Switchable Polymerization Catalysis
Discovering how to selectively polymerize monomer mixtures to give well-controlled copolymers remains a very major and fundamental challenge in polymer synthesis. Solving this problem could provide an efficient means to deliver reproducible chain sequences, important both in terms of polymer chemistry and physics understanding and to improve materials properties. Understanding catalysis using mixtures is fundamentally important to enable re-configurable polymerization processes and products. In 2014, we reported a form of switchable polymerization catalysis whereby mixtures of monomers, such as epoxides, carbon dioxide, lactones and anhydrides, are selectively transformed, accessing different catalytic cycles, into specific and single copolymer chain sequences. Since then, we’ve worked to understand the catalysis and apply it in many different materials fields. Switchable catalysis efficiently and quantitatively produces completely new classes of multi-block polyesters, -ethers and –carbonates. These new copolymer sequences would be very difficult and sometimes impossible to access by any other means. Both the repeat unit sequence and polymer structure are controllable. In switchable polymerization catalysis, the slower polymerization frequently occurs before the faster reaction (rate differences can span orders of magnitude): this surprising result contravenes conventional monomer reactivity theories. We used detailed kinetics, structure-activity studies, operando spectroscopy and DFT models to understand the factors governing selectivity. We propose a switchable catalysis mechanism whereby monomer enchainment order is governed by both the chain end group stability and lability; both factors can be controlled externally. With this mechanistic insight, it’s straightforward to direct the catalyst into a desired catalytic cycle using the presence or absence of monomers as the switch. The switches between polymerization cycles are typically rapid and reversible allowing for multi-block polymer patterning.
Switchable Catalysis Using One Catalyst and Mixtures of CO2, Epoxide and Lactone to Make Block Polymers.
We are researching new switchable polymerization catalysts and investigate their performances using operando spectroscopy (IR and NMR), kinetic analyses, investigations into copolymer structures and computational models to rationalize the data. Active on-going areas include increasing activity, understanding substrate scope, accessing new polymer structures and correlating polymer structure-activity performances. Further, we use our switchable and CO2-catalysis to make plastics, elastomers, surfactants, electrolytes and adhesives.
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