Self-amplifying degradable polyurethanes and their upcycling application

Polyurethanes are a type of polymeric material that have found use in applications, including in paints, coatings, elastomers, and insulating foams. Polyurethanes can demonstrate thermoplastic, thermoset, or elastomeric properties depending on their formulation. Because polyurethanes are used in many industrial applications, the ability to degrade and recycle or repurpose these materials has attracted considerable attention. For example, chemical recycling methods such as glycolysis can recover the starting polyol for further polymerization. However, most of the chemical recycling methods that have been reported require a large amount of energy. Thus, the development of new methodologies to degrade polyurethanes under mild conditions to generate monomers for further conversion to useful materials is desirable. Fmoc containing compounds have been reported as base-triggered small molecules with amplified degradation properties. Chapter 2 investigates the synthesis as well as degradation of a novel base-triggered self-amplifying degradable polyurethane formed from an Fmoc derivative triol or Fmoc diol monomer. Firstly, Fmoc derivative diol monomer was used to synthesize a linear polymer incorporated with a base-sensitive moiety in every repeating unit to enable high sensitivity to base-triggered degradation. 1H NMR was utilized to characterize the degradation profile of the linear polymer and a sigmoidal degradation curve was observed at room temperature, suggesting a self-amplifying degradation mechanism. Successful fitting of the polymer degradation data into an autocatalytic degradation equation also supports a self-amplifying degradation mechanism. Furthermore, bulk material was synthesized from an Fmoc-based triol monomer and its self-amplifying degradation property was monitored visually and by rheology. The successful development of a base-triggered self-amplifying degradable polyurethane provides a potential solution to the disposal of polyurethane waste under mild conditions. Compared to other stimuli, light has accurate spatiotemporal control. In Chapter 3, we investigate the copolymerization methodology to synthesize photo-triggered self-amplifying degradable polyurethane materials. The incorporation of a small amount of an ortho-nitrobenzyl carbamate unit as a photo-sensitive moiety in the polymer backbone enables basic amine species generation after UV irradiation for amplified degradation of Fmoc carbamate as the base-sensitive moiety in the polymer backbone. 1H NMR analysis indicated that UV irradiation at 365 nm could degrade the photo-sensitive ortho-nitrobenzyl carbamate moiety followed by the degradation of the base-sensitive Fmoc carbamate moiety. Cross-linked bulk material encapsulated with a pH indicator revealed that local UV irradiation at the peripheral edges of a material could trigger the degradation of the whole material. To demonstrate the concept that this type of self-amplifying degradable polymeric material could be repurposed into useful material after degradation, a cross-linked polymeric material incorporating an epoxide monomer was synthesized. It was shown that the one-pot epoxide degradation product could be applied directly on glass substrates to form an extremely strong epoxide adhesive. This strategy to repurpose the photo-triggered self-amplifying degradable polyurethane provides a potential solution to the environmental problems caused by the generation of polyurethane waste. Further, this strategy requires much less energy compared to traditional methods like glycolysis.