High elasticity, chemically recyclable, thermoplastics from bio-based monomers: carbon dioxide, limonene oxide and ε-decalactone†
One solution to problems with petroleum derived plastics is to design polymers for the circular economy. In this regard, polymer chemistries, like ester or carbonate linkages, which are closer to equilibrium are very promising but to use these materials requires improvements to their properties and methods of manufacture. Here, efficient polymerization catalyses are used to transform wastes and bio-sourced monomers into thermoplastics which combine high elasticity and strength and which can be degraded to allow for some chemical recycling. The plastics are prepared from carbon dioxide, limonene oxide (from waste citrus fruit peel) and ε-decalactone (from triglycerides). These monomers are polymerized, using catalyzed controlled polymerizations with high conversion efficiencies, to selectively form ABA block polymers (A = high Tg polycarbonate, B = low Tg polyester). The series of 5 poly(limonene carbonate)-b-poly(ε-decalactone)-b-poly(limonene carbonate) (PLC-PDL-PLC) samples allow for systematic variations in the overall molar masses (Mn = 50–100 kg mol−1) and hard-block compositions (21–63 wt% PLC). All the polymers are fully characterized using a range of spectroscopies, gel permeation chromatography, thermal and tensile mechanical measurements. The leading plastic combines tensile strength (stress at break, σb = 21.2 MPa, Young's Modulus, Ey = 321 MPa) and high elasticity (elongation at break, εb = 400%) – an enhancement of more than 20× in elongation at break and tensile toughness over poly(limonene carbonate), overcoming the well-known brittleness and processing limitations of PLC. It undergoes selective, catalyzed depolymerization to limonene oxide, carbon dioxide and the precursor polyester providing a future chemical recycling and upcycling opportunity.