The Lewis acidic BDICF3-Zn-N(SiMe3)2 catalyst is able to both catalyze the ring-opening polymerization (ROP) of lactones like β-butyrolactone (BBL) and the copolymerization of epoxides with carbon dioxide. Poly(hydroxybutyrate) - the ring-opening product of BBL - is a very soft material in its atactic form (Tg = 5 °C) whereas poly(cyclohexene carbonate) obtained through the coupling of cyclohexene oxide (CHO) and CO2 is rather brittle with a high glass transition temperature. It is expected that combining both polymer types by one single catalyst gives a terpolymer with enhanced thermal and mechanical properties. Utilizing this catalyst in one-pot terpolymerizations of BBL, CHO and CO2 results in a CO2-selective polymerization: Applying 40 bar CO2 leads to the exclusive incorporation of CHO and CO2. Only upon removal of the CO2 pressure, ROP of BBL is started. Similarly, application of 40 bar CO2 to an ongoing BBL polymerization will induce copolymerization. Hence, by the time of CO2 addition, it can be selectively switched between the two polymerization types. A reduced pressure of 3 bar CO2 results in similar reaction rates for both the ring-opening polymerization of BBL and the copolymerization of CHO and CO2 leading to a simultaneous incorporation of both monomer types. Two-dimensional NMR spectroscopy and polarimetry provide a deeper understanding of the underlying mechanism. The statistical route at 3 bar CO2 yields polymers with decisive differences regarding thermal properties, especially the glass transition temperature. While the terpolymers in block structure exhibit two independent Tg's, the statistical analog shows a mixed-Tg tunable depending on the composition ranging between 10 °C and 91 °C.

Tuning material properties: CO2-selective terpolymerizations from β-butyrolactone, epoxides and CO2 and their kinetic, thermal and mechanical characterization

2019 Fall National Meeting

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