Synthesis of Semicrystalline Long Chain Aliphatic Polyesters by ADMET Copolymerization of Dianhydro- D -glucityl bis(undec-10-enoate) with 1,9-Decadiene and Tandem Hydrogenation

+81-42-677-2547 Abstract: Acyclic diene metathesis (ADMET) copolymerization of dianhydro- D -glucityl bis(undec-10-enoate) (M1) with 1,9-decadiene (DCD) using ruthenium-carbene catalyst, RuCl 2 (IMesH 2 )(CH-2-O i Pr-C 6 H 4 ) [IMesH 2 = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene, HG2 ], afforded unsaturated polyesters ( M n = 9300–23,400) under the optimized conditions. Subsequent tandem hydrogenation (H 2 1.0 MPa, 50 ◦ C) with the addition of a small amount of Al 2 O 3 resulted in the saturated polymers having a melting temperature of 71.7–107.6 ◦ C, depending on the molar ratio of M1 and DCD.

Synthesis of long chain aliphatic polyesters placing ester functionalities in different methylene spacing units by adopting ADMET copolymerization of undec-10-en-1-yl undec-10-enoate and undeca-1,10-diene (Mn = 7000-10,300, before hydrogenation) followed by hydrogenation of the olefinic double bonds in the presence of two different ruthenium catalysts (Scheme 2, top) has been reported [20]. The melting temperature (Tm) of the resultant polymer was depended upon the number of the methylene units employed. Hydrogenation of the isolated unsaturated copolymers by RuHCl(H2)(PCy3)2 (Cy = cyclohexyl) catalyst required severe conditions (40 bar, 110 °C, 2 days) [20]. As in Scheme 1 above, we established a tandem system (one pot synthetic method) under mild conditions, and demonstrated one pot synthesis of bio-based saturated polyesters by tandem ADMET copolymerization of M1 with 1,9-decadiene (DCD) and subsequent hydrogenation (Scheme 2, bottom).
It was noted that the M n value increased when chloroform solvent in the reaction mixture was replaced during the polymerization (every 30 min), and repetitive replacement seemed more effective for obtaining high molecular weight copolymers (run 2 vs. runs 9-14, Table 1, Figure 1b). The effect was due to removal of ethylene that remained in the mixture by replacement of the solvent. The M n value of 23,400 (M w /M n = 1.48) was attained by replacement of the solvent six times, although this is not be a productive method from a practical viewpoint. Figure 2b shows the 1 H NMR spectrum (in CDCl 3 at 25 • C) for the resultant poly(M1co-DCD), and the spectrum for poly(M1) is also placed for comparison ( Figure 2a). Resonances assigned to protons of the internal olefins were observed at 5.29-5.38 ppm, whereas those assigned to the terminal olefins (at 4.84, 4.91, and 5.72 ppm) in M1 and DCD were no longer seen and other resonances were remained (resonances ascribed to protons in the internal olefins (5.29-5.38 ppm), protons adjacent to olefins (1.94 ppm) and methylene (1.43-1.21) overlapped with DCD, the other resonances corresponded to the protons from M1; details, see Materials and Methods). This result clearly indicates formation of polymers by the ADMET polymerization [13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28]. Moreover, resonances ascribed to the olefinic double bonds, and those to protons adjacent to the double bond (-CH 2 -CH=CH-), disappeared in the sample after hydrogenation. The results also suggest conversion to the hydrogenated polymers.
We reported that the resultant polymer prepared by ADMET polymerization of M1 could be hydrogenated under mild conditions (1.0 MPa, 50 • C), compared to those reported previously (such as 4.0 MPa, 110 • C, 2 days, two-step process) [20,[29][30][31][32], without isolation of unsaturated polymers, by adding small amount of alumina (Al 2 O 3 ) into the reaction mixture. As reported previously [28], the completion of the hydrogenation of olefinic double bonds should be monitored (confirmed) by DSC thermograms (observed as single melting temperature with uniform composition), although disappearance of resonances ascribed to olefinic protons was observed after a short period [28]. Since we need to check whether the hydrogenation of the copolymer was complete under similar conditions, tandem hydrogenations were conducted under various conditions (hydrogen pressure, time; runs 9-11). Figure 3 shows DSC thermograms of the resultant poly(M1-co-DCD)s (molar ratio of M1:DCD = 1:10) prepared under various conditions. It turned out that no significant Catalysts 2021, 11, 1098 4 of 9 differences in the thermograms, or the T m (melting temperature) values, were observed irrespective of the hydrogenation conditions, clearly suggesting that the hydrogenation reached completion even after 3 h under 1.0 MPa of hydrogen in this catalysis (in the presence of Al 2 O 3 at 50 • C). The resultant copolymers were, however, insoluble for ordinary GPC analysis (in THF at 40 • C, in ortho-dichlorobenzene at 145 • C), and were poorly soluble in chloroform in conventional NMR analysis. M1:DCD = 1:10) prepared under various conditions. It turned out that no significant differences in the thermograms, or the Tm (melting temperature) values, were observed irrespective of the hydrogenation conditions, clearly suggesting that the hydrogenation reached completion even after 3 h under 1.0 MPa of hydrogen in this catalysis (in the presence of Al2O3 at 50 °C). The resultant copolymers were, however, insoluble for ordinary GPC analysis (in THF at 40 °C, in ortho-dichlorobenzene at 145 °C), and were poorly soluble in chloroform in conventional NMR analysis.     Table 1. Figure 4 shows DSC thermograms in the resultant poly(M1-co-DCD)s prepared under various M1:DCD molar ratios; the thermogram for poly(M1) is placed for comparison. It turned out that the Tm value in the resultant copolymer increased upon increasing the DCD molar ratios (the ratio was highly close to that charged in the reaction mixture). The resultant copolymer prepared with a DCD/M1 molar ratio of 10 possessed a Tm value of  It turned out that the T m value in the resultant copolymer increased upon increasing the DCD molar ratios (the ratio was highly close to that charged in the reaction mixture). The resultant copolymer prepared with a DCD/M1 molar ratio of 10 possessed a T m value of ca. 105-106 • C, and the value seemed rather low in the low molecular weight samples (runs 1,4-6). These results suggest that thermal resistant polymers (T m higher than 100 • C) could be prepared by conducting copolymerization of biobased monomer (M1) with nonconjugated diene (DCD).  Table 1. Figure 4 shows DSC thermograms in the resultant poly(M1-co-DCD)s prepared under various M1:DCD molar ratios; the thermogram for poly(M1) is placed for comparison. It turned out that the Tm value in the resultant copolymer increased upon increasing the DCD molar ratios (the ratio was highly close to that charged in the reaction mixture). The resultant copolymer prepared with a DCD/M1 molar ratio of 10 possessed a Tm value of ca. 105-106 °C, and the value seemed rather low in the low molecular weight samples (runs 1,4-6). These results suggest that thermal resistant polymers (Tm higher than 100 ºC) could be prepared by conducting copolymerization of biobased monomer (M1) with nonconjugated diene (DCD).  Table 1.

ADMET Copolymerization of M1 with 1,13-Tetradecadiene (TDCD) and Tandem Hydrogenation
Copolymerizations of M1 with 1,13-tetradecadiene (TDCD) were also conducted under similar conditions (TDCD:M1 = 10:1, molar ratio), and the results are summarized in Table 2. Although the polymerizations were conducted with different catalyst loading (1.0 and 0.5 mol%) as well as different numbers of solvent exchanges to remove ethylene by product in this polycondensation, the resultant polymers possessed rather low molecular weights and no improvements in the Mn values were attained.   Table 1.

ADMET Copolymerization of M1 with 1,13-Tetradecadiene (TDCD) and Tandem Hydrogenation
Copolymerizations of M1 with 1,13-tetradecadiene (TDCD) were also conducted under similar conditions (TDCD:M1 = 10:1, molar ratio), and the results are summarized in Table 2. Although the polymerizations were conducted with different catalyst loading (1.0 and 0.5 mol%) as well as different numbers of solvent exchanges to remove ethylene by product in this polycondensation, the resultant polymers possessed rather low molecular weights and no improvements in the M n values were attained.

Concluding Remarks
Copolymerizations of bio-based dianhydro-D-glucityl bis(undec-10-enoate) (M1) with 1, 9- hydrogenation system under rather mild conditions (1.0 MPa, 3 h at 50 • C) was also demonstrated in this catalysis. The attempted copolymerization with 1,13-tetradecadiene in place of DCD yielded rather low molecular weight polymers, suggesting that further improvements should be considered as a future project. Synthesis of rather thermal resistant polymers (T m higher than 100 • C) containing isosorbide (derived from a glucose) unit was demonstrated by copolymerization of a biobased monomer (M1) with nonconjugated diene (DCD). The approach adopted here should be beneficial to development of a green sustainable process with materials that should be promising alternatives to those based on fossil fuels.
Acyclic diene metathesis (ADMET) polymerization. The typical polymerization procedure is as follows. In the drybox, a prescribed amount of 1,9-decadiene (DCD), and a CHCl 3 solution (0.14 mL, anhydrous) containing a prescribed amount of ruthenium catalyst (HG2) was placed into a 50 mL scale sealed Schlenk tube. After stirring the solution for 10 min at 25 • C under a nitrogen atmosphere in the drybox, dianhydro-D-glucityl bis(undec-10-enoate) (M1 0.325 mmol, 150 mg) was added to the reaction mixture. The reaction tube was taken out and was magnetically stirred in an oil bath at 50 • C. The mixture was then placed into a liquid nitrogen bath to remove ethylene from the reaction by opening the valve connected to the vacuum line for a short period (1 min). The valve was then closed, and the tube was returned into the oil bath to continue the reaction [26,28]. The procedure removing ethylene was repeated after a measured period (30 min for the first time then every 1.0 h until 6 h). The polymerization mixture was then cooled to room temperature and was quenched with excess ethyl vinyl ether (two drops, ca. 100 mg) while stirring for 1.0 h. The resultant solution was then dissolved in chloroform (2.0 mL) for dilution, and the solution was added dropwise into the stirred cold methanol (50 mL). The solution was stirred for ca. 15 min, and the precipitates were then collected by filtration and dried in vacuo to yield poly(M1-co-DCD) as a white solid. During the reaction in certain experimental runs, CHCl 3 was removed in vacuo and was replaced every 30 min at the initial stage (noted as solvent exchange in Table 1).