Sequence-Controlled Copolymerization of 6-/7-Membered Cyclic Carbonates with l -Lactide: Wide-Range Regulation of Copolymer Properties

Abstract

The synthesis of sequence-controlled poly(lactide-carbonate) copolymers via ring-opening copolymerization (ROCOP) of l-lactide (l-LA) with cyclic carbonates under industrially relevant conditions (in bulk and melt) is highly challenging owing to the lack of highly active and thermally stable catalysts. Herein, we systematically investigated the melt and bulk ROCOPs of l-LA with 6-membered trimethylene carbonate (TMC) and 7-membered cyclic 1,4-butylene carbonate (CBC), respectively, using the (amidoalkyl)pyridine–phenolate aluminum methyl complexes as catalysts. The kinetic differentiation and reactivity ratios for l-LA/TMC and l-LA/CBC monomer mixtures were determined in solution polymerization to deeply understand the catalyst-dependent ROCOP behavior. Poly(LA-TMC) and poly(LA-CBC) copolymers with varying comonomer incorporation ratios and tunable sequence length of PLA segments were further synthesized under bulk and melt conditions with different catalysts. The thermal/mechanical properties and degradation behavior of the resulting poly(LA-TMC) and poly(LA-CBC) samples were thoroughly investigated to elucidate the significant effects of comonomer distribution and chain sequences on material properties. Notably, the aluminum complexes exhibited a higher degree of control over the ROCOP process compared with stannous octoate (Sn(Oct)2), affording poly(LA-TMC) and poly(LA-CBC) copolymers with higher molecular weights and superior thermal/mechanical properties under identical conditions. This systematic investigation of the relationships between catalyst/monomer structure, chain composition, and material properties provides valuable insights into the development of high-performance aliphatic copolyesters and the optimization of their practical application performance.