The 13C NMR and 1H NMR spectra of poly(l,3-cyclohexadiene) (PCHD) were analyzed. Anionically polymerized samples, cationically polymerized samples, and samples polymerized with a Ziegler-Natta catalyst were investigated. The NMR and 13C NMR spectra were taken at 270 and 67.88 MHz, respectively. The resolution of the former spectra was incomplete and they were deconvoluted by computer simulation. Relative intensities of the computer-resolved 1H NMR peaks were used in the calculation of the isomeric composition of the investigated PCHD's. 1H NMR results were confirmed qualitatively by 13C NMR results. 3,3'-Bicyclohex-l-enyl (BCH) was used as a model compound for the verification of the proposed assignment of the experimentally observed chemical shifts. The effect of solvents on the microstructure of the anionically polymerized 1,3-cyclohexadiene has been found to be essentially analogous to that observed for the acyclic dienes. Significant differences were, however, detected. For example, even in polar solvents the fraction of 1,2 isomers did not exceed 50%. Apparently, steric hindrance precludes the formation of long sequences of 1,2 units. The formation of intermittent 1,2 and 1,4 sequences is feasible and their fraction increases with increasing temperature. The anionic polymerization of 1,3-cyclohexadiene in hexane and in bulk yields the 1,4 isomer in a predominantly cis-type pianomeric conformation. The stereoselectivity of the cationic and the Ziegler-Natta systems is lower than that of the anionic ones.

SynopsisThe anionic polymerization of 1.3-cyclohexadiene (1.3-CHD) was investigated in temperatures that ranged from 25 to -77OC. Initiation by lithium naphthalene (N;,Li+) in tetrahydrofuran at -2OOC yields polymers with fairly narrow molecular weight distribution. The of t.hese polymers so prepared is ca. 20,000. Polymerization of 1.3-CHD conducted a t room temperature is accompanied by the dehydrogenation and disproportionation of the monomer, especially when NT,K+ acts as initiator.The mechanism of the initiation of the polymerization of 1.3-CHD by N:,Li+ was elucidated and the rate constants at -2OOC in tetrahydrofuran of the elementary reactions were determined. It was established that the dianions formed by disproportionation of N;,Li+ act as effective initiators for 1.3-CHD. The adducts formed constitute the cyclohexanyl and naphthyl carbanionic groups. The former carbanions ( A , , ,-275 nm) propagate the polymerization. The initially formed dimeric adducts are stabilized by the separation of the carbanionic end groups by the additional monomer units. Chain transfer to the monomer limits the growth of the polymers. The isomerization of the cyclohexadienyl anions, formed as result of chain transfer, may be followed by the elimination of lithium hydride. The latter reaction represents a termination step. Addition of 1.4-CHD to the reaction mixture enhances the chain transfer and the termination.Oligomers are formed when hexamethylphosphoramide is used as a solvent.

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