Cationic copolymerization of 1,3-pentadiene with 1,3-cyclopentadiene

Copolymerizations of 1,3-pentadiene (PD) with 1,3-cyclopentadiene (CPD) initiated by aluminium trichloride were carried out in toluene. The addition of CPD in the PD polymerization system does not affect the molecular weight but greatly increases the softening point of the polymer due to the introduction of cyclic structures. The Gardner color scale of the polymer is also raised by introduction of unsaturated rings of CPD. The copolymerization gives a complete conversion but generates insoluble crosslinked gels at high CPD content due to the high crosslinking reactivity of CPD. The integral intensities of unsaturated protons from PD and CPD segments of the copolymer chain on the ¹H-NMR spectrum give a perfect correlation with the copolymer compositions. The low-conversion experiments were carried out with small amounts of CPD in order to determine the reactivity ratio in this copolymerization system (M₁ = PD and M₂ = CPD). The result of r₁ = k₁₁/k₁₂ = 0.46 demonstrates that CPD has a higher reactivity than PD toward PD growing carbocations, and hence the copolymer shows a higher CPD proportion than the corresponding comonomer. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 1883–1887, 1997