Temperature-Driven Switching Between Block, Near-Statistical, and Gradient Copolymers Enabled by Multinuclear Aluminum Catalysis.

Precise control over microstructure in the ring-opening copolymerization of ε-caprolactone (CL) and lactide (LA) remains challenging because of intrinsic monomer reactivity differences and concomitant transesterification, which often obscure the origin of the final sequence distribution. Here we show that a single tetrameric multinuclear aluminum catalyst provides programmable access to block, near-statistical, and gradient CL/LA copolymers within one catalytic platform. The complex mediates well-controlled ring-opening polymerization of both monomers, enabling the synthesis of diblock, triblock, and multiblock architectures by sequential monomer addition under insertion-dominated conditions. Under simultaneous copolymerization conditions, variation of the reaction temperature modulates the balance between propagation and exchange processes and thereby governs the copolymer microstructure. At lower temperature, the copolymers display reactivity ratios close to unity, average sequence lengths near two, and thermal behavior consistent with near-statistical incorporation. At elevated temperature, enhanced transesterification leads to pronounced growth of homologous sequences and compositional drift along the chains, characteristic of gradient architectures. Taken together, these findings establish a unified kinetic-thermodynamic framework for sequence control in CL/LA copolymerization and reveal multinuclear aluminum catalysis as an effective strategy to traverse distinct copolymer microstructures using an earth-abundant metal system.