Article pubs.acs.org/Macromolecules
Formation of Bundle Assemblies of Stereoregular Polymers in Thermal Solid-State Polymerization of 7,7,8,8Tetrakis(aryloxycarbonyl)‑p‑quinodimethanes Takahito Itoh,*,† Erica Morita,† Ryohei Takakura,† Hiroto Nakajima,† Takahiro Uno,† Masataka Kubo,† Norimitsu Tohnai,‡ and Mikiji Miyata‡ †
Division of Chemistry for Materials, Graduate School of Engineering, Mie University, 1577 Kurima Machiya-cho, Tsu, Mie 514-8507, Japan ‡ Department of Material and Life Science, Graduate School of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565-0871, Japan S Supporting Information *
ABSTRACT: 7,7,8,8-Tetrakis(aryloxycarbonyl)-p-quinodimethanes with bulky aryloxy groups such as benzyloxy (1a), pentafluorobenzyloxy (1b), and both benzyloxy and pentafluorobenzyloxy (1c) were synthesized. We investigated effects of these bulky groups on thermal solid-state polymerization reactivities on the basis of crystal structures of 1a−1c. Thermal polymerizations gave 1,6-trans-type stereoregular polymers in quantitative yields in 1 day at 110 °C for 1a, 1 day at 150 °C for 1b, and 6 days at 110 °C for 1c. Their initial crystal shapes were retained in appearance during polymerization to yield solid bundle assemblies of their polymeric chains. X-ray single-crystal structure analysis indicates that their crystals adopt molecular arrangements suitable for one-dimensional polymerization with the 1,6-trans-type addition along one crystallographic axis. Such arrangements led to expansion polymerization of 1b and contraction one of 1c. The resulting stereoregular polymers form less ordered bundle assemblies than those prepared by the conventional topochemical polymerization. In this manner, the bulky aryloxy groups enabled us to observe a close relation between the molecular assembly modes and the polymerization behaviors, providing the first example for proving diversity of thermal solid-state polymerizations.
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INTRODUCTION The polymerization methods to obtain highly controlled polymer structures such as repeating units, molecular weight, molecular weight distribution, chain-end structure, tacticity, and so on have been attracting considerable interest because the chemical and physical properties of the polymers are significantly dependent upon their primary structures. A variety of polymerization techniques in solution such as living polymerization methods and catalysts have been developed for the control of the primary polymer structures, and the highly controlled polymer structures have been realized to a certain extent.1 On the other hand, polymerizations of ordered assemblies in confined space are known as one of the methods to achieve the precise control of polymer structures. From viewpoints of mobility as well as directionality, such polymerizations exhibit various relative effects on the basis of the reaction spaces and are classified into three categories (Figure 1): (1) very large spaces close to infinite, (2) a little bigger space than monomers, and (3) spaces similar to or less than monomers. In case 1, polymerization affords less controlled polymer structures because the monomer molecules are able to move freely in the isotropic space like solution and melt polymerizations. A wide range of monomers are suited for the use in the polymerization of case 1, and their high polymerization © XXXX American Chemical Society
Figure 1. Diverse relativity between reaction spaces and monomers. Polymerization behaviors depend upon mobility and directionality of monomer assemblies.
reactivity might be easily realized. But, in order to attain highly controlled polymer structures, any controls of the propagating chain-end are required. In case 2, monomer assemblies can get restricted mobility and anisotropic properties in the confined spaces. The typical Received: February 18, 2016 Revised: June 7, 2016
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DOI: 10.1021/acs.macromol.6b00349 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
The difference of molecular movement in crystals is intimately related to some interactions serving between molecules in crystals. Therefore, it is interesting to make clear what interactions affect the molecular packing, the molecular mobility, and the polymerization reactivity to understand the polymerization behavior of the substituted quinodimethanes in the solid state. As compared with alkoxy and haloalkoxy groups, we focused the bulky benzyl and perfluorobenzyl groups as the aryloxy group for 7,7,8,8-tetrakis(aryloxycarbonyl)-p-quinodimethanes, where in addition to CO···H hydrogen-bonding interaction, CH/π, halogen−halogen, hydrogen−halogen, aromatic ring stacking interactions, and so on are expected. Especially, phenyl-perfluorophenyl stacking interaction is interesting because the interaction has been applied to the solid-state behavior of polyynes,19 [2 + 2] photodimerization and photochemical polymerization of olefin and diolefin,20 topochemical polymerization of triacetylene,21 and formation of alternating diacetylene copolymer22 and investigated widely. In this work, we synthesized novel substituted quinodimethanes with bulky aryloxy groups, such as symmetrical 7,7,8,8tetrakis(benzyloxycarbonyl)-p-quinodimethane (1a) and 7,7,8,8tetrakis(pentafluorobenzyloxycarbonyl)-p-quinodimethane (1b) and unsymmetrical 7,7-bis(benzyloxycarbonyl)-8,8-bis(pentafluorobenzyloxycarbonyl)-p-quinodimethane (1c) (Chart 1),
polymerizations can be recognized in various organized media such as micelles,2 vesicles,3 mono- and multilayers,4 liquid crystals,5 inorganic porous materials,6 and inclusion compounds.7 The mobility and anisotropy affect polymerization reactivities, structures of polymer chains, and assembly formation. In case 3, when monomer molecules are anisotropically assembled in the crystals and take molecular arrangement suitable for polymerization, the monomer assemblies undergo polymerization reactions in high yield and high selectivities. In special cases, the least movement of molecules in the crystals can bring about the polymerization reaction, termed topochemical polymerizations, leading to polymers with completely controlled structure as well as higher order assemblies. Recently, topochemical polymerizations impressed us great advantages for preparing attractive shapes and structures such as nanotubes,8 nanorods,9 and two-dimensional sheet.10 However, strict requirements for topochemical polymerizations so far afforded only a limited number of monomers such as diacetylene derivatives,11 2,5-distyrylpyridine derivatives,12 triene and triacetylene derivatives,13 diene derivatives such as muconic acid and sorbic acid,14 [2,2′-bi-1H-indene]-1,1′-dione3,5-diyldialkylcarboxylate,15 and substituted quinodimethanes such as 7,7,8,8-tetrakis(alkoxycarbonyl)-p-quinodimethane.16 For the past decades, we investigated thermal and photochemical polymerizations of substituted quinodimethanes and substituted quinone methides in the solid state. We found that 7,7,8,8-tetrakis(alkoxycarbonyl)-p-quinodimethanes with an alkoxy group such as methoxy, 2′-chloroethoxy, and 2′-bromoethoxy undergo the trans-type topochemical polymerization16 and cis-specific topochemical alternating copolymerization with 7,7,8,8-tetracyanoquinodimethane17 and that the 2-fold helical polymerizations as a novel polymerization mode take place in the thermal solid-state polymerization of 7-cyano7-(2′-haloethoxycarbonyl)-p-benzoquinone methides.18 And also, we proposed a general rule to predict the polymerization reactivity for the topochemical polymerization of substituted quinodimethane monomers in the solid state.16 Very recently, we succeeded to obtain a single polymer crystal of 7,7,8,8tetrakis(bromoethoxycarbonyl)-p-quinodimethane by the polymerization under γ-ray irradiation and reported that both monomer and resulting polymer crystals belong to the same space group P-1, and the distance (ds = 6.80 Å) of the repeating monomer unit in the polymer crystal is very close to the stacking distance (6.91 Å) of the quinodimethane molecules in the monomer crystals.16 During a course of research related to the polymerizations of substituted quinodimethanes and quinone methides in the solid state, we observed the following events in the polymerization behaviors: no polymerization, formation of glass-like polymers like melt polymerizations, formation of amorphous polymer retaining initial crystal shapes in appearance, and formation of completely single polymer crystals. These events resemble polymerization behaviors in confined spaces as mentioned previously. That is, the formation of glass-like polymers is similar to case 1, corresponding to the polymerization without control of crystal lattice like the solution and melt polymerizations. In contrast, the formation of single polymer crystals is similar to case 3, corresponding to the polymerization under the complete control of crystal lattice, called topochemical polymerization. However, case 2 is unclear in a series of quinodimethanes and quinone methides so far. Now that we established the criterion for discussing case 2 on the basis of case 3,16 we can evaluate any controls of crystal lattice to a certain extent, not a complete one.
Chart 1. 7,7,8,8-Tetrakis(aryloxycarbonyl)-pquinodimethanes (1a−1c)
and investigated effects of bulky aryloxy group on their crystal structures and on thermal solid-state polymerization reactivities for the purpose of evaluation of case 2 under any controls of crystal lattice to a certain extent, not a complete one.
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EXPERIMENTAL SECTION
Measurements. All melting points were obtained with a Yanaco MP-50 melting point apparatus. The number-average molecular weights, Mn, of the polymers were determined by gel permeation chromatography (GPC) on a Jasco PU-2080 Plus equipped with TOSOH UV-8020 ultraviolet (254 nm) detector and TSK gel G2500H8 (bead size with 10 μm, molecular weight range 1.0 × 102−2.0 × 104) and TSK gel G3000H8 (bead size with 10 μm, molecular weight range 1.0 × 102− 6.0 × 104) using tetrahydrofuran (THF) as an eluent at a flow rate of 1.0 mL/min and polystyrene standards for calibration. The NMR and IR spectra were recorded on a JEOL JNM-EX270 FT NMR spectrometer using chloroform-d with tetramethylsilane as an internal standard at 25 °C and JASCO IR-700 spectrometer, respectively. The powder X-ray diffraction (XRD) measurement of the monomers and the reaction mixtures obtained at a given time was carried out using Rigaku Rotaflex RU-200B in the 2θ range from 10° to 90° at a scan speed of 0.5°/min with sampling width of 0.02°. The graphitemonochromated Cu Kα line (λ = 1.541 78 Å) was used with the power of the X-ray generator 40 kV and 150 mA. The single-crystal X-ray data were collected on a Rigaku R-AXSIS RAPID diffractometer with 2D area using Cu Kα radiation (λ = 1.541 78 Å) monochromated with graphite at the power of X-ray generator 40 kV and 150 mA. A direct method (SIR-2004) was used for the structure solution.23 B
DOI: 10.1021/acs.macromol.6b00349 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules
1-[Di(benzyloxycarbonyl)methylene]-4-[di(pentafluorobenzyloxycarbonyl)methylene]cyclohexane (3c). 4-[Di(pentafluorobenzyloxycarbonyl)methylene]cyclohexanone (2). Titanium tetrachloride (5.6 mL, 50 mmol) was added dropwise under nitrogen to dry stirred THF (100 mL) cooled in an ice bath. This gives a bright yellow precipitate after an exothermic reaction. 1,4-Cyclohexanedione monoethylene ketal (1.56 g, 10 mmol) and pentafluorobenzyl malonate (4.64 g, 10 mmol) in dry THF (50 mL) were added into this yellow mixture and then stirred for 1 h. Dry pyridine (3.2 mL) in dry THF (20 mL) was added dropwise to the resulting brown suspension over 1 h, and the reaction mixture was stirred at room temperature for 23 h. Water (100 mL) and chloroform (50 mL) were added to the reaction mixture, and then the organic layer was extracted with chloroform (3 × 100 mL). The combined organic fractions were successively washed with saturated aqueous sodium chloride solution (3 × 100 mL), saturated aqueous sodium hydrogen carbonate (3 × 100 mL), and dried over anhydrous magnesium sulfate. It was placed under reduced pressure to remove the volatile materials to give a pale yellow product, to which was added a 20 mL of 2% aqueous sulfuric acid solution, and refluxed for 2.5 h. After cooling, the reaction mixture was extracted with chloroform (50 mL × 3). The combined organic fractions were washed twice with 100 mL of saturated aqueous sodium hydrogen carbonate, dried over anhydrous magnesium sulfate, and filtered, and the solvent of the filtrate was evaporated under reduced pressure. The crude product was purified by silica gel column chromatography using chloroform as an eluent, followed by recrystallization from a mixture solution of chloroform and hexane to give 0.42 g (81.2% yield) of 2 as white plates; mp 83.5−84.0 °C. 1H NMR (270 MHz, CDCl3, δ): 5.28 (s, 4H; CH2), 2.97 (t, J = 6.92 Hz, 4H; CH2), 2.50 (t, J = 6.59 Hz, 4H; CH2). 13C NMR (67.5 MHz, CDCl3, δ): 209.0 (CO), 163.6 (CO), 160.0 (C⟨), 145.7 (ddd, JC−F = 248.6, 14.53, 6.70 Hz; ArF), 141.8 (ddd, JC−F = 243.6, 13.41, 6.70 Hz; ArF), 137.5 (ddd, JC−F = 254.2, 10.62, 5.03 Hz; ArF), 122.4 (C⟨), 108.6 (dd, JC−F = 21.23, 16.76 Hz; Ar), 54.0 (CH2), 37.7 (CH2), 28.6 (CH2). 19F NMR (564.46 MHz, CDCl3, δ): −142.09 (dd, J = 0.037, 0.015 Hz, 2F, o-F), −151.66 (t, J = 0.037 Hz, 1F, p-F), −161.27 (td, J = 0.037, 0.015 Hz, 2F, m-F). IR (KBr): ν = 2971 (CH), 1723 (CO), 1509 (CC), 1432 (CC of Ar), 1251 (C−O), 1047 (C−F) cm−1. Anal. Calcd for C23H12F10O5: C 49.48, H 2.17. Found: C 49.50, H 2.47. 1-[Di(benzyloxycarbonyl)methylene]-4-[di(pentafluorobenzyloxycarbonyl)methylene]cyclohexane (3c). Titanium tetrachloride (0.7 mL, 50 mmol) was added dropwise under nitrogen to dry stirred THF (10 mL) cooled in an ice bath. This gives a bright yellow precipitate after an exothermic reaction. 2 (0.56 g, 1.0 mmol) and benzyl malonate (0.28 g, 1.0 mmol) in dry THF (5 mL) were added into this yellow mixture and then stirred for 1 h. Dry pyridine (0.32 mL) in dry THF (3 mL) was added dropwise to the resulting brown suspension over 1 h, and the reaction mixture was stirred at room temperature for 24 h. Water (50 mL) and chloroform (20 mL) were added to the reaction mixture, and then the organic layer was extracted with chloroform (3 × 50 mL). The combined organic fractions were successively washed with saturated aqueous sodium chloride solution (3 × 50 mL) and saturated aqueous sodium hydrogen carbonate (3 × 50 mL), dried over anhydrous magnesium sulfate, and filtered; the solvent of the filtrate was evaporated under reduced pressure. The crude pale yellow product was purified by recrystallization from a mixture solution of chloroform and hexane to give 0.73g (87.9% yield) of 3c as white needles; mp 100.0−100.5 °C. 1H NMR (270 MHz, CDCl3, δ): 7.27−7.32 (m, 10H; ArH), 5.25 (s, 4H; CH2), 5.17 (s, 4H; CH2), 2.73 (s, 8H; CH2). 13C NMR (67.5 MHz, CDCl3, δ): 164.7 (CO), 163.7 (CO), 161.9 (C⟨), 158.4 (C⟨), 145.8 (ddd, JC−F = 226.8, 13.97, 6.70 Hz; ArF), 141.5 (ddd, JC−F = 296.7, 10.06, 5.59 Hz; ArF), 136.7 (ddd, JC−F = 241.4, 14.53, 3.35 Hz; ArF), 128.5 (Ar), 128.3 (Ar), 128.2 (Ar), 123.2 (C⟨), 121.3 (C⟨), 108.8 (dd, JC−F = 21.23, 16.76 Hz; Ar), 108.8 (Ar), 66.9 (CH2), 53.8 (CH2), 29.4 (CH2), 29.0 (CH2). 19F NMR (564.46 MHz, CDCl3, δ): −142.06 (dd, J = 0.040, 0.015 Hz, 2F, o-F), −151.86 (t, J = 0.037 Hz, 1F, p-F), −161.36 (td, J = 0.037, 0.015 Hz, 2F, m-F). IR (KBr): ν = 2952 (CH), 1731 (CO), 1507 (CC), 1459 (CC of Ar), 1235 (C−O),
All calculations were performed with the observed reflection [I > 2σ(I)] by the program CrystalStructure crystallographic software package24 except for refinement, which was performed by SHELEX-97.25 All nonhydrogens were placed in idealized positions and refined as rigid atoms with the relative isotropic displacement parameters. Materials. Malonic acid, benzyl malonate, pentafluorobenzyl alcohol, p-toluenesulfonic acid monohydrate, 1,4-cyclohexanedione, and 1,4-cyclohexanedione monoethylene ketal (all six materials from Tokyo Kasei Kogyo Co. Ltd.) and activated manganese(IV) dioxide (Aldrich Co.) were used without further purification. Synthesis of Monomers (1a−1c). Pentafluorobenzyl Malonate. Malonic acid (2.60 g, 25.1 mmol), pentafluorobenzyl alcohol (9.90 g, 50.0 mmol), and p-toluenesulfonic acid monohydrate (0.08 g, 0.39 mmol) were refluxed in 40 mL of benzene using a Dean−Stark water separator to isolate water formed for 21 h. The reaction mixture was washed with saturated aqueous sodium carbonate solution, dried over anhydrous magnesium sulfate, and filtered. The filtrate was placed under reduced pressure to remove solvents to yield pentafluorobenzyl malonate (11.0 g, 95% yield) as white crystals; mp 51.5−52.0 °C. 1H NMR (270 MHz, CDCl3, δ): 5.26 (s, 4H; CH2), 3.45 (s, 2H; CH2). 13 C NMR (67.5 MHz, CDCl3, δ): 165.2 (CO), 145.7 (ddd, JC−F = 247.5, 13.97, 7.26 Hz; ArF), 141.9 (ddd, JC−F = 253.6, 11.73, 7.82 Hz; ArF), 137.5 (ddd, JC−F = 253.1, 11.17, 8.38 Hz; ArF), 108.7 (dd, JC−F = 14.53, 3.91 Hz; Ar), 54.2 (CH2), 40.6 (CH2). 19F NMR (564.46 MHz, CDCl3, δ): −141.80 (dd, J = 0.037, 0.012 Hz, 2F, o-F), −151.79 (t, J = 0.037 Hz, 1F, p-F), −161.34 (td, J = 0.037, 0.013 Hz, 2F, m-F). IR (neat): ν = 2981 (CH), 1737 (CO), 1457 (CC of Ar), 1344 (C−O), 1058 (C−F) cm−1. Anal. Calcd for C17H8F10O4: C 43.98, H 1.30. Found: C 43.94, H 1.53. 1,4-Bis[di(aryloxycarbonyl)methylene]cyclohexanes (3a and 3b). General Preparation Method. Titanium tetrachloride (6 mL, 55 mmol) was added dropwise under nitrogen to dry stirred THF (160 mL) cooled in an ice bath. This gives a bright yellow precipitate after an exothermic reaction. 1,4-Cyclohexanedione (7.6 mmol) and malonate (15.2 mmol) in dry THF (3 mL) were added into this yellow mixture and then stirred for 1 h. Dry pyridine (9 mL) in dry THF (10 mL) was added dropwise to the resulting brown suspension over 1 h, and the reaction mixture was stirred at room temperature for 3 days. Water (100 mL) and dichloromethane (50 mL) were added to the reaction mixture, and then the organic layer was extracted with dichloromethane (3 × 100 mL). The combined organic fractions were successively washed with saturated aqueous sodium chloride solution (3 × 100 mL) and saturated aqueous sodium hydrogen carbonate (3 × 100 mL), dried over anhydrous magnesium sulfate, and filtered; the solvent of the filtrate was evaporated under reduced pressure. The pale yellow crude product was purified by silica gel column chromatography using chloroform as an eluent, followed by recrystallization from a mixture solution of benzene and hexane for 3a or chloroform and hexane for 3b. 1,4-Bis[di(benzyloxycarbonyl)methylene]cyclohexane (3a). From benzyl malonate, 3a was obtained as white needles (66.0% yield); mp 134.5−135.0 °C. 1H NMR (270 MHz, CDCl3, δ): 7.30 (m, 20H; Ar), 5.17 (s, 8H; CH2), 2.71 (s, 8H; CH2). 13C NMR (67.5 MHz, CDCl3, δ): 164.7 (CO), 159.0 (C⟨), 135.4 (Ar), 128.2 (Ar), 128.1 (Ar), 122.9 (C⟨), 66.8 (CH2), 29.3 (CH2). IR (KBr): ν = 2962 (CH), 1725 (CO), 1643 (CC), 1457 (CC of Ar), 1231 (C−O) cm−1. Anal. Calcd for C40H36O8: C 74.51, H 5.64, O 19.85. Found: C 74.60, H 5.61, O 19.79 1,4-Bis[di(pentafluorobenzyloxycarbonyl)methylene]cyclohexane (3b). From pentafluorobenzyl malonate, 3b was obtained as white powder (42.9% yield); mp 169.5−170.0 °C. 1H NMR (270 MHz, CDCl3, δ): 5.25 (s, 8H; CH2), 2.76 (s, 8H; CH2). 13C NMR (67.5 MHz, CDCl3, δ): 163.6 (CO), 161.2 (C⟨), 145.7 (ddd, JC−F = 247.5, 13.97, 7.26 Hz; ArF), 141.9 (ddd, JC−F = 252.0, 10.06, 5.03 Hz; ArF), 137.5 (ddd, JC−F = 248.6, 14.53, 3.35 Hz; ArF), 121.6 (C⟨), 108.7 (dd, JC−F = 14.53, 3.91 Hz; Ar), 53.9 (CH2), 29.1 (CH2). 19F NMR (564.46 MHz, CDCl3, δ): −142.09 (dd, J = 0.037, 0.013 Hz, 2F, o-F), −151.78 (t, J = 0.037 Hz, 1F, p-F), −161.34 (td, J = 0.037, 0.013 Hz, 2F, m-F). IR (KBr): ν = 2980 (CH), 1735 (CO), 1507 (CC), 1462 (CC of Ar), 1231 (C−O), 1010 (C−F) cm−1. Anal. Calcd for C40H16F20O8: C 47.83, H 1.61. Found: C 47.49, H 1.88. C
DOI: 10.1021/acs.macromol.6b00349 Macromolecules XXXX, XXX, XXX−XXX
Article
Macromolecules 1069 (C−F) cm−1. Anal. Calcd for C40H26F10O8: C 58.26, H 3.18. Found: C 58.06, H 3.66. 7,7,8,8-Tetrakis(aryloxycarbonyl)-p-quinodimethanes (1a−1c). General Procedure Method. 1,4-Bis[di(benzyloxycarbonyl)methylene]cyclohexane (3a), 1,4-bis[di(pentafluorobenzyloxycarbonyl)methylene]cyclohexane (3b), or 1-[di(benzyloxycarbonyl)methylene]4-[di(pentafluorobenzyloxycarbonyl)methylene]cyclohexane (3c) (0.6 mmol) was dissolved in benzene (60 mL), and this solution was added as one portion to activated manganese dioxide (37.2 mmol) and molecular sieves 4A (1.80 g) in benzene (220 mL) at reflux. After stirring for 15 min at reflux, the activated manganese dioxide was removed by filtration, and the filtrate was placed under reduced pressure to yield yellow solid as crude products. The yellow solid was dissolved a small amount of chloroform, and the resulting solution was passed through a silica gel column; the first elution band was collected, and the chloroform was evaporated to yield the yellow solid, which was purified by recrystallization from chloroform/hexane (1/3 v/v) to give yellow plate for 1a and yellow needles for both 1b and 1c. 7,7,8,8-Tetrakis(benzyloxycarbonyl)-p-quinodimethane (1a). 21.8% yield; mp 127.0−128.0 °C. 1H NMR (270 MHz, CDCl3, δ): 7.41 (s, 4H; CH), 7.30 (m, 20H; ArH), 5.23 (s, 8H; CH2). 13C NMR (67.5 MHz, CDCl3, δ): 164.6 (CO), 139.7 (C⟨), 135.3 (Ar), 130.3 (CH), 128.8 (Ar), 128.7 (Ar), 125.8 (C⟨), 67.7 (CH2). IR (KBr): ν = 2906 (CH), 1673 (CO), 1533 (CC), 1470, 1404 (CC of Ar), 1186 (C−O) cm−1. Anal. Calcd for C40H32O8: C 74.98, H 5.04, O 19.98. Found: C 74.57, H 5.01, O 20.42. 7,7,8,8-Tetrakis(pentafluorobenzyloxycarbonyl)-p-quinodimethane (1b). 39.3% yield; mp 170.0−171.0 °C. 1H NMR (270 MHz, CDCl3, δ): 7. 46 (2, 4H; CH), 5.33 (s, 8H; CH2). 13C NMR (67.5 MHz, CDCl3, δ): 163.3 (CO), 146.0 (ddd, JC−F = 230.7, 14.53, 5.59 Hz; ArF), 142.3 (ddd, JC−F = 222.9, 12.85, 7.26 Hz; ArF), 140.4 (C⟨), 137.5 (ddd, JC−F = 248.1, 13.41, 6.70 Hz; ArF), 124.3 (C⟨), 108.4 (dd, JC−F = 23.46, 11.73 Hz, Ar), 54.5 (CH2). 19F NMR (564.46 MHz, CDCl3, δ): −141.95 (dd, J = 0.037, 0.013 Hz, 2F, o-F), −151.36 (t, J = 0.037 Hz, 1F, p-F), −161.14 (td, J = 0.037, 0.012 Hz, 2F, m-F). IR (KBr): ν = 2980 (CH), 1737, 1713 (CO), 1567 (CC), 1526, 1507, 1468 (CC of Ar), 1196 (C−O), 1007 (C−F) cm−1. Anal. Calcd for C40H12F20O8: C 48.02, H 1.21. Found: C 47.37, H 1.55. 7 , 7 - D i ( be n zy l ox y c a rb o n y l) - 8 , 8- d i (p e n ta fl uo ro b e n z yl oxycarbonyl)-p-quinodimethane (1c). 34.4% yield; mp 127.0− 127.5 °C. 1H NMR (270 MHz, CDCl3, δ): 7.47 (d, J = 10.22 Hz, 2H; CH), 7.39 (d, J = 10.22 Hz, 2H; CH), 7.34−7.28 (m, 10H; Ar), 5.32 (s, 4H; CH), 5.25 (3, 4H; CH2). 13C NMR (67.5 MHz, CDCl3, δ): 164.1 (CO), 163.4 (CO), 145.8 (ddd, JC−F = 249.2, 14.53, 6.70 Hz; ArF), 142.3 (ddd, JC−F = 203.4, 12.29, 6.15 Hz; ArF), 140.9 (C⟨), 139.0 (C⟨), 137.4 (ddd, JC−F = 224.0, 12.85, 5.59 Hz; ArF), 130.9 (CH), 129.6 (CH), 128.6 (Ar), 128.5 (Ar), 128.3 (Ar), 126.8 (C⟨), 123.1 (C⟨), 108.7 (dd, JC−F = 11.17, 3.91 Hz; Ar), 108.5 (Ar), 67.6 (CH2), 54.3 (CH2). 19F NMR (564.46 MHz, CDCl3, δ): −141.93 (dd, J = 0.037, 0.012 Hz, 2F, o-F), −151.52 (t, J = 0.037 Hz, 1F, p-F), −161.20 (td, J = 0.037, 0.015 Hz, 2F, m-F). IR (KBr): ν = 2917 (CH), 1735, 1719 (CO), 1574 (CC), 1528, 1507, 1466 (CC of Ar), 1198 (C−O), 1035 (C−F) cm−1. Anal. Calcd for C40H22F10O8: C 58.54, H 2.71. Found: C 58.21, H 2.36. Solid-State Polymerization. A given amount of monomer crystals (1a−1c) was put into a Pyrex ampule, which was degassed under reduced pressure and then sealed. Thermal polymerization was carried out by setting the ampule in an oil bath at 60, 90, 110, 130, or 150 °C for a given time. To dissolve the reaction product, 1 mL of dichloromethane was added, and the resulting solution was poured into large amount of hexane to deposit the reaction product, which was purified by the redissolution−reprecipitation method. Dichloromethane and hexane were used as the solvent and precipitant, respectively. The product was dried under reduced pressure at room temperature until constant weight was attained.
and both benzyloxy and pentafluorobenzyloxy (1c) as bulky aryloxy group were synthesized according to the route as shown in Scheme 1. Scheme 1. Synthesis Route of 7,7,8,8Tetrakis(aryloxycarbonyl)-p-quinodimethanes (1a−1c)
Knoevenagel condensations of 1,4-cyclohexanedione with benzyl malonate or pentafluorobenzyl malonate using titanium tetrachloride and pyridine as a dehydrating reagent gave 1,4-bis[di(benzyloxycarbonyl)methylene]cyclohexane (3a) in 66% yield as white needle or 1,4-bis[di(pentafluorobenzyloxycarbonyl)methylene]cyclohexane (3b) in 43% yield as white powder, respectively. 1-Di(benzyloxycarbonyl)methylene-4di(pentafluorobenzyloxycarbonyl)methylenecyclohexane (3c) was synthesized in 88% yield as white needle by Knoevenagel condensation of benzyl malonate with 4-[di(pentafluorobenzyloxycarbonyl)methylene]cyclohexanone (2), which was prepared in 81% yield as white plate by 1,4-cyclohexanedione monoethylene ketal with pentafluorobenzyl malonate using titanium tetrachloride and pyridine followed by deprotection of the ketal. Oxidations of 3a−3c with activated manganese dioxide in the refluxing benzene followed by recrystallization from a mixture of chloroform and hexane gave 1a in 22%, 1b in 39%, and 1c in 34% yields as yellow plate for 1a and yellow needles for both 1b and 1c. All monomers were identified by 1 H, 13C NMR, IR spectroscopies, and elemental analysis. Solid-State Polymerization. Thermal polymerizations of three monomer crystals (1a−1c) were carried out for 10 h−6 days by heating in dark in the temperature range 60−150 °C, which is lower temperatures by 20−80 °C than their melting points, and the results are summarized in Table 1. The 1a plate crystal kept yellow color and crystal shape in appearance at 60 °C without melting in 1 day, but at 90 °C it changed crystal shape from plate to glass-like solid though yellow color is retained in 1 day. At temperature of 110 °C, it changed color from yellow to white and the crystal shape from plate to glass-like solid in 1 day. Polymer yields at 90 and 110 °C in 1 day were determined by weight amounts of polymer isolated as a product insoluble in hexane to be 51% and 86%, respectively. At 60 °C 1a was recovered quantitatively. Polymers obtained at 90 and 110 °C, which contain a very small amount of THF-insoluble part (
