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

Xiuxiu Wang; Weizhen Zhao; Kotohiro Nomura

doi:10.1021/acsomega.3c00390

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

ACS Omega. 2023 Feb 9;8(7):7222-7233. doi: 10.1021/acsomega.3c00390. eCollection 2023 Feb 21.

Authors

Xiuxiu Wang¹, Weizhen Zhao², Kotohiro Nomura¹

Affiliations

¹ Department of Chemistry, Graduate School of Science, Tokyo Metropolitan University, 1-1 Minami Osawa, Hachioji, Tokyo 192-0397, Japan.
² Beijing Key Laboratory of Ionic Liquids Clean Process, Institute of Process Engineering, Chinese Academy of Sciences, 1 North Second Street, Zhongguancun, Haidian District, Beijing 100190, China.

Abstract

Acyclic diene metathesis (ADMET) polymerization of an α,ω-diene monomer of bis(undec-10-enoate) with isosorbide (M1) using a RuCl₂(IMesH₂)(CH-2-O ⁱ Pr-C₆H₄) (HG2, IMesH₂ = 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]PF₆) 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]PF₆ 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]PF₆-toluene biphasic system upon the addition of Al₂O₃ (1.0 MPa H₂ at 50 °C) gave the corresponding saturated polymers (HP1), which waswere isolated by a phase separation in the toluene layer. The [Bmim]PF₆ layer containing the ruthenium catalyst could be recycled without a decrease in the activity/selectivity of the olefin hydrogenation at least eight times.