Noncovalent side-chain functionalization of terpolymers

Random poly(norbornene)-based terpolymers containing sulfur-carbon-sulfur (SCS) palladated pincer complexes, dibenzo[24]crown-8 (DB24C8) rings, and diaminopyridine moieties were synthesized by ring-opening metathesis polymerization. Examination of the kinetics of the polymerization led to the conclusion that the polymerization of a statistical mixture of the three monomers results in the formation of random terpolymers. The terpolymers have molecular weights between 30 000 and 50 000 Da, with polydispersity indices ranging form 1.3 to 1.5, as determined by gel-permeation chromatography. Side-chain functionalization of these terpolymers was achieved by self-assembling (i) pyridines to the palladated pincer complexes, (ii) dibenzylammonium ions to the DB24C8 rings, and (iii) thymines to the diaminopyridine receptors. ¹H NMR spectroscopy was used to monitor the self-assembly processes and revealed that all self-assembly steps were fast and near quantitative. Isothermal titration calorimetry was employed to determine the association constants for the individual noncovalent functionalization steps. For all the self-assembly steps, the association constants were unaffected by neighboring functionalities on the polymer backbone, demonstrating orthogonality in the recognition expressed by the three recognition sites.