Intra- and intermolecular metathesis reactions in the formation and degradation of unsaturated polymers

Computational study of metathesis degradation of rubber, 1. Distribution of cyclic oligomers via intramolecular metathesis degradation ofcis-polybutadiene

“…4) according to Fig. 3 agrees reasonably with most of the available experimental data with the butadiene tetramers and pentamers being the main products 6,17,[21][22][23] . According to the calculations, the main product of the intramolecular metathesis degradation of cis-PB is the cyclic butadiene pentamer (61 mol-%) followed by tetramer (28 mol-%) and hexamer (11 mol-%).…”

“…If the formation of cyclics is thermodynamically favoured, the intramolecular degradation will completely be shifted towards these cyclic oligomers. The ROMP of 1,5-cyclooctadiene and the intramolecular degradation of cis-PB by W-containing catalysts reaches the equilibrium (the addition of fresh catalyst does not change the oligomeric distributa- tion) giving a set of cyclic butadiene tetramers and pentamers as main products 6,17,[21][22][23] . On the other hand, kinetic studies of the ROMP of 1,5-cycloctadiene and the intramolecular degradation of cis-PB using the stable tungsten carbene complex demonstrated that the formation of butadiene trimers is highly favoured 24) .…”

“…Many studies have been made on the metathesis degradation of rubber 7,8) . The intramolecular metathesis degradation of many polyalkenamers 9,10) and its co-metathesis with linear olefins as chain transfer agents [11][12][13][14][15] using tungsten and molybdenum based metathesis catalysts have been carried out to produce low molecular weight and end-functionalised oligomers. The intramolecular reaction rapidly reaches equilibrium at room temperature.…”

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

“…The detailed investigations show that the intramolecular metathesis degradation of unsaturated polymers is a chain process [1,2] and the reaction rapidly reaches equilibrium at room temperature to yield a set of cyclic oligomers (Figure 1). The composition of the cyclic products depends on the double bonds distribution in the polymer chain and the chain-ring equilibrium is independent of the reaction temperature in certain temperature range [3,4] in contrast to polypentanamer-cyclopentene equlibrium.…”

Molecular mechanics calculations on cyclopentenyl compounds, products obtained by olefin metathesis of norbornadiene derivatives

“…In most cases, however, reformation of the cyclic olefins does not take place except for rings of comparatively low ring strain like cyclopentene. 6 In addition, bulky substituents adjacent to double bonds slow down possible attack. '-'' Thus, polymers resulting from substituted bicyclic monomers (e.g., 2, 3-dimethylnorbornadiene, UI) are of special interest, since they should not be affected in a subsequent metathesis reaction.…”