| Abstract: | 3,4- and 3,5-Dimethylcyclopentenes were prepared as model compounds of the structural unit in polycyclopentadiene. These two isomers give characteristic NMR spectra. The assignment based on the 60 Mc./sec. spectrum was further confirmed by decoupling experiments on the 100 Mc./sec. spectrum of 3,5-dimethylcyclopentene. By comparing the NMR spectra of these compounds with that of polycyclopentadiene methods were developed for estimating the polymer structure from the relative peak area of the methine–methylene and olefinic protons. Polycyclopentadiene obtained with Friedel-Crafts catalysts at lower temperatures was shown to be composed mostly of the 1,4 and 1,2 structures. Polycyclopentadiene obtained with several Ziegler-type catalysts possessed comparable amounts of both structures, contrary to the earlier proposals. |
