CO2-Based Polycarbonates with Low Glass Transition Temperatures Sourced from Long-Chain Terpenes

Abstract

The urgent demand for more sustainable materials has led to significant research in the field of CO₂-based polymers. This work describes monomer synthesis, polymerization, and polymer properties of long chain terpenoid- and CO₂-based polycarbonates. Utilizing (R,R)-(salcy)-Co(III)Cl (Co(Salen)Cl) and bis(triphenylphosphine)iminium chloride ([PPN]Cl) as a binary catalytic system, high molar mass polymers (up to 46.4 kg mol^–1) were achieved with narrow dispersities (M_w/M_n < 1.13) via solvent-free bulk polymerization. Crucially, synthesis of these high molar mass polycarbonates necessitates a reactor design featuring low reactor/gas volumes, as well as CO₂ with very low content of water, a requirement that is independent of the specific monomer employed. For this reason, an extensive evaluation of reactor/gas volume and predrying of CO₂ was conducted to achieve narrow molar mass distributions. A glass transition temperature range between −43 and −29 °C was achieved by employing both saturated and unsaturated terpenoids. When combining various terpenoid-based monomers, an ideally random terpolymerization was observed, confirmed by offline ¹H NMR kinetics. The resulting copolymers characterized by double bonds in their polymer side chains are addressable for further postmodification reactions. Owing to their good thermal stability and low T_g values, the absence of cross-linking reactions and high molar masses, these flexible long chain terpenoid-based polycarbonates emerge as highly promising candidates for use as soft segments in thermoplastic elastomers.