Pd(II)-catalyzed polymerization of optically active norbornene carboxylic acid esters

Abstract

(-)-(1S,2R)-Norbornene-2-carboxylic acid alkyl esters (alkyl = Me, Bz, L-menthyl, or D-menthyl) were successfully prepared by the Diels-Alder reaction of cyclopentadiene with (R)-(-)-pantolactone-O-yl acrylate followed by epimerization and column chromatography. The enantiomeric excess was 99.9%. These monomers were polymerized by Pd(II)-based catalysts, and high yields of the polymers were obtained. The methyl ester gave an optically active polymer of high optical rotation (monomer [alpha](D) = -24.7, polymer [alpha](D) = -98.5). This high rotation value of the polymer was attributed to the isotactic chain regulation of the polymer. This high rotation was not observed with methyl esters prepared by the transesterification of menthyl esters. The stereoregular polymer exhibited notable resonance peaks at 39 ppm in C-13 NMR spectra. No crystallinity was observed. (c) 2005 Wiley Periodicals, Inc.