Synthesis and Characterization of Halogen-ContainingPoly(ether ketone ketone)s

CAROLINA GARCIA, ANGEL E. LOZANO, JOSE G. DE LA CAMPA, J. DE ABAJO

Instituto de Ciencia y Tecnologıa de Polımeros, Consejo Superior de Investigaciones Cientificas, Juan de la Cierva 3,28006 Madrid, Spain

Received 7 February 2002; accepted 8 May 2002Published online 00 Month 2002 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/pola.10351

ABSTRACT: A series of novel poly(ether ketone ketone)s (PEKKs) were synthesizedfrom diphenyl ether and isophthaloyl chloride derivatives such as 5-halo- and 5-tert-butyl-isophthaloyl chloride. The aromatic electrophilic substitution route to poly-ketones was a convenient route for the preparation of the polymers in high yields viaprecipitation polycondensation at a low temperature with aluminum trichloride as acatalyst. High molecular weight PEKKs were achieved with number-average molecularweights of 15,000–100,000 g/mol for polymers that showed good solubility in organicsolvents. The presence of substituents greatly modified the spectroscopic features incomparison with those of unsubstituted isophthaloyl poly(ether ketone ketone)s, par-ticularly for the series containing halogens, for which significant variations of thechemical shifts in both 1H and 13C NMR spectra were observed; these shifts could berelated to the nature of the halogen. Thermal properties were also affected by thepresence of pendent substituents, with clear enhancements of the glass-transitiontemperatures, which could be ascribed to the nature and bulkiness of the substituents.Thermogravimetric analyses showed that the new polymers had good thermal resis-tance, although an important drop in thermal resistance was observed for polymersbearing large halogen atoms, such as bromine and iodine. © 2002 Wiley Periodicals, Inc. JPolym Sci Part A: Polym Chem 40: 2601–2608, 2002Keywords: amorphous; halogenated; NMR; poly(ether ketone)s; precipitation poly-condensation; solubility; thermal properties

INTRODUCTION

Aromatic polyketones, particularly poly(arylether ketone)s, are recognized as polymers of su-perior thermal and mechanical properties.1,2 Ar-omatic poly(ether ether ketone)s (PEEKs), for in-stance, have found special importance as struc-tural materials for applications in advancedtechnologies (e.g., the electronics and aerospaceindustries).3 As with other high-performancepolymers, molecular order and structural rigidity

are responsible for the desirable features of thesespecial polymer materials, but these characteris-tics are responsible also for the remarkable in-tractability of the majority of them.

Most high-performance polymers, such as aro-matic polyamides, aromatic polyimides, poly(phe-nylene sulfide), and poly(ether sulfone), are con-densation polymers that contain mostly para-phenylene rings and polar groups in their mainchain, which make for high molecular packingand high transition temperatures, leading to dif-ficulties in processing. The molecular order can bedisrupted by various approaches, the most effi-cient of which is the incorporation of meta-ori-ented phenylene rings and the presence of bulkypendent substituents. In fact, there are many re-

Correspondence to: J. de Abajo (E-mail: deabajo@ictp.csic.es)Journal of Polymer Science: Part A: Polymer Chemistry, Vol. 40, 2601–2608 (2002)© 2002 Wiley Periodicals, Inc.

2601

cent examples of how these general approacheshave permitted substantial improvements in thesolubility (tractability) of aromatic polyimides,4–6

polyesters,7 and polyamides.8–11 Tractable poly-ketones containing meta-phenylene moieties orside bulky groups have also been reported by anumber of authors.12–15 Another approach to pro-cessable aromatic polymers, which has also beenapplied to aromatic polyketones, is the prepara-tion of reactive oligomers.16,17

The purpose of this work was the preparationand evaluation of novel poly(ether ketone ke-tone)s (PEKKs) with improved processability andproperties by the use of meta-oriented monomersthat, at the same time, contained halogen atomsas substituents. A series of halogens from fluorinethrough iodine were incorporated in this way intothe chemical structures of PEKKs as pendentsubstituents, and the effects of these modifica-tions on the general properties were studied. Thespectral data, solubility, and thermal propertieswere determined and are discussed with respectto the chemical composition, particularly the na-ture of the halogen atoms.

EXPERIMENTAL

Materials

3,5-Dimethylaniline was purified by distillationat reduced pressure (bp � 110 °C at 10 mmHg).Isophthaloyl chloride and diphenyl ether were pu-rified by vacuum distillation before use. Solventsand reactants were used as received unless oth-erwise noted.

Intermediates and monomers were preparedby synthetic routes previously reported. Thismeant the preparation of 5-halo-m-xylenes, 5-halo-isophthalic acids, and the final monomers, 5-halo-isophthaloyl chlorides.18

Polymer Synthesis

Polymerizations were carried out in 1,2-dichloro-ethane from 5-halo-isophthaloyl chlorides and di-phenyl ether in the presence of aluminum trichlo-ride. The general method of synthesis was as fol-lows. A 300-mL, three-necked flask equipped witha magnetic stirrer and a thermometer wascharged with 0.01 mol of diphenyl ether, 0.01 molof the corresponding diacid chloride, and 100 mLof dichloroethane. The colorless solution wascooled to �15 °C, 0.028 mol of aluminum chloride

was added to the solution, and the reaction mix-ture was stirred for 30 min. The temperature wasthen raised to 20 °C over 2 h, and the reaction wasallowed to proceed for 6 h at room temperature.The polymer precipitate was filtered off, washedwith ethanol several times, extracted with boilingethanol for 20 h in a Soxhlet instrument, anddried at 100 °C overnight in vacuo.

Measurements

Microanalyses were carried out by the analysisservice of the Centro Nacional de Quımica Or-ganica in Madrid. Inherent viscosities were mea-sured with an automated Ubbelohde viscometer,with concentrated H2SO4 as a solvent for all poly-mers at a 0.5 g/dL concentration at 25.0 � 0.1 °C.1H and 13C spectra were obtained with a VarianGemini 200 spectrometer operating at 200 and50.38 MHz, respectively, with CDCl3 as a solventand tetramethylsilane as an internal reference.The transmission infrared spectra of monomersand polymers were recorded on a Nicolet 520 Fou-rier transform infrared instrument. Gel perme-ation chromatography experiments were carriedout on a device consisting of a Waters 510 pump,a set of three PL columns of the nominal poresizes 500, 103, and 104 Å, and a Phillips PyeUnicam PU 4025 ultraviolet detector. Chloroformwas used as a solvent, and the analyses werecarried out at room temperature at a flow rate of1.0 mL/min. The molecular weights of the poly-mers were calculated with the aid of polystyrenestandards. Differential scanning calorimetry(DSC) and thermogravimetric analysis (TGA)were performed with PerkinElmer DSC 7andTGA 7 analyzers, respectively. All of the sampleswere tested under nitrogen, at 10 °C/min for TGAand at 20 °C/min for DSC.

RESULTS AND DISCUSSION

Synthesis of the Monomers and Polymers

Polyaryl(ether ketone)s are commonly preparedby two general methods: (1) a synthesis involvingan aromatic electrophilic substitution that yieldsan aryl ketone linkage and (2) a route involvingan aromatic nucleophilic substitution in which anaryl ether linkage is obtained.19 The method ap-plied in this work was the electrophilic one; con-sequently, the first step consisted of the prepara-tion of a set of electrophilic monomers, more pre-

2602 GARCIA ET AL.

cisely, halogen-containing derivatives of isoph-thaloyl chloride.

The synthesis of these 5-halo-isophthaloylchloride monomers was carried out by a multistepsynthetic route, starting from commercially avail-able 3,5-dimethylaniline, as shown in Scheme 1.The classical Sandmeyer reaction was chosen tosynthesize the intermediates 3,5-dimethylchloro-benzene, 3,5-dimethylbromobenzene, and 3,5-dimethyliodobenzene, and a general method forthe introduction of fluorine into the aromatic nu-cleus was used for the synthesis of 3,5-dimethyl-fluorobenzene.20

The oxidations of 3,5-dimethylhalobenzenes tohalo derivatives of isophthalic acid were accom-plished with potassium permanganate in a pyri-dine/water (1:2) mixture, which allowed for thereactions to be performed at a convenient pH. Infact, substantially higher yields than previouslyreported18 could be achieved. The 5-halo-isoph-thaloyl chlorides were prepared from the corre-sponding diacids in good yields by a reaction withthionyl chloride. They could be purified to poly-condensation-grade monomers by conventionalmeans.

The synthesis of polymers was performed bythe route depicted in Scheme 2. For the polycon-densation of electrophilic halogenated isophtha-loyl chlorides with the nucleophile diphenyl ether,a process defined as precipitation polycondensa-

tion was chosen. This approach has recently beenimplemented as a suitable method for preparinghigh molecular weight polyketones under mildconditions.15,21 This technique was used in thiswork, with an initial reaction temperature be-tween �15 and 0 °C, which was found to be themost effective. In the course of the reaction, apolymer/catalyst complex precipitated from thereaction media in the form of swollen, isolatedparticles. After completion of the reaction, thepolymer particles formed were isolated from thereaction media in high yields (Table 1).

Data for related PEKKs have been includedin Table 1 for comparison. Therefore, polymerPEK-H can be considered a reference because it isa nonhalogenated polymer prepared from isoph-thaloyl chloride and diphenyl ether. PolymerPEK-tert-but can be assigned to the same familyof modified PEKKs because it is prepared fromthe same nucleophile and 5-tert-butyl-isophtha-loyl chloride.15

The polymers were identified by spectroscopicmeans. As an example, the 1H NMR spectrum ofpolymer PEK-Br has been reproduced in Figure 1.As can be seen, all the signals could be properlyassigned, as was also the case for the otherPEEKs investigated. 13C NMR spectra were alsoconsistent with the chemical compositions of all ofthe polymers listed in Table 1.

Scheme 1. Synthesis of the 1,3-dimethyl-5-halobenzene monomer precursors.

HALOGEN-CONTAINING POLY(ETHER KETONE KETONE)S 2603

Aside from the simple identification of poly-mers, some interesting features could be observedin the NMR spectra. It was noted that the natureof the halogen greatly affected the 1H NMR spec-tra as the chemical shift of the isophthalic ringprotons shifted downfield when halogen electro-negativity decreased, with a more marked effecton the protons in the ortho position with respect

to the halogen. 13C NMR spectra were also quiteconclusive because the nature of the halogenclearly affected the signal shifts. In this case, thecarbon directly joined to the halogen (C ipso)showed the largest shift variation, the nature ofthe halogen playing a determinant role for thesign of the shifting effect, either upfield or down-field. Therefore, although the strong �I effect offluorine moved downfield the resonance peak ofipso carbons, the big, polarizable electronic cloudof iodine caused a predominant �M effect, withthe signals of ipso carbons moving upfield.

In an attempt to quantitatively evaluate theseeffects, we estimated the electronic density in thevicinity of ipso carbons by quantum mechanicalcalculations with the semiempirical methodAM1.22 By this method, the theoretical chargedensities of Mulliken-Coulson on the isophthalicring were calculated, with the molecular modeldepicted in Figure 2. A plot of the charge versusthe chemical shift for ipso and ortho carbons isshown in Figure 3, in which a good correlationbetween calculated and NMR experimental datacan be observed.

Polymer Properties

Gel permeation chromatography and solution vis-cosity results are given in Table 1. For sampleswith a narrower molecular distribution, polymerswere extracted with methyl ethyl ketone to elim-inate low molecular weight fractions and oli-gomers. Despite this, polydispersity indices of2.3–4.5 were measured for number-average mo-lecular weights (Mn’s) of soluble polymers of15,000–109,000 g/mol. The relatively high poly-

Scheme 2. Synthesis of PEKKs from diphenyloxideand 5-haloisophthaloyl chlorides.

Table 1. Synthesis and Characterization of PEKKs

Polymer

Elemental Analysisa

�inh (dL/g)b Mn (g/mol)c Mw (g/mol)c Mn (g/mol)d Mw (g/mol)dC (%) H (%)

PEK-He 78.17 (80.00) 3.96 (4.00) 2.3 — — — —PEK-F 73.21 (73.61) 3.67 (3.37) 0.32 12,000 33,000 18,000 43,000PEK-Cl 70.36 (71.75) 3.47 (3.28) 0.43 9,000 31,000 16,000 38,000PEK-Br 63.02 (63.34) 2.94 (2.90) 0.40 11,000 37,000 15,000 42,000PEK-I 55.36 (56.33) 2.67 (2.58) 0.35 16,000 57,000 21,000 68,000PEK-tert-but 80.55 (80.89) 5.89 (5.61) 0.65 11,000 84,000 24,000 109,000

a Theoretical percentages are in parentheses.b In concentrated H2SO4 at 25 °C.c As prepared.d Extracted with methyl ethyl ketone.e PEK-H was insoluble in DMF � LiBr.

2604 GARCIA ET AL.

dispersity [weight-average molecular weight/number-average molecular weight (Mw/Mn)] val-ues can be attributed to the method of polymersynthesis. Table 1 shows the average molecularweights found for extracted and nonextractedpolymer samples. A significant improvement wasachieved in every case upon the extraction of thepolymers with methyl ethyl ketone. Inherent vis-cosities followed the same trend as the molecularweights, with the polymer PEK-tert-but showingthe highest inherent viscosity and Mw values, 0.7dL/g and 109,000 g/mol, respectively.

This result is interesting because a higher re-activity (higher molecular weight) should be ex-pected for halogenated monomers than for 5-tert-

butylisophthaloyl chloride, and the reason for thevery high molecular weight achieved for polymerPEK-tert-but then should be associated with itsbetter solubility in the reaction media, which pre-vented it from premature precipitation.

All PEKKs obtained in this work were solublein sulfuric acid and highly polar protic solvents,such as trifluoroacetic acid or cresols, and inhighly polar solvents as well; most of them weresoluble even in common organic solvents, such astetrahydrofuran (THF) or chloroalkanes. Thismeans a significant advance over conventionalPEKs previously reported, which were insolublein common organic solvents, as is the unsubsti-tuted polymer PEK-H. Transparent, tough filmscould be made from all of the PEKKs of this reportby film casting and solvent evaporation for poly-mer solutions in chloroform, except for polymerPEK-H, which had to be dissolved in a 1:1 mix-ture of trifluoroacetic acid and tetrachloroethane.

Thermal properties were investigated withDSC and TGA. Results of measurements con-ducted in nitrogen are given in Table 2. Only thepolymer PEK-H showed a crystallization exo-therm at about 310 °C, whereas the other PEKKsshowed no crystallization exotherm. In fact, nomelting endotherm, and only an inflection in thecurve of the heat capacity versus the tempera-

Figure 1. 1H NMR spectrum of polymer PEK-Br.

Figure 2. Molecular model for the calculation ofcharge densities.

HALOGEN-CONTAINING POLY(ETHER KETONE KETONE)S 2605

ture, could be detected, and this was associatedwith the glass-transition temperature (Tg). There-fore, it can be stated that the only crystallizablespecies is polymer PEK-H and that substitutedPEKKs of this report are essentially amorphous.A microstructure study performed by wide-angle

X-ray scattering (WAXS) did confirm that thesubstituted PEKKs were amorphous because theygave WAXS diagrams with no diffraction peaks,showing only the typical halo of amorphous ma-terials.

It is worth noting that Tg values followed atrend that is related to the size of the substituentson the 5-position of the isophthaloyl moiety.Therefore, the bigger the volume was of the halo-gen, the higher the Tg was, with a minimum forfluorine (150 °C) and a maximum for iodine (194°C), even though the polarity of the halogen de-creases with increasing atomic volume, so thatmost of the Tg increments must be attributed to aloss of rotational freedom, which surpasses otherattraction forces that could be due to the dipolarnature of the carbon–halogen bonds. This effecthas been illustrated in Figure 4, which shows aplot of Tg versus the halogen size for the series ofsubstituted PEKKs. An excellent linearity can beobserved, which indicates that the volume of thesubstituents plays the most determinant role for

Figure 3. 13C NMR chemical shifts versus the charge density of carbon atoms next tohalogens.

Table 2. Properties of PEKKs

Polymer

Solubilitya

Tg

(°C)Td

(°C)bYc

(%)cNMP THF CHCl3

PEK-H – – – 159 590 62PEK-F �� �� �� 150 585 67PEK-Cl �� �� �� 164 575 65PEK-Br �� �� �� 179 550 60PEK-I �� �� �� 194 470 56PEK-tert-but �� �� �� 179 520 53

a �� � soluble at room temperature; – � insoluble.b Temperature of 10% weight loss by TGA.c Char yield at 700 °C.

2606 GARCIA ET AL.

the elevation of Tg. This behavior was consistentwith earlier results reported for halo poly-amides.18 Nevertheless, the polymer PEK-tert-but did not show the highest Tg, although thetert-butyl group is the bulkiest. This phenomenoncan be explained by the nonpolar nature of thetert-butyl group and the polar nature of carbon–halogen bonds. Polymer PEK-H also did not fol-low the trend because hydrogen has a lower vol-ume than fluorine and PEK-H showed a Tg (159°C) higher than that of PEK-F (150 °C). The semi-crystalline character of PEK-H should account inthis case for the elevation of Tg of PEK-H.

Dynamic thermogravimetry in nitrogen wasused to study the thermal stability of the variouspolymers; the results of the study are given inTable 2. All of the polymers showed a decomposi-tion temperature (Td) well above 400 °C, as wasexpected for aromatic condensation polymers.However, it must be pointed out that the incorpo-ration of halogens produced a decrease in Td inevery case, and that this effect also had to do withthe nature of the substituents. The nature of thehalogen also influenced the value of Td, and so thehigher the dissociation energy was of the carbon–halogen bond, the higher Td was, with the highestTd (585 °C) for PEK-F and the lowest Td (470 °C)for PEK-I. The dissociation energy of the carbon–halogen bond follows the trend COF � COCl� COBr � COI,23 which is the opposite of theorder for the volume of the halogens, so that Tdcould also be related to the volume of the halogen,

with the highest Td in this case for the unsubsti-tuted PEK-H, which showed a Td value of 590 °C.PEK-tert-but showed a reasonably high Td valueof 520 °C.

CONCLUSIONS

5-Halo- and 5-tert-butyl-substituted derivativesof isophthaloyl chloride have proven to be suitablecondensation monomers for the preparation ofPEKKs in combination with nucleophiles such asdiphenyl ether. High molecular weight PEKKswere attained by precipitation polycondensationwith 5-halo- and 5-tert-butyl-isophthaloyl chlo-rides as electrophiles. The presence of substitu-ents on the 5-position of the isophthaloyl mono-mer greatly improved the solubility in organicsolvents with respect to PEEKs prepared fromjust isophthaloyl chloride, which are in turn vir-tually insoluble in common organic solvents.

Polymers of this class are essentially amor-phous, with good film-forming capabilities; theyshow relatively high Tg’s, ranging from 150 to 190°C (ca. 145 °C for commercial PEEKs). The natureof the substituent on the 5-position of the isoph-thaloyl moiety greatly affected Tg, which in-creased with an increase in the size of the sub-stituent. This effect could even be quantified forthe series of halogens as a linear relationshipbetween the Tg value and the volume of the sub-stituents. The thermal resistance, as revealed byTGA, did not drop much for substituents such asfluorine or tert-butyl, but it dramatically de-creased when a bulky halogen, such as iodine,was incorporated.

This work was financially supported by the SpanishComision Iinterministerial de Ciencia y Tecnologıa(MAT2001-2263) and the Consejerıa de Educacion de laComunidad de Madrid (PGE 2000).

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