Article pubs.acs.org/Macromolecules
Twofold Helical Polymerization: Thermal Solid-State Polymerization of 7‑Cyano-7-(2′-haloethoxycarbonyl)-1,4-benzoquinone Methides Takahito Itoh,*,† Kyoko Tachino,† Naoki Akira,† Takahiro Uno,† Masataka Kubo,‡ Norimitsu Tohnai,§ and Mikiji Miyata§ †
Division of Chemistry for Materials, Graduate School of Engineering, and ‡Graduate School of Regional Innovation Studies, 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-Cyano-7-(2′-haloethoxycarbonyl)-1,4-benzoquinone methides bearing 2′-haloethoxy groups such as 2′fluoroethoxy (1a), 2′-chloroethoxy (1b), 2′-bromoethoxy (1c), and 2′-iodoethoxy (1d) were synthesized. The halogen atoms of the haloalkoxy group in the quinone methide skeleton greatly affected their crystal structures, which belong to space group P21/c for 1a, P21/a for 1b, and P-1 for 1c and 1d. The thermal solid-state polymerizations in vacuo at 60 or 80 °C gave amorphous polymers with regular head-to-tail configuration and proceeded with retention of the crystal shapes in appearance. Relations between the molecular assembly modes and the polymerization modes indicate that 21 (2-fold) assemblies of 1b are able to undergo 21 helical polymerization with handedness.
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INTRODUCTION A helix is well-known as a motif that exhibits chirality with right- and left-handedness. Naturally occurring polymers such as proteins, polysaccharides, nucleic acids, and so on have helical structures and show the characteristic functionalities such as molecular recognition ability and catalytic activity. Inspired by such helical structures, a variety of helical polymers and supramolecules have been intensively investigated.1,2 So far, however, handedness of the 2-fold (21) helix has not been discussed from a crystallographic viewpoint, since symmetry operations with 180° rotation afford no handedness mathematically.3 For example, cellulose crystal is known to belong to the space group P21, but the handedness of the 21 helical polymer in the cellulose crystal is not distinguished.4 Recently, during researches of crystalline supramolecular assemblies of steroids, alkaloids, and organic salts, Miyata et al. found that the handedness of the 21 helical molecular assemblies can be briefly discriminated and defined by the supramolecular-tilt-chirality method (STCM).5,6 Such a finding directed us toward 2-fold (21) helical polymerization which is schematically compared with the conventional polymerization. Figure 1 schematically demonstrates these polymerizations induced by molecular assembly modes. Namely, three-axially discriminable molecules (Figure 1a) are arranged along an axis in three different modes of head and tail parts with belly and back attachments. Thus, a parallel head-to-tail mode with belly-to-back attachment can undergo trans-type polymerization (Figure 1b (i)), while an antiparallel head-to-tail mode with belly-to-back attachment undergoes cis© 2015 American Chemical Society
type one (Figure 1b (ii)). In addition, 21 assembly involves head-to-tail mode with belly-to-belly or back-to-back attachment and can be inclined to the right or left in front of a 21 screw axis to yield a right- or left-handed 21 assembly, respectively. Their 21 helical polymerizations may produce the corresponding right- or a left-handed polymer, respectively (Figure 1b (iii)), and may be realized in the solid state, as described below. Polymerizations in the solid state like crystals have received considerable attention as an environmental-friendly polymerization method in recent years. In particular, topochemical polymerization as a specific case in the solid-state polymerizations has been a focus of great interest because it may offer the possibility of providing polymers with highly controlled structures such as regioselectivity, stereoregularity, and molecular weight on the basis of molecular assembly modes. Since topochemical polymerization proceeds with only slight movements and rotations around the center of the gravity of the monomer molecules, the crystallographic position and symmetry of the monomer crystals are retained in the resulting polymer crystals. Such strict requirements for topochemical polymerizations so far afforded only a limited number of monomers such as derivatives of diacetylene,7 2,5-distyrylpyrazine,8 triene and triacetylene,9 muconic acid and sorbic acid,10 and [2,2′-bi-1H-indene]-1,1′-dione-3,3′-diyl alkylcarboxylate.11 Received: December 28, 2014 Revised: April 9, 2015 Published: April 17, 2015 2935
DOI: 10.1021/ma502606s Macromolecules 2015, 48, 2935−2947
Article
Macromolecules
Figure 1. (a) Schematic representation of a molecule with orthorhombic three axes and (b) (i) trans-type polymerization, (ii) cis-type polymerization, and (iii) 2-fold (21) helical polymerization with handedness. The 21 helical assembly with three-axial and tilt chirality causes the 21 helical polymerization with handedness.
suitable for topochemical polymerization of the substituted 1,4benzoquinone methides. Moreover, as shown in Figure 2, 1,4-
Recently, we found that 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes undergo the trans-type topochemical polymerizations and also proposed a general rule to predict the polymerization reactivity for the topochemical polymerizations of substituted quinodimethane monomers in the solid state.12 Especially, in the cases of 7,7,8,8-tetrakis(alkoxycarbonyl)quinodimethanes with halogen-containing alkoxy group such as 2′-chloroethoxy and 2′-bromoethoxy, topochemical polymerization reactions were found to proceed easily, suggesting some contribution to molecular assembly by the halogen−halogen interaction.13 Moreover, the cis-type topochemical polymerization was supplied by using cocrystal of 7,7,8,8-tetrakis(methoxycarbonyl)quinodimethane and 7,7,8,8-tetracyanoquinodimethane.14 Subsequently, we focused on quinone methides which are a member of quinoid family as well as quinodimethanes. Conveniently, they become isolable crystals at room temperature, when they are substituted with electron-donating and/or electron-accepting substituents at exo-methylene carbon. We investigated polymerization behavior of their isolable substituted quinone methides in solution and solid state.15 7Cyano-7-alkoxycarbonyl-1,4-benzoquinone methides as one of the substituted quinone methides do not polymerize topochemically in the solid state to give their amorphous polymers.16 However, it is noteworthy that halogen-containing substituents enable us to change crystal structures owing to socalled halogen bond effects.13 Introduction of halogencontaining substituents into the substituted 1,4-benzoquinone methides might support formation of molecular assembly
Figure 2. Schematic representation of 7-cyano-7-(alkoxycarbonyl)-1,4benzoquinone methide as a molecule with orthorhombic three axes and definition of Re- and Si-faces in a 7-cyano-7-(alkoxycarbonyl)-1,4benzoquinone methide molecule.
benzoquinone methides involving different substituents on the exo-methylene exhibit three-axial asymmetry: head and tail (or leg), right and left, as well as back and belly.5,6 Therefore, two planar faces of a prochiral sp2-hybridized group can be designated by the terms Re-face and Si-face according to the Cahn−Ingold−Prelog priority rules.17 This feature tells us that the substituted 1,4-benzoquinone methides with halogencontaining substituents at the 7-position might form the 21 helical assemblies and undergo 21 helical polymerization in the solid state. 2936
DOI: 10.1021/ma502606s Macromolecules 2015, 48, 2935−2947
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Macromolecules
dimethylaminopyridine (6 mmol) and then stirred for 16 h at 0 °C under nitrogen. The reaction mixture was extracted with dichloromethane (100 mL × 3). The extracts were combined and washed with saturated sodium chloride solution and saturated sodium bicarbonate solution and then dried over anhydrous magnesium sulfate. After filtration, the solvent was evaporated under reduced pressure. The crude product was purified by silica gel column chromatography using chloroform as eluent. 2-Fluoroethyl cyanoacetate (2a): From 2-fluoroethanol, 2a was obtained as colorless oil (73.1% yield). 1H NMR (500 MHz, CDCl3, δ): 4.65 (dt, JH−F = 47.50 Hz, J = 4.00 Hz, 2H; CH2), 4.45 (dt, JH−F = 29.00 Hz, J = 4.00 Hz, 2H; CH2), 3.57 (s, 2H; CH2). 13C NMR (125.7 MHz, CDCl3, δ): 163.4 (CO), 113.1 (CN), 80.6 (OCH2) (d, JC−F = 169.5 Hz), 65.0 (CH2F) (d, JC−F = 19.6 Hz), 24.2 (CH2). IR (neat): ν = 2973, 2939 (CH), 2265 (CN), 1748 (CO), 1184 (C−O), 1061 (C−F) cm−1. 2-Chloroethyl cyanoacetate (2b): From 2-chloroethanol, 2b was obtained as colorless oil (95.1% yield). 1H NMR (500 MHz, CDCl3, δ): 4.53 (t, J = 4.00 Hz, 2H; CH2), 3.77 (t, J = 4.00 Hz, 2H; CH2), 3.59 (s, 2H; CH2). 13C NMR (125.7 MHz, CDCl3, δ): 162.8 (CO), 112.9 (CN), 65.8 (OCH2), 40.9 (CH2Cl), 29.5 (CH2). IR (neat): ν = 2972, 2933 (CH), 2265 (CN), 1752 (CO), 1184 (C−O), 665 (C− Cl) cm−1. 2-Bromoethyl cyanoacetate (2c): From 2-bromoethanol, 2c was obtained as colorless oil (91.1% yield). 1H NMR (500 MHz, CDCl3, δ): 4.53 (t, J = 6.00 Hz, 2H; CH2), 3.57 (s, 2H; CH2), 3.55 (t, J = 6.00 Hz, 2H; CH2). 13C NMR (125.7 MHz, CDCl3, δ): 162.8 (CO), 112.8 (CN), 65.6 (OCH2), 27.7 (CH2Br), 24.5 (CH2). IR (neat): ν = 2972, 2931 (CH), 2267 (CN), 1749 (CO), 1190 (C−O), 570 (C− Br) cm−1. 2-Iodoethyl cyanoacetate (2d): From 2-iodoethanol, 2d was obtained as colorless oil (69.4% yield). 1H NMR (270 MHz, CDCl3, δ): 4.47 (t, J = 6.93 Hz, 2H, CH2), 3.52 (s, 2H, CH2), 3.34 (t, J = 6.83 Hz, 2H, CH2). 13C NMR (67.5 MHz, CDCl3, δ): 163.1(CO), 113.5(CN), 66.8 (OCH2), 25.2 (CH2), 0.0 (CH2I). IR (neat): ν = 2970 (CH), 2264 (CN), 1751 (CO), 1176 (C−O), 574 (C−I) cm−1. 4-[Cyano(2′-haloethoxycarbonyl)methylene]-1,4-dioxaspiro[4.5]decanes (3a−3d). General Preparation Method. 1,4-Cyclohexanedione monoethylene ketal (4.48 g, 28.7 mmol) and 2-haloethyl cyanoacetate (2a−2d) (28.7 mmol) were refluxed in the presence of ammonium acetate (0.69 g, 11.5 mmol) and acetic acid (0.24 g, 3.12 mmol) in 22 mL of toluene using a Dean−Stark water separator to isolate water formed for 12 h. Into the reaction mixture was added chloroform (50 mL). The resulting solution was washed with water (50 mL), saturated aqueous sodium bicarbonate solution (50 mL), and saturated aqueous sodium chloride solution (50 mL), dried over anhydrous magnesium sulfate, and filtered, and then the solvents of the filtrate was evaporated under reduced pressure. The crude product was purified by recrystallization from a mixture solution of chloroform and hexane. 4-[Cyano(2′-fluoroethoxycarbonyl)methylene]-1,4-dioxaspiro[4.5]decane (3a): From 2a, 3a was obtained as yellow powder (77.8% yield); mp 106.0−107.0 °C. 1H NMR (500 MHz, CDCl3, δ): 4.68 (dt, JH−F = 48.00 Hz, J = 4.00 Hz, 2H; CH2), 4.47 (dt, JH−F = 48.00 Hz, J = 4.00 Hz, 2H; CH2), 4.00 (s, 4H; CH2), 3.17 (t, J = 6.50 Hz, 2H; CH2), 2.88 (t, J = 6.50 Hz, 2H; CH2), 1.90 (t, J = 6.50 Hz, 2H; CH2), 1.83 (t, J = 6.50 Hz, 2H; CH2). 13C NMR (125.7 MHz, CDCl3, δ): 177.9 ( C⟨), 161.3 (CO), 114.9 (CN), 106.8 (⟩C⟨), 102.7 (C⟨), 80.7 (CH2F) (d, JC−F = 171.5 Hz), 64.6 (CH2), 64.4 (OCH2) (d, JC−F = 20.7 Hz), 35.0 (CH2), 34.7 (CH2), 33.6 (CH2), 28.0 (CH2). IR (KBr): ν = 2957, 2888 (CH), 2230 (CN), 1726 (CO), 1604 (CC), 1217 (C−O), 1125 (C−O), 1094 (C−O), 1032 (C−F) cm−1. Anal. Calcd for C13H16FNO4: C 57.98, H 6.00, N 5.20. Found: C 58.01, H 5.97, N 5.34. 4-[Cyano(2′-chloroethoxycarbonyl)methylene]-1,4-dioxaspiro[4.5]decane (3b): From 2b, 3b was obtained as pale yellow powder (79.1% yield); mp 110.5−111.5 °C. 1H NMR (500 MHz, CDCl3, δ): 4.48 (t, J = 6.00 Hz, 2H; CH2), 3.95 (s, 4H; CH2), 3.75 (t, J = 6.00 Hz, 2H; CH2), 3.18 (t, J = 6.50 Hz, 2H; CH2), 2.88 (t, J = 6.00 Hz, 2H; CH2),
This paper deals with syntheses, crystal structures as well as thermal solid-state polymerizations of novel series of 7-cyano-7(2′-haloethoxycarbonyl)-1,4-benzoquinone methides bearing 2′-haloethoxy group such as 2′-fluoroethoxy (1a), 2′chloroethoxy (1b), 2′-bromoethoxy (1c), and 2′-iodoethoxy (1d) (Chart 1). It is described that halogen atoms greatly Chart 1. Quinoid Monomer Family: 7,7,8,8Tetrakis(alkoxycarbonyl)quinodimethanes and 7-Cyano-7(2′-halethoxycarbonyl)-1,4-benzoquinone Methides (1a− 1d)
influence on both the crystal structures and the thermal polymerizations in the solid state and that 1b is a promising monomer for searching the 2-fold (21) helical polymerization with right- or left-handedness.
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EXPERIMENTAL SECTION
Measurements. All melting points were obtained with a Yanaco MP-S3 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 JEOL JNMEX270 FT NMR or JEOL JNM-A500 FT NMR spectrometers using chloroform-d with tetramethylsilane as an internal standard at 25 °C and JASCO FT/IR-4100 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 graphite-monochromated 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. The direct method (SIR-2004) was used for the structure solution.18 All calculations were performed with the observed reflection [I > 2σ(I)] by the program CrystalStructure crystallographic software package19 except for refinement, which was performed by SHELEX-97.20 All non-hydrogens were placed in idealized positions and refined as rigid atoms with the relative isotropic displacement parameters. Materials. Cyanoacetic acid, 2-fluoroethanol, 2-chloroethanol, 2bromoethanol, 2-iodoethanol, N-ethyl-N′-(3-(dimethylamino)propyl)carbodiimide hydrochloride, ammonium acetate, acetic acid and 1,4cyclohexanedione monoethylene ketal (all nine materials from Tokyo Kasei Kogyo Co. Ltd.), and activated manganese(IV) dioxide (Aldrich Co.) were used without further purification. Synthesis of Monomers 1a−1d. 2-Haloethyl Cyanoacetates 2a−2d. General Preparation Method. N-Ethyl-N′-(3(dimethylamino)propyl)carbodiimide hydrochloride (82 mmol) solution in dichloromethane (40 mL) was added dropwise to a mixture of cyanoacetic acid (5.2 g, 60 mmol), 2-haloethanol (65 mmol), and 2937
DOI: 10.1021/ma502606s Macromolecules 2015, 48, 2935−2947
Article
Macromolecules 1.90 (t, J = 6.50 Hz, 2H; CH2), 1.84 (t, J = 6.50 Hz, 2H; CH2). 13C NMR (125.7 MHz, CDCl3, δ): 178.0 (C⟨), 161.2 (CO), 114.8 (CN), 106.7 (CO), 102.5 (C⟨), 64.9 (CH2), 64.6 (OCH2), 40.8 (CH2Cl), 34.9 (CH2), 34.6 (CH2), 33.6 (CH2), 28.0 (CH2). IR (KBr): ν = 2962 (CH), 2227 (CN), 1728 (CO), 1604 (CC), 1214 (C−O), 1094 (C−O), 1033 (C−O), 776 (C−Cl) cm−1. Anal. Calcd for C13H16ClNO4: C 54.64, H 5.66, N 4.90. Found: C 54.70, H 5.57, N 4.93. 4-[Cyano(2′-bromoethoxycarbonyl)methylene]-1,4-dioxaspiro[4.5]decane (3c): From 2c, 3c was obtained as pale brown powder (82.3% yield); mp 97.0−98.0 °C. 1H NMR (500 MHz, CDCl3, δ): 4.54 (t, J = 6.50 Hz, 2H; CH2), 4.00 (s, 4H; CH2), 3.57 (t, J = 6.50 Hz, 2H; CH2), 3.18 (t, J = 6.50 Hz, 2H; CH2), 2.88 (t, J = 6.50 Hz, 2H; CH2), 1.90 (t, J = 6.50 Hz, 2H; CH2), 1.84 (t, J = 6.50 Hz, 2H; CH2). 13 C NMR (125.7 MHz, CDCl3, δ): 178.1 (C⟨), 161.1 (CO), 114.9 (CN), 106.8 (⟩C⟨), 102.6 (C⟨), 64.6 (CH2), 64.2 (OCH2), 38.1 (CH2Br), 35.0 (CH2), 33.8 (CH2), 32.1 (CH2), 28.0 (CH2). IR (KBr): ν = 2962 (CH), 2226 (CN), 1727 (CO), 1604 (CC), 1212 (C−O), 1094 (C−O), 1034 (C−O), 575 (C−Br) cm−1. Anal. Calcd for C13H16BrNO4: C 47.27, H 4.89, N 4.24. Found: C 47.31, H 4.85, N 4.29. 4-[Cyano(2′-iodoethoxycarbonyl)methylene]-1,4-dioxaspiro[4.5]decane (3d): From 2d, 3d was obtained as brown powder (69.9% yield); mp 86−87 °C. 1H NMR (270 MHz, CDCl3, δ): 4.53 (t, J = 6.92 Hz, 2H; CH2), 4.00 (s, 4H; CH2), 3.57 (t, J = 6.92 Hz, 2H; CH2), 3.18 (t, J = 6.60 Hz, 2H; CH2), 2.88 (t, J = 6.60 Hz, 2H; CH2), 1.90 (t, J = 6.60 Hz, 2H; CH2), 1.84 (t, J = 6.92 Hz, 2H; CH2). 13C NMR (67.5 MHz, CDCl3, δ): 179.0 (C⟨), 161.8 (CO), 115.8 (CN), 107.7 (⟩C⟨), 103.6 (C⟨), 66.5 (OCH2), 65.6 (CH2), 35.9 (CH2), 35.7 (CH2), 34.6 (CH2), 29.0 (CH2), 0.0 (CH2I). IR (KBr): ν = 2950, 2872 (CH), 2222 (CN), 1725 (CO), 1604 (CC), 1212 (C−O), 1132 (C−O), 1091 (C−O), 516 (C−I) cm−1. Anal. Calcd for C13H16INO4: C 41.39, H 4.28, N 3.71. Found: C 42.40, H 4.29, N 3.81. 4-[Cyano(2′-haloethoxycarbonyl)methylene]cyclohexanones (4a−4d). General Preparation Method. 3a−3d (4.2 mmol) was dissolved in 47 mL of THF containing a 20% aqueous hydrochloric acid solution (8 mL) and stirred at room temperature for 19 h. The reaction mixture was placed under reduced pressure to remove THF, and then the residue was extracted with chloroform (100 mL × 3). The combined organic fractions were washed with water (100 mL), saturated sodium chloride solution (100 mL), and saturated sodium bicarbonate solution (100 mL), 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. 4-[Cyano(2′-fluoroethoxycarbonyl)methylene]cyclohexanone (4a): From 3a, 4a was obtained as white powder (66.1% yield); mp 75.0− 76.0 °C. 1H NMR (500 MHz, CDCl3, δ): 4.69 (dt, JH−F = 46.00 Hz, JH−H = 4.00 Hz, 2H; CH2), 4.50 (dt, JH−F = 27.50 Hz, JH−H = 4.00 Hz, 2H; CH2), 3.41 (t, J = 6.50 Hz, 2H; CH2), 3.15 (t, J = 6.50 Hz, 2H; CH2), 2.58 (t, J = 6.50 Hz, 2H; CH2), 2.56 (t, J = 6.50 Hz, 2H; CH2). 13 C NMR (125.7 MHz, CDCl3, δ): 208.1 (CO), 175.7 (C⟨), 161.0 (CO), 114.3 (CN), 104.2 (C⟨), 80.6 (CH2F) (d, JC−F = 171.5 Hz), 64.4 (OCH2) (d, JC−F = 20.6 Hz), 36.8 (CH2), 36.7 (CH2), 31.9 (CH2), 28.1 (CH2). IR (KBr): ν = 2964, 2918 (CH), 2224 (CN), 1726 (CO), 1591 (CC), 1252 (C−O), 1065 (C−F) cm−1. Anal. Calcd for C11H12FNO3: C 58.66, H 5.38, N 6.22. Found: C 58.56, H 5.23, N 6.13. 4-[Cyano(2′-chloroethoxycarbonyl)methylene]cyclohexanone (4b): From 3b, 4b was obtained as white powder (83.9% yield); mp 84.5−86.0 °C. 1H NMR (500 MHz, CDCl3, δ): 4.50 (t, J = 5.50 Hz, 2H; CH2), 3.76 (t, J = 5.50 Hz, 2H; CH2), 3.41 (t, J = 7.00 Hz, 2H; CH2), 3.16 (t, J = 7.00 Hz, 2H; CH2), 2.58 (t, J = 7.00 Hz, 2H; CH2), 2.56 (t, J = 7.00 Hz, 2H; CH2). 13C NMR (125.7 MHz, CDCl3, δ): 208.1 (CO), 175.8 (C⟨), 160.8 (CO), 114.3 (CN), 104.2 ( C⟨), 65.1 (OCH2), 40.9 (CH2), 36.9 (CH2), 36.8 (CH2), 32.0 (CH2), 28.1 (CH2Cl). IR (KBr): ν = 2972 (CH), 2224 (CN), 1723 (CO), 1595 (CC), 1286 (C−O), 775 (C−Cl) cm−1. Anal. Calcd for
C11H12ClNO3: C 54.66, H 5.01, N 5.79. Found: C 54.57, H 5.03, N 5.81. 4-[Cyano(2′-bromoethoxycarbonyl)methylene]cyclohexanone (4c): From 3c, 4c was obtained as white powder (80.9% yield); mp 91.0−92.0 °C. 1H NMR (500 MHz, CDCl3, δ): 4.57 (t, J = 6.00 Hz, 2H; CH2), 3.59 (t, J = 6.00 Hz, 2H; CH2), 3.41 (t, J = 7.00 Hz, 2H; CH2), 3.16 (t, J = 7.00 Hz, 2H; CH2), 2.60 (t, J = 7.00 Hz, 2H; CH2), 2.57 (t, J = 7.00 Hz, 2H; CH2). 13C NMR (125.7 MHz, CDCl3, δ): 208.1 (CO), 175.8 (C⟨), 160.7 (CO), 114.3 (CN), 104.3 ( C⟨), 64.9 (OCH2), 36.9 (CH2Br), 36.8 (CH2), 32.0 (CH2), 28.2 (CH2), 27.7 (CH2). IR (KBr): ν = 2971 (CH), 2224 (CN), 1723 (CO), 1595 (CC), 1254 (C−O), 580 (C−Br) cm−1. Anal. Calcd for C11H12BrNO3: C 46.16, H 4.23, N 4.89. Found: C 45.69, H 4.15, N 4.97. 4-[Cyano(2′-iodoethoxycarbonyl)methylene]cyclohexanone (4d): From 3d, 4d was obtained as white powder (66.9% yield); mp 84− 86 °C. 1H NMR (270 MHz, CDCl3, δ): 4.51 (t, J = 6.93 Hz, 2H; CH2), 3.41 (t, J = 6.93 Hz, 2H; CH2), 3.37 (t, J = 6.93 Hz, 2H; CH2), 3.16 (t, J = 6.93 Hz, 2H; CH2), 2.59 (t, J = 6.93 Hz, 2H; CH2), 2.56 (t, J = 6.93 Hz, 2H; CH2). 13C NMR (67.5 MHz, CDCl3, δ): 209.0 (C O), 176.8 (C⟨), 161.5 (CO), 115.3 (CN), 105.2 (C⟨), 66.7 (OCH2), 37.8 (CH2Br), 37.7 (CH2), 33.0 (CH2), 29.2 (CH2), 0.0 (CH2I). IR (KBr): ν = 3036, 2966 (CH), 2222 (CN), 1722 (CO), 1594 (CC), 1251 (C−O), 533 (C−I) cm−1. Anal. Calcd for C11H12INO3: C 39.66, H 3.64, N 4.20. Found: C 40.76, H 3.69, N 4.27. 7-Cyano-7-(2′-haloethoxycarbonyl)-1,4-benzoquinone Methides (1a−1d). General Procedure Method. About 0.4 g of 3a−3d was dissolved in 200 mL of chloroform, and then into the resulting solution was added 1.5 g of activated manganese dioxide. The mixture was refluxed with stirring for 30 min, cooled, and then filtered. The orange filtrate was placed under reduced pressure to remove chloroform to give 1a−1d as red solid residue, which was purified by recrystallization from a mixture solution of chloroform and hexane (1/5 v/v). 7-Cyano-7-(2′-fluoroethoxycarbonyl)-1,4-benzoquinone Methide (1a): Orange needles; yield 56.7%; mp 79.0−80.0 °C. 1H NMR (500 MHz, CDCl3, δ): 8.54 (dd, J = 10.00, 2.50 Hz, 1H, CH), 7.73 (dd, J = 10.00, 2.50 Hz, 1H, CH), 6.63 (dd, J = 10.30, 2.00 Hz, 1H, CH), 6.55 (dd, J = 10.30, 2.00 Hz, 1H, CH), 4.73 (dt, JH−F = 47.50 Hz, J = 4.00 Hz, 2H, CH2), 4.60 (dt, JH−F = 27.50 Hz, J = 4.00 Hz, 2H, CH2). 13C NMR (125.7 MHz, CDCl3, δ): 186.0 (CO), 160.3 (C O), 149.0 (C⟨), 136.1 (CH), 133.6 (CH), 132.7 (CH), 132.6 (CH), 114.2 (CN), 110.6 (C⟨), 80.4 (CH2F) (d, JC−F = 172.6 Hz), 65.6 (OCH2) (d, JC−F = 20.7 Hz). IR (KBr): ν = 3063, 2962 (CH), 2216 (CN), 1733 (CO), 1644 (CC), 1239 (C−O), 1062 (C−F) cm−1. UV−vis (CHCl3): λ = 320 nm (log ε = 4.40). Anal. Calcd for C11H8FNO3: C 59.70, H 3.65, N 6.33. Found: C 59.30, H 3.98, N 6.35. 7-Cyano-7-(2′-chloroethoxycarbonyl)-1,4-benzoquinone Methide (1b): Orange needles; yield 46.2%; mp 80.0−81.0 °C. 1H NMR (500 MHz, CDCl3, δ): 8.54 (dd, J = 10.25, 2.75 Hz, 1H, CH), 7.73 (dd, J = 10.00, 3.00 Hz, 1H, CH), 6.63 (dd, J = 10.50, 2.00 Hz, 1H, CH), 6.55 (dd, J = 10.25, 1.75 Hz, 1H, CH), 4.60 (t, J = 5.50 Hz, 2H, CH2), 3.80 (t, J = 5.50 Hz, 2H, CH2). 13C NMR (125.7 MHz, CDCl3, δ): 186.0 (CO), 160.0 (CO), 149.1 (C⟨), 136.0 (CH), 133.4 (CH), 133.0 (CH), 114.1 (CN), 110.5 (C⟨), 66.0 (OCH2), 40.7 (CH2Cl). IR (KBr): ν = 3060, 2974 (CH), 2222 (CN), 1731 (CO), 1641 (CC), 1239 (C−O), 742 (C−Cl) cm−1. UV−vis (CHCl3): λ = 321 nm (log ε = 4.40). Anal. Calcd for C11H8ClNO3: C 55.60, H 3.39, N 5.89. Found: C 55.51, H 3.34, N 6.27. 7-Cyano-7-(2′-bromoethoxycarbonyl)-1,4-benzoquinone Methide (1c): Orange needles; yield 47.0%; mp 75.5−76.0 °C. 1H NMR (500 MHz, CDCl3, δ): 8.54 (dd, J = 10.08, 2.76 Hz, 1H, CH), 7.72 (dd, J = 10.10, 2.74 Hz, 1H, CH), 6.62 (dd, J = 10.08, 1.84 Hz, 1H, CH), 6.54 (dd, J = 10.52, 1.84 Hz, 1H, CH), 4.64 (t, J = 5.96 Hz, 2H, CH2), 3.62 (t, J = 5.96 Hz, 2H, CH2). 13C NMR (125.7 MHz, CDCl3, δ): 186.1 (CO), 160.2 (CO), 149.2 (C⟨), 136.2 (CH), 133.7 (CH), 132.8 (CH), 114.2 (CN), 110.6 (C⟨), 66.2 (OCH2), 27.5 (CH2Br). IR (KBr): ν = 3060, 2972 (CH), 2224 (CN), 1726 (CO), 2938
DOI: 10.1021/ma502606s Macromolecules 2015, 48, 2935−2947
Article
Macromolecules Scheme 1. Synthesis of 7-Cyano-7-(2′-haloethoxycarbonyl)-1,4-benzoquinone Methides (1a−1d)
Table 1. Crystallographic Data for Crystals 1a−1d monomer
1a (F)
1b (Cl)
1c (Br)
1d (I)
formula formula weight crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3) Z ρc (g/cm3) unique reflecns no. obsd reflecns R1 R; Rw GOF 2θmax (deg) temp (°C)
C11H8O3NF 221.19 monoclinic P21/c (#14) 10.072(2) 5.665(1) 17.929(3) 90 103.34(2) 90 995.3(3) 4 1.476 710 1778 0.135 0.0800; 0.2310 0.928 136.4 −180
C11H8O3NCl 237.64 monoclinic P21/a (#14) 9.396(2) 11.516(2) 9.933(1) 90 97.59(1) 90 1065.4(3) 4 1.481 1030 1912 0.046 0.0514; 0.1330 0.722 136.5 −180
C11H8O3NBr 282.09 triclinic P-1 (#2) 4.108(1) 11.388(2) 11.496(2) 93.34(2) 94.58(2) 90.96(2) 535.0(2) 2 1.751 1639 1803 0.057 0.0669; 0.2127 1.897 136.5 −180
C22H16O6N2I2 658.19 triclinic P-1 (#2) 8.2224(3) 9.2785(3) 15.4339(7) 70.007(3) 90.047(3) 96.421(3) 1170.09(8) 2 1.868 3625 4157 0.150 0.1495; 0.4875 7.767 136.5 −180
1640 (CC), 1238 (C−O), 559 (C−Br) cm−1. UV−vis (CHCl3): λ = 321 nm (log ε = 4.47). Anal. Calcd for C11H8BrNO3: C 46.84, H 2.86, N 4.97. Found: C 47.08, H 2.79, N 5.24. 7-Cyano-7-(2′-iodoethoxycarbonyl)-1,4-benzoquinone Methide (1d): Orange plates; yield 28.3%; mp 103−105 °C. 1H NMR (270 MHz, CDCl3, δ): 8.56 (dd, J = 10.23, 2.64 Hz, 1H, CH), 7.73 (dd, J = 9.90, 2.64 Hz, 1H, CH), 6.63 (dd, J = 10.22, 1.98 Hz, 1H, CH), 6.55 (dd, J = 10.23, 1.32 Hz, 1H, CH), 4.61 (t, J = 6.60 Hz, 2H, CH2), 3.41 (t, J = 6.92 Hz, 2H, CH2). 13C NMR (67.5 MHz, CDCl3, δ): 186.0 (CO), 159.9 (CO), 149.2 (C⟨), 136.1 (CH), 133.6 (CH), 132.6 (CH), 114.1 (CN), 110.5 (C⟨), 66.8 (OCH2), −1.76 (CH2I). IR (KBr): ν = 3032, 2968 (CH), 2218 (CN), 1726 (CO), 1641 (CC), 1245 (C−O), 603 (C−I) cm−1. UV−vis (CHCl3): λ = 322 nm (log ε = 4.45). Anal. Calcd for C11H8INO3: C 40.20, H 2.45, N 4.26. Found: C 39.90, H 2.58, N 4.22. Thermal Solid-State Polymerization. A given amount of monomer crystals (1a−1d) 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 temperature lower by 15−25 °C than each melting point of the monomers for a given time. An aliquot of the reaction product in an ampule was taken out and dissolved in chloroform-d, and the 1H NMR spectrum was measured in order to determine the conversion. Conversion was calculated from peak area ratios of quinoid protons of the monomer to phenylene protons of the polymer. 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. Reaction product obtained by thermal solid-state polymerization of 1a in 25 days: White powder; yield 90%; Mn = 20 000. 1H NMR (270 MHz, CDCl3, δ): 7.77 (d, J = 8.91 Hz, 2H, Ar), 7.19 (d, J = 8.91 Hz, 2H, Ar), 4.61−4.42 (m, 4H, CH2). 13C NMR (67.5 MHz, CDCl3, δ): 164.0 (CO), 155.9 (Ar), 127.8 (Ar), 127.6 (Ar), 118.3 (Ar), 118.1 (Ar), 114.6 (CN), 80.2 (d, JC−F = 173.3 Hz, CH2F), 78.3 (⟩C⟨), 66.5 (OCH2). Anal. Calcd for (C11H8FNO3)n: C 59.73, H 3.65, N 6.33. Found: C 59.15, H 3.61, N 6.25. Reaction product obtained by thermal solid-state polymerization of 1b for 25 days: White powder; yield 92%; Mn = 16 900. 1H NMR (270 MHz, CDCl3, δ): 7.78 (d, J = 8.91 Hz, 2H, Ar), 7.21 (d, J = 8.91 Hz, 2H, Ar), 4.48 (t, J = 5.60 Hz, 2H, CH2), 3.63 (t, J = 5.61 Hz, 2H, CH2). 13C NMR (67.5 MHz, CDCl3, δ): 163.8 (CO), 155.9 (Ar), 127.8 (Ar), 127.6 (Ar), 118.3 (Ar), 118.1 (Ar), 114.5 (CN), 78.2 (⟩C⟨), 67.0 (OCH2), 40.7 (CH2). IR (KBr): ν = 3086, 2968 (CH), 2352 (CN), 1766 (CO), 1505 (CC), 1222 (C−O), 838 (C−Cl) cm−1. Anal. Calcd for (C11H8ClNO3)n: C 55.60, H 3.39, N 5.89. Found: C 54.73, H 3.21, N 5.76. Reaction product obtained by thermal solid-state polymerization of 1c for 25 days. White powder; yield 96%; Mn = 18 100. 1H NMR (270 MHz, CDCl3, δ): 7.78 (d, J = 8.91 Hz, 2H, Ar), 7.21 (d, J = 8.91 Hz, 2H, Ar), 4.54 (t, J = 5.70 Hz, 2H, CH2), 3.45 (t, J = 5.61 Hz, 2H, CH2). 13C NMR (67.5 MHz, CDCl3, δ): 163.7 (CO), 155.9 (Ar), 127.9 (Ar), 127.6 (Ar), 118.3(Ar), 114.5 (CN), 78.2 (⟩C⟨), 66.8 (OCH2), 27.3 (CH2). IR (KBr): 3072, 2958 (CH), 2324 (CN), 1767 (CO), 1504 (CC), 1219 (C−O), 658 (C−Br) cm−1. Anal. Calcd for (C11H8BrNO3)n: C 46.84, H 2.86, N 4.97. Found: C 46.96, H 2.70, N 5.01. 2939
DOI: 10.1021/ma502606s Macromolecules 2015, 48, 2935−2947
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Macromolecules
Figure 3. (a) Molecular arrangement along b-axis in the 1a crystal. (b) Schematic representation for its molecular arrangement. (c) The distances (in Å) between an exo-carbonyl oxygen of a given molecule and substituted exo-methylene carbons of peripheral molecules and the distance of F···F short contact in the 1a crystal. Hydrogen atoms are omitted for clarity. Reaction product obtained by thermal solid-state polymerization of 1d for 10 days. White powder; yield 68%; Mn = 10 000. IR (KBr): ν = 3079, 2966 (CH), 2327 (CN), 1766 (CO), 1505 (CC), 1226 (C−O), 526 (C−I) cm−1. 1H NMR (270 MHz, CDCl3, δ): 7.79 (d, J = 8.58 Hz, 2H, Ar), 7.24 (d, J = 7.25 Hz, 2H, Ar), 4.51−4.48 (m, 2H, CH2), 3.23 (t, J = 6.27 Hz, 2H, CH2). 13C NMR (67.5 MHz, CDCl3, δ): 163.5 (CO), 155.9 (Ar), 128.0 (Ar), 127.5 (Ar), 118.3 (Ar), 114.5 (CN), 78.1 (⟩C⟨), 67.6 (OCH2), 27.3 (CH2). Anal. Calcd for (C11H8INO3)n: C 40.15, H 2.45, N 4.26. Found: C 40.14, H 2.40, N 4.25.
mixture solution of chloroform and hexane, gave 1a (orange needles) in 57%, 1b (orange needles) in 46%, 1c (orange needles) in 47%, and 1d (orange plates) in 28% yields, respectively. All monomers were identified by 1H NMR, 13C NMR, and IR spectroscopies and elemental analysis. And also, 1a−1d showed the only one melting peak by differential scanning calorimetry (DSC), indicative of no formation of polymorphism under these recrystallization conditions. Crystal Structures and Molecular Assembly Modes. To clarify the molecular assembly modes in the crystals, we investigated the crystal structures of 1a−1d by X-ray crystallography. The single crystals of 1a−1d were prepared successfully by slow solvent evaporation from a mixture solution of chloroform and hexane for 1a and 1d or of dichloromethane and hexane for 1b and 1c. The crystallographic data of 1a−1d are summarized in Table 1. The molecular arrangement in the crystals, a schematic representation for the molecular arrangement, and the distances (dco in Å) between an exo-carbonyl oxygen of a given molecule and substituted exo-methylene carbons of peripheral molecules are
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RESULTS AND DISCUSSION Monomer Synthesis. 7-Cyano-7-(2′-haloethoxycarbonyl)1,4-benzoquinone methides (1a−1d) were synthesized according to the method as shown in Scheme 1. Knoevenagel condensations of 1,4-cyclohexanedione monoethylene ketal with 2-haloethyl cyanoacetates (2a−2d) followed by deprotection of the corresponding ketals (3a− 3d) gave 4-[cyano(2′-haloethoxycarbonyl)methylene]cyclohexanones (4a−4d) in 66−84% yields as white powders. Oxidations of 4a−4d with activated manganese dioxide in the refluxing chloroform, followed by recrystallization from a 2940
DOI: 10.1021/ma502606s Macromolecules 2015, 48, 2935−2947
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Macromolecules
Figure 4. (a) Molecular arrangement along b-axis in the 1b crystal. (b) Schematic representation for a right-handed arrangement with Re-face attachments (upper) and a left-handed arrangement with Si-face attachments (lower). (c) The distances (in Å) between an exo-carbonyl oxygen of a given molecule and substituted exo-methylene carbons of peripheral molecules and the distance of Cl···Cl short contact in the 1b crystal. Hydrogen atoms are omitted for clarity.
to the right from the 21 helical axis so as to yield the righthanded 21 helical assembly (upper helix in Figure 4b). On the other hand, attachments of their Si-faces yield the left-handed assembly (lower helix in Figure 4b). The right- or left-handed helical assemblies align in the same direction to afford right- or left-handed layers, which stack alternatively to give multilayered structures through the halogen bonds. 1c crystal belongs to a space group of P-1 (No. 2) and has triclinic cell with a = 4.108(1), b = 11.388(2), c = 11.496(2), α = 93.34(2), β = 94.58(2), and γ = 90.96(2), where two molecules are included. This crystal has only inversion centers without 21 screw axes in contrast to both the 1a and 1b crystals. 1c molecules stack along a-axis to form columns which are connected through weak halogen bonds (Br···Br, 4.11 Å). In addition, along the b-axis, the molecules construct columns which align in antiparallel, resulting in a characteristic monolayer sheet (Figure 5a,b). The sheets are connected through alternative halogen bonds (Br···Br, 3.46 Å). 1d crystal belongs to a space group of P-1 (No. 2) and has triclinic cell with a = 8.2224(3), b = 9.2785(3), c = 15.4339(7), α = 90.007(3), β = 90.047(3), and γ = 96.421(3), where two molecules are included. This crystal has only inversion centers without 21 screw axes like 1c crystal. 1d molecules form a characteristic monolayer sheet through weak halogen bonds (I···I, 4.83 Å), where 1d molecules are arranged along c-axis in a head-to-tail mode. Moreover, a couple of 1d molecules (dimer)
shown in Figure 3 for 1a, Figure 4 for 1b, Figure 5 for 1c, and Figure 6 for 1d. 1a crystal belongs to a space group of P21/c (No. 14) involving inversion centers and 21 (twofold) axes and has monoclinic cell with a = 10.072(2), b = 5.665(1), c = 17.929(3), α = 90, β = 103.34(2), and γ = 90, where four molecules are included (Table 1). This crystal has 21 helical assemblies along b-axis through weak halogen bonds (F···F, 3.48 Å) of tail (leg) parts. Their handedness can be determined by using a long molecular axis of the quinone methide structure (Figure 3a,b). The inversion centers produce both right- and left-handedness in addition to the opposite head-to-tail directionality. In addition, the crystal has one-dimensional columnar assemblies along b-axis through stacking. The former assemblies may induce 21 helical polymerizations, while the latter ones trans- or cis-type polymerization. 1b crystal belongs to a space group of P21/a (No. 14) involving inversion centers and 21 axes and has monoclinic cell with a = 9.396(2), b = 11.516(2), c = 9.933(1), α = 90, β = 97.59(1), and γ = 90, where four molecules are included (Table 1). Figure 4a shows that the molecules arrange along b-axis in a head-to-tail direction to form 21 helical assemblies which are connected with the neighbored ones through weak halogen bonds (Cl···Cl, 3.28 Å). Their handedness can be determined as follows (Figure 4b). The molecules attach to each other with their Re-faces, arrange in a head-to-tail fashion, and are inclined 2941
DOI: 10.1021/ma502606s Macromolecules 2015, 48, 2935−2947
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Figure 5. (a) Molecular arrangement along b-axis in the 1c crystal. (b) Schematic representation for its molecular arrangement. (c) The distances (in Å) between an exo-carbonyl oxygen of a given molecule and substituted exo-methylene carbons of peripheral molecules and the distance of Br···Br short contact in the 1c crystal. Hydrogen atoms are omitted for clarity.
with an antiparallel arrangement are stacked along a-axis with translational arrangement to form a one-dimensional column as shown in Figure 6a,b. Thermal Solid-State Polymerizations. We carried out thermal polymerizations of four monomer crystals (1a−1d) in the solid state by heating in dark at a temperature of 60 °C for 1a−1c and 80 °C for 1d, which are lower by 15−25 °C than each melting point, and the results are summarized in Table 2. 1a changed from orange needles to orange semisolid with slight shrinking in 7 days and then to pale brown semisolid in 25 days without melting at 60 °C. Both 1b and 1c retained their orange needle shapes in 7 days and then changed to pale orange slightly shrinking semisolid in 25 days without melting at 60 °C. 1d changed orange plate to orange semisolid with slight shrinking in 5 and 10 days at 80 °C, but around 20 days purple color developed on the orange semisolid and then in 30 days changed to brown-to-black solid, which is insoluble in chloroform, THF, and dimethyl sulfoxide. This indicates that some decomposition reaction including elimination of iodine took place around 20 days. Therefore, further characterization of the resulting brown-to-black semisolid was not carried out. Conversions were determined by measuring the weight of isolated polymers, and they were 55% in 7 days and 90% in 25 days for 1a, 15% in 7 days, 32% in 9 days, and 92% in 25 days for 1b, 80% in 7 days and 96% in 25 days for 1c, and 40% in 5 days and 68% in 10 days for 1d. Although both 1a and 1b have almost same melting points (79−80 °C for 1a and 80−81 °C for 1b), polymerization of 1b proceeds slowly in comparison to that of 1a from the conversions at 7 days, probably due to the
difference in the crystal structures between 1a and 1b and/or in their polymerization modes. The number-average molecular weights (Mn) of isolated polymers were determined to be 10 000−25 100 by GPC measurement, and they are soluble in chloroform, THF, benzene, and dichloromethane but insoluble in hexane and isopropyl ether. 1H NMR spectra of polymers obtained for 1a− 1d are shown in parts a−d of Figure 7, respectively. The each peak can be assigned to the respective protons of corresponding polymers illustrated therein. And also, elemental analysis values of the polymers were good agreements with the calculated values of the corresponding monomers. Moreover, a characteristic absorption band at around 1640 cm−1 assigned to the exocyclic conjugated carbon−carbon double bond in monomers 1a−1d disappeared in the IR spectra of the resulting polymers (see Experimental Section). Therefore, polymerizations of 1a−1d take place at substituted exomethylene carbon and exo-carbonyl oxygen with a formation of the stable aromatic structure, resulting in the polymers with regular head-to-tail configuration. Thermal solid-state polymerization of 1b in vacuo was investigated by electron spin resonace (ESR) spectroscopy. When the 1b crystal was heated at 60 °C, a broad peak with a g value of 2.0038 appeared in a few minutes and increased with time (Figure S1). This peak was assigned to cyano(chloroethoxycarbonyl)benzyl carbon radical, indicating that this polymerization proceeds via the radical mechanism. Addition Modes of Polymerizations. As mentioned above, thermal solid-state polymerization of 1a−1d provided only polymers with regular head-to-tail configuration, which 2942
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Figure 6. (a) Molecular arrangement along b-axis in the 1d crystal. (b) Schematic representation for its molecular arrangement. (c) The distances (in Å) between an exo-carbonyl oxygen of a given molecule and substituted exo-methylene carbons of peripheral molecules and the distance of I···I short contact in the 1d crystal. Hydrogen atoms are omitted for clarity.
Table 2. Thermal Polymerizations of 1a−1d in the Solid State run 1 2 3 4 5 6 7 8 9 10
monomer (mg) 1a (F), 100 100 1b (Cl), 66 62 102 1c (Br), 100 98 1d (I), 103 106 149
mp (°C) 79−80 80−81
75−76 103−105
temp (°C)
time (days)
form
conv (%)
Mn
60 60 60 60 60 60 60 80 80 80
7 25 7 9 25 7 25 5 10 30
orange semisolid pale brown semisolid orange needle orange needle pale orange semisolid orange needle pale orange semisolid orange semisolid orange semisolid black brown semisolid
55 90 15 32 92 80 96 40 68
12 300 20 000 16 600 12 600 16 900 10 900 18 100 10 000 10 000
other neighbored monomer. Instead, the dco distances of 6.85 and 6.86 Å seem to be suitable for the trans-type polymerization through the one-dimensional columnar assemblies. The other distances of 8.52 and 8.54 Å are too long for polymerizations. It is considered that the solid-state thermal polymerization might proceed through one-dimensional columnar assemblies in spite of the long distances.
serves as a basis for seeking any preferable polymerization. Moreover, we can employ the distances (dco) around an exocarbonyl oxygen for evaluating the plausible trans-type, cis-type, and 21 helical polymerizations. In the case of 1a (Figure 3c), the shortest dco distance of 5.37 Å may lead to the cis-type polymerization, but the subsequent reaction seems to be inhibited due to steric hindrance of the 2943
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Å would be suitable for the trans-type thermal polymerization in a monolayer sheet. Crystallinity Changes in the Polymerizations. To investigate the crystallinity of polymers obtained, we carried out the powder X-ray diffraction (PXRD) measurement at different conversions for thermal solid-state polymerizations of 1a−1c at 60 °C and 1d at 80 °C. The PXRD patterns of each monomer and the reaction mixtures at 55% and 90% conversions for 1a, at 33% and 92% conversions for 1b, at 41% and 96% conversions for 1c, and at 40% and 68% conversions for 1d are shown in parts a, b, c, and d of Figure 8, respectively. The PXRD patterns of 1a show both sharp and broad peaks at 55% conversion, indicative of coexistence of monomer crystal phase and polymer amorphous one, and then mainly a broad peak is observed at 90% conversion. This indicates that 1a forms amorphous polymer with a progress of polymerization, although crystal shape is retained in appearance. From the dco distances (6.85 Å for the trans-type polymerization and 8.52 Å for the 21 helical polymerization), it is considered that the polymerization in the 1a crystal proceeds in the onedimensional column. However, the dco of 6.85 Å is fairly far to form a carbon−oxygen single bond for polymer formation; the molecules in the crystals have to move long distance with a progress of the polymerization, resulting in collapse of the crystals and formation of amorphous polymer. The PXRD patterns of 1b show still sharp peaks even at 32% conversion in contrast to the case of 1a, though broad peaks are observed at conversion as high as 92% as well as 1a. As 1b yields its polymer with Mn of 12 600 in 32% yield, it is certain that the polymerization reaction obviously take place at 32% conversion. Therefore, no observation of a broad peak indicates that this polymerization proceeds topochemically until a conversion as low as 32%. The dco distances of 3.52 Å along b-axis implies that the polymerization in the 1b crystal might proceed via the 21 helical mode. Unfortunately, a single polymer crystal of 1b was not obtained. Nonetheless, we compared the distance for a repeating molecular unit in the 1b crystal with that for the corresponding helical structure of a polymeric model optimized by the Molecular Mechanics program 2 (MM 2) calculation (Figure 9). The distance of a repeating molecular unit is 11.52 Å in the 1b crystal and 12.41 Å in the 21 helical polymeric model of 1b. These close distance values suggest that carbon−oxygen single bond formations require only slight movements of the molecules in the crystals. PXRD patterns of 1b show sharp peaks at 32% conversion (Figure 8), indicating that the 21 helical polymerization proceeded topochemically until around this conversion, as shown in Figure S3. However, the crystal structure collapsed at 92% conversion to yield amorphous polymers. The resulting polymers are theoretically composed of an equimolar mixture of polymers with right-handedness and Re-attachments as well as polymers with left-handedness with Si-attachments on the basis of the inversion centers in the crystals (Figure S2). As far as we know, this thermal solid-state polymerization of 1b is the first example for the 21 helical polymerization. The PXRD patterns of 1c show both sharp and broad peaks at 41% conversion, indicative of coexistence of monomer crystal phase and polymer amorphous phase, and then mainly a broad peak is observed at 96% conversion. This indicates that 1c forms amorphous polymer with a progress of polymerization. The distances (dco) of 6.17 and 6.41 Å indicate that the molecules have to move fairly long distances with a progress of
Figure 7. 1H NMR spectra in chloroform-d of polymers obtained by the thermal solid-state polymerizations of (a) 1a, (b) 1b, (c) 1c, and (d) 1d.
The dco distances of 1b give us some suitable routes for the solid-state polymerization (Figure 4c). The shortest dco distance of 3.52 Å supports the occurrence of 21 helical polymerization along the 21 and b-axes. Regarding the same b-axis, the onedimensional columnar assemblies with a long distance dco of 6.29 Å may induce the trans-type polymerization. On the other hand, along the a-axis, the second shortest dco distance of 4.20 Å may cause the cis-type polymerization. Considering translational and rotational movements of the gravity centers of the monomer molecules, the 21 helical polymerization is the most preferable among the three kinds of polymerizations. In addition, the 21 helical or cis-type polymerization proceeds on each layer or among the layers respectively, meaning that the former tends to retain the halogen bonds between the layers. It is considered, therefore, that the solid-state polymerization proceeds in a head-to-tail fashion along 21 axes in parallel to baxis via the route with the shortest distance. Theoretically, the inversion centers may yield racemic mixtures of right-handed polymers with Re-face attachments as well as left-handed polymers with Si-face attachments, as schematically shown in Figure S2. 1c crystals seem to have two possible paths for the polymerization as follows (Figure 5c). Among the distances dco, the shortest one of 6.00 Å accompanies a head-to-head and tail-to-tail arrangement, prohibiting a polymerization reaction. The second shortest dco distance of 6.17 Å is suitable for the trans-type polymerization along b-axis, and furthermore the one of 6.41 Å may cause another trans-type polymerization along aaxis. The similar distances dco suggest that the polymerization reaction might proceed through the same layer sheet along baxis and/or among the neighbored sheets along a-axis. Figure 6c shows the distances dco for 1d. Along a-axis, the shortest distance dco of 3.75 Å is suitable for an initial dimerization but is not for the subsequent polymerization (dco = 7.53 Å). On the other hand, along the c-axis, the next short dco distance of 5.86 2944
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Figure 8. PXRD patterns of (a) monomer 1a and reaction mixtures at 55% and 90% conversions, (b) monomer 1b and reaction mixtures at 32% and 92% conversions, (c) monomer 1c and reaction mixtures at 41% and 96% conversions, and (d) monomer 1d and reaction mixtures at 40% and 68% conversions in the solid-state thermal polymerization.
bromoethoxy (1c), and 2-iodoethoxy (1d) as a 2′-haloethoxy group were synthesized. In the crystals of 1a−1d, the halogen atoms of the haloalkoxy group in the quinone methide skeleton significantly affected the crystal structures like P21/c for 1a, P21/a for 1b, and P-1 for 1c and 1d. Such different structures enabled us to consider different polymerization modes in the solid state. In spite of the long dco distances for 1a, 1c, and 1d, thermal polymerizations of 1a, 1c, and 1d took place to give the corresponding polymers with regular head-to-tail configuration, probably due to the enhancement of the molecular mobility in the crystals by heating. In contrast, the short dco distance (3.52 Å) for 1b indicates that 2-fold (21) helical polymerization took
the polymerization, leading to the collapse of the crystal structure and formation of amorphous polymer. The PXRD of 1d show both sharp and broad peaks at 40% and 68% conversions. The increase of the broad peaks with increasing the conversions indicates that 1d forms amorphous polymers with a progress of polymerization. It seems that the molecules in the crystals have to move fairly long distances with a progress of the polymerization, as in the case of 1c.
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CONCLUSION 7-Cyano-7-(2′-haloethoxycarbonyl)-1,4-benzoquinone methides bearing 2-fluoroethoxy (1a), 2-chloroethoxy (1b), 22945
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Figure 9. (a) Molecular arrangement of 21 right-handedness and Reface attachments in the 1b crystal and (b) the corresponding helical structure of a polymeric model optimized by MM 2 calculation. Hydrogen atoms are omitted for clarity.
place topochemically in the 1b crystal. Interestingly, if chiral crystals with P21 or P212121 would be obtained, optically active polymers might be produced by the topochemical polymerization. In addition to the above-mentioned halogen bond effect, further intermolecular interactions will be available to design such crystals.
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ASSOCIATED CONTENT
S Supporting Information *
Crystallograhic data of 1a−1d in CIF format, electron spin resonance (ESR) spectra (Figure S1), schematic representation of twofold helical polymerization (Figure S2), and XRD patterns (Figure S3). This material is available free of charge via the Internet at http://pubs.acs.org.
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AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected] (T.I.). Notes
The authors declare no competing financial interest.
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ACKNOWLEDGMENTS This work was supported by Grant-in-Aid for Scientific Research (No. 18350062 and No. 22550110) from the Ministry of Education, Culture, Sports, Science and Technology, Japan.
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