Cationic cyclization of cis‐1,4‐polybutadiene II. Physico‐chemical characterization of the polymer

Information on the structure of cyclized cis‐1,4‐polybutadiene (CBR) was obtained by means of extensive physico‐chemical investigations. Fractionation of typical samples of CBR showed a constant distribution of unsaturations in all fractions. No presence of co‐catalyst (aromatic) moiety and conjugated double bonds was found in CBR having a degree of cyclization lower than 40%. Combined IR and 13C‐NMR analysis allowed to calculate the average length of the polycyclic sequences postulated by the cyclization process. The average length was found to range between three and four cyclohexane rings for a cyclization extent ranging from 15 to 60%. Direct evidence of polycyclic sequences having up to three rings was collected by vapour‐phase‐chromatograph‐mass‐spectroscopy (VPC‐MS) analysis of the products coming from the pyrolysis of CBR: fragments having higher molecular weight were not detected by our work. Ozonolysis experiments, performed under both reducing and oxidizing conditions, showed only the formation of very large fragments(about 18 butadiene units). The collected data support the cyclization mechanism proposed and account for the technological properties of CBR.