Ring-opening metathesis polymerizations in D-limonene: A renewable polymerization solvent and chain transfer agent for the synthesis of alkene macromonomers

D-Limonene has been utilized as a renewable solvent and chain transfer agent for the ring-opening metathesis polymerization (ROMP) of alkene macromonomers. The polymerization of various strained monomers, such as norbornene and 1,5-cyclooctadiene (COD), and low-strain monomers, such as cyclopentene, trans.trans,trans-1,5,9-cyclododecatriene and cycloheptene, have been initiated with a ruthenium carbene complex. The metathesis reactions with D-limonene resulted in decreased weight-average (M_w) molecular weight values compared to ROMP in toluene and hydrogenated D-limonene. For the ROMP of COD in D-limonene, the amount of chain transfer and chain degradation increased with increasing time (1-20 h) and temperature (23-70°C). The formation of the trisubstituted alkene during chain transfer, as evidenced by a model compound, was characterized by ¹H NMR (δ 5.14 ppm). Optimization of the reaction conditions for the ROMP of COD resulted in the synthesis of alkene macromonomers without the need for postpolymerization reactions.