Synthesis of High-Molecular-Weight Biobased Aliphatic Polyesters by Acyclic Diene Metathesis Polymerization in Ionic Liquids.

Acyclic diene metathesis (ADMET) polymerization of an α,ω-diene monomer of bis(undec-10-enoate) with isosorbide ( M1 ) using a RuCl 2 (IMesH 2 )(CH-2-O i Pr-C 6 H 4 ) ( HG2 , IMesH 2 = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) catalyst and conducted at 50 °C (in vacuo) in ionic liquids (ILs) afforded higher-molecular-weight polymers ( P1 , M n = 32 200-39 200) than those reported previously ( M n = 5600-14700). 1- n -Butyl-3-methyl imidazolium hexafluorophosphate ([Bmim]PF 6 ) and 1- n -hexyl-3-methyl imidazolium bis(trifluoromethanesulfonyl)imide ([Hmim]TFSI) were suitable as effective solvents among a series of imidazolium salts and the pyridinium salts. The polymerization of α,ω-diene monomers of bis(undec-10-enoate) with isomannide ( M2 ), 1,4-cyclohexanedimethanol ( M3 ), and 1,4-butanediol ( M4 ) in [Bmim]PF 6 and [Hmim]TFSI also afforded the higher-molecular-weight polymers. The M n values in the resultant polymers did not decrease even under the scale-up conditions (300 mg to 1.0 g scale, M1 , M2 , and M4 ) in the polymerizations in [Hmim]TFSI; the subsequent reaction of P1 with ethylene (0.8 MPa, 50 °C, and 5 h) gave oligomers (proceeded via depolymerization). Tandem hydrogenation of the resultant unsaturated polymers ( P1 ) in a [Bmim]PF 6 -toluene biphasic system upon the addition of Al 2 O 3 (1.0 MPa H 2 at 50 °C) gave the corresponding saturated polymers ( HP1 ), which waswere isolated by a phase separation in the toluene layer. The [Bmim]PF 6 layer containing the ruthenium catalyst could be recycled without a decrease in the activity/selectivity of the olefin hydrogenation at least eight times.