Long Range Chirality Transfer in Free Radical Polymerization of Vinylterphenyl Monomers Bearing Chiral Alkoxy Groups

摘要

In this work,the synthesis and chiroptical properties of two series of optically active helical styrenic polymers,poly[2-(4'-alkoxyphenyl)-5-(4'-hexyloxyphenyl) styrene] (S-(+)-ImHex (m =0,1,2,3)/R-(-)-IOHex) and poly[2-(4'-hexyloxyphenyl)-5-(4'-alkoxyphenyl)styrene] (S-(+)-HexIm (m =0,1,2,3)/R-(-)-HexI0),are reported (Scheme 1).Each polymer contains laterally attached para-terphenyl pendants terminated with an achiral hexyloxy group and a chiral alkoxy group.The long range chirality transfer from the stereocenter of side-group to polymer backbone during polymerization is investigated by a combination of 1H-and 13C-NMR,polarimetry,circular dichroism spectroscopy,liquid crystal induced circular dichroism,and computer simulation.All the polymers,except for that from S-(+)-HexⅡ3,display optical rotations and Cotton effects in the UV-vis absorption region of aromatic pendant quite different from the corresponding model compounds and monomers,suggesting the formation of chiral secondary structures (Fig.1),i.e.