Photo- and Biodegradable Thermoplastic Elastomers: Combining Ketone-Containing Polybutadiene with Polylactide Using Ring-Opening Polymerization and Ring-Opening Metathesis Polymerization

Abstract

We report the synthesis of a new bio- and photodegradable ABA triblock copolymer that combines the high modulus of biodegradable poly(lactic acid) (PLA) with a novel photodegradable polybutadiene (PB). First, the central block was made by ring-opening metathesis polymerization (ROMP) of a mixture of 1,5-cyclooctadiene and an unsaturated cyclic ketone in the presence of cis-1,4-butenediol. The resulting hydroxyl-functionalized telechelic PB macroinitiator was then chain-extended by DBU-catalyzed ring-opening polymerization (ROP) of lactide. Using this combination of ROMP and ROP, the molecular weights of the A and B blocks were varied, and the resulting copolymers formed robust films with rubbery plateau moduli ranging from 180 to 1600 MPa as measured by dynamic mechanical analysis (DMA). Thermal analysis revealed that the polymers were thermally stable up to 273 °C and exhibited glass transition temperatures at −111 and 55 °C. Accelerated UV weathering was performed on thin polymer films with concentrations of the photodegradable monomer in the PB backbone ranging from 0 to 9 mol %. The degradation occurred through Norrish photocleavage and was tracked by IR spectroscopy, size exclusion chromatography, and DMA until complete mechanical loss.