Sustainable aliphatic polyester material design

Abstract

Plastics are ubiquitous materials that are primarily made out of synthetic polymers. There are many global problems that stem from the way societies produce, use, and discard plastic materials. A majority of synthetic polymers are synthesized from finite fossil fuel feedstocks. Waste management infrastructures have failed to coral large portions of discarded plastics, resulting in their proliferation in natural environments. Recycling technologies are severely limited due to problems from the collection and sorting infrastructures and the reduced mechanical performance of most reprocessed materials. Sustainable material design is one of many approaches which seeks to invent and discover new materials, processes, and technologies that can help remediate these issues. This dissertation presents several projects—each motivated by one or more subcategories defined in the NSF Center for Sustainable Polymers’ “Sustainable Polymer Framework”— that explore various aspects of aliphatic polyesters as sustainable materials. Chapter 1 provides historical perspectives on the rise of synthetic plastic use and the shifting value of sustainable development. Chapter 2 focuses on the metal-free polymerization of methyl-ε-caprolactone (MCL) isomers using the organocatalysts diphenyl phosphate and dimethyl phosphate. Chapter 3 focuses on the use of poly(methyl-ε-caprolactone) (PMCL) to synthesize mechanically strong thermoplastic poly(urethane-urea)s and chemically crosslinked polyurethanes. Additionally, chemical recyclability of these materials is explored through monomer recovery experiments with Lewis acid catalysts. Chapter 4 comprises multiple studies assessing the end-of-life of PMCL-based materials and its hydrolysis products. The cytotoxicity of PMCL-based elastomers and the hydrolysis products are explored as well as the degradation of the elastomer materials in industrial composting conditions. The biodegradation of PMCL is explored in further detail through the study of isotopomers of the hydrolysis product in natural soil incubation studies.