Effects of Molecular Weight Distribution on the Thermal-Mechanical Performance and Recycling of CO₂‑Derived...

Poly-(cyclopentene carbonate) (PCPC) is a recyclable, CO₂-derived thermoplastic with high tensile strength and low entanglement molecular weight. Such CO₂-derived polycarbonates typically show bimodal molecular weight distributions, but how these distributions influence their properties is not yet understood. Here, the tensile, mechanical, thermal, and recycling properties are investigated for PCPC samples with different bimodal molecular weight distributions. Samples with high molecular weights (M _n ∼ 81 kg mol^-1) and narrow-gap bimodality, showing a relative 1:2 chain length distributions, are prepared using variable alcohol:diol ratios. These narrow-gap bimodality PCPC samples all show the same high tensile strength (σ_max ∼ 60 MPa) and glass transition temperature (T _g,∞ = 88 °C). A second series features different relative amounts of high molecular weight PCPC (M _n = 76 kg mol^-1) blended with low molecular weight samples (M _n = 9 or 16 kg mol^-1). These wide-gap bimodality PCPC samples generally show compromised thermal and mechanical performance, with properties only being retained when low amounts of chains with molecular weights above chain entanglement are added. All the high-M _n PCPC samples are rapidly depolymerized, using neat polymer-catalyst blends, to produce cyclopentene oxide and carbon dioxide, regardless of molecular weight distribution. Complete conversion to epoxide (CPO) and CO₂ is achieved in <15 min at 140 °C (1:300 catalyst:PCPC repeat unit).