The presentation highlights a series of catalysts that switch between different polymerization cycles and deliver block copolymers from monomer mixtures (Fig. 1). The polymerizations include the alternating copolymerizations of epoxides and anhydrides; the alternating copolymerizations of epoxides and carbon dioxide and the ring-opening polymerizations of lactones and lactide. By controlling the inorganic chemistry of the metal-polymer chain end-group the catalysis is directed to produce a particular (block) polymer enchainment. The selectivity arise because of the orthogonal reactivity of metal-alkoxide/carboxylate and carbonate linkages towards certain monomers. Thus, upon exposure of the catalysts to mixtures of epoxide, carbon dioxide, anhydride and lactone the reaction is directed to selectively produce block copolymers with distinct sequences and structures, including AB, ABA, ABC type block copolymers as well as multi-block copolymers comprising repeating sequences of up to 7 blocks. The catalyst synthesis, characterization and application data will be presented, including <i>in situ</i> spectroscopic studies which provide evidence to demonstrate the catalytic selectivity. Characterization data confirming the copolymers’ structures will also be presented including studies using spectroscopy, size exclusion chromatography and differential scanning calorimetry. The switchable catalysis is also examined using DFT calculations which are compared with experimental findings and used to rationalize and understand the basis for the switchable catalysis. The potential to use this catalysis to deliver useful new block and alternating copolymers is demonstrated in fields including as elastomers and specialty polymers.

Switchable polymerization catalysts: Selective block copolymers from monomer mixtures

253rd National Meeting (2017)

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