Polymerizationof alpha,omega-Bis(o-methoxyphenyl)arenes with trans-1,4-Cyclohexanedicarboxylic acid: Yielding Organosoluble Semi-Aromatic Polyketones

1. Introduction

Aromatic polyketones such as poly(ether ether ketone)(PEEK) and poly(ether ketone ketone)(PEKK) have been attractive for their excellent physical and chemical stability as alternative materials to metals, which are applied for HPLC piping, airplanes, automobiles, fuel cells, and so on [1,2,3]. Almost of typical aromatic polyketones are ocher-colored and opaque. On the other hand, we have also reported aromatic polyketones with good heat-resistance and good solubility to typical organic solvents [4,5,6,7,8,9,10,11,12,13,14]. In addition, we have reported semi-aromatic polyketones via nucleophilic aromatic substitution polymerization of bis(4-fluorobenzoylated) alicyclic compounds with bisphenols. The resulting polyketones have good heat-resistance, good solubility to typical organic solvents, and moderate colorless transparency [15].

Electrophilic aromatic acyl-substitution reaction is general to connect an aromatic ring with a ketonic group. When an acyl group is introduced to an aromatic ring, no further acylation reaction on the ring proceeds because the introduced acyl group decreases the electron density of the ring, which leads to deactivation of the mono-acylated arene.

We have developed to synthesize aromatic polyketones by using acyl-acceptant monomers such as 2,2'-dimethoxybiphenyl and 2,2'-dimethoxy-1,1’-binaphthyl [4,10,11]. Two methoxy groups in these monomers increase the electron density of arenes. In addition, these monomers have non-coplanarity with large dihedral angles by steric hindrance between two o-substituted aromatic rings, which leads to reduction of resonance effects between two aromatic rings. Therefore, the reactivity at the second reactive site (5' position for 2,2'-dimethoxybiphenyl and 6' position for 2,2'-dimethoxy-1,1’-binaphthyl) is kept after the first acylation and sustainable polymerization proceeds. Incorporation of aromatic non-coplanar units to the main chains also contributes to excellent organosolubility of the resulting polyketones.

In our previous paper, we reported P₂O₅-CH₃SO₃H mediated polycondensation of trans-1,4-cyclohexanedicarboxylic acid with 2,2’-dialkoxybiphenyls, affording cyclohexanediyl-bearing aromatic polyketones [16]. Almost of the resulting polyketones have sufficient heat-resistance, organosolubility, and colorless transparency. However, the cyclohexanediyl-bearing aromatic polyketone derived from 2,2’-dimethoxybiphenyl and trans-1,4-cyclohexanedicarboxylic acid is insoluble in typical organic solvents such as CHCl₃. On the other hand, the cyclohexanediyl-bearing aromatic polyketone derived from 2,2’-dipropyloxybiphenyl and trans-1,4-cyclohexanedicarboxylic acid is soluble in typical organic solvents such as CHCl₃ and DMF. Introduction of noncoplanar units such as 2,2’-dimethoxy-5,5’-biphenylene is insufficient to solubilize the resulting polyketones. Introduction of longer alkoxy groups to acyl-acceptant monomers is effective to solubilize the resulting polyketones. However, the glass transition temperature(T_g) of the polyketone decreases drastically.

Two methoxy-substituted benzene rings of 2,2'-dimethoxybiphenyl are connected to each other with a large dihedral angle. This motivated us to develop novel acyl-acceptant monomers where two methoxy-substituted aromatic rings are connected through an aromatic linker (Figure 1). Introduction of aromatic linkers, which consist of bent and/or non-coplanar units, between two o-methoxyphenyl groups will improve the solubility of the resulting aromatic polyketones.

In this article, we would like to report the facile preparation of five acyl-acceptant monomers (3a-e) via Suzuki-Miyaura coupling reaction and their application to effective and regioselective synthesis of aromatic polyketones bearing 1,4-cyclohexanedicarbonyl units through P₂O₅-MsOH-mediated direct condensation. The resulting polyketones 5a-e have sufficiently high thermal stability and excellent organosolubility, and sufficient colorless transparency.

2. Materials and Methods

2.1. Materials

1,3-Dibromobenzene (1a), 1,2-dibromobenzene (1b), 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, 2,2'-biphenol, trans-1,4-cyclohexanedicarboxylic acid (4), and methanesulfonic acid (MsOH) were purchased from Tokyo Chemical Industry Co., Ltd (>98%, Tokyo, Japan). Iodomethane, P₂O₅, and Pd(PPh₃)₄ were purchased from Kanto Chemical Co., Inc(>97%, Tokyo, Japan). N-Bromosuccinimide (NBS) and K₂CO₃ were purchased from Wako Pure Chemicals Industry Ltd (>97%, Osaka, Japan). These reagents were used as received. 1,4-Dioxane, chloroform, and N-dimethylformamide (DMF) were purchased from Kanto Chemical Co., Inc (>97%, Tokyo, Japan) were used after distillation.

Dibromides 1c-e were prepared via the reaction of 1,3-dimethoxybenzene, 1,4-dimethoxybenzene, and 2,2'-dimethoxybiphenyl with NBS in CHCl₃ under reflux in 92, 94, and 98% yields, respectively. 2,2’-Dimethoxybiphenyl was prepared through the reaction of 2-biphenol with CH₃I in the presence of K₂CO₃ in acetone [4]. P₂O₅-MsOH mixture (w/w=1/10) was prepared according to Eaton's procedure [17].

2.2. Instruments

¹H NMR spectra were recorded on a JEOL ECX-400 (400 MHz) spectrometer (JEOL, Tokyo, Japan). Chemical shifts are expressed in parts per million (ppm) relative to the internal standard of Me₄Si (δ=0.00). ¹³C NMR spectra were recorded on a JEOL ECX-400 (100 MHz) spectrometer (JEOL, Tokyo, Japan). Chemical shifts are expressed in parts per million (ppm) relative to the internal standard of CDCl₃ (δ=77.0). IR measurement was recorded on a JASCO FT/IR-4100 (JASCO, Tokyo, Japan). Mass spectra measurements were performed on a JEOL JMS-T100GCV High Performance Gas Chromatograph-Time-of-Flight Mass Spectrometer using FD ionization technique. Gel permeation chromatography (GPC) measurement was carried out at a flow rate of 1.0 mL min^-1 at 40 ^oC using CHCl₃ as an eluent on a JASCO PU-2080 equipped with a UV detector (254 nm) and a Shodex K-804L column (Showa Denko, Tokyo, Japan). Glass transition temperatures (T_g) were estimated on the basis of DSC thermograms. The DSC thermograms (50-300 ^oC) were recorded on a Perkin Elmer DSC 4000 differential scanning calorimeter with a heating rate of 10 K min^-1. Thermal degradation temperatures (T_d) were estimated on the basis of TGA thermograms. The TGA thermograms(50-800 ^oC) were recorded on a Perkin Elmer TGA 4000 thermogravimeter with a heating rate of 10 K min^-1. UV-vis spectra were measured as a coating film on a ca.1.2 mm thin microscope slide on a JASCO V-630 spectrophotometer (JASCO, Tokyo, Japan).

2.3. Preparation of monomers 3a-e

To a 30 mL two-necked flask equipped with a reflux condenser and a N₂ balloon were added dibromoarene (1a-e, 1 mmol), o-methoxyphenylboronic acid (2, 455.9 mg, 3 mmol), Pd(PPh₃)₄ (231.2 mg, 0.2 mmol), K₂CO₃ (829.3 mg, 6 mmol), 1,4-dioxane (6 mL), and H₂O (3 mL). After the mixture was stirred at 90 ^oC for 8 h, it was poured into aqueous 2M HCl in a beaker. The separated aqueous layer was extracted with ethyl acetate three times. The combined extracts were dried over anhydrous MgSO₄. After removal of the drying agent, ethyl acetate was removed under reduced pressure. The residue was purified by column chromatography (CHCl₃) to afford the corresponding monomer 3a-e in 58-97% yields.

Monomer 3a [18]: Yield: 94%. ¹H NMR δ (400 MHz, CDCl₃): 3.81 (6H, s), 6.96-7.07 (4H, m), 7.31 (2H, t, J = 7.8 Hz), 7.36 (2H, d, J = 7.8 Hz), 7.43 (1H, t, J = 6.8 Hz), 7.49 (2H, d, J = 6.8 Hz), 7.67 (1H, s) ppm. ¹³C NMR δ (100 MHz, CDCl₃): 55.7, 111.2, 120.9, 127.7, 128.3, 128.7, 130.7, 130.9, 131.2, 138.3, 156.6 ppm. IR υ(KBr): 1119, 1242, 1463, 1492, 1583, 1599 cm^-1.

Monomer 3b [19]: Yield: 97%. ¹H NMR δ (400 MHz, CDCl₃): 3.47 (6H, s), 6.69 (2H, d, J = 7.8 Hz), 6.81 (2H, t, J = 7.8 Hz), 7.06 (2H, d, J = 7.8 Hz), 7.14 (2H, t, J = 7.8 Hz), 7.39 (4H, s) ppm. ¹³C NMR δ (100 MHz, CDCl₃): 55.0, 110.2, 119.9, 127.2, 128.2, 130.6, 130.6, 131.0, 131.5, 156.3 ppm. IR υ(KBr): 1122, 1181, 1237, 1247, 1432, 1465, 1495 cm^-1.

Monomer 3c [20]: Yield: 87%. ¹H NMR δ (400 MHz, CDCl₃): 3.79 (6H, s), 3.83 (6H, s), 6.64 (1H, s), 6.93-7.01 (4H, m), 7.17 (1H, s), 7.23-7.32 (4H, m) ppm. ¹³C NMR δ (100 MHz, CDCl₃): 55.8, 55.8, 95.9, 111.1, 119.5, 120.4, 127.6, 128.4, 132.0, 134.3, 157.2, 157.3 ppm. IR υ(KBr): 1202, 1241, 1319, 1458, 1480 cm^-1.

Monomer 3d [20]: Yield: 58%. ¹H NMR δ (400 MHz, CDCl₃): 3.72 (6H, s), 3.89 (6H, s), 6.90 (2H, s), 6.98-7.06 (4H, m), 7.31-7.37 (4H, m) ppm. ¹³C NMR δ (100 MHz, CDCl₃): 55.8, 56.6, 111.2, 115.3, 120.5, 127.4, 127.9, 128.8, 131.7, 150.9, 157.1 ppm. IR υ (KBr): 1119, 1248, 1433, 1488, 1513 cm^-1.

Monomer 3e: Yield: 69%. ¹H NMR δ (400 MHz, CDCl₃): 3.81 (6H, s), 3.82 (6H, s), 6.93-7.06 (6H, m), 7.28 (2H, d, J = 7.3 Hz), 7.34 (2H, d, J = 7.3 Hz), 7.49-7.57 (4H, m) ppm. ¹³C NMR δ (100 MHz, CDCl₃): 55.6, 55.8, 110.6, 111.1, 120.8, 127.3, 128.1, 129.8, 130.4, 130.5, 130.9, 133.0, 156.3, 156.5 ppm. IR υ (KBr): 1119, 1253, 1483, 1508 cm^-1. HRMS(FD) calcd for C₂₈H₂₆O₄ 426.1832. found 426.2665.

2.4. Synthesis of aromatic polyketones 5a-e

To a 30 mL one-necked flask equipped with a N₂ balloon were added dibromoarene 3a-e (0.5 mmol), trans-1,4-cyclohexanedicarboxylic acid (4, 86.1 mg, 0.5 mmol), and P₂O₅-CH₃SO₃H mixture (1.5 mL). The mixture was stirred at 60 ^oC for 8 or 24 h(24 h for 5a-d, 8 h for 5e). After dilution with 7.5 mL of MsOH, the mixture was poured into MeOH in a beaker. The precipitate was collected by suction filtration to yield aromatic polyketone 5a-e as white powders in 86-95% yields.

Polyketone 5a: Yield: 86%. ¹H NMR δ (400 MHz, CDCl₃): 1.60-1.85(4H, m), 1.93-2.15 (4H, m), 3.21-3.48 (2H, m), 3.75-4.05 (6H, m), 6.96-7.12 (2H, m), 7.41-7.60 (3H, m), 7.63-7.74 (1H, m), 7.92-8.10 (4H, m) ppm. ¹³C NMR δ (100 MHz, CDCl₃): 28.9, 44.6, 55.9, 110.7, 128.0, 128.7, 129.1, 129.8, 130.7, 131.5, 137.5, 160.5, 202.0 ppm. IR υ (KBr): 1672 cm^-1.

Polyketone 5b: Yield: 92%. ¹H NMR δ (400 MHz, CDCl₃): 1.35-1.83 (8H, m), 2.95-3.11 (2H, m), 3.52-3.68 (6H, m), 6.72-6.83 (2H, m), 7.34-7.48 (2H, m), 7.61-7.68 (2H, m), 7.74-7.83 (2H, m) ppm. ¹³C NMR δ (100 MHz, CDCl₃): 28.9, 44.4, 55.5, 110.3, 127.8, 128.3, 129.5, 130.5, 130.5, 132.0, 137.1, 160.2, 201.1 ppm. IR υ (KBr): 1672 cm^-1.

Polyketone 5c: Yield: 86%. ¹H NMR δ (400 MHz, CDCl₃): 1.62-1.74 (4H, m), 1.96-2.12 (4H, m), 3.24-3.36 (2H, m), 3.76-3.98 (12H, m), 6.62-6.67 (1H, m), 6.96-7.04 (2H, m), 7.14-7.20 (1H, m), 7.90-8.02 (4H, m) ppm. ¹³C NMR δ (100 MHz, CDCl₃): 28.9, 44.6, 55.9, 56.0, 95.7, 110.7, 118.4, 127.2, 128.6, 129.7, 132.8, 134.1, 157.6, 161.1, 202.2 ppm. IR υ (KBr): 1671 cm^-1.

Polyketone 5d: Yield: 95%. ¹H NMR δ (400 MHz, CDCl₃): 1.62-1.74 (4H, m), 1.96-2.12 (4H, m), 3.24-3.36 (2H, m), 3.76-3.98 (12H, m), 6.62-6.67 (1H, m), 6.96-7.04 (2H, m), 7.14-7.20 (1H, m), 7.90-8.02 (4H, m) ppm. ¹³C NMR δ (100 MHz, CDCl₃): 28.9, 44.7, 56.1, 56.6, 110.7, 114.9, 126.8, 127.7, 128.7, 130.1, 132.4, 150.8, 161.0, 202.1 ppm. IR υ (KBr): 1671 cm^-1.

Polyketone 5e: Yield: 87%. ¹H NMR δ (400 MHz, CDCl₃): 1.49-1.83 (4H, m), 1.85-2.19 (4H, m), 3.21-3.43 (2H, m), 3.71-4.05 (12H, m), 6.85-7.16 (4H, m), 7.38-7.65 (4H, m), 7.82-8.14 (4H, m) ppm. ¹³C NMR δ (100 MHz, CDCl₃): 28.9, 44.6, 55.9, 55.9, 110.7, 110.8, 127.2, 129.1, 129.3, 129.4, 129.9, 130.5, 131.4, 132.9, 156.6, 160.5, 202.1 ppm. IR υ (KBr): 1671 cm^-1.

3. Results and Discussion

3.1. Preparation of monomers 3a-e

At first, 1,3-dibromobenzene (1a) was treated with 3 equimolar amounts of o-methoxyphenylboronic acid (2) in the presence of 10 mol% Pd(PPh₃)₄ and 6 equimolar amounts of K₂CO₃ in DMF at 110 ^oC for 8 h. However, the major product wasn't compound 3a but monoarylated arene, due to insufficient reactivity. Next, the reaction was performed in a bilayer system using 1,4-dioxane/H₂O mixed solvents (v/v=2/1) at 90^oC for 8 h, affording compound 3a as a single product in 87% yield. ¹H NMR spectrum of monomer 3a is shown in Figure 2((a), in total)/((b), 6.7-8.2 ppm). The signals(overlapping of a doublet signal and a triplet one) are observed at 6.96-7.07 ppm, which are assignable to the o-protons(d and f, indicated in Figure 2(b)) to OMe group. The signals derived from the central benzene ring are observed at 7.43(triplet, c), 7.49(doublet, b), and 7.67(singlet, a) ppm, respectively. Use of the bilayer system is effective because K₂CO₃ dissolves well in 1,4-dioxane/H₂O. Other monomers 3b-3e were prepared in a similar manner in 58-97% yields. In the reactions of 1d and 1e, the yields decreased to 58 and 69%. ¹H NMR spectra of monomers 3b-e are shown in Figure S1-4.

Scheme 1. Preparation of α,ω-bis(o-methoxyphenyl)arenes 3a-e.

Scheme 1. Preparation of α,ω-bis(o-methoxyphenyl)arenes 3a-e.

Table 1. Preparation of α,ω-bis(o-methoxyphenyl)arenes 3a-e via Suzuki-Miyaura coupling reaction¹.

1	3	Yield/%
1a	3a	94
1b	3b	97
1c	3c	87
1d	3d	58
1e	3e	69

¹Reaction conditions: arene 1a-e (1 mmol), o-methoxyphenylboronic acid (2, 3 mmol), K₂CO₃ (6 mmol), Pd(PPh₃)₄ (0.2 mmol), 1,4-dioxane (6 mL), H₂O (3 mL), 90^OC, 8 h.

Table 1. Preparation of α,ω-bis(o-methoxyphenyl)arenes 3a-e via Suzuki-Miyaura coupling reaction¹.

1	3	Yield/%
1a	3a	94
1b	3b	97
1c	3c	87
1d	3d	58
1e	3e	69

¹Reaction conditions: arene 1a-e (1 mmol), o-methoxyphenylboronic acid (2, 3 mmol), K₂CO₃ (6 mmol), Pd(PPh₃)₄ (0.2 mmol), 1,4-dioxane (6 mL), H₂O (3 mL), 90^OC, 8 h.

3.2. Synthesis of aromatic polyketones 5a-e

Monomers 3a-e were treated with trans-1,4-cyclohexanedicarboxylic acid (4) in P₂O₅-CH₃SO₃H mixture (w/w=1/10) at 60 ^oC for 24 h, affording the corresponding cyclohexanediyl-bearing aromatic polyketones (5a-e)(Table 2). They were characterized by FT-IR, ¹H-NMR, and ¹³C-NMR. IR spectra of polyketones 5a-e have a strong peak at 1671-1672 cm^-1, which is assignable to an aromatic-alicyclic ketone C=O stretching vibration.

¹H NMR spectrum of polyketone 5a is shown in Figure 2((c), in total)/((d), 6.7-8.2 ppm). The signals derived from cyclohexanediyl units are observed at 3.21-3.48 (2H, α-proton to C=O, h’ indicated in Figure 2(c)), 1.93-2.15 (4H, i’), and 1.60-1.85(4H, i’) ppm, respectively. The signal at 6.96-7.12 ppm is assignable to o-proton(2H, d’) to OMe group. The broad signal at 7.41-7.60 ppm is assignable to the protons(3H, b’ and c’) of 1,3-phenylene ring. Appearance of the broad signal at 7.92-8.10 ppm, which is assignable to o-protons(2H, e’ and g’) to C=O groups, indicates that diacylation proceeds at p-positions to the OMe group, regioselectively. ¹H NMR spectra of polyketones 5b-e are shown in Figure S5-S8. In all spectra, the new broad signals above 7.8 ppm are observed like polyketone 5a. In every ¹³C NMR spectrum, the signal assignable to C=O carbon is observed at ~200 ppm. These observations also support that diacylation proceeds certainly. It should be noted that diacylation reaction always occurs at the p-positions to OMe groups of o-methoxyphenyl rings at both ends, regioselectively. Diacylation polymerization of monomers 3a and 3b occurs on more electron-rich aromatic rings at both ends than on the central benzene ring without OMe groups. In monomers 3c and 3d, the central benzene ring, which has two OMe groups, is more electron-rich than the aromatic rings at both ends, which has one OMe group. However, diacylation reaction occurs not on the central benzene ring but on the aromatic rings at both ends. Diacylation reaction at p-positions to OMe group, with less steric hindrance, occurs preferentially over at o/m-positions. It is supported by the fact that diacylation reaction of 2,2’-dimethoxybiphenyl occurs at 5,5’-positions, that is, at p-positions to OMe groups [4,6,16].

Incorporation of two o-methoxyphenyl groups at both ends makes monomers more active. GPC measurement disclosed molecular weights of polyketones 5a-e are sufficiently high (M_w: 9600-35200) as shown in Table 2.

All of polyketones 5a-e are highly soluble in typical organic solvents such as THF, CHCl₃, DMF, and NMP as shown in Table 3. Polyketones 5b-d are more soluble than polyketones 5a and 5e. Incorporation of o-phenylene and dimethoxyphenoxy units as the central aromatic linkers improves the solubility of polyketones 5b-d. Dihedral angles between the aromatic linker and o-methoxyphenyl group at both ends are larger, probably.

Scheme 2. Synthesis of aromatic polyketones 5a-e.

Scheme 2. Synthesis of aromatic polyketones 5a-e.

Table 2. P₂O₅-CH₃SO₃H-mediated synthesis of aromatic polyketones 5a-e¹.

3	5	Time/h	Yield/%	Mn2	Mw2	Mw /Mn 2
3a	5a	24	86	6900	28200	4.1
3b	5b	24	92	8200	14200	1.7
3c	5c	24	86	13200	35200	2.7
3d	5d	24	95	7100	25400	3.6
3e	5e	8	87	6000	9600	1.6

¹Reaction conditions: arene 3a-e (0.5 mmol), trans-1,4-cyclohexanedicarboxylic acid (4, 0.5 mmol), P₂O₅- CH₃SO₃H (1.5 mL), 60^oC.² Estimated by GPC (eluent; CHCl₃) based on polystyrene standards.

Table 2. P₂O₅-CH₃SO₃H-mediated synthesis of aromatic polyketones 5a-e¹.

3	5	Time/h	Yield/%	Mn2	Mw2	Mw /Mn 2
3a	5a	24	86	6900	28200	4.1
3b	5b	24	92	8200	14200	1.7
3c	5c	24	86	13200	35200	2.7
3d	5d	24	95	7100	25400	3.6
3e	5e	8	87	6000	9600	1.6

¹Reaction conditions: arene 3a-e (0.5 mmol), trans-1,4-cyclohexanedicarboxylic acid (4, 0.5 mmol), P₂O₅- CH₃SO₃H (1.5 mL), 60^oC.² Estimated by GPC (eluent; CHCl₃) based on polystyrene standards.

Figure 2. H NMR spectra of monomer 3a(a,b) and aromatic polyketone 5a(c,d).

Figure 2. H NMR spectra of monomer 3a(a,b) and aromatic polyketone 5a(c,d).

3.3. Thermal properties of aromatic polyketones 5a-e

Thermogravimetric analysis (TGA) in a nitrogen stream disclosed that polyketones 5a-e have excellent thermal stability, No weight loss below ca. 400 ^oC is observed. There are no discriminative differences among thermal degradation of the five polyketones. Char yields at 800 ^oC are in the order to 5e(48%)>5d(44%)>5c(32%)>5a(26%)>5b(20%). In most cases, the char yield increases with decreasing the ratio of the alicyclic(cyclohexanediyl) unit.

Glass transition temperatures (T_g) of polyketones 5a-e were estimated by differential scanning calorimetry (DSC). The T_g value of the polyketone derived from 2,2’-dimethoxybiphenyl and 1,4-trans-cyclohexanedicarboxylic acid(4) [16] is 217 ^oC. Compared with this temperature, T_g values of the resulting polyketones (5a-e) are about the same or slightly lower. They are in the order to 5c(219 ^oC)>5e(214 ^oC)>5d(205 ^oC)>5a(201 ^oC)>5b(188 ^oC). Introduction of more OMe groups increases T_g values to some extent due to their polarity(5c-e > 5a,b).

Table 3. Solubility and thermal property of aromatic polyketones 5a-e.

5	Solubility1					Tg/oC2	Td10/oC3
	THF	CHCl3	DMF	DMSO	NMP
5a	++	++	++	+-	++	201	456
5b	++	+	++	+	++	188	447
5c	++	++	++	+	++	219	411
5d	++	++	++	+	++	205	428
5e	++	++	++	+-	++	214	442

¹ ++: soluble at room temperature. +: soluble on heating. +-: partially soluble. -: insoluble. ² Determined on the basis of DSC curve. Heating rate: 10 K/min. ³ Temperature where a 10% weight was lost. Heating rate: 10 K/min.

Table 3. Solubility and thermal property of aromatic polyketones 5a-e.

5	Solubility1					Tg/oC2	Td10/oC3
	THF	CHCl3	DMF	DMSO	NMP
5a	++	++	++	+-	++	201	456
5b	++	+	++	+	++	188	447
5c	++	++	++	+	++	219	411
5d	++	++	++	+	++	205	428
5e	++	++	++	+-	++	214	442

¹ ++: soluble at room temperature. +: soluble on heating. +-: partially soluble. -: insoluble. ² Determined on the basis of DSC curve. Heating rate: 10 K/min. ³ Temperature where a 10% weight was lost. Heating rate: 10 K/min.

Figure 3. TGA thermograms of aromatic polyketones 5a-e.

Figure 3. TGA thermograms of aromatic polyketones 5a-e.

Figure 4. DSC thermograms of aromatic polyketones 5a-e.

Figure 4. DSC thermograms of aromatic polyketones 5a-e.

3.4. Optical properties of aromatic polyketones 5a-e

Figure 5 shows the UV-visible spectra of polyketone films 5a-e(thickness: 3 mm), which were coated by solution casting from CHCl₃ solutions on a glass plate. Light transmittance values of films 3a-e at 400 nm are 95%(5a), 90%(5b), 97%(5c), 84%(5d), and 94%(5e). Cutoff wavelengths range from 290 to 325 nm. All polyketones are sufficiently transparent as transparent materials. Probably, introduction of both alicyclic units and non-coplanar aromatic ones inhibits the interaction between polyketone chains suitably, which improves both organosolubility and transparency. In addition, introduction of alicyclic units inhibits formation of charge transfer complexes causing colorization to pale yellow.

Figure 5. UV-vis spectra of aromatic polyketone films 5a-e(thickness 3 μm).

Figure 5. UV-vis spectra of aromatic polyketone films 5a-e(thickness 3 μm).

4. Conclusions

A series of α,ω-bis(o-methoxyphenyl)arenes(3a-e) are prepared via palladium-catalyzed Suzuki-Miyaura coupling reaction of dibromoarenes with o-methoxyphenyl boronic acid. Aromatic polyketones bearing alicyclic units were synthesized through P₂O₅-MsOH-mediated direct condensation of α,ω-bis(o-methoxyphenyl)arenes(3a-e) with trans-1,4-cyclohexanedicarboxylic acid (4) proceeded effectively and regioselectively to afford aromatic polyketones bearing alicyclic units (5a-e). All of the resulting polyketones exhibit excellent thermal stability, solubility in organic solvents, and transparency. These materials will be applied to high-performance transparent materials such as displays, camera lens, and photolithography.