Controlled Synthesis Of Star Polymers Carrying Helical Polyisocyanide Arms And Their Applications In Enantiomer Separation

Star polymers,a class of branched polymers,have attracted great attention over the past few decades because of their greater accessibility by structural diversity in coreshell architectures,unique properties and functions being different from those of the corresponding linear counterparts.Although a variety of star polymers with a varying number of arms,chemical compositions,and functional groups have been prepared,most of the star polymers prepared to date are optically inactive.Optically active star polymers,in particular those carrying rodlike one-handed helical arms,are quite rare in spite of their potential in practical applications as novel chiral materials for enantioselective catalysis and adsorbents because of their unique helix-bundle structures generated by selfassembled helical arms,which may provide confined chiral environments for the efficient chiral recognition of enantiomers and chiral polymers.In this paper,we synthesied optically active star polymers carrying helical poly(phenyl isocyanide)arms.The micro chiral environments of optically active star polymers can be used in the chiral recognition and chiral resolution.In the first part of our work,we reported a novel strategy for synthesis of core cross-linked star polymers carrying poly(phenyl isocyanide)arms via "core-first" strategy through the combination of ROMP and alkyne-Pd(II)initiate isocyanide polymerization.A norbomene functionalized alkyne-Pd(II)complex was first prepared,and copolymerized with a bisnorbomene linker via ROMP,afforded a cross-linked Pd(II)macroinitiator.Living polymerization of phenyl isocyanides with the in-situ generated Pd(II)macroinitiator lead to the formation of well-defined star polymer.The active living chain ends of Pd(II)units were located at the surface of the star polymers,which can be further functionalized.Optically active star polymer carrying excess of one-handed helical arms was obtained by using enantiopure phenyl isocyanide monomer.These core cross-linked star polymers carrying unique helical poly(phenyl isocyanide)arms possessing a plenty of chiral microenvironments come from the excess of one-handed helical conformation of the poly(phenyl isocyanide)arms.Thus,they may exhibited excellent chiral recognition capability.The star polymers have good ability on chiral recognition and chiral resolution of D/L-phenylglycinol.The chiral star polymers have been demonstrated the exciting utility for enantioselective crystallization of racemic Boc-alanine and alanine.In the second section,we report on the synthesis of an optically active and thermoresponsive star block copolymer carrying amphiphilic block helical poly(phenyl isocyanide)s arms via "arm-first" strategy through the combination of the ring-opening metathesis polymerization(ROMP)and the Pd(II)-initiated isocyanide polymerization.Star polymers were got by copolymerization of helical poly(phenyl isocyanide)s with a bisnorbornene linker.The active living chain ends of Pd(II)units were located at the surface of the star polymers.They re-initiated a new polymerization of isocyanide monomer containing three triethylene glycol monomethyl ether chains leading to the formation of amphiphilic block star copolymer.Such polymers exhibited excellent thermo-responsiveness.Taking advantage of the thermo-responsiveness,the synthetic star polymers possessing a plenty of chiral micro environments exhibited good performance on chiral resolution.Taking advantage of the thermoresponsiveness,the enantiomers can be facilely separated.Furthermore,the optically active star polymers have good chiral recognition ability of chiral fluorescence molecule.