Formation and degradation of 1,4‐polybutadiene via metathesis: new results concerning cyclic oligomers

Abstract

The ring-opening metathesis polymerization (ROMP) of cyclic oligomers of butadiene (c,c-l,5-cyclooctadiene -COD -, f,t,f-l,5,9-cyclododecatriene -CDT -), the acyclic diene metathesis (ADMET) of 1,5-hexadiene and the intramolecular metathesis degradation of 1,4-polybutadiene (1,4-BR) were studied using stable tungsten and molybdenum carbene complexes as well as conventional metathesis catalysts. The determination of cyclic oligomers up to rings containing eight butadiene units shows, compared to the literature, different results regarding the distribution, concentration and cishrans ratio. Kinetic studies of the ROMP of COD and the intramolecular metathesis of 1,4-BR allow to explain the discrepancy. The ROMP product spectrum for the cyclobutene system known and accepted until now in the literature as ring-chain equilibrium is controlled kinetically and far apart from thermodynamic equilibrium according to our results.

Computional Study of Metathesis Degradation of Rubber, 2. Distribution of Cyclic Oligomers via Intramolecular Metathesis Degradation of Natural Rubber

“…Mole fraction of oligomers in % [9,21] Calculated mole fraction of oligomers in % contrast to cis,cis-1,5-dimethyl-1,5-cyclooctadiene, cis,-cis-1,5-cyclooctadiene easily participates in the ring-opening metathesis oligomerization producing all-trans oligomers. Figure 6 shows the equilibrium between these cyclooligomers.…”

“…These results are in reasonable agreement with recent experimental data. [9,21] The calculations show that NR in the presence of appropriate high stable catalysts can degrade to a set of cis cyclic oligomers which undergo the further metathesis degradation to the thermodynamically more stable rings with the all-trans cyclic isoprene trimers being the main products ( Figure 7). It is well known that if the formation of a certain cycle becomes thermodynamically favored, the intramolecular metathesis degradation of polyalkenamers can be shifted completely towards these rings.…”

Chemical modifications of polydiene elastomers: A survey and some recent results

“…Such back-bitting reactions induce the formations of cyclic oligomers and bimodal molecular weight distributions as in ringopening metathesis polymerizations (ROMP) and in acyclic diene metathesis (AD-MET). [32][33][34][35] • By cross metathesis with a symmetric alkene R-CHACH-R (Fig. 6).…”

Depolymerization of 1,4-polybutadiene by metathesis: high yield of large macrocyclic oligo(butadiene)s by ligand selectivity control

“…[24][25][26][27] The particular synthesis of macrocycles from 1,4-PB is only scarcely described, mainly in the context of PB degradation. Though old generation tungsten and molybdenum-based alkylidene complexes have been tested in the cyclodepolymerization of 1,4-PB, [28][29][30][31][32] novel Ru-based catalysts have been unexplored, likely because the so far reported catalysts predominantly produced CDT, which is not competitive with the established butadiene tricyclization process. Thanks to the great devotion of several researchers in exploring new ligands for metathesis complexes over the past years, a broad range of Ru-based alkylidene complexes with a variation of steric and electronic properties is available, [33][34][35] and their influence on the activity and product selectivity has been demonstrated.…”