New Ru-Vinylidene Catalysts in the Cross-Metathesis of Natural Rubber and Poly(Styrene-co-Butadiene) with Essential Oils

The new ruthenium vinylidene catalysts with general formula [RuCl2(=C=CHR)(PCy3)2] (R= -p- C6H4CF3 (I), -p-C6H4F (II) and -C6H9 (III)) were used in the cross-metathesis degradation of natural rubber (NR) using essential oils, β-pinene and d-limonene as chain transfer agents (CTAs). The isolated isoprene oligomer products with molecular weight around Mn x 104 g/mol were obtained when the reactions were carried out at 50 °C. An enhancement of the catalytic activity was achieved at 80 °C showing a decrease in the molecular weights of products with around Mn x 103 g/mol. Experiments also demonstrated that the poly(styrene-co-butadiene) (SB) depolymerized in the presence of essential oils and d-limonene as CTAs by vinylidene catalysts to give the butadiene oligomers with molecular weight values around Mn = 295-698 g/mol. According to GS/MS (EI) analysis, the main products of the degradation of SB with d-limonene were limonene-terminated butadiene oligomers with m = 1-3.