Synthesis of Polyesters from CO2 and Non-Conjugated Terminal Alkynes and Alkyl Halides

Previous work has shown success in copolymerizing CO2 with aryl-conjugated diynes and dihalides in the presence of silver catalysts, resulting in polyesters with moderate molecular weights. We hypothesized that AB-type monomers, containing both non-conjugated terminal alkynes and alkyl bromides, would allow for a broader scope of monomers to be polymerized, derived from commercial propargyl bromide and bio-derived phenols. Polymerizing propargyl bromide under 14 atm of CO2 in the presence of Cs2CO3 and catalytic AgI and NHC ligand resulted in an intractable powder. As such, we sought to probe this reaction via a series of small-molecule studies. Most surprisingly, these studies revealed that the bromide functional group was susceptible to a competitive SN2 reaction with Cs2CO3, which we believe partially explains the inability of previous systems to reach high molecular weights. Following these preliminary studies, we polymerized a series of nonconjugated diyne monomer with alkyl dibromides, resulting in polymers with moderate Mn values and narrow dispersities. Finally, we synthesized AB-type monomers from bioderived phenols including vanillin and 4-hydroxybenzaldehyde. Polymerization of monomers with benzyl bromides resulted in poorly-soluble molecules due to the competitive carbonate formation. However, the longer alkyl chain a phloretic acidderived monomer allowed for successful polymerization, with a comparable molecular weight to the successful AA/BB-type polymerizations. The modularity of this system will allow us to target new polyesters with desired physical and thermal properties while allowing for further postpolymerizations using the internal alkyne moieties.