4-Carboalkoxylated Polyvalerolactones from Malic Acid: Tough and Degradable Polyesters.

Eight 4-carboalkoxyvalerolactones (s), varying in the composition of their alkyl () side chains, were synthesized from malic acid and subjected to ring-opening transesterification polymerization (ROTEP) using diphenyl phosphate [DPP, (PhO)POH] as a catalyst. Each produced a semicrystalline poly(4-carboalkoxyvalerolactone) (), and the nature of the group impacted the thermal transitions of these polyesters. Bulk polymerizations at 70 °C allowed for preparation of high molar mass samples that contained small amounts of branching, as evidenced by H NMR spectroscopy, MALDI spectrometry, size-exclusion chromatography, and eliminative degradation. Tensile testing of these lightly branched, high molar mass samples revealed that these polyesters are tough (tensile toughness values up to 88 ± 33 MJ•m) and have Young's moduli () up to 186 ± 13 MPa. The acid- and base-catalyzed hydrolytic degradation of the s was quantitatively monitored using total organic carbon analysis, and effect of the alkyl chain length on hydrolysis rate was determined. Finally, the methyl ester variant of these malic acid-derived thermoplastics is known to be chemically recyclable.