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 () using a RuCl(IMesH)(CH-2-O Pr-CH) (, IMesH = 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 (, = 32 200-39 200) than those reported previously ( = 5600-14700). 1--Butyl-3-methyl imidazolium hexafluorophosphate ([Bmim]PF) and 1--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 (), 1,4-cyclohexanedimethanol (), and 1,4-butanediol () in [Bmim]PF and [Hmim]TFSI also afforded the higher-molecular-weight polymers. The values in the resultant polymers did not decrease even under the scale-up conditions (300 mg to 1.0 g scale, , , and ) in the polymerizations in [Hmim]TFSI; the subsequent reaction of with ethylene (0.8 MPa, 50 °C, and 5 h) gave oligomers (proceeded via depolymerization). Tandem hydrogenation of the resultant unsaturated polymers () in a [Bmim]PF-toluene biphasic system upon the addition of AlO (1.0 MPa H at 50 °C) gave the corresponding saturated polymers (), which waswere isolated by a phase separation in the toluene layer. The [Bmim]PF layer containing the ruthenium catalyst could be recycled without a decrease in the activity/selectivity of the olefin hydrogenation at least eight times.