PROMOTING PLASTIC SUSTAINABILITY THROUGH COPOLYMERIZATION OF EPOXIDES WITH BIORENEWABLE MONOMERS: ALIPHATIC POLYESTERS WITH IMPROVED THERMAL AND RHEOLOGICAL PROPERTIES
Olefin polymerization remains the dominant way to make plastics. However, current olefin production relies on finite petroleum feedstock and polyolefins are persistent in environment for very long period of time. It is projected that in the year of 2050, plastics’ share of global oil consumption will reach 20% and there will be more plastics than fish (by weight) in the ocean. To help achieve the sustainability goal of society, epoxide copolymerization represents a promising way for plastic production. There are three major reasons for this argument: 1) olefins can be converted to epoxides through an epoxidation reaction utilizing oxygen in air; 2) various biorenewable comonomers including CO2 have been proven to copolymerize with epoxides; 3) oxygen containing polymers especially polyesters are known to be biodegradable. We report the alternating copolymerization of furan-based cyclic anhydrides with various epoxides catalyzed by aluminum-salen complexes. Furan, 2-methylfuran and 2,5-dimethlfuran can be easily obtained from sugar. Two series of anhydride monomers with systematic methyl substituents are obtained from Diels-Alder reaction of furans and maleic anhydride followed by hydrogenation or dehydration. Copolymerization of these anhydride with propylene oxide, cyclohexene oxide and 1-butene oxide is explored, and glass transition temperatures (Tg) of the resulting amorphous polymers are measured by differential scanning calorimetry. Through this study, we not only report the record-high glass transition of aliphatic polyesters, but also observe an unexpected structure-property relationship regarding the influence of methyl substituents on glass transition temperatures. Positron annihilation lifetime spectroscopy and DFT calculations are conducted and a new understanding of polymer backbone flexibility is proposed. We report a new catalytic motif that allows us to tune the amount of CO2 incorporated in the polyols during the copolymerization of propylene oxide and CO2 under alcohol initiators. While the alternating copolymerization of propylene oxide and CO2 gives the most CO2 incorporation, the Tg and viscosity of the resulting polyol is too high to be used in most polyurethane applications. We developed a series of cobalt-based bimetallic catalysts that can alter the amount of CO2 through the choice of catalyst, the CO2 pressure and the equivalence of ionic cocatalyst. The glass transition temperatures of polyols obey a Fox-Flory equation with CO2 content, while an Arrhenius relation between viscosity and CO2 content is observed.
Coates, Geoffrey W.
Wolczanski, Peter T.; Lancaster, Kyle M.
Chemistry and Chemical Biology
Ph. D., Chemistry and Chemical Biology
Doctor of Philosophy
dissertation or thesis