Facile Synthesis And Chiral Recognition Of Block And Star Copolymers Containing Stereoregular Helical Poly (Phenyl Isocyanide) And Polyethylene Glycol Blocks

A new Pd(?) initiator bearing an alkyne headgroup was designed and synthesized.Living polymerization of phenyl isocyanide using this Pd(?) initiator afford well-defined alkyne-terminated helical poly(phenyl isocyanide) (PPI) with controlled molecular weights (Mns) and narrow molecular weight distributions (Mw/Mns). The alkyne end group of PPI coupled with azide-terminated random-coil poly(ethylene glycol) (PEG) via copper-catalyzed alkyne-azide cycloaddition (CuAAC) "click"chemistry formed a novel class of helical-random block copolymer PPI-b-PEG. Coupled the alkyne-terminated PPI with a PEG bearing azides on both chain ends, afforded a helical-random-helical triblock copolymer PPI-b-PEG-b-PPI. When optically active alkyne-terminated PPIs bearing L- or D-menthol ester pendants were used in the coupling reaction, optically active di- and triblock copolymers were facilely achieved,which exhibited intense Cotton effect on circular dichroism (CD) spectra due to the one-handed helical conformation of the PPI segments. Moreover, a Pd(?) complex bearing two alkyne headgroup were designed and synthesized, which initiate a living polymerization of phenyl isocyanide lead to the formation of well-defined PPI with desired Mn and narrow Mw/Mn and bearing two alkyne groups on the same chain end.Coupling this helical polymer with azide-terminated PEG via CuAAC "click" chemistry formed a miktoarm helical-(random)2 star copolymer containing two random PEG segments and one helical PPI block. The amphiphilic block and star polymers containing hydrophobic PPI and hydrophilic PEG segments were found to self-assembly into well-defined spherical nanoparticles in water. Interestingly, these supramolecular architectures showed excellent chiral recognition to dansyl modified L-and D-phenylalanine (L- or D-DNSP) in high enantiomeric selectivity.