A diastereomeric pair of novel N-propargylphosphonamidates, HC=CCH2NHP(=O)(CH3)O-L-menthyl was synthesized by the successive condensations of methylphosphonic dichloride with L-menthol and propargylamine. The (R)-P-isomer (1a) was isolated, and the absolute configuration was determined by XRD. Polymerization of 1a, and a mixture of la and (S)-P-isomer (1b) was carried out with a zwitterionic Rh complex as a catalyst. cis-Stereoregular polymers with number-average molecular weights of 5 600-9 800 were obtained in good yields. Poly(1a) and poly(1a(29)-co-1b(71)) exhibited large specific rotations (+408 and -146 degrees), and intense Cotton effects ([theta] = +2.25 and -0.9 x 10(4) deg . cm(2) . dmol(-1)) based on the conjugated polyacetylene backbone around 325 nm in CHCl3, indicating that these polymers have helical structures, whose predominant helical senses are opposite.