Helical Polymers: Synthesis, Conformation, and Function

Abstract

Asymmetric polymerization of acrylic monomers and an isocyanate derivative leading to a helical conformation is described. 1-Phenyldibenzosuberyl methacrylate, triphenylmethyl acrylate, and N,N-diphenylacrylamide were polymerized using the complexes of diphenylethylenediamine monolithium amide with (-)-sparteine, (S,S)-(+)-2,3-dimethoxy-1,4-bis(dimethylamino)butane, and (S)-(+)-1-(2-pyrrolidinylmethyl)pyrrolidine. The methacrylate gave a purely one-handed helical, optically active polymer ([α]₃₆₅ +1670° ~ +1780°) having a perfect isotactic structure; the polymer exhibited chiral recognition ability to some racemic compounds. This monomer gave optically active polymers also by radical mechanism. The acrylate also gave an optically active, helical polymer ([α]₃₆₅ +102°) having a dyad isotacticity of 70% using the pyrrolidine complex. The poly(methyl acrylate) derived from the polyacrylate showed a specific rotation which appears to be based on configurational chirality of the main chain. The acrylamide gave an optically active polymer ([α]₃₆₅-429°) which may have a helical structure by asymmetric anionic polymerization; the polymer had a dyad isotacticity of 86%. m-Methylphenyl isocyanate was polymerized using optically active lithium alkoxides and amides to produce a polymer having a chiral group at the α-end. A prevailing one-handed helical structure was induced for the main chain due to the chiral end group.