In preceding papers the reliable characteristics of the structure fragments of polyisoprene and copolymers of isoprene and butadiene were found, using I3C NMR spectroscopy. Proceeding from these data we tried to describe in detail the peculiarities of the structure of 1 -methylcyclobutene polymer prepared by ringopening polymerization. A previous short communication3) contains only a general information concerning the presence of isoprene, butadiene, and 2,3-dimethyl-1,3-butadiene unitsa) in the structure of this polymer. This paper reports on the assignment of main resonance lines in the I3C NMR spectra of the polymer of 1 -methylcyclobutene and its hydrogenated analogue and the identification of the repeating units and their steric configurations.
Experimental PartI3C and 'H NMR spectra were obtained on a Bruker HX-270 spectrometer with frequencies of 67,88 and 270 MHz, respectively, using TMS as internal standard. The carbon spectra were recorded after = 500 acquisitions in the computer memory of 8 K with pulse spacing of 7 s. 1 -Methylcyclobutene was polymerized using a catalytic system based on WCl, under conditions already described4) with adding a promoting agent.
Results and DiscussionThe 'H NMR spectrum of the polymer exhibits in its olefinic region signals at 6 = 5,32 and 5,09, which correspond to butadiene and isoprene units, respectively. In the aliphatic region of this spectrum, besides the signals at 6 = 2,0, due to methylene protons, and at 6 1,67 and 1,59 due to protons of methyl groups in cis and trans isoprene units, respectively, the signal at 6 = 1,62, characteristic of the protons of methyl groups in 2,3-dimethyl-1,3-butadiene units, is also observed.In the I3C NMR spectrum of the hydrogenated polymer the strong lines at 37,423, 32,231, 24,51, and 19,74 ppm, corresponding to the regular polyisoprene chain fragment having a "head-to-tail" monomer addition, can easily be seen I). Besides a) Here and in the following, units means monomeric units.
