29

Poly(ether ketonejsPHILIP A. STANILANDICI PLC, Wilton, Cleveland, UK

29.1 INTRODUCTION

29.2 BACKGROUND

29.3 ELECTROPHILIC ROUTE

29.3.J Early Wo.rk29.3.2 AlCl3 Route29.3.3 HF Process29.3.4 Use of Phosgene29.3.5 Other Catalytic Systems

29.4 NUCLEOPHILIC ROUTE

29.4.1 Stoichiometry and Molecular Weight Control29.4.2 Carbonate Process29.4.3 Poly (ether ether ketone) PEEK29.4.4 Other Polymers Derived From 4,4'-Difluorobenzophenone (BDF)29.4.5 Ether Cleavage29.4.6 Variants of the Nucleophilic Process

29.5 PROPERTIES OF POLY(ETHER KETONES)

29.5.1 Miscibility and Isomorphism

29.6 CHEMISTRY OF POLY(ETHER KETONES)

29.6.1 Characterization29.6.2 Stabilization29.6.3 Thermal Decomposition29.6.4 Sulfonation29.6.5 Crosslinking

29.7 REFERENCES

29.1 INTRODUCTION

483

484

484

484486487488488

489

490490491492492493

494

494

495

496496496496496

496

Poly(ether ketones) comprise the class of polymers in which arylene groups are linked by etherand carbonyl groups. Since alkylene linkages are generally not present, and are undesirable, theacronym PAEK [poly(aryl ether ketone)] may be used! to describe the general class.

A polymer marketed as Stilan (RTM) by the Raychem Corporation had structure (1), usuallyreferred to as PEK, while the polymer with structure (2) is PEEK, produced commercially byImperial Chemical Industries as Victrex PEEK (RTM). The systematic name of (2) is poly(oxy­1,4-phenyleneoxy-l,4-phenylenecarbonyl-l,4-phenylene), which is sufficiently cumbersome to justifythe use of the acronym.

+-O-co-Qj-(1)

+-<r-o-co-Qj-(2)

In these cases 1,4-phenylene groups have been assumed, but other poly(ether ketones) maycontain such groups as 1,3-phenylene, biphenylene, naphthylene, etc.

483

484

29.2 BACKGROUND

Synthesis by Step Polymerization

The poly(ether ketones) are a desirable class of polymers which are attracting increasing interestat the present time. Their development has been the subject of recent reviews;2,3 however, newpublications, mainly in the form of patents, are becoming ever more frequent. Their desirability stemsfrom their extremely high thermal stability, and in this they resemble the polysulfones whosesynthesis and development has also been reviewed.2,3 However, the polysulfones are, with fewexceptions, amorphous and subject to attack by solvents. Liquids which may cause cracking,softening, etc. are present among those which occur in or around aircraft, e.g. dichloromethane(paint stripper), isopropanol (de-icing fluid), hydraulic fluid, kerosene, etc. Poly(ether ketones) areusually crystalline and are therefore resistant to attack by solvent, which is especially importantwhen they are used, as is commonly the case, in an aerospace environment. The only commonroom-temperature solvent known for PEK or PEEK is concentrated sulfuric acid.

While crystallinity gives the poly(ether ketones) a unique set of properties among thermoplastics,it is this property, coupled with melting points generally above 300°C, which makes their synthesisso difficult. The problem is how to keep the polymers in solution and so obtain high molecularweights. This can be achieved by working at very high temperatures" (the 'nucleophilic' process) orby working in strongly acidic medias (the 'electrophilic' process) in which the carbonyl groups areprotonated, allowing the polymer to remain in solution.

The first generally acknowledged attempt" to produce a poly(ether ketone) (Scheme 1) failed toproduce high molecular weight polymer because the product came out of solution prematurely. Thiswas an example of the electrophilic approach (or Friedel-Crafts acylation) to the synthesis, as wasthe first attempt7 to make PEK (Scheme 2); again, the molecular weight was too low to give usefulmechanical properties. An inherent viscosity (IV) of about 0.6 (or a reduced viscosity (RV) of about0.8), measured in sulfuric acid, is required before useful mechanical properties, particularly tough­ness, are obtained. This is very approximate, as the solution viscosity required will vary according tostructure and the presence of structural defects such as branching."

Q-o-O + OOCiCIOC

AICI~ ~

PhN02

Scheme 1

~~-c0-Q'l\=T-r<:»: -cf

IV = 0.18

o-0-oCOCIRV = 0.57

Scheme 2

The properties of the PAEKs are such that high selling prices are possible, allowing the use ofcostly raw materials and/or costly processes. However, there is undoubted pressure to utilize cheapand available starting materials, such as phosgene, diphenyl ether, terephthaloyl chloride, etc., toproduce another generation of these polymers, and in this respect the first attempts at synthesizingPAEKs are instructive.

29.3 ELECTROPHILIC ROUTE

29.3.1 Early Work

The first attempt" to produce poly(ether ketones) used aluminum chloride (1.5 mols per mol of-COCI) in nitrobenzene to condense isophthaloyl chloride (IC) or terephthaloyl chloride (TC) withdiphenyl ether (DPO) or biphenyl. Poly(ether ketone ketone) (PEKK) with IV =0.18 was produced(Scheme 1) at 65°C from IC/DPO, from which fibres could be drawn. The material 'softened' at250°C and was soluble in m-cresol and tetrachloroethylene. The first PEK was produced 7 in a

Poly (ether ketone)s 485

similar manner using aluminum chloride (1.4 mols per mol of -CaCl) in dichloromethane tocondense p-phenoxybenzoyl chloride at room temperature (Scheme 2). The polymer was soluble indichloroacetic acid and had a viscosity ratio (VR) of 1.57(equivalent to a reduced viscosity of 0.57) ata concentration of 1% in that solvent. Among others, the polymers (3H5) were also synthesized(Scheme 3). Polymer (4) yielded tough coherent film on pressing at 270°C, while (5) was said not tomelt below 310°C.

C10CQCOCI +~AICIJ ~ +o-O-eCH 2CI 2

(3)

CIOCOOCI + 0-0-0AICIJ ~ +o--o-cCH 2CI 2

(4) VR = 1.60

cotO-OCOCI

(5)

Scheme 3

It is clear that, in general, the polymers made in these first experiments were too low in molecularweight to give really useful properties, and in some cases must have been of low crystallinity, asshown by their solubility, this possibly being due to the presence of aberrant structures.

PEK was prepared from p-phenoxybenzoic acid, using polyphosphoric acid (PPA)9 as solventand catalyst (equation 1).

(1)

IV = 0.53

The polymer was reported to have a melting point (Tm) of 360°C and to be insoluble in organicsolvents, but, surprisingly, was described as 'essentially amorphous'. m-Phenoxybenzoic acid wasalso polymerized to give a polymer of IV = 0.45 and Tm = 350°C. A more effective acidic system,which led to the first truly high molecular weight poly(ether ketone), was the use of a mixed HF/BF3

solvent/catalyst combination.5.30 p-Phenoxybenzoyl chloride was polymerized in a stainless steelreactor to give a 970/0 yield of PEK of IV = 2.76, glass transition temperature (Tg ) = 163°C andTm = 361 "C. The latter properties are essentially those now accepted for PEK polymer.

BF3 was used at 2 or 3 mol per carbonyl group and HF at 2-10 mol per mol of BF 3. Molecularweight, it was suggested, could be controlled by varying reaction time, with IV values as high as 7-8being accessible. Polymer (5) was synthesized with IV = 1.7, which could be moulded at 530°C to ahard rigid chip. In all, some 63 examples of homopolymers and copolymers were reported, but not indetail.

An attempt tc produce PEK by reaction of phosgene with diphenyl ether under these conditions,gave only a low yield of low molecular weight material (equation 2). The main interest appears tohave been in film- and fibre-forming materials. It was shown that a cast film of PEK could bebiaxially drawn to give oriented films of high modulus and tensile strength and capable ofelongations up to 82%.

r.t.COCl2 + o-o--Q -------I.~ 1.5%yield of (I)

IV = 0.13(2)

486 Synthesis by Step Polymerization

29.3.2 AICI3 Route

The crystalline poly(ether ketones) are insoluble in the commonly used Friedel-Crafts reactionsolvents such as dichloromethane, 1,2-dichloroethane, nitrobenzene, carbon disulfide, etc., andit is this which prevents attainment of high molecular weight. Nevertheless, because of its easeas a laboratory technique, the AICl3-catalyzed process has been extensively used,' 0 - 15 to produceresearch quantities of, usually, low molecular weight polymers.

The realization that the polymer/catalyst complex is solubilized if large excesses of AICl3 are usedhas enabled the production of high molecular weight polymers. 16 - 20

The use of AICl3 in the ratio of 2.6-5.6 mol per mol of reacting acid chloride group, in the presenceof a Lewis base (which is believed to reduce alkylation by the reaction solvent), has yielded a numberof high molecular weight compositions (Scheme 4).16

o-0-Q---o-D + ClOCOCOCI AICI33.73/DMF

CH2Cl 2

AICI35.0j'base'

CH2Cl 2o-oV°C1~-0-co-Q-o-D + ClOCO°Cl

Scheme 4

A wide variety of Lewis bases may be employed, but DMF, n-butyronitrile, tetramethyl­ammonium chloride and lithium chloride are favoured.

The effect of varying the ratio of AICl3 to monomer is shown in Figure 1. The process has seenfurther development with the use of dispersants'? (e.g. lithium stearate) and liquefaction agents '?

(e.g. liquid HCI).

1.20

1.10

1.00

0.90

IV0.80

0.70

0.60

r>:•

I I I1.6 2 2.4 2.8

Mole AICI3 /mole-COCI

Figure 1 Effect of Alel3 / p-phenoxybenzoyl chloride ratio on IV of PEK produced

The route appears now to be commercially viable, although requiring the use and disposal of largeamounts of aluminum chloride. It is versatile, and has been used 22 to prepare complex copoly(etherketones) containing imide, amide, ester, azo, quinoxaline, benzimidazole, benzoxazole and benzo­thiazole structures, of which (6) is an example.

o 0

-fO-o--O-N~C~N-Q-o-Q-CO-o-COto 0

(6)

Poly (ether ketone)s 487

HF/BF3

29.3.3 OF Process

Polymerization in HF/BF3 has also seen considerable developmentS, 2 3 - 2 6 and has been usedcommercially. When p-phenoxybenzoyl chloride is polycondensed in a non-metallic reactor, e.g. ofpoly(tetrafluoroethylene) (PTFE) construction, PEK of improved colour and melt stability, capableof elongations of 50% or more, is obtained.i" The molecular weight is controlled in an IV range of0.8 to 1.65 by inclusion of a capping agent, such as biphenyl or diphenyl ether.

The mechanical properties of PEK made by this process are improved when low polymer isremoved by acetone extraction.i" Further improvements in colour, stability and reduced branchingare achieved by 'double end capping'r'? in which a nucleophilic and an electrophilic reagent areincluded in the recipe, as shown in Scheme 5. The process is versatile and has been used to preparethe polymers (7)28 and (8) to (11)31 (Scheme 6).

+ Q-o-OCOCI + 0-0100 0.4-0.9

O-co-fO--o-O-eScheme 5

O-O-o-OCOCI HF/BF, ..

0-0-0-0-0 + C10COCOCI

Q-o-O-o-O + CIoc0°Cl

(7) IV = 1.42

-----i~~ PEEKK(8) IV = 0.90

--------4~~ PEEKK (m)(9) IV = 1.36

Cef

00-0-0-0 + C10Co-o-OCOCl

Scheme 6

__~~ PEEKEK(10) IV = 1.62

PEKEKK~ (II) IV = 1.31

Polymers prepared from terephthaloyl and isophthaloyl chloride with diphenyl ether contain0.6-1.00/0 of 9-phenylenexanthydrol end groups" (12),which limit molecular weight and cause meltinstability. These are detectable by absorbance in the UV at 455 nm, and can be chemicallyreduced P to the corresponding 9-phenylenexanthene (13), thereby improving melt stability.

(12) (13)

488 Synthesis by Step Polymerization

By incorporating an appropriate comonomer, such as 1,4-diphenoxybenzene, the amount ofxanthydrol end groups is reduced, and an IV of up to 2.55 is attained.i!

A variant of the usual process'" uses derivatives of thio- or dithio-carbonic acids in combinationwith a difunctional nucleophilic substrate (Scheme 7). This process is claimed to use cheap startingmaterials but does not appear to have been used commercially.

Q-o-O + EtSCOCIHF/BF,l

IV = 1.24

Scheme 7

29.3.4 Use of Phosgene

The synthesis of useful (tough, high molecular weight) PEK from the cheap reagents phosgene anddiphenyl ether (Scheme 8) has long been a desirable target, but one not so far achieved. Generally,low yields of low molecular weight material have been obtained; 18,30 no systematic study of thereasons for this has been carried out, but instability of diphenyl ether under certain conditions hasbeen postulated.P and clearly there is increased scope for non-para structures.

Scheme 8

Polymerization in 1,2-dichloroethane with AICI3/LiCI16 yields PEK with IV =0.60, but this was

brittle on annealing. Polymerization in carbon disulfide!" gave IV values of 0.59-0.73, while Alel3in trifluoromethanesulfonic acid gave a polymer of IV = 0.95.

29.3.5 Other Catalytic Systems

Systems other than those based on AICl3 or HF have been used on the laboratory scale.Trifluoromethanesulfonic acid (triflic acid), a 'superacid', has been used as solvent and catalyst topolycondense acid chloridesr'? for example, those shown in Scheme 9. Triflic acid also allowscondensation of aromatic carboxylic acids;33,34 some examples are shown in Scheme 10.

The polymers were shown by 13CNMR to have all parastructures. Terephthalic acid fails to reactwith aryl ethers under these conditions, and, in a systematic study, it was found that electron-with­drawing substituents para to the carboxyl group inhibit acylation. This must also explain the failureto produce high polymers in other systems using terephthaloyl chloride.": 7,14,30,35,36

Triflic acid does not catalyze the polycondensation of 4-phenoxybenzoic acid; this, and work withmodel compounds, shows that both rings in diphenyl ether are deactivated following mono­acylation. This is presumed to be the result of partial positive charge induction on the bridgingoxygen (Scheme 11).

O-OCOCI

RV = 0.86

ClOCOCOCI + 0-0-0RV = 0.23

Scheme 9

Poly (ether ketone)s 489

r.t.

RV = 2.31

H01Co-0-oC01H + o-o-Q-o-o-fO-o-O-o--Oc0-o-0-o-cot

RV = 2.68

Scheme 10

d°Urr ~4~~ et +

o

Scheme 11

AI: 10 combination of phosphorus pentoxide in methanesulfonic acid (PPMA) has been pro­posed as a substitute for polyphosphoric acid."? PPMA has been used to synthesize polyketones'"(Scheme 12). PPMA was the solvent for the production of polyketones containingdibenzoj Ibjcrown-S'" and of thermotropic polyketones.t?

H01COC01H + 0-0-0Scheme 12

29.4 NUCLEOPHILIC ROUTE

PPMA24h,IOO°C

The polymerization process by nucleophilic displacement, originally developed for the productionof polysulfones," has been successfully adapted by ICI to the production of poly(ether ketones).Essential features in the reaction (Scheme 13)of aromatic halides and alkali metal salts of phenols, toproduce sulfone and ketone polymers, are the use of a dipolar aprotic solvent and activation of thehalide X by an electron-withdrawing group Q in the ortho or para position.

_~ dipolar aprotic solventM+O~ ~

Scheme 13

f-O-o-otThe nature of the electron-withdrawing group, the halide, the cation and the solvent all have a

marked influence on the course and rate of reaction. The power of the electron-withdrawing grouplies in the order N02 ~ S02 > C=O > N=N; for the halogens, F ~ CI > Dr > I; and for the alkalimetal cations in the order Cs > K > Na > Li. The choice of solvent is complicated, with dimethylsulfoxide (b.p. 180°C) being favoured for polymers which will form and remain in solution below170°C.

Crystalline poly(ether ketones) generally require a solvent which can be used at higher tem­peratures without decomposition which may have a reduced catalytic effect; diphenyl sulfone (DPS)is a favoured example.

490 Synthesis by Step Polymerization

Poly(ether ketones) will usually be prepared from a halide activated by the carbonyl group, andcan be produced from one-monomer or two-monomer reactions, of which equations (3) and (4) areexamples.

~~ t-c«.» + MX (3)

~oD-co-01t + 2MX (4)

While chlorine is sufficiently activated by a sulfone group it is usually not sufficiently activated bya carbonyl group, and it may be necessary to employ fluorine.V While an adequate molecularweight can sometimes be achieved using chloro monomers the polymer may be brittle and of highmelt viscosity, due, it is believed, to the presence of aberrant structures, branching in particular.

In practice, it was found that fluorine was approximately 100 times more reactive than chlorine ina model synthesist:' (equation 5). Although diaryl sulfones have been found to be the most effectivesolvents in the preparation of high molecular weight crystalline poly(ether ketones)," benzophenonehas also been employed.t"

Q-Co-{)-o-QoK + xQ-co-Q ~

Q-eo-{)-o-Q-o-Q-co-Q (5)X =CI, F

29.4.1 Stoichiometry and Molecular Weight Control

The attainment of high molecular weight is dependent upon accurate control of stoichiometry,i.e. the molar ratios of reactants (which may also include the base) undergoing polycondensation.

Since it is usually possible to obtain a polymer of undesirably high molecular weight when themonomers are stoichiometrically in balance, it is usual? to arrange for a reactant, most often thedihalide, to be in a slight excess. In the case of the one-monomer reaction (equation 3) it is necessaryto incorporate a small amount of another reactant, wich could be a mono- or di-halide.

Molecular weight control can also be achieved by monitoring the course of the polymerizationand, at the desired point, making an addition of a monofunctional reagent, which may be a phenolor phenoxide or an active halogen compound. This technique not only stops the polymerization butmay be used to convert unstable end groups, such as phenoxide or phenol, to the more stable etherend group (equation 6).

--~~ ~OR + MX (6)

29.4.2 Carbonate Process

Controlling stoichiometry on an industrial scale can be problematic. The use of alkali metalhydroxides to prepare phenoxide monomers requires careful stoichiometric control in addition tothat required for the balance with dihalide. If the salt formation is carried out in situ by reaction of

Poly (ether ketone)s 491

the phenol with alkali metal carbonate't'"?" it is found that the amount of the latter is not critical,since excess carbonate (unlike hydroxide) does not lead to hydrolysis of the halo monomer.

The problems of insolubility and instability of the salts, most marked in the case of hydroquinone,are alleviated, because disalts do not appear to be formed. Monosalt, as soon as it is formed, reactswith dihalo compound to form a soluble phenol ether, which goes on to react with more carbonate, asshown in Scheme 14.

HOQ-R-{}M + x~-Qx ~

HoQ-R-Q-o-Q-o-QX + MXScheme 14

While the carbonate route has many advantages, it does suffer from some disadvantages. There ispresent throughout the polymerization a finite concentration of phenolic hydroxyl groups not yetconverted to phenoxide. These acidic conditions may cause decomposition of DMSO,47 and thebisphenol itself may undergo decomposition, particularly if the reaction temperature is raised toorapidly. The evolution of water vapour and carbon dioxide may cause foaming problems; this isavoided by extending the reaction at specific hold temperatures.

29.4.3 Poly(ether ether ketone) PEEK

The nucleophilic process and its difficulties can be illustrated by the specific example of PEEK, apolymer produced commercially''" by the chemistry of equation (7).42 Hydroquinone (HQ) iscommerically available; its salts are very unstable, being subject to oxidation, and only the carbonateroute is workable. In this instance 4,4'-difluorobenzophenone (BDF) must be used; this monomer isnot a commodity material but can be produced via a variety of Friedel-Crafts processes, such asthose shown in Scheme 15.

DPSHOOOH + FQ-C~F

-fo-O-o-O-co-Qt + 2KF + CO2 + H20 (7)

Scheme 15

492 Synthesis by Step Polymerization

Alternatively, the synthesis starts from 4,4'-diaminodiphenylmethane (DADM), an intermediatederived from aniline and formaldehyde, used in methylene diisocyanate manufacture on a large scale(Scheme 16).

NH2Q-eH2-QNH2 N~~02~ FQ-eHCOFH~~J~ FQ-eo-OFDADM

Scheme 16

Sodium carbonate cannot be used alone to produce PEEK, but can be used in the presence of thecarbonate of an alkali metal of higher atomic weight.r"

PEEK has a melting point (Tm ) of 334°C, and, in order to keep the polymer in solution, the finalreaction temperature must be not less than about 300 °C. PEEK and its composites have beenreviewed/"

29.4.4 Other Polymers Derived from 4,4'-Difluorobenzophenone (BDF)

Early workers considered difluoro monomers to be too expensive for commercial use,"? but thecurrent availability of BDF makes possible a number of polymers derived from commerciallyavailable bisphenols, such as those shown in Scheme 17.

DPS~

(14)

DPS ~

280"C

(IS)

BDF + HoQ-OoH 3:SC~ +-O-Co-o-(16)

Scheme 17

The same sort of considerations apply to these syntheses as for PEEK, but where the crystallinepolymers have a higher Tm , such as (14)and (16), then higher reaction temperatures are required. Inthe case of (15), the polymer is amorphous and lower temperatures may be employed. In the case of(14)and (16), sodium carbonate may be used alone. At the present state of knowledge, conditions forindividual syntheses must be determined experimentally. Other fluoro ketones, such as (17)8 and(18),50 have been polymerized with bisphenols to provide additional classes of poly(ether ketones).

(17) (18)

29.4.5 Ether Cleavage

Under certain conditions, activated ether links in poly(aryl ethers) can be broken in a processwhich is the reverse of the nucleophilic polycondensation.' If KF is present, for example, the

Poly (ether ketone) s 493

Scheme 18

polymerization reaches an equilibrium portrayed in Scheme 18. This process may be of nuisancevalue in the case where an end-capping agent RX is present in excess, since the phenoxide end groupwill react with RX instead of re-forming polymer. 51 The process may be inhibited by the presence ofakali or alkaline earth metal salts of a non-oxidizing anion; lithium chloride is preferred.' On theother hand, the ether cleavage process may be turned to advantage in the preparation of blockcopolymers. 52,53 The block precursors (19) may be synthesized by the electrophilic route and thensubjected to ether interchange in a nucleophilic process, as shown in Scheme 19.

CloeGeoel + QeoCl + 0-0-0 1,2-dichloroethane

Q-e~o-Qeo-c}-O-eo-o(19) RV = 0.58

Scheme 19

Where transetherification is the route to block-polymer formation, the oligomer need not possessfunctional end groups.

29.4.6 Variants of the Nucleophilic Process

Nitro groups may be displaced by nucleophilic attack to form polymers;54,55 see, for example,equa tion (8).

DMSO ...14S'C. 20h

(8)

RV = 0.18, Tm = 236-255°C

This process gave a low molecular weight polymer of dubious melting point. Production of highmelting poly(ether ketones) requiring high reaction temperatures is likely to fail, as a result ofoxidation reactions involving nitrite by-product.

BDF has been condensed with trimethylsilyl derivatives of'bisphenols'" in the presence of caesiumfluoride catalyst (Scheme 20).

The advantage claimed for this melt process is that the polymer is obtained in a pure form, notrequiring separation from solvents and by-product salts. However, the process still requires therelatively costly difluoro compound.

The problem of insolubility with the crystalline poly(ether ketones), which necessitates use of hightemperatures, can be avoided if the polymer is first produced in an amorphous form, which cansubsequently be converted into the crystalline form. This may be achieved for PEK by converting4,4'-dihydroxybenzophenone into an acetal derivative (20),57,58 as illustrated in Scheme 21.

PS5.-Q

CsF 0.1%

494 Synthesis by Step Polymerization

+ FQ-eO-QF

o-OtRV = 1·21

Scheme 20

+ 2FSiMe3

(20)

HC) (aq)

175°C

KlC0.l ~

DMAC,lSOJC

Scheme 21

As shown, the amorphous poly(acetal ketone) can be prepared at low temperatures and is solublein solvents such as chloroform. However, the process still requires the relatively costly difluoro­benzophenone, and complete hydrolysis to the polyketone may prove impractical on a commercialscale.

29.5 PROPERTIES OF POLY(ETHER KETONES)

The crystalline poly(ether ketones) are stiff and tough, and resist wear, abrasion and fatigue. Theyexhibit high temperature performance; that is the polymers withstand the high (400°C) temperaturesrequired for processing and, subsequently, can be used at high temperatures (~200°C) withoutoxidation and loss in properties.

They possess low flammability and, when burning, give low levels of smoke and toxic gas. Theyare solvent resistant and resistant to radiation.

Detailed property data are available in review articles, papers and trade literature referred totherein.' - 4,8,9,41, 59 However, the important properties of glass transition temperature, Tg , andcrystalline melting point, Tm , obtained by differential scanning calorimetry, are shown for a numberof polymer structures in Table 1.

It can be seen that the Tg values can range from about 100°C to over 200°C and Tm values fromabout 300°C to well over 400 °C. Relatively small changes in structure, such as substitution ofmethylene for carbonyl in the chain, can prevent crystallization from occurring.

29.5.1 Miscibility and Isomorphism

An interesting and unusual property of the poly(ether ketones) is that blends may exhibitmiscibility and isomorphic behaviour.P''

Blends are either miscible and isomorphic or immiscible and not isomorphic. The proposedexplanation is that the unit cells of the PAEKs are nearly identical, i.e. the units PhO- and PhCO­are interchangeable in the crystalline lattice,"! and, if a blend is miscible in the melt, the two types ofchains can be in close proximity during crystallization and will be isomorphic. PEEK is misciblewith PEK but not with PEKK, while PEKK is miscible with PEK and PEEKK.

Poly(ether ketone)s 495

Table 1 Glass Transition Temperature (Tg)and Crystalline Melting Point (Tm) for some Representative Poly(ether ketones)

Structure TgCC) t; (OC) Ref.

- o-Q- 129 324 a

f , -«: 144 335 b-

-o-o-co-Q- 154 367 b

~~o-Q- 165 391 a

-0 ~o-Q- 150 365 c

--0 o-Q- 167 416 b

-0 o-Q- 210 440 d

~H2 o-Q- 123 e

Me

o-Q- 155 e

~S02~o-Q- 181 e

co-o- 155 e

a J. E. Harris and L. M. Robeson, J. Polym. Sci., Polym. Phys. Ed.; 1987,25, 311.b T. E. Attwood, P. C. Dawson, J. L. Freeman, L. R. 1. Hoy, J. B. Rose and P. A. Staniland, Polym. J., 1981, 22, 1096.c K. 1. Dahl and V. Jansons (Raychem Corp.), US Pat. 3956240 (1976) (Chem. Abstr., 1976, 85, 63655).d K. J. Dahl (Raychem Corp.), Br. Pat. 1383393 (1975) (Chem. Abstr., 1973, 78, 98766).e Author's unpublished results.f Does not crystallize on cooling at 20°C min - 1 from the melt.

29.6 CHEMISTRY OF POLY(ETHER KETONES)

Analysis and characterization of PAEKs is made difficult by the absence of room temperaturesolvents; in spite of this, many of the laboratory techniques applicable to polymers have beensuccessfully employed. IR spectroscopy is possible using powder or film samples, NMR spec­troscopy may be carried out in sulfuric or triflic acids, etc.

496 Synthesis by Step Polymerization

29.6.1 Characterization

Crystallinity and crystal structure have been elucidated by means of wide and small angle X-raydiffraction.6 1

-6 3 Morphology has been studied by electron microscopy'r" and light-polarizing

microscopy.P?Molecular weights have been measured by light scattering and by gel permeation chro­

matography (GPC), run in a mixed phenoljtrichlorobenzene solvent at 115°C.6 5

29.6.2 Stabilization

The poly(ether ketones) are inherently very stable, but their high melting points lead to elevatedprocessing temperatures, generally above those at which conventional antioxidants can function,and under these conditions oxidative changes can occur. It has been found'i" that certain amphotericoxides can function as antioxidants for PAEKs, with y-alumina apparently being most effective.

29.6.3 Thermal Decomposition

Isothermal decomposition of PEEK and PEK has been studied by thermogravimetry.f" Volatiledecomposition products were analyzed by mass spectroscopy and were found to contain phenol anddibenzofuran.

29.6.4 Sulfonation

Poly(ether ketones) containing phenylene groups unprotected by an electron-withdrawing group,such as in PEEK, may be sulfonated in sulfuric acid. 36,68,69 The sulfonated polymer can beconverted into its sodium salts 70 by neutralization with sodium acetate. The Tg increases from 143°Cto 415 °C for 100% sodium sulfonate PEEK; ionic clustering is believed to occur at below 25-30%sodium sulfonate. Fully sulfonated PEEK polymer is water soluble.

29.6.5 Crosslinking

Crosslinking may be deliberately induced to improve high temperature performance. This hasbeen achieved using elemental sulfur,"! by insertion of biphenylene into the chain, 10,11 by incorpor­ation of alkynic groups 12 and by incorporation of butadiene moieties. 7

2

29.7 REFERENCES

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* In some instances the Chern. Abstr. references cited are not for the patents quoted, but for equivalent patents.