Exploring bio-based and biodegradable polymers: free-radical polymerization, hydrolysis and applications

Sammanfattning: Increasing concerns regarding the depletion of fossil-based resources and theaccumulation of plastic waste in the environment have resulted in extensiveresearch aimed at finding more sustainable alternatives to today’s plastics.In this work, bio-based and biodegradable polymers have been synthesizedusing free-radical polymerization in homogeneous and heterogeneoussystems. The polymers have been characterized with respect to chemicalstructure, thermal properties and degradation. This is a step towards thedevelopment of materials that are bio-based and biodegradable, ultimately toreduce 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 fossilbasedmeth(acrylate) monomers, are capable of yielding polymers withsimilar or even superior properties compared to their fossil-basedcommodity counterparts. The differences in monomer reactivity affect thestructure of the copolymer which, in turn, influences the polymer properties,for instance, thermal behaviour (glass transition temperature). Theseproperties were later evaluated after the incorporation of MeMBL in thepolymeric shell of thermally expandable microspheres by free-radicalsuspension polymerization. Replacing fossil-based methyl methacrylate(MMA) with bio-based MeMBL resulted in partially bio-based thermallyexpandable microspheres (TEMs) where it was seen that the expansionproperties were affected as the expansion temperatures increased. It waseven possible to synthesize TEMs with a fully bio-based polymer shell with amuch higher expansion temperature window than TEMs with a fully fossilbasedpolymer shell.Free-radical ring-opening polymerization (rROP) has been used to synthesizedegradable polymers using cyclic ketene acetals (CKAs) which weresynthesized using a new more efficient synthesis route. Unlike traditionalring-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 beenevaluated by introducing CKA in the free-radical suspension polymerizationof microcapsules with a polymer shell from acrylonitrile (AN) and vinylacetate. However, their incorporation into the polymer backbone could notbe verified. This as the use of CKA in heterogeneous systems is challengingdue to their sensitivity towards hydrolysis and their low reactivity duringcopolymerization, especially toward acrylonitrile.