Synthesis And Chiroptical Properties Of Helical Polystyrene Stabilized By Intramolecular Hydrogen Bonding Interactions

Two novel enantiopure styrene derivatives(L-and D-1)bearing chiral amide groups were designed and synthesized.Polymerization of these monomers using reversible addition fragment transfer(RAFT)radical polymerization afforded a series of poly-L-lmS and poly-D-lmS in high yields with controlled molecular weights(Mns)and narrow molecular weight distributions(Mw/Mns).Interestingly,these polymers can adopt a stable helical conformation when the degree of the polymerization reached to ca.60 owing to the intramolecular hydrogen bonding between the adjacent repeating units as revealed by circular dichroism(CD),UV-vis spectroscopies,and polarimetry as well.The helicity of these polymers could be tuned by solvent and temperature.Increasing temperature or polarity of the solvents will weaken the intramolecular hydrogen bonding,and thus the helical structure may be transferred to random coil,which making these polymers have multi-responsiveness.Moreover,such helical polymers can be further copolymerized with a cross linker,lead to the formation of a core cross-linked star polymer carrying helical arms.Because of the chirality of the helical arms,the star polymer showed excellent ability in enantioselective crystallization by using racemic D/L-threonine as model compounds.The enantiomeric excess(ee)of the induced crystals is up to 95%.