Stereochemistry in cationic polymerization of alkenyl ethers. I. 1H‐ and 13C‐NMR spectra of poly(propenyl ethers)

Abstract

AbstractBenzyl, ethyl, and deuterated ethyl propenyl ethers (BzPE, EPE, and EPE‐d5, respectively) with different cis/trans isomer ratios were polymerized by BF3O(C2H5)2 at −78°C in toluene, methylene chloride, and nitroethane solvents. Poly(propenyl alcohol) [poly(PA)] was also prepared by treating poly(BzPE) with HBr gas. The steric structure of these polymers was studied by 1H‐ and 13C‐NMR spectroscopy. The poly(EPE‐d5) obtained from a trans‐rich monomer mixture was crystalline, while one from a cis‐rich monomer mixture was amorphous. Poly(BzPE) was always amorphous. Poly(BzPE), poly(PA), and poly(EPE‐d5) gave 1H‐NMR spectra with two β‐methine peaks, relative intensities of which depended on the geometric structure of the monomers. Their spectra of β‐methyl protons decoupled from β‐methine proton were also split into two peaks, relative intensities of which corresponded to those of the two α‐methine peaks. 13C‐NMR spectra of α‐OCH2 and β‐CH3 of poly(EPE), respectively, consisted of two peaks. These observations show that the poly(propenyl ethers) examined, whether crystalline or amorphous, have only two dyad structures (probably threo or erythro‐meso and racemic), and that their α‐ and β‐carbons have the same dyad structure, irrespective of the kind of the alkoxyl groups.