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

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.

Synthesis of High Molecular Weight Biobased Aliphatic Polyesters Exhibiting Tensile Properties Beyond Polyethylene

“…The method also faces the difficulty of stirring due to high viscosity. 15 Recently, the polymerization of M1 and M2 conducted in ionic liquid (IL, no vapor pressure) with continuous removal of ethylene byproduced afforded polymers with M n value higher than 30000 (Scheme 1), 15 whereas the polymerization conducted in toluene or CHCl 3 (even under optimized conditions with careful removal of ethylene) afforded polymers of M n values up to 15000. 21,32 We thus herein communicate that the synthesis of high molar mass polymers (M n = 44000− 49400 g/mol), which exhibit better tensile properties than conventional polyethylene, has been achieved by using the molybdenum-alkylidene catalyst, Mo(CHCMe 2 Ph)(2,6-Me 2 C 6 H 3 )[OC(CH 3 )(CF 3 ) 2 ] (Mo cat.…”

“…Aliphatic polyesters derived from plant resources are attracting considerable attention − not only as an alternative of petroleum-based polymers but also in terms of their circular economy − due to rather facile chemical recycling by the depolymerization (through transesterification, etc. ) − compared to conventional polyolefins. These polyesters would also provide a possibility as new promising materials with better mechanical properties through interpolymer interactions as well as better compatibility with biobased fibers (described below).…”

“…An olefin metathesis route consisting of acyclic diene metathesis (ADMET) polymerization − and the subsequent hydrogenation (Scheme ) have been considered as the synthetic route due to the wide polymer scope (especially the polymer main chain, called the middle segment in Scheme ) in addition to the condensation–polymerization route . In spite of the number of reports by ADMET polymerization in the presence of ruthenium-carbene catalysts, ,− however, synthesis of the high molecular weight polymers still seems to be difficult . Two studies , reported the synthesis of the high molar mass polyesters under bulk conditions (80–90 °C, G2, 16–20 h).…”

“…Two studies , reported the synthesis of the high molar mass polyesters under bulk conditions (80–90 °C, G2, 16–20 h). However, polymerization at such high temperature led to catalyst decomposition which not only causes isomerization and undesired side reactions by formed radicals (metal particles) ,, but also causes the separation of metals from the resultant polymers to be difficult. The method also faces the difficulty of stirring due to high viscosity …”

“…The small dumbbell-shaped test specimens were prepared by cutting the polymer sheet (prepared by a hot press, the detailed procedures are described in SI), and at least three specimens of each polymer were tested (additional data are shown in SI). Samples ( P1 , HP1 ) of different (rather low) M n values were prepared by using ruthenium catalysts, , and the details are shown in Table S2. The polymer sheets prepared by the hot press method were chosen because these samples showed better tensile properties than those prepared through solvent cast methods (detailed comparisons are shown in the SI).…”