Utilizing Pi-Systems as a Synthetic Handle for Sustainable Materials and Polymer Upcycling

Understanding how molecular structure influences the bulk physical properties of soft polymers is essential for accessing next-generation, bespoke materials. This is especially true for novel macromolecules that branch into underexplored chemical space. The impacts of uncommon structural motifs on polymer thermomechanical properties are often difficult to predict a priori. Overcoming this challenge necessitates the investigation of fundamental structure-property relationships in a wide array of macromolecules.

Nature, which is replete with examples of macromolecular complexity, is an excellent starting point for discovering new scaffolds to incorporate within polymers. Terpenoids display exceptional skeletal, functional group, and stereochemical variety; thus, this family of molecules represents a rich assortment of building blocks for polymers. Terpenoids (such as the pinenes) can be considered constitutional isomers of traditional monomers (norbornene). As such, incorporating terpenoids into polymers can create the opportunity to benchmark their impacts on bulk physical properties against established systems. Achieving this outcome, however, necessitates the development of new polymerization strategies.

Decorating terpenoids with allenes could afford new classes of monomers, given the enhanced polymerization propensity of allenes. A simple Ni-allyl catalyst was highly competent for these polymerizations, and we could prepare a variety of (co)polymers with good control over molar mass and in good yield. This strategy afforded macromolecules that displayed multicyclic motifs in their repeating units; thus, we could compare the structure-property relationships in our materials to those of traditional, petrochemically derived cyclic olefin copolymers.

The staggering scale of global polymer production has created an equally pressing problem: polymer waste remediation. Developing new methods for plastic waste valorization is one potential avenue to address this issue, but doing so requires the exploration of novel chemistries that can transform extant polymers into value-added products. We previously demonstrated that polyalkenamers could be electrochemically transformed into functional macromers via radical-cation intermediates. Photoredox catalysis struck us as an obvious candidate to overcome these limitations. Pyrillium-based photoredox catalysts were highly active in the degradation of various polyalkenamers. Prolonged irradiation enabled the formation of industrially relevant products (C₁₆ – C₄₀ materials). We could also intercept intermediates during the degradation process with exogenous nucleophiles, which allowed us to prepare functionalized macromers.