Controlled Carbon Dioxide Terpolymerizations to Deliver Toughened yet Recyclable Thermoplastics

• Published in: Macromolecules 2024-05, Vol.57 (9), p.4199-4207
• Main Authors: Poon, Kam C., Smith, Madeleine L., Williams, Charlotte K.
• Format: Article
• Language: English
• Subjects: brittleness; carbon dioxide; carbonates; catalysts; catalytic activity; compression molding; cyclohexenes; glass transition; glass transition temperature; lead; molecular weight; tensile strength; thermal stability; thermoplastics
• ISSN: 0024-9297; 1520-5835; 1520-5835
• DOI: 10.1021/acs.macromol.4c00455

Using CO2 polycarbonates as engineering thermoplastics has been limited by their mechanical performances, particularly their brittleness. Poly­(cyclohexene carbonate) (PCHC) has a high tensile strength (40 MPa) but is very brittle (elongation at break 250 °C). All the polymers are amorphous with a single, high glass transition temperature (96 < T g < 108 °C). The polymer entanglement molar masses, determined using dynamic mechanical analyses, range from 4 < M e < 23 kg mol–1 depending on the polymer composition (PCHC:PCPC). These polymers show superior mechanical performance to PCHC; specifically the lead material (PCHC0.28-grad-PCPC0.72) shows 25% greater tensile strength and 160% higher tensile toughness. These new plastics are recycled, using cycles of reprocessing by compression molding (150 °C, 1.2 ton m–2, 60 min), four times without any loss in mechanical properties. They are also efficiently chemically recycled to selectively yield the two epoxide monomers, CHO and CPO, as well as carbon dioxide, with high activity (TOF = 270–1653 h–1, 140 °C, 120 min). The isolated recycled monomers are repolymerized to form thermoplastic showing the same material properties. The findings highlight the benefits of the terpolymer strategy to deliver thermoplastics combining the beneficial low entanglement molar mass, high glass transition temperatures, and tensile strengths; PCHC properties are significantly improved by incorporating small quantities (23 mol %) of cyclopentene carbonate linkages. The general strategy of designing terpolymers to include chain segments of low entanglement molar mass may help to toughen other brittle and renewably sourced plastics.