Alternating Copolymerization Of Epoxides With Lactones And Cyclic Anhydrides: New Routes To Well-Defined Polyesters With Exceptional Thermal Properties

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While synthetic polymers have largely supplanted natural materials because of their low cost, concerns exist regarding their long-term sustainability. Most current commodity plastics are derived from petroleum, which is non-renewable. Furthermore, items constructed from current commodity materials persist in the environment for decades. Although bio-sourced and biodegradable polymers are commercially available, their widespread application is limited by high costs and physical properties that are inferior to those of comparable petroleum-based polymers. We have developed a family of bio-derived polyesters via the copolymerization of epoxides with cyclic esters that exhibit exceptional thermal properties compared to those of commercial bio-derived polyesters. We report the alternating copolymerization of dihydrocoumarin with epoxides catalyzed by chromium salen complexes. Dihydrocoumarin is a promising monomer because it is relatively inexpensive and can be obtained from renewable resources. This process provides access to a variety of perfectly alternating polyesters with high molecular weights and narrow polydispersities. Atactic poly(cyclohexene dihydrocoumarate) and poly(cyclopentene dihydrocoumarate) were found to be semicrystalline by differential scanning calorimetry. The alternating copolymerization of propylene oxide with terpene-based cyclic anhydrides catalyzed by chromium, cobalt, and aluminum salen complexes is also reported. The use of the Diels-Alder adduct of [alpha]-terpinene and maleic anhydride as the cyclic anhydride comonomer results in amorphous polyesters that exhibit glass transition temperatures of up to 109 °C. The aluminum salen complex exhibits exceptional selectivity against transesterification and epimerization side reactions, which allows these copolymerizations to be run to full conversion. The resulting polyesters are highly alternating and have high molecular weights and narrow polydispersities. Finally, we report an optimized process for the copolymerization of less bulky tricyclic anhydrides with excess PO that achieves full monomer conversion with minimal side reactions to produce well-defined aliphatic polyesters. The rates of undesirable transesterification and epimerization are controlled by i) the ratio of aluminum salen complex to cocatalyst and ii) the Lewis acidity of the aluminum salen complex. Optimal selectivity and activity are achieved through a careful balance of these two parameters.

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Polymer chemistry; Copolymerization; Polyesters
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Collum,David B
Dichtel,William Robert
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Chemistry and Chemical Biology
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Ph. D., Chemistry and Chemical Biology
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Doctor of Philosophy
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