Cyclopropanation of poly(isoprene) using NHC‐Cu(I) catalysts: Introducing carboxylates

The incorporation of functional groups into unsaturated polyolefine‐polymers often represent a challenging task. Based on the known cyclopropanation of double bonds with diazoesters in the presence of metal‐catalysts of low molecular weight compounds, we in this article develop an approach to decorate the polymer backbone of poly(diene)s with ester as well as carboxylic groups via cyclopropanation. Therefore, predominantly cis‐1,4‐poly(isoprene)s are converted with ethyl or tert‐butyl diazoacetate using copper(I) N‐heterocyclic carbene (NHC) catalysts, while focusing on the technically relevant cyclohexane as solvent. The application of commercially available NHC‐Cu(I) catalysts results in modification degrees of 4–5%, while an increased solvent polarity, like dichloromethane, results in up to 17% modification. The resulting esters were further converted to the corresponding free carboxylic groups by deprotection using trifluoroacetic acid. Thus, an introduction of functional groups along the polymer backbone with a wide variety of application, like ionic interaction or hydrogen bonding motifs, was successfully demonstrated. Its potential for upscaling makes this approach feasible for an application in large‐scale production processes, such as for manufacturing of modified synthetic rubbers. Predominantly cis‐1,4‐poly(isoprene)s were modified with ester groups via cyclopropanation using diazoacetates and copper(I) NHC catalysts. Modification yields up to 17% of the corresponding double bonds were achieved by varying the solvent polarity, concentration, and catalysts. The obtained esters were deprotected by TFA, yielding free carboxylic groups, which were able to promote hydrogen bonding or ionic interactions. The formation of supramolecular networks could be proven, making the approach suitable for synthetic rubber modifications related to the tire industry.