Chinese Journal of Chemistry, 2005, 23, 200—203 Full Paper

* E-mail: cheng@hqu.edu.cn Received July 5, 2004; revised September 24, 2004; accepted November 2, 2004. Project supported by the Key Natural Science Foundation of Fujian Province (No. E0320003). © 2005 SIOC, CAS, Shanghai, & WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Facile Synthesis of New Aromatic Polyamides Based on 1,2-Dihydro-2-(4-carboxylphenyl)-4-[4-(4-carboxyl-

phenoxy)-3-methylphenyl]phthalazin-1-one

CHENG, Lin*,a(程琳) YING, Leia(应磊) YANG, Xiao-Linga(杨小玲) JIAN, Xi-Gaob(蹇锡高)

a Department of Materials Science & Engineering, Huaqiao University, Quanzhou, Fujian 362021, China b Department of Polymer Science & Engineering, Dalian University of Technology, Dalian,

Liaoning 116012, China

A new monomer diacid, 1,2-dihydro-2-(4-carboxylphenyl)-4-[4-(4-carboxylphenoxy)-3-methylphenyl]phtha- lazin-1-one (3), was synthesized through the aromatic nucleophilic substitution reaction of a readily available un-symmetrical phthalazinone 1 bisphenol-like with p-chlorobenzonitrile in the presence of potassium carbonate in N,N-dimethylacetamide and alkaline hydrolysis. The diacid could be directly polymerized with various aromatic diamines 4a—4e using triphenyl phosphite and pyridine as condensing agents to give five new aromatic poly(ether amide)s 5a—5e containing the kink non-coplanar heterocyclic units with inherent viscosities of 1.30—1.54 dL/g. The polymers were readily soluble in a variety of solvents such as N,N-dimethylformamide (DMF), N,N-dimethyl- acetamide (DMA), dimethylsulfoxide (DMSO), N-methyl-2-pyrrolidinone (NMP), and even in m-cresol and pyri-dine (Py). The transparent, flexible and tough films could be formed by solution casting. The glass transition tem-peratures Tg were in the range of 286—317 ℃.

Keywords poly(arylene ether amide), heterocyclic polymer, high-performance polymer, direct polycondensation, phthalazinone

Introduction

Aromatic polyamides constantly attract much inter-est because of their high-temperature resistance and ex-cellent mechanical properties. To tailor polymer for specific applications, one often has to design and syn-thesize new aromatic heterocyclic monomers that impart the desired properties to the macromolecular polyam-ides. Ideally, the design and synthesis should be flexible enough that many monomers can be derived from a sin-gle or building block. In this way, the features of the core can be incorporated into many polymer systems, leading to a range of new advanced materials.

One of the versatile core, being of recent interest to us, is the 1,2-dihydro-4-(4-hydroxyphenyl)phthalazin- 1-one, which is bisphenol-like monomer found in 1993 by Hay et al.1 There are two kinds of active hydrogen in nonsymmetrical and kink non-coplanar fused heterocyc-lic structure, an active O—H and an active N—H. Ex-perimentally, the acidity of the N—H group is higher than that of O—H group. These monomers could be polymerized by a novel C—N coupling reaction with the activated aryl dihalide monomers to give amorphous high-temperature soluble polymers with very high glass transition temperature, excellent thermal and hydrolytic

stability. Incorporation of the aromatic heterocycles into the polymer backbone will generally increase mechani-cal and adhesive properties as well as transition tem-perature Tg of the polymers, while retain thermal stabil-ity and processability.2 We have prepared the aromatic diamine and polyamides containing phthalazinone moi-ety.3-5 The unique structural feature of the diamines lies in nonsymmetrical and kink non-coplanar conformation of monomer 1. Of particular interests is to investigate the effect of the non-symmetrical and kink non-coplanar but still rigid monomer functionality on the properties of the polymers. In previous articles,6-9 we have demon-strated that introduction of non-symmetrical and kink non-coplanar heterocyclic units into aromatic polymer backbone improved solubility and processability with-out loss of thermal properties in many polymer systems such as poly(arylene ether ketone) and poly(arylene ether sulfone). Phthalazinone derivates can be used as convenient building blocks in the synthesis of poly(aryl amide)s. It was deemed that incorporation of non- symmetrical and kink non-coplanar conformation of phthalazinone compounds would further decrease hy-drogen bonding and intermolecular interactions between polyamide chains and reduced packing efficiency and crystallinity. Moreover, this should promote solubility

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while maintain very high Tg through controlled seg-mental mobility. Furthermore, the incorporation of non-symmetrical and kink non-coplanar conformation of monomer may be more advantageous than the other modifications such as the introduction of flexible link-ages10 and bulky lateral substituents,11 kink noncoplanar biphenylene moieties,12 organometallic complexation13 and hyperbranched or dendritic architectures14 into the aromatic polymer main chains because it minimizes and even avoids the weakening of inherent thermal and me-chanical properties of the polyamides. In the present work, synthesis and characterization of a novel diacid and three new poly(arylene ether amide)s containing phthalazinone moiety and lateral methyl substituents were described. It should be noted that lateral substitu-ent methyl group in the soluble polymer main chain can be further functionalized for special modifications and applications.

Experimental

Materials

Unless specified otherwise, reagent-grade reactants and solvents were used as supplied. NMP and Py were purified from distillation under reduced pressure over calcium hydride and stored over molecular sieves (4 Å). Reagent-grade calcium chloride was dried under vac-uum at 180 ℃ for 6 h prior to use. Triphenyl phosphite (TPP) was freshly vacuum-distilled before use. 1,2-Dihydro-4-(3-methyl-4-hydroxphenyl)phthalazin-1-one (1) and 4c were prepared according to the reported methods.5

Synthesis of monomer 3

Preparation of 2 A 500 mL of three-necked flask containing 1,2-dihydro-4-(3-methyl-4-hydroxyphenyl)- phthalazin-1-one (1, 0.2 mol), 4-chlorobenzonitrile (0.4 mol), potassium carbonate (0.4 mol), DMA (100 mL) and toluene (50 mL) was equipped with a mechanical stirrer, a Dean-Stark trap, a water condenser, a ther-mometer, and a nitrogen inlet. Under an atmosphere of nitrogen, the mixture was heated and maintained at re-flux temperature for 5—6 h to remove all water by means of azeotropic distillation with toluene. The tem-perature was then increased to 150 ℃ to remove tolu-ene for 1 h and then cooled. The mixture was then poured into an ethanol-water mixture (V/V＝1/1, 300 mL). The precipitate was collected on a filter and crys-tallized from DMF and ethanol to give white solid (68.2 g, yield 75%), m.p. 188—189 ℃; 1H NMR (DMSO-d6) δ: 2.32 (s, 3H, CH3), 7.00—7.20 (m, 3H, ArH), 7.50—8.10 (m, 11H, ArH), 8.58—8.65 (m, 1H, ArH8); IR (KBr) ν : 2925 (w, CH3), 2230 (m, CN), 1683 (s, C＝O), 1595 (m, C＝N), 1250 (m, C—O—C) cm－1; EI-MS m/z (%): 454.5 (M＋ , 100). Anal. calcd for C29H18O2N4 (454.487): C 76.64, H 3.99; found C 76.57, H 3.95.

Preparation of 3 A suspention of the intermediate dinitrile 2 (0.095 mol) in 400 mL of 1∶1 volume of

water and ethanol containing potassium hydroxide (0.095 mol) was heated to reflux for 25 h. The resulting clear solution was acidified to pH＝2—3 by concen-trated HCl. The white precipitate was filtered off, washed with water to neutral and dried to give 46.8 g (yield 100%) of diacid 3: m.p. 333—334 ℃; 1H NMR (DMSO-d6) δ: 2.30 (s, 3H, CH3), 6.82—8.21 (m, 14H, ArH), 8.45—8.66 (m, 1H, ArH8); IR (KBr) ν : 3500—2500 (m, COOH), 1677 (s, C＝O), 1595 (m, C＝N), 1245 (m, C—O—C) cm－1; EI-MS m/z (%): 492.5 (M＋, 100). Anal. calcd for C29H20O6N2 (492.485): C 70.73, H 4.09; found C 70.69, H 4.06.

Polymerization

A typical example of direct polycondensation is shown as follows. Polymer 5a from 3 and 4a: A mixture of 3 (0.9850 g, 2 mmol), 4a (0.4005 g, 2 mmol), cal-cium chloride (0.2 g), NMP (4 mL), pyridine (1 mL), and triphenyl phosphite (1.5 mL), was heated with stir-ring at 100 ℃ for 3 h under nitrogen. The obtained polymer solution was slowly poured into methanol (500 mL) with constant stirring, producing fibrous precipitate. Then it was washed thoroughly with methanol and hot water, collected on a filter, and dried at 100 ℃ under vacuum. The yield was 98%.

Measurements 1H NMR spectra were obtained on a Jeol FX 90Q

spectrometer with DMSO-d6 as the solvent and chemical shifts were given relative to tetramethylsilane (TMS). IR measurements were performed on a Nicolet- 20DXB spectrometer. Mass spectra were obtained using a Fin-nigan MAT/SS220 instrument. Differential scanning calorimetry (DSC) was performed at a heating rate of 10 ℃/min under nitrogen on a Dupont 2000 thermal ana-lyzer system. X-ray diffractograms were recorded with an X-ray diffractometer (Philips Model PW 1710), and measurements were performed on powdered samples of the prepared polymers. Inherent viscosities of all poly-mers were measured using an Ubbelohde viscometer at a concentration of 0.5 g/dL in NMP at 25 ℃.

Results and discussion

Monomer synthesis

Aromatic unsymmetrical extended phthalazinone- containing diacid monomer 3 was prepared according to the reaction sequence shown in Scheme 1. There are two kinds of active hydrogens, an active O—H and an active N—H, in non-symmetrical bisphenol-like com-pound 1,2-dihydro-4-(3-methyl-4-hydroxyphenyl)phth- alazin-1-one (1). The acidity of the N—H group is higher than that of O—H group on basis of their differ-ent chemical shifts in the 1H NMR spectra of 1. The phenolate anion and the aza-nitrogen anion, formed in situ by reaction with potassium carbonate under nitro-gen, underwent a nucleophilic displacement reaction with 4-chlorobenzonitrile to give dinitrile compound 2.

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Subsequent alkaline hydrolysis gave a new diacid monomer 3 in high yield. The structure of new mono-mer 3 was confirmed by FT-IR, 1H NMR, EI-MS and elemental analysis. In the IR spectrum of new dinitrile and diacid, the peak at 2230 cm－1 corresponding to ni-trile group in the dinitrile compound 2 disappeared in the diacid monomer 3. The broad band peaks around 3500—2500 cm－1 appeared instead, indicating the pres-ence of carboxyl group. However, the protons for the acid group of 3 in the 1H NMR spectrum were not ob-served. This was probably due to the exchange of the active hydrogen with a trace amount of moisture associ-ated with the solvent.15

Scheme 1 Synthesis of non-symmetrical heterocyclic diacid

Polymer synthesis and characterization

Direct polycondensation of aromatic diacid with aromatic diamines with triphenyl phosphite (TPP) and pyridine (Py) as condensation agents is well known to be a convenient method to prepare aromatic polyamides due to phosphorylation of the diacid and the phos-phorylated acid is more reactive than the pristine diacid. This method was used to prepare a series of new aro-matic polyamides containing the phthalazinone units with inherent viscosities from 1.30 to 1.54 dL/g (Scheme 2). All polyamidations proceeded in homoge-neous, transparent and viscous solutions throughout the reaction, and the polymers were isolated as fibers or powders in quantitative yields. These observations sug-gest that phthalazinone groups in the non-symmetrically extended diacid monomer 3 did not inhibit polymeriza-tion, and large viscosity increases occurred in very short reaction time during polymerization. The polymers ob-tained were identified with IR and NMR spectra. The IR spectra showed characteristic amide absorptions at ca. 3315—3320 and 1660 cm－1, corresponding to amino (N—H stretching) and carbonyl (C＝O stretching)

groups, respectively. 1H NMR spectra in DMSO-d6 confirmed the chemical structures of 5a—5e with amide proton chemical shifts observed at δ ca. 10.0—10.4 and disappearance of the different amine groups of mono-mer 4 at δ ca. 4.5—5.0 indicated complete conversion of the amine groups into amides. Spectroscopic data, together with inherent viscosity and Tg measurements, confirming the structures of polymers were given in Table 1. The wide-angle X-ray scattering of the prepared aromatic polymers was investigated and only a very broad diffraction trace was observed and no sharp peak was found. This demonstrates that all obtained polymers are amorphous due to incorporation of non- symmetrical and kink non-coplanar phthalazinone het-erocyclic structure with lateral methyl substituent.

Scheme 2 Synthesis of poly(aryl ether amide)s containing phth- alazinone moiety

Polymer properties

The thermal behavior and glass transition tempera-tures (Tg) of the polymers were evaluated with differen-tial scanning calorimetric (DSC) means, respectively. The phthalazinone containing polymers showed high Tg up to 317 ℃. The Tg of the polymers was in the range of 286—317 ℃ , indicating their excellent thermal stabilities, which may be due to the presence of rigid aromatic heterocyclic backbone. The polymer 5c has the highest Tg in the prepared aromatic polymers may be due to the most rigid aromatic heterocyclic repeating units in the main chain.

The solubility behavior of the new aromatic poly-

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Table 1 Synthesis and characterization data of polymers 5a—5e

Polymer [η]a Yield/% 1H NMR δ (90 MHz) IR ν/cm－1 Tgb/℃

5a 1.54 98.0 2.32 (s, 3H, CH3), 6.9—8.5 (m, 23H, Ar—H), 10.10— 10.25 (d, 2H, NH)

3315 (N—H), 2850—2950 (m, C—H), 1658 (amide I), 1601 (C＝N)

291

5b 1.30 98.0 2.33 (s, 3H, CH3), 3.9 (s, 2H, CH2), 6.9—7.9 (m, 23H, ArH), 8.4—8.6 (m, 1H, ArH), 10.0—10.2 (d, 2H, NH)

3320 (N—H), 2850—2950 (m, C—H), 1663 (amide I), 1602 (C＝N)

286

5c 1.46 98.0 2.32 (s, 3H, CH3), 6.9—8.5 (m, 31H, ArH), 10.10— 10.15 (d, 2H, N—H)

3320 (N—H), 2850—2950 (m, C—H), 1659 (amide I), 1602 (C＝N)

317

5d 1.32 98.0 2.32 (s, 3H, CH3), 6.9—8.5 (m, 19H, ArH), 10.10— 10.25 (d, 2H, NH)

3315 (N—H), 2850—2950 (m, C—H), 1658 (amide I), 1601 (C＝N)

NDc

5e 1.35 98.0 2.32 (s, 3H, CH3), 6.9—8.5 (m, 19H, Ar—H), 10.10— 10.25 (d, 2H, NH)

3315 (N—H), 2850—2950 (m, C—H), 1658 (amide I), 1601 (C＝N)

ND

a Measured at a concentration of 0.5 g•L－1 in NMP at 25 ℃; b from DSC measurements conducted at a rate of 10 ℃/min in nitrogen; c no Tg detected from DSC scan.

mers (5a—5e) was determined at concentrations of 10% (W/V) in a number of solvents and the results were listed in Table 2. Almost all prepared polymers exhibited high solubility in polar aprotic solvents such as NMP, DMF, DMA, DMSO, and even in less polar solvents like pyri-dine and m-cresol, but were insoluble in chloroform. Transparent and flexible films were easily prepared by solution casting from DMA solution of all polymers. Their high solubility with excellent thermal stability can be attributed to the introduction of non-symmetrical and kink non-coplanar heterocyclic units along polymer backbone and lateral methyl substituent.

Table 2 The solubility of polymers in various solventsa

Polymer DMA NMP DMF DMSO m-Cresol Py CHCl3

5a ＋ ＋ ＋ ＋ ＋ ＋ －

5b ＋ ＋ ＋ ＋ ＋ ＋ －

5c ＋ ＋ ＋ ＋ ＋ ＋ －

5d ＋ ＋ ＋ ＋ ＋ ± －

5e ＋ ＋ ＋ ＋ ＋ ± － a ＋: Soluble at room temperature; ±: soluble at high tempera-

ture; —: insoluble.

Conclusion

Aromatic polyamides containing the phthalazinone moiety and lateral methyl substituent were synthesized from direct polymerization of a new non-symmetrically extended phthalazinone-containing diacid monomer with various aromatic diamines. The introduction of non-symmetrical and kink non-coplanar heterocyclic and methyl units into aromatic polymer backbone re-sulted in the polymers with high thermal stability as well as excellent solubility in common organic solvents.

As to the aromatic polymers both with good solution processability and excellent thermal stability, the pre-pared polymers could be new candidates for processable high-performance polymeric materials.

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(E0407051 LI, L. T.)