Helix-Sense-Selective and Enantiomer-Selective Polymerization of a Chiral Methacrylate by Anionic and Free-Radical Mechanisms

(±)-10,11-O-Isopropylidene-trans-10,11-dihydroxy-5-phenyl-10,11-dihydro-5H-dibenzo[a,d]cycloheptene-5-yl methacrylate (IDPDMA) was synthesized and resolved into an optically pure form by chiral HPLC. Anionic polymerization of IDPDMA was carried out using the complexes of N,N′-diphenylethylenediamine monolithium amide (DPEDA-Li) with (+)-1-(2-pyrrolidinylmethyl)pyrrolidine. (+)-2,3-dimethoxy-1,4-bis(dimethylamino)butane, and (−)-sparteine in toluene at −78°C or using DPEDA-Li in tetrahydrofuran at −78°C. The polymers obtained from the racemic monomer using the chiral initiators and the polymer obtained from (+)-monomer under the achiral condition appeared to have a helical conformation with excess helicity. The polymerizations of (±)-IDPDMA using the chiral initiators were enantiomer-selective: (+)-monomer was preferentially, polymerized. Free-radical polymerization of optically active IDPDMA having various enantiomeric excesses using x,x′-azobisisobutyronitrile in toluene at 60°C gave almost completely isotactic polymers which probably had a helical conformation with excess helicity. Enantiomer selection was also confirmed in the radical polymerization.