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

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.