Heat-Resistant CO₂-Based Polycarbonate Thermoplastics

Designing biodegradable and sustainable polymeric materials that behave as thermoplastics with enhanced mechanical properties over a wide range of temperatures (−20 to 80 °C) remains a challenge. Polyolefin plastics such as high-density polyethylene (HDPE) and low-density polyethylene (LDPE) do display these characteristics, but they are not degradable and can hardly be hardly recycled. Poly(butylene adipate terephthalate) (PBAT) stands as one leading commercially available polymer that is degradable, with mechanical properties comparable to those of some polyolefins, but its high price is a disadvantage. In this study, we describe the synthesis of a series of polycarbonate-based triblock copolymers (18-36 wt % CO₂), namely, poly(cyclohexene phthalate)-block-poly(ether carbonate)-block-poly(cyclohexene phthalate) (PC-CHP)_n and poly(cyclohexene carbonate)-block-poly(ether carbonate)-block-poly(cyclohexene carbonate) (PC-CHC)_n with both linear and star-shaped architectures that can mechanically withstand high temperatures and behave similarly to polyolefins. For the synthesis of these triblock copolymers, which include a significant content of CO₂, we used a boron-based metal-free polymerization approach and derived both high molar mass two-armed linear and four-armed star triblock copolymer samples, namely, (PC-CHP)₂, (PC-CHP)₄, and (PC-CHC)₄, respectively. The mechanical properties of these triblock copolymer samples were systematically investigated upon varying parameters, such as the polycarbonate content in soft segments, the nature of hard blocks, the balance between hard and soft blocks, and the type of architectures (linear vs stars) across a large range of temperatures (20-60 °C). Remarkably, these (PC-CHP)_n block copolymers behave like HDPE and their mechanical performance even surpasses that of PBAT and LDPE, thus appearing as potential alternatives to polyolefins. Unlike polyolefins, these polycarbonate-based triblock copolymers are degradable, their carbon footprint is minimal, and they exhibit all sustainability attributes. In addition, their synthesis is easily scalable and conducive to industrial production, facilitated by a highly efficient initiating system [>1 kg polymers per gram of triethyl borane (TEB)] and significant CO₂ utilization (18-36 wt %).