Leveraging Stereochemistry to Optimize the Properties of Polyhydroxyalkanoates

The recycling of low-density polyethylene (LDPE) is challenging due to difficulties with sorting and contamination, leading to environmental harm. Polyhydroxyalkanoates (PHAs) are at the forefront of high-performance biodegradable alternatives to olefinic plastics, but few offer LDPE-like properties such as low strength and crystallinity while maintaining high ductility and thermal stability. Herein, we report a series of isoenriched trans-poly(3-hydroxy-2-methylbutyrates) (trans-PHMBs) with tunable mechanical and thermal properties. These polymers were synthesized through ring-opening polymerization of racemic trans-3,4-dimethylpropiolactone (rac-trans-DMPL), sourced from C1 and C4 feedstocks, using a new class of "sandwich" C₂ symmetric rac-(^ArBDI*)ZnOⁱPr catalysts (where BDI = β-diketiminate). Variation of aromatic groups (Ar) and polymerization temperature yielded mm%s between 45-79% and melting temperatures (T_m) between 141-174 °C. trans-PHMB with intermediate isotacticities of 73 and 75 mm% exhibit similar stress-strain profiles to LDPE, indicating that these polymers have the potential to serve as higher melting, degradable substitutes for LDPE.