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Article

Polymerization of Ethylene and 1,3-Butadiene Using Methylaluminoxane-Phosphine Catalyst Systems

by
Nanako Kimura
and
Daisuke Takeuchi
*
Graduate School of Science & Technology, Hirosaki University, Hirosaki 036-8561, Japan
*
Author to whom correspondence should be addressed.
Catalysts 2025, 15(10), 942; https://doi.org/10.3390/catal15100942
Submission received: 13 September 2025 / Revised: 26 September 2025 / Accepted: 27 September 2025 / Published: 1 October 2025
(This article belongs to the Special Issue Innovative Catalytic Approaches in Polymerization)
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Abstract

Although transition metal catalysts have been used extensively for the polymerization of hydrocarbon monomers, several cationic aluminum catalysts have been also known to promote polymerization of ethylene and 1,3-butadiene. Transition-metal catalyzed polymerization generally proceeds via coordination and insertion of the monomer on one metal center. In contrast, in ethylene polymerization using aluminum catalysts, a bimolecular chain growth mechanism, including the reaction between neutral aluminum species and the monomer activated by cationic aluminum species, is proposed. Although previously reported aluminum catalysts are based on a monoaluminum complex, a dialuminum complex is expected to catalyze the polymerization more efficiently, considering the proposed mechanism. In this work, we found that a combination of diphosphines and MAO promotes polymerization of ethylene and 1,3-butadiene. The 1,4-bis(diphenylphosphino)butane (DPPB)/methylaluminoxane (MAO) system showed a much higher activity toward ethylene polymerization than other monophosphine or diphosphine/MAO systems. NMR analysis of a mixture of diphosphine and MAO indicates the formation of cationic dialuminum species in the presence of DPPB, whereas the formation of cationic monoaluminum species occurs in the presence of other diphosphines. The 2,2′-bis(diphenylphosphino)-1,1′-biphenyl (BIPHEP)/MAO system promoted 1,3-butadiene polymerization to give polybutadiene having a cis-1,4 selectivity of up to 93.8%.

1. Introduction

The polymerization of hydrocarbon monomers, such as olefins and conjugated dienes, has attracted considerable attention since the discovery of Ziegler–Natta catalysts [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22]. Most of the catalysts, both heterogeneous and homogeneous ones, used in the polymerization are based on transition metals, which include Ti, Zr, and Hf [1,2,3,4,5]; V [6]; Cr, Fe, and Co [7,8,9,10]; Ni and Pd [1,2,11,12,13,14,15,16,17,18]; and rare-earth metals [19,20,21,22]. As for homogeneous catalysts, organoaluminums such as methylaluminoxane (MAO), Et2AlCl, and Et3Al2Cl3 are frequently used as cocatalysts for the polymerization. Trialkyl aluminums are also used as cocatalysts in combination with boron compounds. In the case of the reactions of transition metal complexes and organoaluminum cocatalysts, the resulting cationic transition metal species formed are the actual active species for the polymerization.
In contrast to transition metal catalysts, aluminum catalysts have been considered not suitable for the polymerization of hydrocarbon monomers. However, Jordan et al. found that cationic aluminum complexes with an amidinate ligand (Scheme 1, 1) can promote ethylene polymerization to afford high-mass polyethylene [23]. Since then, several cationic aluminum complexes with an aminotroponiminate ligand (2) [24], a pyridyliminoamide ligand (3) [25], and a pendant-arm Schiff-base ligand (4) [26] have been found to be effective for achieving activity for polymerization of ethylene. A dialuminum complex with a bis(iminophosphorano)methandiide ligand (5) catalyzes ethylene polymerization in the presence of [Ph3C][B(C6F5)4] [27]. Organoaluminums, in particular in combination with Lewis acids such as MAO or B(C6F5)3, also show activity for ethylene polymerization or propylene polymerization and their copolymerization [28,29]. Aluminum complexes with a pyridylamide ligand (6) have been recently reported to promote the stereoselective polymerization of 1,3-butadiene in the presence of MAO (cis-1,4 selectivity of up to 90.8%) [30]. Recently, we have found that a cationic aluminum complex with an N-heterocyclic carbene (NHC) ligand, formed in situ by the reaction of the NHC–aluminum complex (7) with MAO, can promote the polymerization of ethylene to produce ultra-high-molecular-weight polyethylene [31].
The mechanism of polymerization using aluminum catalysts (1) has been studied by DFT calculations. Initially, it was proposed that a mononuclear cationic organoaluminum complex with an amidinate ligand allows the insertion of ethylene to its carbon–aluminum bond (Scheme 2a) [32]. However, it was proposed that the energy barrier for the chain transfer of an organoaluminum to an ethylene monomer via the six-membered-ring transition state is lower than that for the insertion of ethylene to the organoaluminum via the four-membered-ring transition state [33]. It was also reported that the chain growth via the intermolecular reaction between neutral aluminum species and the ethylene activated by cationic aluminum species is more plausible because the bimolecular chain growth reaction has a lower energy barrier than in the case of chain growth via the unimolecular reaction (Scheme 2b) [34].
Based on the results of DFT studies, it is interesting to apply dialuminum catalysts for the polymerization of hydrocarbon monomers. As an extension of our study on ethylene polymerization using an NHC-Al catalyst, herein, we report the polymerization of ethylene and 1,3-butadiene catalyzed by MAO in combination with monophosphines and diphosphines. Most suitable phosphines depend on the type of hydrocarbon monomer. In particular, the NMR analysis of the phosphine/MAO mixture indicates that dialuminum and monoaluminum species are effective for the polymerization of ethylene and 1,3-butadiene, respectively.

2. Results and Discussions

2.1. Polymerization of Ethylene Catalyzed by Phosphine/MAO Systems

The polymerization of ethylene was investigated using methylaluminoxane (MAO) in combination with various monophosphines (Table 1). PPh3 and PCy3 produced polyethylene in relatively low yield (runs 1 and 2). In contrast, the use of CyJohnPhos (Cy2PC12H9) showed higher catalytic activity than PPh3 and PCy3 (run 3). Neither JohnPhos (tBu2PC12H9) nor XPhos (Cy2PC12H5iPr3), which also has a biaryl-phosphine structure, was effective for the polymerization (runs 4 and 5). The reaction by MAO alone did not afford any polymer under the same reaction conditions, and phosphine is necessary for the polymerization to proceed (run 6). The ethylene polymerization catalyzed by the CyJohnPhos/MAO system was further investigated under various conditions. Increasing the amount of CyJohnPhos increased the polymer yield (run 7), whereas reducing the amount of MAO to half decreased the polymer yield (run 8). The use of modified methylaluminoxane (MMAO) instead of MAO also decreased the polymer yield (run 9). Decreasing the amount of the solvent also decreased the polymer yield (run 10).
In addition to monophosphines, diphosphines were also used for the polymerization. Diphosphines having a short oligomethylene spacer, such as 1,1-bis(diphenylphosphino)methane (DPPM), 1,2-bis(diphenylphosphino)ethane (DPPE), and 1,3-bis(diphenylphosphino)propane (DPPP), only produced polyethylene in low yield (runs 11–13). In contrast, the use of 1,4-bis(diphenylphosphino)butane (DPPB) resulted in a marked increase in polymer yield (run 14). The activity of DPPB/MAO is higher than those of the monophosphine/MAO systems. GPC and DSC analyses of the produced polymer showed Mn = 737,000 and Tm = 137.4 °C. The use of diphosphines having a longer oligomethylene spacer also produced a low yield of polyethylene (runs 15 and 16). Rigid rac-2,2′-bis(diphenylphosphino)-1,1′-binaphthyl) (rac-BINAP) also shows activity toward ethylene polymerization in the presence of MAO to give polyethylene with Mn = 97,000 (run 17). Similarly to the ethylene polymerization catalyzed by CyJohnPhos/MAO, that catalyzed by DPPB/MAO with a decreased amount of MAO or the solvent resulted in low yield (runs 18 and 19). Thus, the diphosphine having a tetramethylene spacer is suitable for ethylene polymerization in the presence of MAO.

2.2. Polymerization of 1,3-Butadiene Catalyzed by MAO/Phosphine Systems

MAO/phosphine systems were also used for the polymerization of 1,3-dienes (Table 2). The CyJohnPhos/MAO system, under similar conditions to the ethylene polymerization, did not afford a polymer (run 1). However, the catalyst produced a polybutadiene with 84.9 mol% 1,4-unit in low yield (1.4%) under reduced amounts of MAO and the solvent (run 2). DPPE, DPPP, DPPB, or 1,6-bis(diphenylphosphino)hexane (DPPHex) in combination with MAO gave a low yield, which prevented its detailed characterization (runs 3–6). As for the DPPB/MAO system, a sufficient amount of polybutadiene was produced; thus, the 1H NMR analysis of the polybutadiene could be conducted, which revealed that the polymer contains 78.9 mol% 1,4 unit (run 5).
In contrast to these diphosphines having flexible spacers, rac-BINAP and 2,2′-bis(diphenylphosphino)biphenyl (BIPHEP), having rigid spacers between diphenylphosphino groups, afforded polybutadiene in 10.3 and 3.1% yields, respectively (runs 7 and 8). The 1H and 13C{1H} NMR spectra of the polymer indicated that the polymer formed is rich in the cis-1,4 unit. In particular, the polymer obtained with BIPHEP/MAO contained 93.8 mol% cis-1,4 unit (run 8) (Figure S1). This value is higher than that of polybutadiene obtained using an Al catalyst reported previously [30]. Increasing the amount of BIPHEP from 20 μmol to 40 μmol increased the polymer yield (run 9), but a further increase in the amount to 60 μmol resulted in a negligible yield of the polymer (run 10). As the cationic aluminum species is expected to be the active species for the polymerization, 1,3-butadiene polymerization using BIPHEP/Me3Al in the presence of [Ph3C][B(C6F5)4] was also conducted, but no polymer was obtained (run 11). The polymerization of isoprene or myrcene did not proceed when using the BIPHEP/MAO system.

2.3. Characterization of Species Active for Polymerization

The species active for polymerization was characterized by NMR. The 1H NMR spectrum of a mixture of DPPP and MAO (Al/P = 4) showed a triplet signal at δ −0.29 (JHP = 4.5 Hz) in addition to a large singlet signal at δ −0.36 corresponding to AlMe3, which is contained in MAO (Figure 1c). The presence of the triplet signal in the DPPP/MAO agrees with the report by Bochman [35] and indicates the formation of cationic monoaluminum diphosphine species, [Me2Al(dppp)]+, in the reaction of DPPP and MAO. [Me2Al(dppp)]+ is considered to form via the reaction of DPPP with the Me3Al contained in MAO and the abstraction of one of the Me groups on Al by MAO.
1H NMR spectra of a mixture of DPPM and MAO (Al/P = 5.7) (Figure 1a) or DPPE and MAO (Al/P = 4) (Figure 1b) showed several small singlet signals at around δ 0 to 0.3 and δ −0.3 to −0.5, but no distinctive triplet signal, and possible aluminum complexes formed in the mixture could not be confirmed. These results agree again with previously reported data [35].
In contrast to the above results, the 1H NMR spectrum of a mixture of DPPB and MAO (Al/P = 4) showed a relatively large doublet signal at δ −0.23 (JHP = 3.5 Hz) in addition to a broad signal at δ −0.31 due to the AlMe3 (Figure 1d). The observation of a doublet signal, not a triplet signal, indicates the coordination of two phosphines to different Al centers, rather than the coordination of two phosphines to one Al center. It is considered that a cationic dialuminum species, [(Me3Al)(Me2Al)(dppb)]+, is formed in the reaction of DPPB and MAO. Considering the highly electron-deficient character of the cationic aluminum center, one of the methyl groups would interact with the two aluminum centers to form [(μ−Me)(Me2Al)2(dppb)]+. The bridged methyl group should appear as a triplet signal, but no triplet signal was observed on the 1H NMR. This would be due to the rapid exchange of Me groups between the two aluminum centers. The 31P{1H} NMR spectrum of DPPB/MAO showed signals at δ −15.2 and −15.4 (Figure S2). The HMBC experimental results revealed a correlation between the CH3 groups on the Al and P atoms of DPPB, which confirms that the signal at δ −0.23 appears as a doublet owing to its coupling with the phosphorus signal of DPPB (Figure S4). Selective formation of a cationic dialuminum complex with the DPPP ligand has been also reported recently in the reaction of DPPP, iBu3Al, iBu2AlH, and [PhMe2NH][B(C6F5)4] [36].
Although no distinct triplet or doublet signals were observed in the 1H NMR spectrum of DPPPen/MAO with Al/P = 4, a clear and large triplet signal was observed at δ −0.22 (JHP = 2.3 Hz) in the 1H NMR spectrum of DPPPen/MAO with Al/P = 1 (Figure 1e), indicating the formation of the cationic monoaluminum species [Me2Al(dpppen)]+. As for DPPHex/MAO, no triplet or doublet signals were observed in the 1H NMR spectrum at the Al/P ratio of either 5.7 or 1, and the aluminum complexes formed in the mixture could not be confirmed (Figure 1f).
1H NMR analyses of BIPHEP/MAO (Al/P = 10) (Figure 1g) and rac-BINAP/MAO (Al/P = 1.6) (Figure 1h) were also conducted, and triplet signals were observed for both systems (δ = −0.12 (JHP = 4.0 Hz) and δ = 0.05 (JHP = 3.8 Hz), respectively). A strong correlation was observed between the triplet 1H NMR signal and the phosphine 31P NMR signal in the HMBC experiment (Figures S5 and S6). These results indicate that the monoaluminum species [Me2Al(biphep)]+ and [Me2Al(rac-binap)]+ are formed for those diphosphines, although BIPHEP and rac-BINAP have four carbon atoms between two phosphines, similarly to DPPB. The rigid biaryl structures of BIPHEP and rac-BINAP would facilitate the formation of monoaluminum species rather than dialuminum species.
To isolate the cationic aluminum species, the trimethylaluminum complex of DPPB was synthesized and reacted with [Ph3C][B(C6F5)4]. [(Me3Al)2(dppb)] was synthesized by the reaction of Me3Al with dppb in hexane. X-ray analysis of the crystal confirmed the formation of [(Me3Al)2(dppb)] (Figure 2). Two types of complex structures, one with Me3Al units directed toward the opposite side (Al-Al distance of 9.399 Å) and the other with Me3Al units directed toward the same side (Al-Al distance of 8.295 Å), were contained in the crystal. The Al-P distances of the two molecules are almost the same (2.514 and 2.512 Å for the former, 2.509 Å for the latter). The 1H NMR spectrum of the complex showed a signal due to AlMe at δ −0.23 (Figure S7). The signal appeared as a singlet, not doublet, which would be due to the equilibrium between [(Me3Al)2(dppb)] and free Me3Al and DPPB in the benzene-d6 solution. The integration of the signal is ca. 12H, which does not agree with the value expected from the formula (18H). This inconsistency in the integration of the signal may be due to the above equilibrium and/or the difference in the relaxation time of those signals. The addition of [Ph3C][B(C6F5)4] to the benzene-d6 solution of [(Me3Al)2(dppb)] (B/Al = 0.5) resulted in several broad signals in the region of δ 3.0 to −1.0, and no marked doublet signals were observed (Figure S8). The 31P{1H} NMR spectrum of the mixture of [(Me3Al)2(dppb)] and [Ph3C][B(C6F5)4] showed signals at δ 30.7 and 30.2 in addition to those at δ −15.2 and −15.4 (Figure S8). The signals at δ 30.7 and 30.2 plausibly correspond to phosphonium species formed by the reaction of [Ph3C][B(C6F5)4] with DPPB. Thus, some part of the AlMe3 center is dissociated from the DPPB.
On the basis of the results of NMR studies, the plausible mechanism of the polymerization of hydrocarbon monomers when using the phosphine/MAO catalyst is proposed (Scheme S1). The polymerization of ethylene most efficiently proceeded when the DPPB/MAO system was used, compared with MAO in combination with other phosphines. This result is accounted for by the formation of the cationic dialuminum complex [(Al2Me5)(dppb)]+, rather than the cationic monoaluminum complex [(AlMe2)(dppb)]+, in the reaction of DPPB with MAO. As [(Al2Me5)(dppb)]+ contains both neutral and cationic Al centers, it enables the activation of ethylene by the cationic Al center, as well as the reaction of the neutral alkyl aluminum with the activated ethylene monomer intramolecularly. In contrast, other diphosphines, such as DPPP and DPPPen, tend to afford a cationic monoaluminum complex in their reactions with MAO. The ethylene polymerization catalyzed by the monoaluminum complex proceeds via the intramolecular reaction between cationic and neutral complexes, which is less efficient than the intramolecular chain growth catalyzed by the dialuminum complex.
The chain growth of 1,3-butadiene would involve the reaction of an allylaluminum species with 1,3-butadiene. This reaction catalyzed by the monoaluminum complex proceeds via the six-membered transition state, and its energy barrier is much lower than that for the reaction via the four-membered transition state. Thus, the BIPHEP/MAO system, where the cationic monoaluminum species [Me2Al(biphep)]+ is generated, allows the polymerization of 1,3-butadiene. The rigid but less strained structure of [Me2Al(biphep)]+ would facilitate the high cis-1,4-selectivity of the polymerization.

3. Materials and Methods

3.1. General

All the manipulations of the reactions were carried out under nitrogen using standard Schlenk techniques. The NMR (1H and 13C{1H}) spectra were recorded on a JEOL JNM-ECZ500R spectrometer. The 1H NMR chemical shifts were referenced to CHCl3 (δ 7.26) in CDCl3 solvent, 1,1,2,2-tetrachloroethane (δ 5.91) in the 1,1,2,2-tetrachloroethane-d2 solvent, C6D5H (δ 7.16) in C6D6 solvent and PhCH3 (δ 2.11) for 1H and CDCl3 (δ 77.0), and 1,1,2,2-tetrachloroethane-d2 (δ 74.2) for 13C. Gel permeation chromatography (GPC) was performed at 40 °C on a TOSOH HLC-8020 high-speed liquid chromatograph system using THF as eluent or at 160 °C on a TOSOH HL-8321GPC/HT liquid chromatograph system using 1,2,4-trichlorobenzene as eluent. DSC was recorded on Seiko DSC6200R instruments.
The toluene and hexane were deoxygenated and dried by using a Glass Contour solvent purification system (Nikko Hansen & Co., Ltd., Osaka, Japan). The MAO and MMAO were purchased from Tosoh Chemical Co. Other chemicals were purchased and used as received. The X-ray crystal structure analysis was performed at 123 K on a Rigaku RAXIS Rapid imaging plate diffractometer using Mo Kα radiation (λ = 0.71069 Å). The data analysis was conducted using the OLEX2 software package. Elemental analysis was carried out using a vario MICRO cube CHNS.

3.2. General Procedure for Ethylene Polymerization

Typically, a 100 mL autoclave containing phosphine ligand was dried in vacuo, and ethylene gas was introduced. Toluene and MAO (toluene solution) were added, and ethylene gas was introduced for purging at 1 MPa. Then, the reaction mixture was stirred at 30 °C and 750 rpm. Polymerization was quenched with EtOH, and the mixture was poured into MeOH:HCl = 3:1 solution. The precipitate formed was collected by filtration. The obtained polymer was analyzed by GPC and DSC.

3.3. General Procedure for 1,3-Butadiene Polymerization

Typically, a 20 mL Schlenk flask containing phosphine ligand was dried in vacuo, and N2 gas was introduced. Toluene, 1,3-butadiene (toluene solution), and MAO (toluene solution) were added to the flask and the reaction mixture was stirred at r.t. and 750 rpm. Isolation and characterization of the produced polymer were the same as for the ethylene polymerization. The microstructure of the produced polymer was characterized by 1H and 13C{1H} NMR according to a previous report [37].

3.4. Synthesis of [(Me3Al)2(dppb)]

A 20 mL Schlenk flask containing DPPB (0.426 g, 1 mmol) was dried in vacuo, and N2 gas was introduced. Hexane (1.2 mL) and Me3Al (2.1 mmol) (1 M solution in hexane (2.1 mL)) were added to the flask and the reaction mixture was stirred at r.t overnight to give a suspension. The reaction mixture was heated until the white precipitation formed was dissolved completely. Then, the reaction mixture was cooled to r.t. to afford the [(Me3Al)2(dppb)] as colorless crystals. Cooling the reaction mixture to −20 °C resulted in improved yield of the product (85%). 1H NMR (500 MHz, C6D6): 7.33 (dt, J = 1.5, 7.5 Hz, 8H, Ph), 7.05 (m, 12H, Ph), 1.85 (m, 4H, (CH2)4), 1.45 (m, 4H, (CH2)4), −0.23 (s, 12H, AlCH3). 31P{1H} NMR (202 MHz, C6D6): −15.3 (s). Anal. Calcd for C34H46Al2P2: C, 71.56; H, 8.13; N, 0.00, Found: C, 70.87; H, 8.254; N, 0.00.

4. Conclusions

The DPPB/MAO system promoted ethylene polymerization efficiently. Its activity is much higher than those of other monophosphine or diphosphine/MAO systems. The NMR analysis of a mixture of DPPB and MAO showed the formation of the cationic dialuminum species [(Al2Me5)(dppb)]+, which indicates an intramolecular chain growth mechanism through the cooperation between the two aluminum centers. The BIPHEP/MAO system promoted 1,3-butadiene polymerization to give polybutadiene having a cis-1,4 selectivity of up to 93.8%. In this case, the formation of cationic monoaluminum species is indicated by the NMR result.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/catal15100942/s1. Figure S1: 1H (up) and 13C{1H} (down) NMR spectra of polybutadiene obtained by BIPHEP/MAO system (CDCl3, r.t.) (Table 2, run 8); Figure S2: 31P{1H} NMR spectrum of a mixture of DPPB and MAO (Al/P = 4) (C6D6, r.t.); Figure S3: HMBC spectrum of a mixture of DPPP and MAO (Al/P = 4) (C6D6, r.t.); Figure S4: HMBC spectrum of a mixture of DPPB and MAO (Al/P = 1) (C6D6, r.t.); Figure S5: HMBC spectra of a mixture of BIPHEP and MAO (Al/P = 5) (C6D6, r.t.); Figure S6: HMBC spectra of a mixture of rac-BINAP and MAO (Al/P = 4) (C6D6, r.t.); Figure S7: 1H (up) and 31P{1H} (down) NMR spectra of (dppb)(AlMe3)2 (C6D6, r.t.); Figure S8: 1H (up) and 31P{1H} (down) NMR spectra of a mixture of [(AlMe3)2(dppb)] and [Ph3C][B(C6F5)4] (B/Al = 0.5) (C6D6, r.t.); Scheme S1: Plausible mechanism of (a) ethylene polymerization by DPPB/MAO and (b) 1,3-butadiene polymerization by BIPHEP/MAO; Scheme S2: Results of the calculation on the energy of the monoaluminum and dialuminum complexes. References [38,39,40,41,42,43,44,45,46,47,48,49,50,51,52] are cited in the Supplementary Materials.

Author Contributions

N.K.: methodology, investigation, data curation; X-ray diffraction, funding acquisition, writing—original draft preparation, and writing—review and editing; D.T.: conceptualization, methodology, supervision, funding acquisition, writing—original draft preparation, writing—review and editing, and project administration. All authors have read and agreed to the published version of the manuscript.

Funding

This work was partly supported by JSPS KAKENHI 23K23394 and JST SPRING, Grant Number JPMJSP2152.

Data Availability Statement

CCDC reference number 2486584 contains supplementary crystallographic information for [(Me3Al)2(dppb)].

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 15 00942 sch001
Scheme 1. Previously reported Al complex catalysts for polymerization of hydrocarbon monomers.
Scheme 1. Previously reported Al complex catalysts for polymerization of hydrocarbon monomers.
Catalysts 15 00942 sch001
Catalysts 15 00942 sch002
Scheme 2. (a) Unimolecular and (b) bimolecular chain growth mechanisms in ethylene polymerization by 1.
Scheme 2. (a) Unimolecular and (b) bimolecular chain growth mechanisms in ethylene polymerization by 1.
Catalysts 15 00942 sch002
Catalysts 15 00942 g001
Figure 1. 1H NMR spectra (C6D6, 20 °C) of a mixture of diphosphines and MAO and possible cationic species. (a) DPPM/MAO, (b) DPPE/MAO, (c) DPPP/MAO, (d) DPPB/MAO, (e) DPPPen/MAO, (f) DPPHex/MAO, (g) BIPHEP/MAO, and (h) rac-BINAP/MAO.
Figure 1. 1H NMR spectra (C6D6, 20 °C) of a mixture of diphosphines and MAO and possible cationic species. (a) DPPM/MAO, (b) DPPE/MAO, (c) DPPP/MAO, (d) DPPB/MAO, (e) DPPPen/MAO, (f) DPPHex/MAO, (g) BIPHEP/MAO, and (h) rac-BINAP/MAO.
Catalysts 15 00942 g001
Catalysts 15 00942 g002
Figure 2. Molecular structures of [(Me3Al)2(dppb)] confirmed by X-ray crystal structure analysis (CCDC reference number 2486584).
Figure 2. Molecular structures of [(Me3Al)2(dppb)] confirmed by X-ray crystal structure analysis (CCDC reference number 2486584).
Catalysts 15 00942 g002
Table 1. Polymerization of ethylene by phosphine/MAO systems. a
Table 1. Polymerization of ethylene by phosphine/MAO systems. a
RunPhosphine
(/μmol)		Al
(/mmol)		Toluene/mLYield/gActivity/g·mmol[P]−1·h−1Mn bMw/Mn b
1PPh3 (20)MAO (30)200.00380.010--
2PCy3 (20)MAO (30)200.00810.020--
3CyJohnPhos (20)MAO (30)200.04410.11092,00050.4
4JohnPhos (20)MAO (30)200.00160.004--
5XPhos (20)MAO (30)20trace---
6-MAO (30)20trace---
7CyJohnPhos (40)MAO (30)200.08110.101254,000172
8CyJohnPhos (20)MAO (16)200.02960.148248,000144
9CyJohnPhos (40)MMAO (30)200.00240.012--
10CyJohnPhos (40)MAO (16)10trace---
11DPPM (20)MAO (30)200.00870.022--
12DPPE (20)MAO (30)200.02180.055--
13DPPP (20)MAO (30)200.00570.014--
14DPPB (20)MAO (30)201.11882.797737,00040
15DPPPen (20MAO (30)200.00620.150--
16DPPHex (20)MAO (30)200.01050.026--
17rac-BINAP (20)MAO (30)200.03250.08197,00064
18DPPB (20)MAO (16)100.13130.328--
19DPPB (20)MAO (30)100.17460.437--
a Ethylene = 1 MPa, 30 °C, 20 h; b Determined by GPC.
Table 2. Polymerization of 1,3-butadiene by phosphine/MAO systems a.
Table 2. Polymerization of 1,3-butadiene by phosphine/MAO systems a.
RunPhosphine
(/μmol)		Al
(/μmol)		Toluene
/mL		Time
/h		Yield
(%)		cis-1,4
(%) b		trans-1,4
(%) b		1,2
(%) b		Mn cMw/Mn c
1CyJohnPhos (20)MAO (30,000)2020trace-----
2CyJohnPhos (20)MAO (4000)10281.484.915.1--
3DPPE (20)MAO (4000)1072trace-----
4DPPP (20)MAO (4000)1072trace32.350.916.8--
5DPPB (20)MAO (4000)10721.478.921.1--
6DPPHex (20)MAO (4000)10720.5567.033.0--
7rac-BINAP (20)MAO (4000)107210.376.917.06.124,0003.45
8BIPHEP (20)MAO (4000)10723.193.81.15.119,0001.74
9BIPHEP (40)MAO (4000)10725.290.14.85.1--
10BIPHEP (60)MAO (4000)1072trace-----
11BIPHEP (20)Me3Al (40)
[Ph3C][B(C6F5)4]
(20)		1072trace-----
a 1,3-butadien = 10 mmol (0.5409 g), 30 °C; b Determined by NMR (CDCl3, 20 °C); c Determined by GPC.
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Kimura, N.; Takeuchi, D. Polymerization of Ethylene and 1,3-Butadiene Using Methylaluminoxane-Phosphine Catalyst Systems. Catalysts 2025, 15, 942. https://doi.org/10.3390/catal15100942

AMA Style

Kimura N, Takeuchi D. Polymerization of Ethylene and 1,3-Butadiene Using Methylaluminoxane-Phosphine Catalyst Systems. Catalysts. 2025; 15(10):942. https://doi.org/10.3390/catal15100942

Chicago/Turabian Style

Kimura, Nanako, and Daisuke Takeuchi. 2025. "Polymerization of Ethylene and 1,3-Butadiene Using Methylaluminoxane-Phosphine Catalyst Systems" Catalysts 15, no. 10: 942. https://doi.org/10.3390/catal15100942

APA Style

Kimura, N., & Takeuchi, D. (2025). Polymerization of Ethylene and 1,3-Butadiene Using Methylaluminoxane-Phosphine Catalyst Systems. Catalysts, 15(10), 942. https://doi.org/10.3390/catal15100942

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