Tunable adhesion properties of hydrolytically degradable aliphatic polyester triblock/diblock copolymer blends

Abstract

Tuning the molecular architecture of block copolymer blends is a powerful strategy to optimize their performance in pressure-sensitive adhesive (PSA) formulations. To improve the sustainability of typical petroleum derived and non-degradable PSAs, aliphatic polyester block copolymer blends of poly(L-lactide)-block-poly(γ-methyl-ε-caprolactone)-block-poly(L-lactide) (LML) and poly(L-lactide)-block-poly(γ-methyl-ε-caprolactone) (ML) were prepared by combining sequential ring-opening transesterification polymerization and copper-catalyzed alkyne–azido cycloaddition reaction. We systematically investigated the effects of blend compositions on their microstructural, thermal, mechanical, and adhesion properties in PSA formulations that included tackifier. Using optimized triblock content and thermal annealing protocols, the tackified PSAs exhibited competitive adhesion properties when compared to established styrenic PSAs. For example, a PSA of LML/ML (mass ratio = 1 : 1) with 20 wt% tackifier showed a peel strength of 3.66 ± 0.33 N cm⁻¹, a shear resistance of 429 ± 62 min and a desired adhesive failure mode. The competitive adhesion performance is attributed to a balance between dangling and bridging PγMCL end- and mid-blocks in the rubbery matrix that simultaneously allows interfacial adhesion and cohesive strength for favorable PSA bonding and debonding. The LML/ML-based PSAs are hydrolytically degradable into water soluble or dispersible compounds at 45 °C under basic conditions within 25 days. Our results indicate rationally tailoring the molecular architecture of polyester block copolymer blends is a convenient and robust strategy to optimize their adhesion properties for sustainable PSA solutions.