Synthèse de polymères α,ω‐bifonctionnels par réaction de métathèse. Méthodologie d'approche des différences de réactivité des sites carbéniques en présence

Abstract

AbstractThe results of studies of co‐metathesis reactions of 1,5‐cyclooctadiene (1) with dimethyl 3‐hexenedioate (2a) and for comparison, with 4‐octene (2b) and 1,5‐hexadiene (2c) are analyzed in order to approximate the relative reactivities of the carbene species and of the different types of double bonds. To this end, the experimental distributions of the first telomers are compared with theoretical ones calculated on the one hand allowing equal probability of arrangement of alkylidene groups and on the other hand allowing a kinetic control of propagation and transfer reactions. In other respects, the possibilities of mass control of the products obtained by the same co‐metathesis or by degradation of 1,4‐polybutadiene are studied. The results show that the reactivity of the 1,5‐cyclooctadiene double bonds is higher than that of the other types of double bonds, this being in agreement with the hypothesis of stabilization of the β‐carbomethoxycarbene species by carbene/ester complexation. This stabilization allows us to explain the distribution of α,β‐difunctional oligomers in agreement with the hypothesis of kinetic control. The distribution of non‐functional oligomers agrees with a random combination of alkylidene groups. This stabilization is compatible with the controlling method of molecular weights in the products obtained by polymerization of cyclooctadiene and also by degradation of 1,4‐polybutadiene in the presence of 2a.