Research ArticleReceived: 5 December 2012 Revised: 19 February 2013 Accepted: 21 February 2013 Published online in Wiley Online Library:

(wileyonlinelibrary.com) DOI 10.1002/pi.4515

Synthesis and characterization of noveladamantane-based copoly(aryl ether ketone)swith low dielectric constantsZhi Geng, Yaning Lu, Shuling Zhang, Xu Jiang, Pengfei Huo, Jiashuang Luanand Guibin Wang∗

Abstract

A series of novel adamantane-based copoly(aryl ether ketone)s (PAEK-CF3-Ad) with low dielectric constants were preparedby post-amidation of copoly(aryl ether ketone)s containing (3-trifluoromethyl)phenyl and carboxyl groups with 4-adamantylaniline. Compared with the preparation of adamantane-containing poly(aryl ether ketone)s by direct polymerizationof adamantyl-substituted monomers, this side-chain grafting method avoids various problems, such as high polymerizationtemperature and the difficult polymerization of adamantyl-substituted monomers. The dielectric, thermal and mechanicalproperties of the synthesized PAEK-CF3-Ad were characterized using a precision impedance analyzer, differential scanningcalorimetry and thermogravimetric analysis, and a universal tester, respectively. The results indicate that PAEK-CF3-Ad filmsexhibited low dielectric constants ranging from 2.33 to 2.65 at 1 MHz due to the introduction of the adamantyl groups. Thesynthesized PAEK-CF3-Ad copolymers exhibited good thermal and mechanical properties.c© 2013 Society of Chemical Industry

Keywords: poly(aryl ether ketone)s; adamantane; low dielectric constants; thin films

INTRODUCTIONHigh-performance polymers have attracted considerable attentionover the past decade owing to an increasing demand for theiruse as replacements for metals or ceramics. Poly(aryl etherketone)s (PAEKs) are a class of important high-performancearomatic polymers with excellent mechanical properties, goodsolvent resistance, size-accuracy, good electrical characteristics

and superior thermal stability,1–4 which possess some potentialapplications in aerospace, automobile, electronics and other high-

technology fields.5–9

In recent years, there has been a continuous demand forhigh-temperature materials in microelectronic devices. Therefore,aromatic polymers with low dielectric constants, high thermalstability and good mechanical properties have been widelyinvestigated. Introducing fluorine-containing groups or bulkypendant groups can decrease the dielectric constant of PAEKs. Asa bulky pendant group, adamantane has attracted great interestin recent years. The incorporation of adamantane as a pendantgroup into polymers leads to several property modifications,which include enhancement in glass transition temperature

and reduction in dielectric constant.10–13 However, preparationof adamantane-containing PAEKs by direct polymerization ofadamantyl-substituted monomers is associated with variousproblems such as high polymerization temperature and difficultpolymerization process because of the steric hindrance of the bulkyadamantane groups during polymerization. Moreover, adamantyl-substituted hydroquinone requires very complicated purificationprocedures.14

Therefore, in the work reported here, we first synthesized aseries of soluble copoly(aryl ether ketone)s with various amountsof (3-trifluoromethyl)phenyl groups and carboxyl groups (PAEK-CF3-COOH). Then, a series of novel adamantane-based copoly(arylether ketone)s (PAEK-CF3-Ad) were prepared via post-amidationof PAEK-CF3-COOH with 4-adamantylaniline (NH2-Ph-Ad). Lastly,the dielectric, thermal and mechanical properties of PAEK-CF3-Adwith various molar ratios of adamantyl groups were investigated.

EXPERIMENTALMaterialsTetramethylenesulfone (TMS) was obtained from Jinzhou OilRefinery and purified by vacuum distillation before use. 1-Bromoadamantane (AdBr) was purchased from ChongqingWanlikang Co. Ltd, China. Anhydrous aluminium chloridewas supplied by Beijing Chemical Reagent. Anhydrouspotassium carbonate, oxalyl chloride, dimethylacetamide (DMAc),tetrahydrofuran (THF) and acetanilide were provided bySinopharm Chemical Reagent Co. Ltd, China. Phenolphthalein(PPL) was obtained from TCI Shanghai Development Co Ltd, China.

∗ Correspondence to: Guibin Wang, Engineering Research Centre of HighPerformance Plastics of Ministry of Education, College of Chemistry, JilinUniversity, No. 2699, Qianjin Street, Changchun, 130012, PR China.E-mail: wgb@jlu.edu.cn

Engineering Research Centre of High Performance Plastics of Ministry ofEducation, College of Chemistry, Jilin University, No. 2699, Qianjin Street,Changchun, 130012, PR China

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Scheme 1. Synthesis of 4-adamantylaniline (NH2-Ph-Ad).

(3-Trifluoromethyl)phenyl hydroquinone (3FHQ) was synthesizedin our laboratory according to a published method.15,16 4,4′-Difluorobenzophenone (DFB) was purchased from ChangzhouHuashan Chemical Co. Ltd, China. All other common reagentswere obtained from commercial sources and used as received.

Synthesis of NH2-Ph-AdNH2-Ph-Ad was synthesized as shown in Scheme 1. First, to a250 mL three-necked flask equipped with a mechanical stirrer, anitrogen inlet with a thermometer and a condenser were addedAdBr (15.06 g, 0.07 mol) and acetanilide (108.13 g, 0.80 mol). Thereaction mixture was heated to 120 ◦C and anhydrous aluminiumchloride (1.33 g, 0.01 mol) was added as catalyst. Subsequently,the temperature was increased to 140 ◦C. After 36 h, the obtainedmixed solution was poured into distilled water and further purifiedby precipitation in toluene. Then, the product was dissolved inmethanol and refluxed together with aqueous hydrochloric acidfor 24 h. Finally, anhydrous potassium hydroxide was added intothe solution thus obtained to remove excess hydrochloric acid, anda white powder of NH2-Ph-Ad was obtained after the solution waspoured into distilled water. Yield: 77%. MS: 227.4 [M+]; theoreticalmolecular weight: C16H21N (227.34). Elemental analysis: calcd forC16H21N (227.34): C, 84.53%; H, 9.31%; N, 6.16%; found: C, 84.51%;H, 9.27%; N, 6.22%.

Synthesis of PAEK-CF3-AdCopoly(aryl ether ketone)s containing various mole ratios ofPAEK-CF3-COOH were synthesized via aromatic nucleophilicpolycondensation of 3FHQ, PPL and DFB. To a 100 mL three-necked flask equipped with a mechanical stirrer, a nitrogen inletwith a thermometer and a Dean–Stark trap with a condenser wereadded various mole ratios (0.2, 0.4, 0.6) of PPL, 3FHQ (combinedtotal 0.020 mol) and DFB (4.36 g, 0.020 mol), anhydrous K2CO3

(2.90 g, 0.021 mol), TMS (36 mL) and toluene (20 mL). The systemwas refluxed for 2 h at 120 ◦C, and then the resulting waterand toluene were removed. The reaction mixture was heatedto 160–170 ◦C. After 6 h, the copolymerization was completed.The viscous solution was then poured into distilled water. Theflexible threadlike copolymer was pulverized into powder using ablender. The copolymer powder was washed several times withhot distilled water and alcohol, and dried at 80 ◦C for 24 h to obtaina constant weight. Finally a series of PAEK-CF3-COOH copolymerswith different mole ratios of carboxyl groups (0.2, 0.4, 0.6) wereobtained (Scheme 2). These copolymers are denoted PAEK-CF3-COOH (x), where x represents the molar ratio of carboxyl groupsin the copolymers.

PAEK-CF3-COOH (0.2). Yield: 96%. Gel permeation chromatog-raphy (GPC): Mw: 11.01 × 104 g mol−1; Mn: 7.33 × 104 g mol−1;

polydispersity index (PDI): 1.50. PAEK-CF3-COOH (0.4). Yield: 95%.GPC: Mw: 12.32 × 104 g mol−1; Mn: 7.68 × 104 g mol−1; PDI: 1.60.PAEK-CF3-COOH (0.6). Yield: 94%. GPC: Mw: 10.77 × 104 g mol−1;Mn: 6.89 × 104 g mol−1; PDI: 1.56.

Finally, PAEK-CF3-Ad copolymers were prepared via post-amidation of the synthesized PAEK-CF3-COOH with NH2-Ph-Ad,as illustrated in Scheme 2. First, 2 g of PAEK-CF3-COOH (PAEK-CF3-COOH (0.2), PAEK-CF3-COOH (0.4) or PAEK-CF3-COOH (0.6))was dissolved in THF at room temperature, and two times moleratio (compared with carboxyl groups of PAEK-CF3-COOH) oxalylchloride was added. Subsequently, the mixed solution was stirredfor about 24 h at room temperature, ensuring that the carboxylgroups were completely changed into acyl chloride groups, andthe solvent and the excess oxalyl chloride were removed byvacuum distillation. Then, the product was dissolved in THF andtwo times mole ratio (compared with acyl chloride groups ofthe copolymers) NH2-Ph-Ad was added into the solution thusobtained, which was stirred for about 48 h at room temperature.Finally, the homogeneous solution was poured into alcohol andthe obtained copolymer powder was washed several times withalcohol to remove completely the excess NH2-Ph-Ad. After dryingat 80 ◦C under vacuum for 24 h, a series of PAEK-CF3-Adcopolymers was obtained. These are denoted PAEK-CF3-Ad (x),where x represents the molar ratio of adamantyl groups in thecopolymers.

PAEK-CF3-Ad (0.2). Yield: 96%. GPC: Mw: 12.28 × 104 g mol−1;Mn: 8.12 × 104 g mol−1; PDI: 1.51. PAEK-CF3-Ad (0.4). Yield: 95%;GPC: Mw: 14.32 × 104 g mol−1; Mn: 9.18 × 104 g mol−1; PDI: 1.56.PAEK-CF3-Ad (0.6). Yield: 94%; GPC: Mw: 13.57 × 104 g mol−1; Mn:8.52 × 104 g mol−1; PDI: 1.59.

MeasurementsFourier transform infrared (FTIR) spectra (KBr) were obtained usinga Nicolet Impact 410 FTIR spectrometer. 1H NMR spectra wererecorded with a Bruker 510 instrument. Mass spectra were obtainedusing a Shimadzu Axima-CFR mass spectrometer (Japan) with THFas a solvent. Elemental analyses were carried out with a Mod-1106elemental analyzer. GPC was carried out using polystyrene as astandard using a Waters 410 instrument with THF as eluent ata flow rate of 1 mL min−1. DSC measurements were performedwith a Mettler-Toledo DSC 821e instrument. TGA was carried outusing a PerkinElmer TGA-7 instrument in a nitrogen atmosphere.Mechanical properties of rectangular films (45.0 × 5.0 × 0.1 mm3,cast from DMAc onto glass plates) were evaluated at roomtemperature with a Shimadzu AG-I universal tester at a strainrate of 10 mm min−1. The dielectric constants of thin films (area of5.5 mm × 5.5 mm and thickness of 0.1 mm, prepared by castingfrom DMAc onto glass plates, and then coating with silver using

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Scheme 2. Synthesis of adamantane-based copoly(aryl ether ketone)s (PAEK-CF3-Ad).

a vacuum evaporation method) were obtained using a Hewlett-Packard 4285A apparatus at room temperature.

RESULTS AND DISCUSSIONStructural characterizationThe structure of the synthesized NH2-Ph-Ad was confirmed from its1H NMR spectrum with deuterated dimethylsulfoxide (DMSO-d6)as a solvent, as shown in Fig. 1. The peaks from 1.5 to 2.2 ppm areassigned to the adamantyl groups, while the double peaks from 6.5to 7.0 ppm are assigned to the phenyl groups and the single peakat 4.8 ppm is assigned to the amino groups. The coupling constantJ and H number from the 1H NMR spectrum of the synthesizedNH2-Ph-Ad are as follows: 1.671–1.729 (t, 6H, J1 = 15.485 Hz,J2 = 13.168 Hz), 1.768–1.772 (d, 6H, J = 2.625 Hz), 2.013 (s, 3H),4.774 (s, 2H), 6.481–6.498 (d, 2H, J = 8.526 Hz), 6.973–6.991 (d,2H, J = 8.552 Hz). Figure 1 confirms that NH2-Ph-Ad had beensynthesized successfully.

The structures of the synthesized PAEK-CF3-COOH (0.2) and thecorresponding PAEK-CF3-Ad (0.2) were confirmed from their 1HNMR spectra with CDCl3 as a solvent, as shown in Fig. 2. From acomparison of the spectra, the peaks near 2.0 ppm can be assignedto the adamantyl side groups present in PAEK-CF3-Ad. Thecoupling constant J and H number from the 1H NMR spectra of thesynthesized PAEK-CF3-COOH (0.2) and adamantane-functionalizedPAEK-CF3-Ad (0.2) are as follows: 6.901–6.940 (t, 2H, J1 = 9.107 Hz,J2 = 10.5 Hz), 7.004–7.014 (d, 8H, J = 5.458 Hz), 7.113–7.217 (m,11H), 7.258 (s, 1H), 7.471 (s, 1H), 7.552 (s, 1H), 7.665–7.790 (m, 9H),

Figure 1. 1H NMR spectrum of NH2-Ph-Ad in DMSO-d6.

7.859–7.874 (d, 1H, J = 7.595 Hz), 8.054–8.067 (d, 1H, J = 6.637Hz). In summary, from Fig. 2, it is evident that NH2-Ph-Ad hadbeen successfully grafted onto the side-chains of PAEK-CF3-COOHand that adamantane-functionalized PAEK-CF3-Ad copolymer hadbeen synthesized successfully.

The structures of the synthesized NH2-Ph-Ad, PAEK-CF3-COOHand PAEK-CF3-Ad were further confirmed from their FTIR spectra,

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Figure 2. 1H NMR spectra of PAEK-CF3-COOH (0.2) and PAEK-CF3-Ad (0.2)in CDCl3.

as shown in Fig. 3. Figure 3(g) confirms the chemical structureof the synthesized NH2-Ph-Ad: 1514 and 1620 cm−1 (benzenering), 2857 and 2921 cm−1 (adamantyl groups), 3372 and 3468cm−1 (N–H bond of primary amine). Figures 3(a)–(c) confirmthe chemical structure of the synthesized PAEK-CF3-COOH: 1125and 1162 cm−1 (−CF3 groups), 1225 cm−1 (Ar–O–Ar in themain-chain), 1497–1474 and 1598 cm−1 (benzene ring), 1654cm−1 (C O bond of aromatic ketone in the main-chain), 1721cm−1 (C O bond of aromatic carboxyl groups in the side-chain).Figures 3(d)–(f) confirm the chemical structure of the synthesizedPAEK-CF3-Ad: 1125 and 1162 cm−1 (−CF3 groups), 1225 cm−1

(Ar–O–Ar in the main-chain), 1497–1474 and 1598 cm−1 (benzenering), 1540 cm−1 (N–H bond of acid amide), 1654 cm−1 (C Obond of aromatic ketone in the main-chain), 2857 and 2921 cm−1

(adamantyl groups). From a comparison of the FTIR spectra, it isobserved that the characteristic absorption peak at 1721 cm−1 ofC O bond of aromatic carboxyl groups does not appear in thespectra of PAEK-CF3-Ad. Also, the characteristic absorption peakat 1540 cm−1 of N–H bond of acid amide and the characteristicabsorption peaks at 2857 and 2921 cm−1 of adamantyl groupsappear in the spectra of PAEK-CF3-Ad. The FTIR results furtherconfirm that NH2-Ph-Ad, PAEK-CF3-COOH and PAEK-CF3-Ad hadbeen synthesized successfully.

Dielectric properties of PAEK-CF3-AdFigure 4 shows that the dielectric constants of the novel PAEK-CF3-Ad copolymer films are noticeably lower (κ = 2.33–2.65 at1 MHz) than that of pristine commercial PAEK (κ = 3.27 at 1 MHz)under the same measurement conditions. Moreover the dielectricconstants of these copolymers decrease with increasing molarratio of adamantyl groups. Introduction of adamantyl and (3-trifluoromethyl)phenyl groups into the copolymers decreases thedielectric constant due to an increase in the free volume anda decrease in the electronic polarizability.17–19 The dielectricconstant data suggest that the adamantyl groups can moreeffectively decrease the dielectric constant compared to the (3-trifluoromethyl)phenyl groups, which may be ascribed to thefact that the adamantyl group is a fully aliphatic hydrocarbon,leading to lower polarity in addition to increasing the free

Figure 3. FTIR spectra: (a) PAEK-CF3-COOH (0.2); (b) PAEK-CF3-COOH (0.4);(c) PAEK-CF3-COOH (0.6); (d) PAEK-CF3-Ad (0.2); (e) PAEK-CF3-Ad (0.4); (f)PAEK-CF3-Ad (0.6); (g) NH2-Ph-Ad.

Figure 4. Frequency dependence of dielectric constants of PAEK-CF3-Adfilms.

volume of the copolymers at a larger scale. Also, comparedwith the dielectric constants of the adamantane-containing PAEKs(κ = 2.62–2.72 at 1 MHz) that we reported previously,14 the PAEK-CF3-Ad copolymers under investigation have conspicuously lowerκ values. The reason may be that the adamantyl phenyl groupsof PAEK-CF3-Ad in the present case can increase the free volumemore effectively than the adamantyl groups in the copolymers thatwe studied previously. Additionally, the dielectric loss factors (at1 MHz) for these copolymer films have very low values of between1.4 × 10−2 and 2.3 × 10−2. In other words, the side-chain graftingmethod described is an effective and simple way to prepareadamantane-based PAEKs with low dielectric constants.

Thermal properties of PAEK-CF3-AdThe thermal properties of the PAEK-CF3-Ad series of copolymerswere investigated using DSC and TGA and the results are presentedin Table 1. The glass transition temperature (Tg) of the copolymersis in the range 153–183 ◦C, and it increases with increasingmolar content of adamantyl groups. Introduction of bulky rigidadamantyl groups leads to an increased rigidity of the copolymerchains and blocks the movement of segments. As a result, Tg

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Table 1. Thermal properties of PAEK-CF3-Ad

Sample Tg (◦C)a DT5 (◦C)b DT10 (◦C)c

PAEK-CF3-Ad (0.2) 153 370 394

PAEK-CF3-Ad (0.4) 171 357 376

PAEK-CF3-Ad (0.6) 183 330 344

a From the second DSC heating trace conducted at a heating rate of20 ◦C min−1.b 5% weight loss temperature measured using TGA at a heating rateof 10 ◦C min−1 in nitrogen.c 10% weight loss temperature measured using TGA at a heating rateof 10 ◦C min−1 in nitrogen.

Table 2. Mechanical properties of PAEK-CF3-Ad

Sample

Tensile

strength (MPa)

Young’s

modulus (GPa)

Elongation

at break (%)

PAEK-CF3-Ad (0.2) 80.5 1.80 32.3

PAEK-CF3-Ad (0.4) 72.6 1.91 24.1

PAEK-CF3-Ad (0.6) 66.8 1.72 20.7

increases with increasing molar content of adamantyl groups.Moreover, the TGA data reveal that the copolymers exhibit goodthermal stability: the temperature of 5% weight loss for PAEK-CF3-Ad is above 330 ◦C in nitrogen, and the temperature of 10% weightloss is above 344 ◦C in nitrogen.

Mechanical properties of PAEK-CF3-AdThe mechanical properties of PAEK-CF3-Ad thin films aresummarized in Table 2. The copolymer films have tensile strengthof 66.8–80.5 MPa, Young’s modulus of 1.72–1.91 GPa andelongation at break of 20.7–32.3%. Their tensile strength andelongation at break slightly decrease with increasing molar ratioof adamantyl groups, but these PAEK-CF3-Ad copolymer films stillexhibit a good strength. Also, comparing with the mechanicalproperties of the adamantane-containing PAEKs that we reportedin a previous publication, these PAEK-CF3-Ad copolymers havenoticeably higher elongation at break values. In other words, thePAEK-CF3-Ad copolymer films have much better toughness thanthe adamantane-containing PAEKs that we studied previously.14

CONCLUSIONSA series of novel adamantane-based PAEK-CF3-Ad copolymershave been facilely synthesized via a mild post-amidation reaction.Moreover, the synthesized PAEK-CF3-Ad exhibited low dielectricconstants ranging from 2.33 to 2.65 at 1 MHz and low dielectriclosses due to the introduction of adamantyl groups. Thecopolymers also had good thermal and mechanical properties.In other words, the synthesized adamantane-based PAEK-CF3-Adhave the potential for applications in microelectronic devices.

ACKNOWLEDGEMENTThe authors gratefully acknowledge financial support from theNational Nature Science Foundation of China (51073066).

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