Environmentally Degradable Polymers Incorporating Stimuli-Triggered Cleavable Linkages toward Industrial Materials

Abstract

Plastics designed to degrade upon exposure to ambient stimuli after use are emerging as promising alternatives to conventional plastics, considering environmental pollution. The so-called “biodegradable polymers,” which can be degraded by enzymes or microbes, are the most reliable biodegradable polymers, and considerable effort is devoted to their practical application. Several other examples are also developed for the cleavage of chemical bonds in macromolecules, as one part of a vast variety of “stimuli-responsive polymers,” especially for biomedical applications. These chemical insights provide a design concept that can even be extended to plastic materials. Here, stimuli-cleavable linkages, drawing from the chemical insights cultivated in biomedical fields, intended for application in degradable plastics, are outlined. As stimuli for polymer degradation, pH changes, photoirradiation, and redox conditions are selected because polymers released in natural environments may inadvertently be exposed to these stimuli. The degradation pathways are grouped into five categories: 1) stimuli-cleavable linkages, 2) self-amplifying, 3) self-immolative, 4) chain shattering, and 5) double responsive. The classification and organization of the stimuli-cleavable linkages provide insights for designing new, degradable polymers.