Tuning the Morphology, Thermal Behavior, and Toughness of Poly(β-butyrolactone-<i>co</i>-β-valerolactone) Thermoplastics
Agostino Pietrangelo, Carlos R. López‐Barrón, Matthew T. DeRocco, Shuhui Kang, Sarah J. Mattler, Pamela J. Wright
Abstract
Mapping copolymer properties to composition and microstructure enriches our understanding of how these features are correlated and establishes a pathway to tune the structural characteristics of the material to meet the performance demands of its end-use application. Here, racemic β-butyrolactone (B) and β-valerolactone (V) are polymerized by ring-opening to afford a series of syndio-enriched (co)polymers that cover the entire compositional range. The effect of copolymer composition on the thermal properties, crystallinity, morphology, and mechanical properties is reported. A monotonic decrease in elastic modulus with increasing V content is observed, with melt transitions following a similar functional form. Tensile properties, including toughness and tensile strength, show sharp transitions at a V content of 36%, coinciding with changes in crystallinity and crystal structure at the same composition. The copolymer microstructure was investigated using 13 C NMR spectroscopy enabling a partial assignment of resonances at the tetrad level. The results of this study show that at 27% V content, nearly 50% of the copolymer is comprised of syndiotactic tetrads that have at least three B units. At 36% V content, a significant compositional shift is observed whereby the majority of tetrads are syndiotactic with at least two V units or are iso-enriched.