Stereoregular Poly(N-propargylcarbamates) Having Helical Conformation Stabilized by the Intramolecular Hydrogen Bonds

N -Propargylcarbamates ( 2, HC⋮CCH 2 NHCO 2 R), where R = i -Bu ( 2a ) or ( S )-CH 2 CH(CH 3 )C 2 H 5 ( 2b ), were polymerized in the presence of a Rh catalyst, [(nbd)RhCl] 2 −Et 3 N, in CHCl 3, giving stereoregular cis polymers as slightly yellow solids in good yields. The 1 H NMR spectra of poly( 2 ) showed very broad signals at ambient temperature, indicating the limited mobility of the main chain. IR spectroscopic study of the polymers in CHCl 3 revealed that most of the pendant carbamate groups participate in intramolecular hydrogen bonds. The chiral polymer from 2b exists in a helical conformation with an excess of one-handed screw sense, which was supported by the very large optical rotation ([α] D = +777°) and intense CD effects ([θ] max = 81 700 deg cm 2 dmol -1 ). A Rh-based polymer from the corresponding chiral carbonate monomer, ( S )-HC⋮CCH 2 OCO 2 CH 2 CH(CH 3 )C 2 H 5 ( 3 ), obtained as a viscous oil, showed much poorer chiroptical properties ([α] D = +13.8°), meaning that the intramolecular hydrogen bonds rigidify the polymer backbone and simultaneously induce and stabilize the helical conformation of poly( 2 ). The contribution of the hydrogen bonds to the secondary structure was also supported by variation in the CD and UV−vis spectra of poly( 2 ) upon the addition of methanol.