Alternating Copolymerization of Propylene Oxide with Biorenewable Terpene-Based Cyclic Anhydrides: A Sustainable Route to Aliphatic Polyesters with High Glass Transition Temperatures

The alternating copolymerization of propylene oxide with terpene-based cyclic anhydrides catalyzed by chromium, cobalt, and aluminum salen complexes is reported. The use of the Diels-Alder adduct of -terpinene and maleic anhydride as the cyclic anhydride comonomer results in amorphous polyesters that exhibit glass transition temperatures (T-g) of up to 109 degrees C. The polymerization conditions and choice of catalyst have a dramatic impact on the molecular weight distribution, the relative stereochemistry of the diester units along the polymer chain, and ultimately the T-g of the resulting polymer. The aluminum salen complex exhibits exceptional selectivity for copolymerization without transesterification or epimerization side reactions. The resulting polyesters are highly alternating and have high molecular weights and narrow polydispersities.