Sustainable Synthesis of Polymers

Abstract

Traditional polymer development is dependent on petrochemicals, their fabrication includes the use of ecologically unfriendly chemicals, and their permanently crosslinked networks limit their recycling capabilities. This thesis focuses on improving the sustainability of both natural and synthetic polymer advancements in terms of simplified synthesis, recyclability, and circularity. Chapter 1 discusses the concept of artificial catalyst and dynamic thermosets, as well as their current challenges. In Chapter 2, an artificial catalytic triad inspired by the chemical structure of chymotrypsin was prepared using a simple synthetic strategy, yielding a remarkable turnover number (kcat) of 3.3 s^(-1) and a rate acceleration of 4.81*10^4-fold over the background reaction. Chapter 3 outlines the transformation of raspberry ketone derived crosslinker into a dynamic thermoset elastomer. The thermoset networks incorporates catalyst-free bond exchange reactions in catalyst-dependent polyester networks by substituting oxime-esters for conventional ester linkages. The dynamic nature of thermosets allow them to demonstrate stress relaxation behaviour and reprocessability. Chapter 4 reports fully biomass-derived dynamic imine thermosets prepared using widely abundant cheap shrimp and cellulose waste materials. The dynamic nature of Schiff base bonds enable thermosets to exhibit fast stress relaxation behaviour and reprocessability. At the "end of product life", thermosets can be degraded in a home compost within 4-5 days. Chapter 5 outlines the development of a novel and entirely green dynamic thermoset composites using sustainably sourced spent coffee grounds, chia seed oil, which was epoxidized, crosslinked through esterification with kelp-derived alginic acid, without catalyst or solvent, at mild reaction temperature (90-150 C). The resultant suite of material have potential application in industrial field such as plant pot, thin film sheets and beverage container. At the "end of product life", thermoset composites can be readily home composted under natural conditions in 4-5 months. At last, Chapter 6 concludes with a summary of this work and suggestions for potential future research directions.