Chain-end functionalization of living helical polyisocyanides through a Pd(ii)-mediated Sonogashira coupling reaction

Abstract

End-functionalization is an effective strategy for fabricating functional materials. Installing functional groups onto the chain end of helical polymers is of great interest. In this paper, we reported a new method for constructing end-functional helical poly(phenyl isocyanide)s. At first, a family of helical polyisocyanides with controlled M_n and low polydispersity bearing a Pd(II) complex on the chain end was readily prepared via the Pd(II)-mediated living polymerization of isocyanide monomers. To activate the terminal Pd(II)-complex, a variety of phosphine ligands were tested. It was found that the ligand exchange of the Pd(II) complex with Wei-phos provides a terminal Pd(II)-complex with high activity, which can promote the Sonogashira coupling reaction with many terminal alkyne derivatives. Taking advantage of this method, a series of interesting functional groups including dansyl chloride, the F atom, and the aldehyde group can be facilely installed onto the end of helical polyisocyanides. Moreover, a couple of hybrid block copolymers can also be obtained via the Sonogashira coupling reaction of the Pd(II)-terminated helical polyisocyanides with different functional polymers such as poly(ethylene glycol) (PEG), poly(L-lactide) (PLLA) and polycaprolactone (PCL) bearing an alkynyl group on the chain end. This method can not only install interesting functionalities onto the chain end of helical polyisocyanides but also remove the transition metal residue simultaneously facilely.