Home \ Browse Journal \ ASAP \ Synthesis of a New Hyperbranched Pyridylphenylene Polymer Based on an АB2 Monomer and a Pair of АB/АB2 Monomers

2020 ASAP

инэос-open

INEOS OPEN, 2020, 3 (X), XX–XX 

Journal of Nesmeyanov Institute of Organoelement Compounds
of the Russian Academy of Sciences

Download PDF
DOI: 10.32931/io2020a

 

issue_cover_html_asap      

Synthesis of a New Hyperbranched Pyridylphenylene Polymer
Based on an АB2 Monomer and a Pair of АB/АB2 Monomers

A. S. Torozova,*a E. S. Serkova,a I. Yu. Krasnova,a A. A. Korolkova,b and Z. B. Shifrina a  

a Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, ul. Vavilova 28, Moscow, 119991 Russia
b Mendeleev University of Chemical Technology of Russia, Miusskaya pl. 9, Moscow, 125047 Russia

 

Corresponding author: A. S. Torozova, e-mail: torozova@ineos.ac.ru
Received 18 July 2020; accepted 2 September 2020

Abstract

  NNNNPh2O, 210 °CNNO

A hyperbranched pyridylphenylene polymer with the weight average molecular mass of 56000 Da is synthesized for the first time from an AB2 monomer bearing one diene and two internal triple bonds. The introduction of a linear AB comonomer into the reaction system leads to an increase in the yield of the polymer which has the weight average molecular mass of 21400 Da. Due to the limited degree of intramolecular cyclization, the high content of functional groups facilitates the formation of defect-free structures and provides an opportunity to modify the resulting polymers.

Key words: hyperbranched pyridylphenylene polymer, Diels–Alder reaction, AB2 monomer, AB monomer.

 

Introduction

Hyperbranched polymers (HBPs) attract strong interest owing to their unique characteristics, which open the way to different application fields. For example, they are used as additives for linear polymers to improve their rheological properties [1]. Earlier we have shown that HBPs can serve as efficient stabilizing agents for catalytically active nanoparticles [2, 3]. Furthermore, they find use in microelectronics [1].

HBPs refer to dendritic macromolecules with irregular structures, in which the dendritic and linear moieties are distributed randomly. The unique properties of HBPs stem, first of all, from their molecular branched architectures, which define their high solubility, and the possibility of synthesis of macromolecules with terminal functional groups, which enable further modification [4, 5]. These features of HBPs allow for their comparison with ideally branched dendrimers. Dendrimers represent the objects which molar masses and branching degrees can be controlled during stepwise synthesis. At the same time, their synthesis is more tedious due to the intermediate steps of isolation of each generation. However, this provides monodisperse macromolecules with clearly defined structures. In the case of HBP, one-step synthesis affords polydisperse macromolecules featuring nonideal branching. Nevertheless, the one-step synthetic procedure is an important advantage that encourages the application of new materials in the case when the final cost of a product is a crucial factor [1]. Therefore, HBPs are preferred from the viewpoint of saving the raw materials and energy.

As a rule, hyperbranched polymers such as polyphenylenes [6, 7], polyesters [8], polyamides [9], polycarbonates [10], polyurethanes [11], polycarbosilanes [12] are synthesized using an AB2 monomer or a pair of AB/AB2 monomers.

In this report, we used these approaches to produce HBPs based on new substituted aromatic cyclopentadienones bearing phenylene and pyridine units and internal triple bonds. The possibility of synthesis of new HBPs by the Diels–Alder reaction using an АВ2 monomer and a pair of АВ/АВ2 monomers was studied. The reaction conditions, including the temperature, monomer concentration, and duration, were optimized. The molar masses and polydispersity indices of the resulting polymers were defined by the gel permeation chromatography (GPC).

Results and discussion

The target pyridylphenylene polymers were obtained by the polycondensation of an AB2 monomer or copolycondensation of a pair of AB and AB2 monomers. The structures of the monomers are presented in Fig. 1. These monomers were synthesized by the Knoevenagel reaction according to the published procedure [13].

1NNO2NNO

Figure 1. АВ2 (1) and АВ (2) monomers used in the synthesis of new HBPs.

Hyperbranched polymer 3 was obtained from the AB2 monomer bearing one diene and two internal triple bonds by the Diels–Alder reaction (Scheme 1). The reaction conditions suggested by Morgenroth and Müllen [7] for the polyphenylenes afforded an insoluble product (Table 1, sample I). A reduction in the monomer concentration and reaction temperature provided a considerable increase in the yield of the soluble polymer.

NNNNPh2O, 210°C1NNO3

Scheme 1. Synthesis of the HBP based on the АВ2 monomer.

Table 1. Conditions for the polycondensation of the AB2 monomer

Sample

T, °С

Time, h

c, mol/L

Mw, Da

Mn, Da

MMD

I

260

72

0.330

II

260

45

0.170

8500

2400

3.54

III

220

148

0.068

1300

1000

1.30

IV

220

72

0.034

1200

900

1.33

V

200

72

0.032

1400

1300

1.08

VI

180

72

0.010

2000

1800

1.11

VII

180

72

0.005

1400

1300

1.08

VIII

210

99

0.005

56000

25000

2.24

In most cases, the reactions afforded, besides the insoluble product, the low-molecular-weight compounds (Table 1, samples II–VII). This evidences the low reactivity of internal triple bonds in oligomeric compounds as well as the probable steric hindrances that may arise during the synthesis of this polymer. Furthermore, the reaction rate is caused by the low concentration of the monomers.

The high-molecular-weight reaction product (sample VIII) was obtained upon an essential reduction in the monomer concentration compared to sample I (from 0.330 mol/L to 0.005 mol/L) and a considerable increase in the reaction temperature (from 180 to 210 °С) and time (from 72 to 99 h) compared to sample VII. The characteristic viscosity of the resulting polymer was 0.4 dL/g. According to the GPC data (Fig. 2), the weight average molecular mass of polymer VIII was 56000 Da, and its polydispersity was 2.24. The polymer was obtained in 53% yield.

Fig2   

Figure 2. GPC data for polymer 3.

In order to improve the polymer yield, an alternative synthetic route was suggested that was based on the copolycondensation of the AB2 and AB monomers. The use of the АВ monomer—a tetrasubstituted pyridyl-containing cyclopentadienone with one internal triple bond (Fig. 1, compound 2)—facilitated a reduction in the steric hindrances during growth of a macromolecule. The synthetic route for the enol (2а) and diene (2) forms of the АВ monomer is presented in Scheme 2.

sch2

Scheme 2. Synthesis of the AB monomer.

At the first step, the oxidation of 1,4-(diphenylethynyl)benzene (4) afforded compound 5 [14]. The synthesis was carried out for 17 h; the product yield reached 70%. Then, compound 5 was introduced into the Knoevenagel condensation with 1,3-di(pyridyn-2-yl)propan-2-one 6, which resulted in the enol form of the AB monomer (Scheme 2, compound 2а) as a mixture of diastereomers. As it was shown earlier, the enol form of the target product can be converted in situ to the corresponding cyclopentadienone (2) under the conditions of the Diels–Alder reaction [15]. Therefore, the dehydration in ethylene glycol at 165 °С was not required, which significantly simplified the synthesis of the target polymer.

The structure of compound 2а was confirmed by the 1H and 13С NMR spectroscopic data. Thus, the 1Н NMR spectrum of the resulting product shows the doublets at δ = 8.70 (J = 4.3 Hz) and 8.57 ppm (J = 5.0 Hz), which correspond to 1 and 1' α-protons of the nonequivalent pyridine rings, and the multiplets in the ranges of 7.61–7.66 and 7.74–7.78 ppm, which correspond to 2 and 2' β-protons of the pyridine rings. Moreover, the characteristic signals of proton 3 of the enol form are observed at 4.22 and 4.20 ppm. The diene form of the AB monomer was formed in situ under conditions of the copolycondensation. Scheme 3 depicts the synthetic route for the HBP based on the АВ2 and AВ monomers.

2NNO1NNOPh2O, 210°C+NNNNNNNN7

Scheme 3. Synthesis of the HBP based on a pair of the АВ/АВ2 monomers.

The introduction of the AB monomer facilitated the formation of soluble product IX (Table 2) and a reduction in the content of the insoluble fraction compared to sample I (Table 1) obtained under analogous conditions. A further decrease in the monomer concentrations led to growth of the weight average molecular masses of samples X and XI, whereas an extension of the reaction time from 72 to 99 h afforded polymer XII (Table 2) with the weight average molecular mass of 21400 Da and polydispersity index of 1.80.

Table 2. Conditions for the polycondensation of a pair of the AB/AB2 monomers

Sample

T, °С

Time, h

c, mol/L

Mw, Da

Mn, Da

MMD

IX

260

72

0.330

4900

4000

1.23

X

210

72

0.170

7000

5100

1.37

XI

210

72

0.005

11300

8000

1.41

XII

210

99

0.005

21400

11900

1.80

Polymer 3 was used as a stabilizing macromolecule in the synthesis of a ruthenium-containing magnetically separable catalyst based on magnetite. As can be seen from the micrograph obtained by transition electron microscopy (TEM) (Fig. 3), the ruthenium nanoparticles are uniformly distributed over the polymer matrix without formation of aggregates, which is an important criterion for the production of active nanoparticles. Subsequently, the resulting catalyst will be tested for the oxidation of betulin which is used for the production of antiviral, antitumor, and antiseptic agents [16–18].

Fig3

Figure 3. TEM micrograph of the ruthenium-containing magnetic catalyst based on polymer 3.

Experimental

Methods

The 1H and 13С NMR spectra were registered on Bruker Avance 500 and Avance 400 spectrometers.

The elemental analyses were obtained with a Carlo-Erba 1106 automated CHN-analyzer.

Thin-layer chromatography was carried out on ALUGRAMSILG/UV254 silica gel 60 (0.2 mm) plates with a fluorescent indicator (254 nm).

The molecular masses of the polymers were defined by GPC. The measurements were carried out on a chromatographer of Shimadzu production equipped with a RID-20A refractive index detector and a Phenogel 500A (300 ´ 7.8 mm) column. The analyses were performed using tetrahydrofuran as an eluent at the temperature of 40 °С and the flow rate of 1.0 mL/min. The polymer solution in tetrahydrofuran (concentration 35 mg/mL) was filtered through polytetrafluoroethylene membrane filters (0.45 μm). The relative molecular masses (Mw and Mn) and polydispersity indices were calculated with Shimadzu LC solution software based on the calibrating dependence using polystyrene standards.

The characteristic viscosity was determined by extrapolating the concentration dependence of the reduced viscosity to the zero concentration. The flow times of the polymer solution and a solvent (N-methylpyrrolidone) were measured using an Ubbelohde viscometer at 25 °C.

The transmission electron microscopic studies were carried out with a JEM 1400 plus microscope equipped with an OSIS Quemesa 11 MРix camera at the accelerating voltage of 120 kV.

Syntheses

Synthesis of 3,4-bis(4-(phenylethynyl)phenyl)-2,5-di(pyridin-2-yl)cyclopenta-2,4-dien-1-one (1). The enol form of monomer 1 was obtained according to the published procedure [13].

Synthesis of the HBP based on the AВ2 monomer (3). A solution of the enol from of monomer 1 (0.050 g, 0.083 mmol) in diphenyl ether (16.5 mL) was heated under an argon atmosphere at 210 °C for 99 h. After cooling to room temperature, the reaction mixture was poured into hexane. The resulting precipitate was filtered off, washed with hot ethanol, and dried under vacuum at 60 °С until the constant mass to give the target polymer. Yield: 0.020 g (53%).

Synthesis of 1-phenyl-2-(phenylethynyl)phenyl)etane-1,2-dione (5). A mixture of 1,4-bis(phenylethynyl)benzene (4) (0.280 g, 1.006 mmol) and iodine (0.005 g, 0.02 mmol) in DMSO (10 mL) was heated at 155 °С for 17 h. After cooling to room temperature, the reaction mixture was poured into 1% aq. Na2S2O3. The resulting precipitate was filtered off, washed with water, and dried under vacuum at 55 °C to give compound 5. Yield: 0.218 g (70%). 1H NMR (CDCl3, 400 MHz): δ 7.38–7.40 (m, 3H), 7.52–7.58 (m, 4H), 7.65–7.71 (m, 3H), 7.97–8.01 (m, 4H) ppm. 13C{1H} NMR (CDCl3, 100 MHz): δ 88.43, 94.08, 122.34, 128.45, 129.04, 129.78, 129.94, 130.10, 131.80, 131.93, 132.01, 132.85, 134.97, 193.58, 194.18 ppm.

Synthesis of 4-hydroxy-4-phenyl-3-(4-(phenylethynyl)phenyl)-2,5-di(pyridyn-2-yl)cyclopenta-2-en-1-one (2а). A mixture of 1-phenyl-2-(phenylethynyl)phenyl)etane-1,2-dione (5) (0.100 g, 0.322 mmol) and 1,3-di(pyridyn-2-yl)propan-2-one (6) (0.082 g, 0.387 mmol) was dissolved in ethanol (2 mL) and benzene (5 ml) at 85 °C under an argon atmosphere. After dissolution of the reagents, a solution of КОН (0.018 g) in water (2 mL) was added for 3 h. The reaction course was controlled by thin-layer chromatography (eluent: chloroform–ethanol (25:1)). The resulting precipitate was filtered off, washed with ethanol, and dried under vacuum at 50 °C until the constant mass to give compound 2а. Yield: 0.122 g (75%). Mp: 152–154 °C. 1H NMR (CDCl3, 500 MHz): δ 4.20 (s, 1H), 4.22 (s, 1H), 6.97–7.78 (m, 40H), 8.57 (d, 2H, J = 5.0 Hz), 8.70 (d, 2H, J = 4.3 Hz) ppm. 13C{1H} JMOD NMR (CDCl3, 125 MHz): δ 65.72, 65.90, 82.90, 89.20, 89.24, 89.71, 91.15, 122.14, 122.50, 122.62, 122.72, 122.77, 123.06, 123.13, 123.28, 124.37, 125.52, 125.63, 125.68, 127.02, 127.33, 127.90, 128.05, 128.27, 128.41, 128.47, 128.52, 128.58, 128.71, 129.08, 129.21, 129.36, 129.69, 129.78, 130.14, 130.25, 130.92, 131.13, 131.29, 131.70, 131.73, 131.96, 132.88, 133.01, 136.05, 136.13, 136.54, 136.58, 138.04, 138.08, 139.09, 139.17, 144.37, 144.81, 147.79, 147.81, 149.61, 149.65, 149.92, 150.00, 151.77, 151.88, 155.90, 156.01, 172.49, 173.07, 201.09, 201.22 ppm. Anal. Cacld. for C35H24N2O2: C, 83.31; H, 4.79; N, 5.55. Found: C, 83.10; H, 4.84; N, 5.33%.

Compound 6 was synthesized according to the published procedure [19].

Synthesis of polymer 7 based on a pair of the АВ/АВ2 monomers. A mixture of the enol form of the AB2 (0.026 g, 0.043 mmol) and AB (compound 2a) (0.011 g, 0.0215 mmol) monomers in diphenyl ether (3 mL) was heated under an argon atmosphere at 210 °С for 99 h. After cooling to room temperature, the reaction mixture was poured into hexane. The resulting precipitate was filtered off, washed with hot ethanol until the filtrate decoloration, and dried under vacuum at 60 °C until the constant mass to give the target polymer. Yield: 0.007 g (72%).

Conclusions

The polycondensation of the AB2 trifunctional monomer and copolycondensation of a pair of the AB2 and AB monomers afforded the polymers with the weight average molecular masses of 56000 and 21400 Da, respectively. The introduction of the AB monomer led to an increase in the polymer yield from 53% to 72%. The resulting polymer was used for stabilization of magnetite and ruthenium nanoparticles during the synthesis of a magnetically separable ruthenium catalytic system, which will be further tested for the oxidation of betulin in order to produce biologically active substances.

Acknowledgements

This work was supported by the Russian Foundation for Basic Research, project no. 18-33-00609. The NMR spectroscopic studies and elemental analyses were performed with the financial support from the Ministry of Science and Higher Education of the Russian Federation using the equipment of the Center for Molecular Composition Studies of INEOS RAS.

References

  1. B. I. Voit, A. Lederer, Chem. Rev., 2009, 109, 5924–5973. DOI: 10.1021/cr900068q
  2. N. V. Kuchkina, A. K. Haskell, S. A. Sorokina, A. S. Torozova, L. Zh. Nikoshvili, E. M. Sulman, B. D. Stein, D. G. Morgan, L. M. Bronstein, Z. B. Shifrina, ACS Appl. Mater. Interfaces, 2020, 12, 22170–22178. DOI: 10.1021/acsami.0c04357
  3. N. V. Kuchkina, M. S. Rajadurai, M. Pal, S. Basaveni, S. A. Sorokina, I. Yu. Krasnova, E. S. Serkova, Z. B. Shifrina, Russ. Chem. Bull., 2018, 67, 1035–1040. DOI: 10.1007/s11172-018-2176-6
  4. I.-Y. Jeon, H.-J. Noh, J.-B. Baek, Molecules, 2018, 23, 657. DOI: 10.3390/molecules23030657
  5. K. Stumpe, H. Komber, B. I. Voit, Macromol. Chem. Phys., 2006, 207, 1825–1833. DOI: 10.1002/macp.200600422
  6. Y. H. Kim, R. Beckerbauer, Macromolecules, 1994, 27, 1968–1971. DOI: 10.1021/ma00085a048
  7. F. Morgenroth, K. Müllen, Tetrahedron, 1997, 53, 15349–15366. DOI: 10.1016/S0040-4020(97)00967-8
  8. C. J. Hawker, R. Lee, J. M. J. Frechet, J. Am. Chem. Soc., 1991, 113, 4583–4588. DOI: 10.1021/ja00012a030
  9. M. Jikei, K. Fujii, G. Yang, M. Kakimoto, Macromolecules, 2000, 33, 6228–6234. DOI: 10.1021/ma000354a
  10. D. H. Bolton, K. L. Wooley, Macromolecules, 1997, 30, 1890–1896. DOI: 10.1021/ma961746d
  11. R. M. Versteegen, R. P. Sijbesma, E. W. Meijer, Polym. Prepr. (Am. Chem. Soc., Div. Polym. Chem.), 1999, 40, 839–840.
  12. A. M. Muzafarov, M. Golly, M. Moller, Macromolecules, 1995, 28, 8444–8446. DOI: 10.1021/ma00128a070
  13. A. S. Torozova, A. A. Korolkova, I. Yu. Krasnova, Z. B. Shifrina, Russ. Chem. Bull., 2020, 69, 91–96. DOI: 10.1007/s11172-020-2727-5
  14. M. S. Yusubov, V. D. Filimonov, V. P. Vasilyeva, K.-W. Chi, Synthesis, 1995, 10, 1234–1236. DOI: 10.1055/s-1995-4094
  15. N. V. Kuchkina, M. S. Zinatullina, E. S. Serkova, P. S. Vlasov, A. S. Peregudov, Z. B. Shifrina, RSC Adv., 2015, 5, 99510–99516. DOI: 10.1039/C5RA16847C
  16. A. Hordyjewska, A. Ostapiuk, A. Horecka, J. Kurzepa, Phytochem. Rev., 2019, 18, 929–951. DOI: 10.1007/s11101-019-09623-1
  17. М. G. Moghaddam, F. B. H. Ahmad, A. Samzadeh-Kermani, Pharmacol. Pharm., 2012, 3, 119–123. DOI: 10.4236/pp.2012.32018
  18. S. Haque, D. A. Nawrot, S. Alakurtti, L. Ghemtio, J. Yli-Kauhaluoma, P. Tammela, PLoS One, 2014, 9, e102696. DOI: 10.1371/journal.pone.0102696
  19. Z. B. Shifrina, M. S. Rajadurai, N. V. Firsova, L. M. Bronstein, X. Huang, A. L. Rusanov, K. Muellen, Macromolecules, 2005, 38, 9920–9932. DOI: 10.1021/ma051802n