Di‐isotacticity of poly(methyl propenyl ether) and double‐bond opening of methyl propenyl ether in cationic polymerization

The di‐isotacticity of poly(methylpropenyl ether) obtained by the cationic polymerization has been studied by NMR spectra. The NMR spectra of β‐methyl protons of the polymer are decoupled from the β‐methine proton spectra to determine the di‐isotactic fraction in a polymer. The signals of β‐methyl protons at 8.78 and 8.89 τ are estimated as spectra based on threo‐ and erythro‐di‐isotactic diads, respectively. With BF3·O(C2H5)2 as a catalyst, the trans monomer yields a crystalline polymer and its structure is threo‐di‐isotactic. Otherwise, cis monomer produces an amorphous polymer, and it is a mixture of threo‐ and erythro‐di‐isotactic structure. From these results, it is concluded that the double bond in trans monomer is opened exclusively in the cis type, and in cis monomer cis‐ and trans‐openings take place at almost the same rate.