Postfunctionalization of polyoxanorbornene backbone through the combination of bromination and nitroxide radical coupling reactions

The brominated backbone of poly(oxanorbornene imide) (PONB) (PONB-Br) was functionalized with 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO)-acrylate, -epoxy, and poly (ethylene glycol) (PEG) yielding PONB-acrylate, PONB-epoxy, and PONB-PEG through the nitroxide radical coupling (NRC) reaction. Although an excess amount of functional-TEMPOs were used. The observed NRC efficiencies were found in the range of 7-25%. Notably, ¹H NMR spectra of all polymers exhibited a signal at 6.08 ppm after NRC reactions indicating rebuilding of the main chain double bond and further identified by ¹³C NMR analysis. The inevitable formation of double bond through the tendency of the recombination of the formed radicals was supported by a separate experiment conducted without utilizing functional-TEMPO. Besides, the versatility of the ROMP backbone further demonstrated by the introduction hetero functionality onto the polymer by a consecutive reactions.