Our group is interested in structured polymers as scaffolds for catalysts as they present a synthetically accessible method for forming a secondary coordination sphere around a catalytic metal. For example, a star polymer with transition metal complexes confined to the core may provide various non-covalent interactions between the star polymer scaffold and the transition metal complex. Thus, we are examining star polymers made from the following monomers: tert-butyl acrylate, methyl acrylate, N-isopropylacrylamide, styrene, and tert-butyl styrene. These monomers vary in steric bulk and polarity, but because they are all olefinic they can be polymerized via the same synthetic methods. Given the variety of monomers, we can compare and contrast how the environment might affect catalytic activity. We are targeting star polymers made using reversible addition fragmentation chain transfer (RAFT) polymerization, and an “arm first” method. The arm first method starts with the synthesis of relatively short linear polymer chains and is followed by a cross-linking reaction that brings together a number of these chains to form the star polymers. We have characterized both our linear “arms” and star polymers using nuclear magnetic resonance spectroscopy and gel permeation chromatography. The efficiency of the cross-linking reaction changes how many arms are present in each star and the ratio of stars to leftover linear polymer remains at the end of the reaction. Altering the ratio of linear macroinitiator to crosslinker to monomer seems to have a significant effect on this efficiency and we are optimizing our syntheses based on these ratios. We are also investigating methods to purify the star polymers from remaining linear polymer that result in minimal material loss. In the future, we will integrate catalytic complexes into the cross-linked cores of our star polymers to examine how these structured materials affect the catalysis.

Star polymers of various monomers synthesized via an “arm-first” method

ACS Spring 2022

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