Exploring the influence of rigid carbocycles on terpenoid copolymer properties

Abstract

Synthesizing soft polymers with uncommon architectural elements is critical for enhancing our understanding of fundamental structure–property relationships in macromolecules. Terpenoid materials are interesting candidates for addressing this grand challenge, as their constituent monomers can exhibit a diverse array of structural and functional groups. Moreover, these biologically-derived materials can potentially expand the sphere of knowledge surrounding trends in related petrochemically-derived polymers. For example, vinyl-addition copolymers of norbornene and acyclic olefins can exhibit predictable properties (e.g., linear changes in T_g as a function of composition). Due to synthetic limitations, however, it is not well understood if other rigid carbocycles engender similar behavior in a range of copolymers. As numerous terpene scaffolds display rigid motifs (such as pinane systems), terpenoid polymers are uniquely positioned to address this deficiency. Here, we report the synthesis and characterization of terpenoid copolymers (both statistical and block) with systematically tailored compositions of pinene-based comonomers. We found that the pinane core (which is a constitutional isomer of norbornene) appears to promote ideal behavior with regard to bulk thermal properties of statistical copolymers, which mirrors the behavior of norbornene-based systems. We also found that block copolymers exhibited thermomechanical properties that were highly tunable (and apparently correlated to carbocycle composition).