finding more sustainable alternatives to today’s plastics. In this work, bio-based and biodegradable polymers have been synthesized using free-radical polymerization in homogeneous and heterogeneous systems. The polymers have been characterized with respect to chemical structure, thermal properties and degradation. This is a step towards the development of materials that are bio-based and biodegradable, ultimately to reduce the negative impact of plastic materials on the environment. It was found that bio-based α-methylene-γ-butyrolactone and α-methylene-γ-valerolactone (MeMBL) which exhibit similar chemical structures to fossil-based meth(acrylate) monomers, are capable of yielding polymers with similar or even superior properties compared to their fossil-based commodity counterparts. The differences in monomer reactivity affect the structure of the copolymer which, in turn, influences the polymer properties, for instance, thermal behaviour (glass transition temperature). These properties were later evaluated after the incorporation of MeMBL in the polymeric shell of thermally expandable microspheres by free-radical suspension polymerization. Replacing fossil-based methyl methacrylate(MMA) with bio-based MeMBL resulted in partially bio-based thermally expandable microspheres (TEMs) where it was seen that the expansion properties were affected as the expansion temperatures increased. It was even possible to synthesize TEMs with a fully bio-based polymer shell with a much higher expansion temperature window than TEMs with a fully fossil-based polymer shell. Free-radical ring-opening polymerization (rROP) has been used to synthesize degradable polymers using cyclic ketene acetals (CKAs) which were synthesized using a new more efficient synthesis route. Unlike traditional ring-opening polymerization, which results in linear polyesters, rROP of CKAsresults in branched polyesters. The degree of branching and introducing aside-group to the polymer chain influenced the polymer degradability wherethe presence of side-groups slowed the degradation significantly. The possibility to use these monomers in heterogeneous systems has been evaluated by introducing CKA in the free-radical suspension polymerization of microcapsules with a polymer shell from acrylonitrile (AN) and vinylacetate. However, their incorporation into the polymer backbone could not be verified. This as the use of CKA in heterogeneous systems is challenging due to their sensitivity towards hydrolysis and their low reactivity during copolymerization, especially toward acrylonitrile.

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