Synthesis of High-Molecular-Weight Biobased Aliphatic Polyesters by Acyclic Diene Metathesis Polymerization in Ionic Liquids
Xiuxiu Wang, Weizhen Zhao, Kotohiro Nomura
Abstract
High Resolution Image Download MS PowerPoint Slide 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.