Cationic polymerization of penta-1,3-diene - 4. Cationic copolymerization of penta-1,3-diene and isobutene initiated by the system DiCumOCH(3)/TiCl4/DMSO: Reactivity ratios and microstructure [French]

摘要

The cationic copolymerization of 1,3-pentadiene (PD) (cis/trans:45/55) with isobutylene (IB) initiated by the system DiCumOCH(3)/TiCl4/DMSO was carried out in CH2Cl2 at - 60 degrees C. The copolymer compositions were determined from C-13 NMR spectra. Data plotted according to the Kelen-Tudos method indicate that the terminal-unit model adequately described the electrophilic copolymerization of PD and IB. The corresponding reactivity ratios were as follows: r(PD) = 1.3 +/- 0.1 and rls = 1.1 +/- 0.1. The use of a non-linear least squares curve-fitting procedure gives the same results. These values were close to unity and suggest that the cationic copolymerization of the PD/IB pair displays slight deviation from a fully random structure and a small tendency towards block formation. This finding was corroborated by the study of IB-centered triad distributions. Microstructural investigations on the pentadiene residues showed that the PD units were essentially incorporated in a trans-1,4 configuration, accompanied by trans-1,2 and cyclized sequences which did not exceed 25 and 30 mol%, respectively. Up to about 50 mol% of incorporated IB, the microstructure of the pentadienic fraction in the copolymers is unaffected. (C) 1998 Elsevier Science Ltd. All rights reserved. [References: 42]