This application claims priority to the application filed on 09 June 2021 in the UNITED STATES with Nr 63/208574, to the application filed on 16 August 2021 in EUROPE with Nr 21191569.9, and to the application filed on 10 November 2021 in the UNITED STATES with Nr 63/277677, the whole content of each of these applications being incorporated herein by reference for all purposes.

TECHNICAL FIELD

The present invention pertains to a new process for the manufacture of cyclic oligo(arylene ether ketone)s, to new cyclic oligo(arylene ether ketone)s obtainable by this process and to their use for the manufacture of acyclic poly(arylene ether ketone)s by ring-opening polymerization.

BACKGROUND ART

Poly(arylene ether ketone)s, commonly named polyaryletherketones (PAEKs), are a family of high performance thermoplastics with high temperature stability, high mechanical strength, high crystallinity and high resistance to hydrolysis and organic solvents.

The desired high level of thermal, mechanical and chemical properties is generally achieved with PAEKs having a high number of straight repeat units (up to 100%), of which the most common representatives are straight PEEK homopolymers.

An outstandingly high level of thermal, mechanical and chemical properties is reached with PAEKs combining a high number of straight repeat units (up to 100%) and a high carbonyl groups to ether groups ratio (up to 2); a minor amount of kinked repeat units may be incorporated into the PAEK polymer chains to increase their processability. PAEKs that fall within this premium category include polyetherketoneketone (PEKK) and polyetherketoneetherketoneketone (PEKEKK) straight homopolymers; also falling within this category are copolymers comprising predominantly such straight repeat units. Their properties have made them desirable in many applications, including aerospace, coating and insulating materials and medical devices. PEKK copolymers comprising predominantly straight repeat units are widely used in combination with long fibers to form continuous fiber composites. PEKEKK straight homopolymer was commercialized by BASF and used to make surgical implants. PAEKs are usually produced in two ways: the nucleophilic route and the electrophilic route. Just as an example, PEKK can be prepared in solution either via nucleophilic aromatic substitution from bis(fluorobenzoyl)benzene and bis(hydroxybenzoyl)benzene monomers, or via Friedel-Crafts acylation from diphenyl ether and phthaloyl chloride monomers. Irrespectively of the conventional route by which they are made, their high crystallinity and high melt temperatures that provide many of their benefits also result in increasing their melt viscosity and decreasing their processability. So, in all applications, a compromise needs to be reached between the need for good mechanical properties (high molecular weight) and high flow (low viscosity), which is especially prejudicial in composite applications where molten polymer high flow is required to impregnate the fibers.

To overcome this issue, it has been proposed to prepare high molecular weight PAEKs from low viscosity cyclic oligomer precursors by ring-opening polymerization.

CN 1 443 762 (to Changchun Applied Chemistry), published in September 2003, describes a process wherein cyclic oligo(arylene ether ketone)s of general formula are manufactured by causing orthophthaloyl chloride or isophthaloyl chloride monomer to react with a substituted aromatic monomer in solution in a pseudo-high-dilution environment. In Changchun’s examples 1 to 6, orthophthaloyl chloride was used as the acylation agent. By reacting orthophthaloyl chloride with various aromatic compounds in similar reaction conditions, ortho-aromatic cyclic oligomers, including ortho aromatic PEKEKK and PEKK oligomers, were obtained with a yield of respectively 95%, 93%, 81%, 92%, 93% and 88%; the lowest yield (81%) was achieved when reacting diphenyl ether with orthophthaloyl chloride to form cyclic ortho-aromatic PEKK oligomers. In Changchun’s examples 7 to 11, isophthaloyl chloride was used instead as the acylation agent. By reacting isophthaloyl chloride with various aromatic compounds in reaction conditions identical to those previously used for orthophthaloyl chloride, meta-aromatic cyclic oligomers, including meta-aromatic PEKEKK oligomers, were obtained with a much lower yield, namely respectively 64%, 62%,

65%, 61% and 60%. It can be noted that CN 1 443 762 does not provide any example of synthesis of meta-aromatic cyclic PEKK oligomers from diphenyl ether and isophthaloyl chloride, which contrasts with the fact that it systematically provides examples of synthesis of both ortho- and meta-aromatic cyclic oligomers for any other exemplified aromatic compound. The heavy decrease in yield when switching from orthophthaloyl chloride to isophthaloyl chloride is reasonably expected by the skilled person, because meta-phenylene rings are known to form cyclics less readily due to bond geometry. It is also understood by the skilled person that p-phenylene rings of cyclic oligomers would be even more difficult to access due to bond geometry. This is likely to explain why CN 1 443 762 remains totally silent about any process that would be able to produce such para-aromatic cyclic oligomers in spite of their major interest as precursors of high performance PAEKs with straight repeat units.

Seven years later, Guo et al. in Polym. Adv. Technol, 2010, 21, 290, reported additional experimental results on the above described acylation process for preparing cyclic oligo(arylene ether ketone)s. A still heavier decrease in yield was suffered from when switching from orthophthaloyl chloride to isophthaloyl chloride, up to about minus 65%, resulting in yields in meta-aromatic cyclics possibly as low as 21% or 28%. When commenting the results, the Authors confirmed that the poor bond geometry of meta-phenylene rings was the major reason for the much lower yields in meta-aromatic cyclic oligomers: “the major reason for the unoptimized yields of cyclic oligomers derived from isophthaloyl dichloride is that the bond angle between the diacid chloride in isophthaloyl dichloride is over 120°C, which is disadvantageous for forming cyclic product” . This certainly discouraged Guo to work further on the preparation of meta aromatic oligomers by the acylation route, and is likely to explain why Guo’s next study with Hu on the acylation route, published in Applied Mechanics and Materials, 2013, 331, 431, focused on the preparation of cyclic oligomers from orthophthaloyl chloride, which, as Guo and Hu confirmed, “is favorable for forming cyclic oligomers ” . A fortiori, this consolidates the skilled person’s understanding that p-phenylene rings of cyclic oligomers would be even more difficult to access due to their bond geometry, because the bond angle in a diacyl chloride capable of forming para-aromatic cyclics (viz. terephthaloyl chloride) is known to be about 180°C; this is also very likely to explain why Guo, like previously Changchun, remained totally silent about any process that would have been able to produce such para-aromatic cyclic oligomers.

Instead, to manufacture para-aromatic cyclic oligomers, the skilled person developed substantially different or even quite different processes, e.g. processes based on a nucleophilic route. Among these processes, the less distant one is probably the electrophilic process described in CN 101 519399 (to Wuhan Institute of Technology, some inventors of which are the authors of the above scientific paper). Interestingly, the background art section of CN’399 confirms the strong need for a process capable of manufacturing para-aromatic cyclic oligomers (op. cit.): “the existence of ortho-position or meta-position in the products of ring-opening polymerization destroys the regularity of polymer chains and reduces the performance of the polymer. Therefore, how to synthesize aromatic cyclic polyetherketone oligomers with full para-position structure in high yield, especially cyclic prepolymers of polyetheretherketone (PEEK), polyetherketone (PEK) and polyetherketoneketone (PEKK) which have been used in large scale in business and have better performance, is of great significance in this field. The reaction monomers used in the traditional methods for preparing linear polymers are all para-bond structures, which makes cyclization extremely difficult. (...) Chinese patents 02123917.7, and 03105019.0 published a new method for preparing aromatic polyketone cyclic oligomers by electrophilic reaction, wherein o-phthaloyl chloride or m-phthaloyl chloride with a structure favorable to ring formation was used as a starting material to prepare cyclic polyketone oligomers with high yield; however, the ring-opening polymerization products contained ortho- or meta-sub stituted benzene rings, which led to the degradation of polymer properties. Therefore, in the theoretical aspect, it is challenging to synthesize aromatic cyclic oligomers with full para-position structure with high yield starting from cheap raw materials using Friedel-Crafts electrophilic reaction ” .

According to Wuhan’s process, an aromatic compound such as the ones used in Changchun’s process (with the noteworthy exception of diphenyl ether, which remained unconsidered by Wuhan) was caused to undergo an alkylation reaction with one specific alkylation agent, viz. carbon tetrachloride. The reaction is likely to suffer from a rather poor regioselectivity, resulting in a substantial amount of by-products in addition to the desired para-form, mainly ortho-aromatic cyclic oligomers. In addition, and of critical importance, Wuhan’s process is unable to manufacture cyclic oligo(arylene ether ketone)s having a high carbonyl to ether groups ratio, such as PEKK or PEKEKK cyclic oligomers, which yet allow for the preparation of the most performing high molecular weight PAEKs.

Now, overcoming a long-standing prejudice wherein no para-aromatic cyclic oligomer could be manufactured by a process derived from Changchun’s process, a fortiori with a decent yield, the Applicant has conceived and reduced to practice a new process, inspired from Changchun’s process, wherein new para-aromatic cyclic oligo(arylene ether ketone)s, including new cyclic oligo(arylene ether ketone)s having a high carbonyl to ether groups ratio like PEKK or PEKEKK cyclic oligomers, are manufactured with a decent yield. By doing so, the Applicant has met a strong need which had remained unmet for more than a decade, yet in a competitive high- technology field.

MAIN ASPECTS OF THE INVENTION

This need, and still other ones, are met by a process P ¹ for the manufacture of a cyclic oligo(arylene ether ketone) of formula (I) wherein X, which may be the same or different at each occurrence, is hydrogen or methyl,

L, which may be the same or different at each occurrence, is a divalent moiety selected from the group consisting of — O ^— , ^— CX ₂ ^— with X as previously defined, n is an integer ranging from 2 to 20, said process P ¹ comprising causing an aromatic compound A of formula (II) wherein X and L are as defined for the cyclic oligo(arylene ether ketone) of formula (I), to react with terephthaloyl chloride in a reaction medium comprising a solvent S capable of dissolving the cyclic oligo(arylene ether ketone), the aromatic compound A and the terephthaloyl chloride, wherein the reaction medium is a pseudo-high dilution environment.

In general, the aromatic compound A and/or the terephthaloyl chloride are introduced progressively in the reaction medium. The reaction between the aromatic compound A and the terephthaloyl chloride which takes place during the step S ¹ is typically a Friedel-Crafts acylation reaction. The present invention concerns also a process P ² for the manufacture of an acyclic poly(arylene ether ketone) comprising m repeat units of formula (III) said process P ² comprising the steps of:

- manufacturing a cyclic oligo(arylene ether ketone) of formula (I) by the process P ¹ , and

- causing the cyclic oligo(arylene ether ketone) of formula (I) to undergo a ring-opening polymerization, so as to obtain the acyclic poly(arylene ether ketone) comprising m repeat units of formula (III), wherein m is an integer which is greater than 5 times n and wherein X, L and n are as defined for the cyclic oligo(arylene ether ketone) of formula (I).

In a particular embodiment of high industrial importance of the process P ² , the manufactured acyclic poly(arylene ether ketone) comprising m repeat units of formula (III) is comprised in a composite material. In this embodiment, the process P ² comprises the steps of:

- manufacturing the cyclic oligo(arylene ether ketone) of formula (I) by the process P ¹ ,

- impregnating a continuous fiber with the cyclic oligo(arylene ether ketone) of formula (I), so as to form a pre-composite material, and

- causing the cyclic oligo(arylene ether ketone) of formula (I) which is comprised in the pre-composite material to undergo a ring-opening polymerization, so as to form the composite material comprising the acyclic poly(arylene ether ketone) comprising m repeat units of formula (III).

The present invention concerns also a cyclic oligo(arylene ether ketone) of formula as such, wherein X, L and n are as previously defined. Finally, the invention concerns a process P ³ for the manufacture of an acyclic poly(arylene ether ketone) comprising m repeat units of formula (III) (III), said process P ³ comprising causing a cyclic oligo(arylene ether ketone) of formula (I) to undergo a ring-opening polymerization, so as to obtain the acyclic poly(arylene ether ketone) comprising m repeat units of formula (III), wherein m is an integer which is greater than 5 times n and wherein X, L and n are as defined for the cyclic oligo(arylene ether ketone) of formula (I).

In a particular embodiment of high industrial importance of the process P ³ , the manufactured acyclic poly(arylene ether ketone) comprising m repeat units of formula (III) is comprised in a composite material. In this embodiment, the process P ³ comprises the steps of: impregnating a continuous fiber with the cyclic oligo(arylene ether ketone) of formula (I), so as to form a pre-composite material, and causing the cyclic oligo(arylene ether ketone) of formula (I) which is comprised in the pre-composite material to undergo a ring-opening polymerization, so as to form the composite material comprising the acyclic poly(arylene ether ketone) comprising m repeat units of formula (III).

DETAILED DESCRIPTION OF THE INVENTION

An outstanding feature of the present invention is that, in the cyclic oligo(arylene ether ketone) of formula (I), the two carbonyl groups as below framed by dotted rectangles are in para positions with respect to each other. For this reason, the cyclic oligo(arylene ether ketone) of formula (I) shall be referred to as a “para-aromatic cyclic oligo(arylene ether ketone) ” .

In contrast, a cyclic oligo(arylene ether ketone) of formula (IV) with X, L and n as defined for the cyclic oligo(arylene ether ketone) of formula (I), wherein the two carbonyl groups framed by dotted rectangles are in meta position to each other (not in accordance with the present invention) shall be qualified as “meta aromatic Such a meta-aromatic cyclic oligo(arylene ether ketone) can be obtained by causing the aromatic compound of formula (II) to undergo an acylation reaction with isophthaloyl chloride. Likewise, an ortho-aromatic oligo(arylene ether ketone) can be obtained by causing the aromatic compound of formula (II) to undergo an acylation reaction with orthophthaloyl chloride.

In the cyclic oligo(arylene ether ketone) of formula (I) and in all the other compounds and moieties described in the present document which comprise X, X is preferably hydrogen.

In the cyclic oligo(arylene ether ketone) of formula (I) and in all the other compounds and moieties described in the present document which comprise L, a first preferred selection for L consists in selecting L from the group consisting of

Another preferred selection for L consists in selecting L from the group consisting of

More preferably, L is a divalent moiety selected from the group consisting of

Still more preferably, L is ^— O ^— . n ranges preferably from 2 to 10. More preferably, n ranges from 2 to 8; for example, n may be 2, 3, 4, 5, 6, 7 or 8. Still more preferably, n ranges from 2 to 6; it may from 2 to 4, from 3 to 4 or from 3 to 5. As will be explained later on, trimers (n = 3) are of particular interest.

Preferred and of high industrial importance is the cyclic oligo(arylene ether ketone) of formula (V) wherein n ranges from 2 to 20, preferably from 2 to 10, more preferably from 2 to 8, still more preferably from 2 to 6 and even still more preferably from 3 to 4, in particular the cyclic oligo(arylene ether ketone) of formula (V) wherein n is 3, which could be obtained with an especially high selectivity.

As examples of suitable aromatic compounds A, it can be notably cited phenoxybenzene (commonly referred to as diphenyl ether), 1,2-diphenoxybenzene, 1,3- diphenoxybenzene, 1,4-diphenoxybenzene, 4,4’-diphenoxybenzophenone, 4,4'-di(3- methylphenoxy)benzophenone, 4,4'-diphenoxydiphenylsulfone and 4,4’-di(3- methylphenoxy)-diphenylsulfone. In the aromatic compound A of formula (II), L and X meet the same features and preferences as above specified for the cyclic oligo(arylene ether ketone) of formula (I). So, the most preferred aromatic compound A is phenoxybenzene.

The total amount of the aromatic compound A which is introduced in the reaction medium, based on the total amount of the solvent S which is introduced in the reaction medium, does not generally exceed 1 mole by liter of the solvent S, wherein the volume of the solvent S is measured at 25°C and 1 atm (101325 Pa). It is preferably of at most 0.2 mol/1, more preferably of at most 50 mmol/1 and still more preferably of at most 30 mmol/1. Besides, it is generally of at least 0.1 mmol/1, preferably of at least 1 mmol/1, more preferably of at least 5 mmol/1 and still more preferably of at least 10 mmol/1.

The total amount of the terephthaloyl chloride which is introduced in the reaction medium, based on the total amount of the solvent S, does not generally exceed 1 mole by liter of the solvent S, wherein the volume of the solvent S is measured at 25°C and 1 atm (101325 Pa). It is preferably of at most 0.2 mol/1, more preferably of at most 50 mmol/1 and still more preferably of at most 30 mmol/1. Besides, it is generally of at least 0.1 mmol/1, preferably of at least 1 mmol/1, more preferably of at least 5 mmol/1 and still more preferably of at least 10 mmol/1.

The total combined amount of the aromatic compound A and of the terephthaloyl chloride which are introduced in the reaction medium, based on the total amount of the solvent S, does not generally exceed 2 mole by liter of the solvent S, wherein the volume of the solvent S is measured at 25°C and 1 atm (101325 Pa). It is preferably of at most 0.4 mol/1, more preferably of at most 100 mmol/1 and still more preferably of at most 60 mmol/1. Besides, it is generally of at least 0.2 mmol/1, preferably of at least 2 mmol/1, more preferably of at least 10 mmol/1 and still more preferably of at least 20 mmol/1.

The ratio of the total number of moles of the aromatic compound A which is introduced in the reaction medium to the ratio of the total number of moles of the terephthaloyl chloride which is introduced in the reaction medium ranges generally from 0.1 to 10, preferably from 0.5 to 2, more preferably from 0.90 to 1.10, still more preferably from 0.98 to 1.02. The most preferably, the aromatic compound A and the terephthaloyl chloride are introduced in equimolar amounts in the reaction medium. As evidenced by numerous publications, notably those described in the background art section of the present specification, a person skilled in the synthesis of macrocycles is well familiar with the notion of pseudo-high-dilution environment/conditions in/under which macrocycles can be obtained, and how such environment/conditions can be created. In a reaction medium which is a pseudo-high- dilution environment wherein two reactants are caused to react together, at least one of the reactants, here the aromatic compound A and/or the terephthaloyl chloride, is generally present at a sufficiently low instantaneous concentration for a sufficiently high duration for it to cause the formation of a substantial amount of the desired cyclic reaction product, viz. the cyclic oligo(arylene ether ketone) of formula (I), to the detriment of undesired reaction by-products, especially linear poly(arylene ether ketone) oligomers and higher molecular weight polymers.

A pseudo-high-dilution environment is advantageously created by introducing the aromatic compound A and/or the terephthaloyl chloride progressively in the reaction medium. The aromatic compound A and/or the terephthaloyl chloride can be introduced through repeated injections, dropwise or continuously in the reaction medium. Preferably, the aromatic compound A and/or the terephthaloyl chloride are introduced dropwise or continuously in the reaction medium. More preferably, the aromatic compound A and/or the terephthaloyl chloride are introduced continuously in the reaction medium. Still more preferably, the aromatic compound A and/or the terephthaloyl chloride are introduced continuously in the reaction medium at a constant introduction rate.

Let d be the duration of the period of time P enveloping the introduction of the whole amount of the aromatic compound A and the whole amount of the terephthaloyl chloride in the reaction medium. The period of time P starts with the beginning of the introduction of at least part of the amount of the aromatic compound A and/or at least part of the amount of the terephthaloyl chloride in the reaction medium. P finishes with the completion of the introduction of the whole amount of the aromatic compound A and the whole amount of the terephthaloyl chloride in the reaction medium.

Let us divide the period of time P in k parts of equal duration d/k, wherein k is 8, 16, 32, 64, 128, 256 or 512. Let r ¹ a _vg,A , r² _avg,A , …, r ^k a _vg,A represent the k average introduction rates of the aromatic compound A, based on the total amount of the solvent S, respectively during the 1 ^st , 2 ^nd , … and k ^th part of the period of time Π, and let r ¹ a _vg,B , r² _avg,B , …, r ^k a _vg,B represent the k average introduction rates of the terephthaloyl chloride, based on the total amount of the solvent S, respectively during the 1 ^st , 2 ^nd , … and k ^th part of Π. Advantageously, at least half, preferably at least three-quarters, more preferably at least seven-eighths and still more preferably all the k average introduction rates of the aromatic compound A, based on the total amount of the solvent S, r ¹ a _vg,A , r² _avg,A , … r ^k a _vg,A do not exceed a certain value r _A ^max . Likewise, advantageously at least half, preferably at least three-quarters, more preferably at least seven-eighths and still more preferably all the k average introduction rates of the terephthaloyl chloride, based on the total amount of the solvent S, r ¹ a _vg,B , r² _avg,B , … r ^k a _vg,B do not exceed a certain value r _B ^max . r _A ^max and/or r _B ^max may be 10, 5, 4, 3, 2.5, 2, 1, 0.5 or 0.2 mmol/(l.h). r _A ^max and/or r _B ^max may also be even lower, e.g.0.1 or 0.01 mmol/(l.h). The lower r _A ^max and r _B ^max are, the more the reaction medium favors a high selectivity towards the desired cyclic oligo(arylene ether ketone). However, the lower r _A ^max and/or r _B ^max , the lower the amount of the reagents which are susceptible of forming the desired cyclic oligo(arylene ether ketone). So, to achieve a high yield, a compromise needs to be found, which compromise can be often achieved by specifying a r _A ^max and/or r _B ^max value in the range of from 0.5 to 5, e.g.2 or 3. Good results are obtained when the period of time Π is divided in k = 32 or more parts, and either all the k average introduction rates of the aromatic compound A, based on the total amount of the solvent S, r ¹ a _vg,A , r² _avg,A , … r ^k a _vg,A , equal to or different from each other, or all the k average introduction rates of the terephthaloyl chloride, based on the total amount of the solvent S, r ¹ a _vg,B , r² _avg,B , … r ^k a _vg,B , equal to or different from each other, are from 0.5 to 5 mmol/(l.h), especially from 2 to 3 mmol/(l.h). Very good results were obtained when the period of time Π was divided in k = 32 or more parts, and all the k average introduction rates of the aromatic compound A, based on the total amount of the solvent S, r ¹ a _vg,A , r² _avg,A , … r ^k a _vg,A , equal to or different from each other, and all the k average introduction rates of the terephthaloyl chloride, based on the total amount of the solvent S, r ¹ a _vg,B , r² _avg,B , … r ^k a _vg,B , equal to or different from each other, were from 1 to 5 mmol/(l.h), especially from 2 to 3 mmol/(l.h). Excellent results are obtained when, during the whole course of the period of time Π, equimolar amounts of the aromatic compound A and the terephthaloyl chloride are introduced continuously in the reaction medium, at one single, constant rate in the range of from 1 to 5 mmol/(l.h), especially from 2 to 3 mmol/(l.h), that is to say that, during the whole course of the period of time Π _, (i) the introduction rate of the aromatic compound A, based on the total amount of the solvent S, r _A is kept constant at one single value to be chosen in the range of from 1 to 5 mmol/(l.h), especially from 2 to 3 mmol/(l.h) and (ii) the introduction rate of the terephthaloyl chloride B, based on the total amount of the solvent S, r _B is also kept constant at the same, single value as the one chosen for r _A . Once the period of time Π finishes, the reaction between the aromatic compound A and the terephthaloyl chloride may be continued for at least 10 min, at least 30 min, at least 1 h, at least 2 h or even more to ensure the highest achievable conversion into the cyclic oligo(arylene ether ketone) of formula (I). Alternatively, immediately afterwards or less than 10 min after Π finishes, it can be proceeded with a possible subsequent step, which may be for example the purification of the cyclic oligo(arylene ether ketone) of formula (I). The aromatic compound A and the terephthaloyl chloride reagents are advantageously substantially dissolved, preferably completely dissolved, in the reaction medium comprising the solvent S. The cyclic oligo(arylene ether ketone) of formula (I), viz. the reaction product of the reaction which takes place between the aromatic compound A and the terephthaloyl chloride is also advantageously substantially dissolved, preferably completely dissolved, in the reaction medium comprising the solvent S. The whole amount of the solvent S may be present in the reaction medium before the introduction of the aromatic compound A and the introduction of the terephthaloyl chloride have started. Alternatively and preferably, a first part of the solvent S is present in the reaction medium before the introduction of the aromatic compound A and the introduction of the terephthaloyl chloride have started, while another part of the solvent S is used as vehicle to introduce the aromatic compound A and the terephthaloyl chloride in the reaction medium, either (i) through a single mixture comprising the aromatic compound A, the terephthaloyl chloride and the solvent S, or (ii) through a first mixture comprising the aromatic compound A and the solvent S and a second mixture comprising the terephthaloyl chloride and the solvent S; these two parts represent advantageously the whole amount of the solvent S that is introduced in the reaction medium. In accordance with the present invention, advantageously at least half, preferably two-thirds, more preferably three-quarters and still more preferably four-fifths of the whole amount of the solvent S are present in the reaction medium before the introduction of the aromatic compound A and the introduction of the terephthaloyl chloride have started. Besides, preferably at most 95 hundredths, more preferably at most nine-tenths and still more preferably at most 85 hundredths of the whole amount of the solvent S are present in the reaction medium before the introduction of the aromatic compound A and the introduction of the terephthaloyl chloride have started; then, typically, preferably at least 5 hundredths, more preferably at least one-tenth and still more preferably at least 15 hundreths of the whole amount of the solvent S are used as vehicle to introduce the aromatic compound A and the terephthaloyl chloride in the reaction medium.

The solvent S is generally chosen from the group consisting of carbon disulfide, nitroaromatics, nitroalkanes, chloroaromatics and chloroalkanes. As nitroaromatics, it can be cited mononitrobenzene, 2-nitrotoluene and 3-nitrotoluene. As nitroalkanes, it can be cited C1-C4 alkanes, such as nitromethane, nitroethane, 1-nitropropane and 2- nitropropane.

In a first preferred embodiment, the solvent S is a chloroalkane, more preferably a chloroalkane which is free of any carbon atom to which 2 or more than 2 chlorine would be attached. The chloroalkane has generally from 1 to 10 carbon atoms, preferably from 2 to 6 carbon atoms, more preferably from 2 to 4 carbon atoms, still more preferably 2 carbon atoms. As chloroalkanes, it can be cited dichloromethane, 1,1- dichloroethane, dichloropropanes such as 1,2- and 1,3-dichloropropanes, trichlorobutanes such as 1,2,3- and 1,2-4-trichlorobutanes and the chloroalkanes of formula CH2Cl-(CHCl) _j -CH2Cl wherein j is an integer from 0 to 8, especially 1,2- dichloroethane, 1,2,3-trichlororopane and 1,2,3,4-tetrachlorobutane. Good results were obtained when using 1,2-dichloroethane as the solvent S.

In another preferred embodiment, the solvent S is a chloroaromatic. The chloroaromatic is preferably selected from the group consisting of monochlorobenzene, o-, m- and p-dichlorobenzenes, 1,2,3-, 1,2,4- and 1,3,5-trichlorobenzenes, o-, m- and p- monochlorotoluenes and dichlorotoluenes. It is more preferably selected from the group consisting of monochlorobenzene, o-dichlorobenzene, m-dichlorobenzene and p- dichlorobenzene. Good results are obtained when using o-dichlorobenzene as the solvent S.

The reaction medium comprises advantageously a catalyst. The cyclization reaction rate between the aromatic compound A of formula (II) and the terephthaloyl chloride can be increased by the catalyst. The catalyst may be in anhydrous form or in a hydrated form; in accordance with the invention, the catalyst is preferably anhydrous. The catalyst may be a zeolite (in particular a zeolite beta, Y or ZSM-5), a heteropolyacid such as 12-tungstophosphoric acid (H3PW12O40) or an oxide of an element M, wherein M is as detailed hereinafter for the halogenide of formula MYijTbO, such as ZnO or ZrCh. The catalyst is preferably a Lewis acid, especially a halogenide of formula MYijTbO wherein M is an element selected from the group consisting of beryllium, transition metals, post-transition metals and metalloids, wherein Y is a halogen, i is the valence of element M and j is an integer ranging generally from 0 to 6, preferably 0. Transition metals are all the elements of Groups 3 to 12 of the periodic table of the elements. As herein used, post-transition metals denote the set of elements consisting of Al, Ga, In, Tl, Sn, Pb, Bi and Po, while metalloids denote the set of elements consisting of B, Si, Ge, As, Sb and Te. The element M has generally an electronegativity of from 1.3 to 1.9, preferably of from 1.5 to 1.8, possibly of 1.5 or 1.6, and is more preferably Be, Ti, Sn, Al, Fe or Zn. As examples of suitable catalysts of formula MY jTbO, the following anhydrous halogenides (j=0) can be cited: BeCh, BF3, TiCb, SbCb, SnCb, AlCb, FeCh and ZnCh. Good results were obtained when using anhydrous aluminum trichloride (AlCb) as the catalyst. Good results can also be obtained when using anhydrous iron trichloride (FeCh) as the catalyst.

The total amount of the catalyst, based on the total combined amount of the aromatic compound A and the terephthaloyl chloride, ranges usually from 0.3 to 30 mol/mol, preferably from 1 to 10 mol/mol and more preferably from 2 to 5 mol/mol.

The whole amount of the catalyst is advantageously present in the reaction medium before the introduction of the aromatic compound A and the introduction of the terephthaloyl chloride have started. The reaction medium advantageously further comprises a co-catalyst. The co catalyst can further increase the cyclization reaction rate between the aromatic compound A of formula (II) and the terephthaloyl chloride. The co-catalyst may be a complexing agent capable of forming a complex with the catalyst. The co-catalyst may be a Lewis base. The co-catalyst may also be lithium chloride. The co-catalyst is advantageously selected from the set consisting of dialkylsulfoxides, tri-, tetra-, penta- and hexa- alkylphosphoramides, mono-, di-, tri- and tetra- alkylureas, N- alkylalkanamides, N,N-dialkylalkanamides, pyrrolidone and N-alkyl-2-pyrrolidones.

For all the compounds of this set of possible co-catalysts which contain one or more alkyl substituents, the at least one alkyl substituent is preferably Ci-Cs alkyl, more preferably C1-C4 alkyl, still more preferably methyl or ethyl, the most preferably methyl. As examples of suitable co-catalysts, it can be cited dimethylsulfoxide, hexamethylphosphoramide, tetramethylurea, N-methylformamide, N,N- dimethylformamide, N,N-dimethylacetamide, pyrrolidone and N-methylpyrrolidone.

The co-catalyst is preferably pyrrolidone or a N-alkyl-2-pryrrolidone, more preferably a N-C _I -4 alkyl-2-pyrrolidone, still more preferably N-methyl-2-pyrrolidone.

The total amount of the catalyst, based on the total combined amount of the aromatic compound A and the terephthaloyl chloride, ranges usually from 0.1 to 10 mol/mol, preferably from 0.3 to 3 mol/mol and more preferably from 0.5 to 2 mol/mol.

The whole amount of the co-catalyst is advantageously present in the reaction medium before the introduction of the aromatic compound A and the introduction of the terephthaloyl chloride have started.

Before the introduction of the aromatic compound A and the introduction of the terephthaloyl chloride have started, the reaction medium may consist of the solvent S, or it may consist of the solvent S and the catalyst, or it may consist of the solvent S, the catalyst and the co-catalyst. Alternatively, the reaction medium may comprise, in addition to the solvent, or in addition to the solvent and the catalyst, or in addition to the solvent, the catalyst and the co-catalyst, as the case may be, at least one other ingredient such as a diluent, a viscosity modifier or a heat stabilizer.

Advantageously, the reaction between the aromatic compound A and the terephthaloyl chloride takes place at a temperature of from 0 to 120°C, preferably of from 10°C to 100°C and more preferably of from 15°C to 80°C (possibly at room temperature, typically from 15°C to 35°C). Advantageously, it takes place at a pressure of from 0.1 to 10 bar, preferably from 0.8 to 1.2 bar and still more preferably at the atmospheric pressure (about 101325 Pa).

The reaction between the aromatic compound A and the terephthaloyl chloride takes advantageously place under stirring.

The reaction medium may be in contact with air or under an inert atmosphere, such as a nitrogen or argon atmosphere.

The process P ¹ may result in the manufacture of one or several cyclic oligo(arylene ether ketone)s of formula (I). In general, several oligo(arylene ether ketone)s of formula (I) are manufactured.

The cyclic oligo(arylene ether ketone) of formula (I) can be concentrated and/or isolated from the reaction medium using conventional concentration and isolation methods that are well-known to the skilled person. When several cyclic oligo(arylene ether ketone)s of formula (I) are manufactured, they can be concentrated and/or isolated from the reaction medium and from each other using the same conventional concentration and isolation methods as above described.

A surprising and advantageous aspect of the present invention lies in that the process P ¹ generally results in the manufacture of a reduced number of cyclic oligo(arylene ether ketone)s of formula (I), when compared to homologue prior art processes using orthophthaloyl chloride or isophthaloyl chloride instead of terephthaloyl chloride. Without being bound by any theory, the Applicant believes that this results from the fact that the para-aromatic cyclic oligomers in accordance with the present invention are more difficult to access due to bond geometry, allowing for a reduced number of possible cyclic configurations.

More precisely, when one and only one aromatic compound A is caused to react with terephthaloyl chloride in the process P ¹ , two and only two cyclic oligo(arylene ether ketone)s complying with the same generic formula (I) are often obtained, which ones differed from each other only by the number of repeat units they contained (degree of oligomerization n). In contrast, with the homologue prior art processes, at least 3 up to 6, and may be even more, cyclic oligo(arylene ether ketone)s having different degrees of oligomerization are manufactured; for example, the Applicant, by mimicking prior art processes, obtained mixtures of trimers, tetramers, etc. up to heptamers, consistently with the results reported by Guo et al. in Polym. Adv. TechnoL, 2010, 21, 290, wherein mixtures of dimers, turners, etc. up to heptamers were similarly obtained.

Hence, an aspect of the present invention concerns a mixture comprising, as sole cyclic oligo(arylene ether ketone)s complying with general formula (I) wherein X, L and n are as previously defined, one and only one first cyclic oligo(arylene ether ketone) of formula (I ¹ ) wherein X ¹ has the same definition as and complies with the same preferences as previously defined X, except that X ¹ is necessarily the same at each occurrence, wherein L ¹ has the same definition and complies with the same preferences as previously defined L, except that L ¹ is necessarily the same at each occurrence, wherein n ¹ is has the same definition and complies with the same preferences as previously defined n, and one and only one second cyclic oligo(arylene ether ketone) of formula (I ² ) wherein X ² , which is the same at each occurrence, is identical to X ¹ , wherein L ² , which is the same at each occurrence, is identical to L ¹ , and wherein n ² is an integer which is equal to n ¹ + 1. It is understood that, since both n ¹ and n ² = n ¹ + 1 must be within the specified limits for n, n ¹ is ipso facto of at most 19 when n is of at most 20, ipso facto of at most at most 5 when n is of at most 6, etc. In particular, the first oligomer is a trimer (n ¹ = 3) and the second oligomer is a tetramer (n ² = 4). A related and also advantageous aspect of the present invention lies in that the process P ¹ makes it often possible to manufacture one cyclic oligo(arylene ether ketone) of formula (I) in a much higher amount than the one or more concomitantly prepared other cyclic oligo(arylene ether ketone)(s) of formula (I). For example, the Applicant could obtain a para-aromatic cyclic trimer with a selectivity in the trimer exceeding 80%, based on the whole content of cyclic oligo(arylene ether ketone)s. The cyclic oligo(arylene ether ketone) of formula (I) or the above mixture of cyclic oligo(arylene ether ketone)s is advantageously used for the manufacture of a higher molecular weight acyclic poly(arylene ether ketone) comprising repeat units of formula (III). The higher molecular weight acyclic poly(arylene ether ketone) comprising repeat units of formula (III) is advantageously linear; otherwise said, it is advantageously acyclic and free of ramifications. The repeat units comprised in the higher molecular weight acyclic poly(arylene ether ketone) may be kinked or straight. The higher molecular weight acyclic poly(arylene ether ketone) may comprise m repeat units of formula (III), wherein m is an integer which is greater than 5 times n and is possibly greater than 50 times n, with n as previously defined for the cyclic oligo(arylene ether ketone) of formula (I). In the absolute, m may be of at least 20, 50, 100, 150 or 200; besides, m is generally of at most 500 or 1000. It may be a copolymer or a homopolymer. It may comprise the repeat units of formula (III) in a weight amount which is of at least or which exceeds advantageously 50% The repeat units of formula (III) can be notably characterized by the ratio ^K / _O of the number of carbonyl groups to the number of ether groups they contain. Provided the ratio ^K / _O is of at most 1.5, which is generally the case except when the repeat units of formula (III) are para-aromatic PEKK repeat units, the higher molecular weight acyclic poly(arylene ether ketone) comprises the repeat units of formula (III) in a weight amount which exceeds preferably 90% and more preferably 99% of the total weight of its repeat units; still more preferably, it may comprise repeat units of formula (III) as sole repeat units. Exemplary higher molecular weight acyclic para-aromatic poly(arylene ether ketone) homopolymers with a ^K /o ratio of at most 1.5 are para-aromatic PEKEKK homopolymers ( ^K /o=1.5) and para-aromatic PESEKK and PEEKK homopolymers (having both a ^K /o ratio of 1).

When the ratio ^K /o exceeds 1.5, which is the case when the repeat units of formula (III) are para-aromatic PEKK repeat units of formula (VI) the higher molecular weight acyclic poly(arylene ether ketone) comprises the repeat units of formula (III), in particular the repeat units of formula (VI), in a weight amount which ranges preferably from 50% to 95%, more preferably from 50% to 90%, still more preferably from 50% to 85%, based on the total weight of its repeat units. Then, the remaining repeat units may be notably repeat units of formula (III) other than (VI) characterized by a ratio ^K /o of at most 1.5 and/or repeat units of formula (VII)

(whatever with a ratio ^K /o of at most 1.5 or above 1.5), in particular repeat units of formula (VIII)

Of special interest for their outstanding high temperature stability, high mechanical strength, high crystallinity and high resistance to hydrolysis and organic solvents, are the PEKK homo- or co- polymers comprising as sole repeat units, repeat units of formula (VI) as above represented and repeat units of formula (VIII) as also above represented.

Of most industrial importance are the PEKK copolymers comprising, as sole repeat units, from 50 to 85 wt. % of repeat units of formula (VI) and from 50 to 15 wt. % of repeat units of formula (VIII).

The higher molecular weight acyclic poly(arylene ether ketone) comprising repeat units of formula (III) may be notably prepared by the process P ² or by the process P ³ in accordance with the present invention.

The ring-opening polymerization of the cyclic oligo(arylene ether ketone) of formula (I) may take place “in solution”, that is to say in a polymerization medium comprising a solvent which dissolves the cyclic oligo(arylene ether ketone) of formula (I) and the higher molecular weight acyclic poly(arylene ether ketone) comprising repeat units of formula (III). Alternatively and preferably, the ring-opening polymerization of the cyclic oligo(arylene ether ketone) of formula (I) takes place “in the melt”, that is to say in a polymerization medium wherein the cyclic oligo(arylene ether ketone) of formula (I) and the higher molecular weight acyclic poly(arylene ether ketone) comprising repeat units of formula (III) are at molten state. Polymerizing the cyclic oligo(arylene ether ketone) of formula (I) “in the melt” is especially preferred said cyclic oligo(arylene ether ketone) is impregnated on a continuous fiber.

The ring-opening polymerization of the cyclic oligo(arylene ether ketone) of formula (I) takes advantageously place in the presence of an initiator, preferably (i) cesium fluoride, (ii) an optionally substituted sodium, potassium or cesium phenolate, such as sodium, potassium or cesium phenolate, sodium, potassium or cesium 4-phenyl- phenolate, or sodium, potassium or cesium 4,4’-biphenolate, or (iii) a sodium, potassium or cesium salt of 4-hydroxybenzophenone.

The initiatoncyclic oligo(arylene ether ketone) molar ratio is generally 0.001-

0.05:1.

The ring-opening polymerization takes usually place at a temperature of from 100° to 450°C. It is preferably of at least 200°C, more preferably of at least 300°C. Besides, it is preferably of at most 400°C, more preferably of at most 380°C and still more preferably of at most 350°C. The ring-opening polymerization may take place in an inert atmosphere, under vacuum or under air.

The ring-opening polymerization may be carried out in an extruder.

When a composite material comprising a poly(arylene ether ketone) and a continuous fiber is formed, the ring-opening polymerization may be notably carried out in an extruder or during the continuous fiber impregnation. Since low viscosity is generally desired during the continuous fiber impregnation, the ring-opening polymerization is preferably carried out after the continuous fiber impregnation, possibly immediately thereafter or during or after the laminate formation (tape assembly). The continuous fiber impregnation may be notably melt impregnation, solution impregnation or slurry impregnation.

The initiator and cyclic oligo(arylene ether ketone) are advantageously heated until the polymerization temperature is reached.

Then, the ring-opening polymerization is allowed to proceed generally for 0.1- 600 min, preferably for 2-180 min and more preferably for 3-60 min, so as to obtain the higher molecular weight acyclic poly(arylene ether ketone). If the ring-opening polymerization is carried out in an extruder, the ring-opening polymerization is typically allowed to proceed for a duration which is lower than or equal to the residence time of the reaction mixture in the extruder, which may be very short, possibly below 10 min. Otherwise, longer durations may be applied, for example of at least 10, at least 20 or at least 30 min.

A transfer agent, such as monofluorobenzophenone, monochlorobenzophenone or monochlorodiphenylsulfone, may be added in the polymerization medium, possibly at start or during the course of the ring-opening polymerization.

When one cyclic oligo(arylene ether ketone) of formula (I) is caused to undergo the ring-opening polymerization, the higher molecular weight acyclic poly(arylene ether ketone) comprising repeat units of formula (III) which is manufactured is a homopolymer. Homopolymers are also manufactured when causing several cyclic oligo(arylene ether ketone)s of formula (I) differing from each other only by their degree of oligomerization (n) to undergo the ring-opening polymerization together.

Copolymers are manufactured notably when at least two cyclic oligo(arylene ether ketone)s of formula (I) differing from each other by their X and/or L are caused to undergo the ring-opening polymerization together. Copolymers are also manufactured when a cyclic oligo(arylene ether ketone) of formula (I) is caused to undergo the ring opening polymerization together with a cyclic oligo(arylene ether ketone) other than a cyclic oligo(arylene ether ketone) of formula (I), possibly a cyclic oligo(arylene ether sulfone), an ortho-aromatic cyclic oligo(arylene ether ketone) or a meta-aromatic cyclic oligo(arylene ether ketone) such as wherein n, in above formula (V), is as defined for the cyclic oligo(arylene ether ketone) of formula (I).

For example, when the cyclic oligo(arylene ether ketone) of formula (V) wherein n, in above formula (V), is as defined for the cyclic oligo(arylene ether ketone) of formula (I), is caused to undergo a ring-opening polymerization together with the cyclic oligo(arylene ether ketone) of formula (IX), a PEKK copolymer comprising, as sole repeat units, repeat units of formula (VI) and repeat units of formula (VIII) is manufactured.

By modifying the weight ratio of the cyclic oligo(arylene ether ketone) of formula (V) to the cyclic oligo(arylene ether ketone) of formula (IX), PEKK copolymers having various relative weight amounts of repeat units (VI) and repeat units (IX) can be obtained.

When a composite material is manufactured in accordance with the present invention, the continuous fiber is advantageously carbon fiber or glass fiber, preferably carbon fiber.

Composite materials incorporating a PEKK homo- or co- polymer [especially, a PEKK copolymer comprising, as sole repeat units, from 50 to 85 wt. % of para repeat units of formula (VI) and from 50 to 15 wt. % of meta repeat units of formula (VIII)], and a continuous fiber (such as glass fiber or carbon fiber), are worth being cited as high-performance composite materials of particular industrial importance that can be made in accordance with the process P ² and the use of the present invention. The present invention has numerous advantages.

It provides a new process capable of manufacturing para-aromatic cyclic oligo(arylene ether ketone)s, especially para-aromatic cyclic oligo(arylene ether ketone)s rich in carbonyl groups, with a decent yield, which can exceed 40%. A high selectivity towards the desired para-form is also advantageously obtained. The reaction products of the new process, which uses terephthaloyl chloride as the acylating agent, are generally a mixture of para-aromatic cyclic oligo(arylene ether ketone)s with different degrees of oligomerization, of which the distribution is advantageously narrower than the distribution obtained with homologue prior art processes using orthophthaloyl chloride or isophthaloyl chloride. The new process makes it often possible to manufacture one para-aromatic cyclic oligo(arylene ether ketone) in a much higher amount than the one or more other cyclic oligo(arylene ether ketone)(s) of the mixture; for example, the Applicant could obtain a para-aromatic cyclic trimer with a selectivity in the trimer well exceeding 80%.

The present invention provides also new para-aromatic cyclic oligo(arylene ether ketone)s, including para-aromatic cyclic PEEKK or PESEKK oligomers. Para-aromatic oligomers are required for forming PAEKs with straight repeat units; for example, para- aromatic cyclic PEEKK or PESEKK oligomers are required for the synthesis of straight high molecular weight PEEKK or PESEKK homopolymers respectively, which both exhibit a high level of thermal, mechanical and chemical properties.

In particular, the present invention provides new para-aromatic cyclic oligo(arylene ether ketone)s rich in carbonyl groups, especially para-aromatic cyclic PEKEKK or PEKK oligomers, which allow for the synthesis of the most performing acyclic high molecular weight PAEKs in terms of thermal, mechanical and chemical properties, among which straight PEKEKK homopolymers, straight PEKK homopolymers and acyclic PEKK copolymers comprising predominantly straight repeat units are worth being cited, with emphasis on the PEKK copolymers for their utmost industrial importance.

The para-aromatic cyclic oligo(arylene ether ketone)s of the present invention can be easily polymerized by ring-opening polymerization. They offer a wide processing window for the preparation of composite materials, which one can be adjusted notably via the nature and degree of oligomerization of the oligo(arylene ether ketone)(s) which is/are caused to be polymerized. This makes the ring-forming reaction route have an important application prospect in the field of preparing high-performance composite materials. Composite materials incorporating the above cited high molecular weight PAEKs and a continuous fiber such as glass fiber or carbon fiber, are worth being cited as high-performance composite materials of particular industrial importance that can be made from the cyclic oligo(arylene ether ketonejs of the present invention.

The present invention could not have been made without overcoming a long standing prejudice wherein no para-aromatic cyclic oligomer could be manufactured, a fortiori with a decent yield, by a process which would have been derived from Changchun’s process. By doing so, the Applicant has met a strong need which had remained unmet for more than a decade, yet in a competitive high-technology field.

For the avoidance of doubt, wherever used throughout the present patent title, represents a carbonyl

For the avoidance of doubt, wherever used throughout the present patent title, representations and the like, which are used in formulae and the like of para- or meta-aromatic cyclic oligo(arylene ether ketone)s, represent invariably a direct single bond which

“closes the loop” of the cyclic oligo(arylene ether ketone)s by connecting two of their repeat units. For example, in the cyclic oligo(arylene ether ketone) of formula (I), represents a direct single bond which “closes the loop” by connecting a carbon atom of a benzene ring to a carbonyl moiety; it does not represent a - CH ₂ - CH ₂ - CH ₂ - CH ₂ - moiety.

Wherever used throughout the present patent title, the indefinite article “a” is intended to encompass both the singular and the plural forms of the noun to which it relates, and has thus the same meaning as “at least one”. Likewise, the definite article “the” is intended to encompass both the singular and the plural forms of the noun to which it relates, and has thus the same meaning as “the at least one”.

Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence.

The present invention will now be illustrated by the following examples, which are not intended to be limiting.

EXAMPLES Comparative examples CE1 to CE10. Syntheses of ortho- and meta-aromatic cyclic oligo(arylene ether ketone)s under the same operating conditions

Various aromatic compounds were caused to react with orthophthaloyl chloride or isophthaloyl chloride so as to obtain respectively ortho- or meta-aromatic cyclic oligo(arylene ether ketone)s. All the syntheses were described in CN 1 443 762, assigned to Changchun Applied Chemistry. Comparative example CE1 is an English translation of example 1 of CN 1 443 762:

“Preparation of polyethersulfoneetherketoneketone cyclic oligomer comprising ortho-ketoneketone structure. 4.68 g (0.035 mol) of anhydrous aluminum trichloride and 200 mL of 1,2- dichloroethane were placed in a 500 mL three-necked flask provided with a spherical condenser tube with a calcium chloride drying tube connected at the top and a gas absorber connected to the drying tube. 1.0 mL of N-methylpyrrolidone was added dropwise into the three-necked flask under stirring. Additionally, 2.0302 g (0.01 mol) of o-phthaloyl chloride and 4.0238 g (0.01 mol) of 4,4 ’-diphenoxydiphenylsulfone were dissolved in 50 mL of 1 ,2-dichloroethane, and the solution was slowly added dropwise at a constant speed into the three-necked flask at room temperature within 8 h with vigorous stirring. Thereafter, the reaction mixture was further stirred for 2 h, and then 50 mL of 0.1 M dilute hydrochloric acid was added thereto to terminate the reaction.

The mixture was separated to obtain an organic phase. The organic phase was washed three times with 100 mL of distilled water to remove the catalyst, concentrated, and added dropwise into methanol for precipitation to obtain 5.05 g of cyclic oligomer with a yield of 95% ”. The operating modes used for comparative examples CE2 to CE10 differed from the one used for CE1 only by the nature of the monomer(s), viz. the aromatic compound and/or the phthaloyl chloride (either orthophthaloyl chloride or isophthaloyl chloride). Each monomer was used in the same molar amount as in CE1 (0.01 mol). For the rest, the same reaction conditions and the same treatment steps were applied. The yields are reported in table 1 here below.

Table 1

By comparing the yield of comparative example CE1 with the yield of comparative example CE2, the yield of CE3 with CE4, the yield of CE5 with CE6, the yield of CE7 with CE8, and also the yield of CE9 with CE10, it can be seen that the replacement of orthophthaloyl chloride by isophthaloyl chloride, everything else being left unchanged, resulted systematically in a high decrease of the yield, viz. about - 30%. Comparative example CE11. Synthesis of an ortho-aromatic cyclic PEKK oligomer under the same operating conditions as in CE1. This synthesis was also described in CN 1 443 762 (to Changchun Applied Chemistry). The operating mode used for comparative example CE11 differed from the one used for CE1 only by the nature of the aromatic compound monomer: diphenyl ether was used in CE11 (versus 4,4’-diphenoxy-diphenylsulfone in CE1). Thus, 0.01 mol of diphenyl ether and 0.01 mol of orthophthaloyl chloride were used, and the same reaction conditions and the same treatment steps were applied. The yield obtained in CE11 is reported in table 2 here below. Table 2 It can be observed that, when diphenyl ether was used as the aromatic compound (that is to say when an ortho-aromatic cyclic PEKK oligomer was prepared), the lowest yield in ortho-aromatic cyclic oligomers was obtained, when compared to any other aromatic compound the use of which was exemplified in CN 1443762 under the same operating conditions (minus about 10-15% yield when compared to any one of the other aromatic compounds). It can also be noted that CN 1443762 does not contain any example of synthesis of a meta-aromatic cyclic PEKK oligomer from diphenyl ether and isophthaloyl chloride, which contrasts with the fact that it systematically provides examples of synthesis of both ortho- and meta-aromatic cyclic oligomers when any aromatic compound other than diphenyl ether is concerned. Comparative example CE12 (not part of the prior art – for comparison purposes only). Synthesis of a meta-aromatic cyclic PEKK oligomer. In a 250 ml double-jacket reactor under N ₂ were charged successively 1,2- dichloroethane (100 ml), AlCl ₃ (2 g, 15 mmol, 6 eq.), 1,2-dichloroethane again (25 ml) and N-methyl-2-pyrrolidone (0.248 g, 0.241 ml, 2.5 mmol, 1 eq.), so as to form a yellow mixture 1. The yellow mixture 1 was stirred at 300 rpm at 25°C for 10 min. Then, a mixture 2 of isophthaloyl chloride (0.508 g, 2.5 mmol, 1 eq.) and diphenyl ether (0.426 g, 0.397 ml, 2.5 mmol, 1 eq.) in 1,2-dichloroethane (25 ml) was added slowly over a period of time of 8 hours to the yellow mixture 1, so as to form a reactive mixture 3. The addition rate of isophthaloyl chloride and diphenyl ether was kept approximately constant during this 8-hour period of time, and equal to about 1.058 mg/min of isophthaloyl chloride and about 0.8875 mg/min of diphenyl ether. During the 8-hour period of time, the mixture3 turned progressively from yellow to deep red, and an insoluble solid by-product4 appeared during this period. Then, IN HC1 (50 ml) was added to the deep red mixture 3, which comprised cyclic oligo(phenylene ether ketone)s and unreacted AlCh, so as to form a new reactive mixture 5. The reactive mixture 5 was stirred at 50°C for 4 hours, so as to allow for the quenching of unreacted AlCh. After 4 hours, a triphasic mixture 6 consisting of an organic phase 6a comprising cyclic oligo(phenylene ether ketone)s, an aqueous phase 6b comprising quenched AlCh, and the insoluble solid by-product4 was obtained. The triphasic mixture 6 was cooled to 25 °C and filtered to remove the insoluble solid by-product 4. The filtrate recovered after filtration consisting of the organic phase 6a and the aqueous phase 6b was left to settle during 5 min in a separating funnel, with the organic phase 6a at its bottom and the aqueous phase 6b at its top. The phases 6a and 6b were separately drawn off from the separating funnel. About 20 ml of di chi orom ethane were added to the aqueous phase 6b under stirring to form a biphasic mixture 7 comprising an organic phase 7a and an aqueous phase 7b. The biphasic mixture 7 was left to settle during 5 min in a separating funnel, with the organic phase 7a at its bottom and the aqueous phase 7b at its top. The phases 7a and 7b were separately drawn off from the separating funnel. Again, about 20 ml of dichloromethane were added to the aqueous phase 7b under stirring to form a new biphasic mixture 8 comprising an organic phase 8a and an aqueous phase 8b. The biphasic mixture 8 was in turn left to settle during 5 min in a separating funnel, with the organic phase 8a at its bottom and the aqueous phase 8b at its top. The phases 8a and 8b were separately drawn off from the separating funnel. The organic phases 6a,7a and 8a were mixed together so as to form an organic phase 9. The organic phase 9, which contained cyclic oligo(phenylene ether ketone)s and HC1, was washed with about 20 ml of water under stirring to form a biphasic mixture 10, with an organic phase 10a and an aqueous phase 10b. The biphasic mixture 10 was left to settle during 5 min in a separating funnel, with the organic phase 10a at its bottom and the aqueous phase 10b at its top. The pH of the aqueous phase 10b was measured; it was well below 4. Again, about 20 ml of water were added to the organic phase 10a under stirring to form a biphasic mixture 11 with an organic phase 11a and an aqueous phase lib. The biphasic mixture 11 was in turn left to settle during 5 min in a separating funnel, with the organic phase 11a at its bottom and the aqueous phase lib at its top. The pH of the aqueous phase lib was measured; it was substantially above 4. Should the pH had still been below 4, a further wash with H2O could have been desirable to remove further HC1 residues from the organic phase 11a. Then, 5 g of anhydrous MgSCE were added under stirring to the organic phase 11a which comprised a residual amount of water. The so- obtained MgS0 ₄ -organic phase admixture 12 was then filtered using a sintered filter, which retained hydrated MgSCE on the filter. An organic filtrate 13 essentially free of water was recovered; it comprised cyclic oligo(phenylene ether ketone)s, 1,2- dichloroethane and dichloromethane as main components. The 1,2-dichloroethane and dichloromethane were then evaporated from the organic filtrate 13 using a Buchi rotary evaporator at a temperature of 40°C and under reduced pressure (300 mbar), so as to afford 415 mg of a green solid 14 comprising cyclic oligo(phenylene ether ketone)s, corresponding to a yield of 55%, as defined by the ratio of the weight of the green solid 14 to the theoretical weight of oligo(phenylene ether ketone) repeat units obtainable by the full conversion of isophthaloyl chloride and diphenyl ether starting reagents into such oligo(phenylene ether ketone) repeat units.

As previously evidenced through comparative examples CE1 to CE10, the replacement of orthophthaloyl chloride by isophthaloyl chloride, everything else being left unchanged, resulted systematically in a decrease of the yield by about 30%; more precisely, the yield dropped by 28% with triphenyl diether, which could be seen as Changchun’s aromatic compound which is the most “similar” to diphenyl ether. The yield of 55% which the Applicant obtained with diphenyl ether/isophthaloyl chloride couple of monomers is consistent with Changchun’s reported yields, as it is also about 30% lower (26% lower exactly) than the yield Changchun obtained by coupling the same diphenyl ether with orthophthaloyl chloride in experiment CE11. Characterization of the green solid 14 HPLC

The HPLC chromatogram showed the presence of cyclic oligo(phenylene ether ketone)s, more precisely of: cyclic PEKK trimer having a retention time of 3.7 min, cyclic PEKK tetramer having a retention time of 5.3 min, cyclic PEKK pentamer having a retention time of 6.4 min, cyclic PEKK hexamer having a retention time of 7.3 min, and cyclic PEKK heptamer having a retention time of 7.9 min.

The distribution of the cyclic PEKK oligomers, estimated from the respective surface areas they develop on the HPLC chromatogram, was as follows:

47% of cyclic PEKK trimer,

31% of cyclic PEKK tetramer,

15% of cyclic PEKK pentamer,

5% of cyclic PEKK hexamer, and 2% of cyclic PEKK heptamer.

On the other hand, no cyclic PEKK dimer, which would have had a retention time of about 1.9-2.2 min, was identified.

NMR

Green solid 14 (1H, CDCh): 7.9 - 8.2 ppm (m, 2H), 7.7 - 7.9 ppm (m, 4H), 7.5 - 7.65 ppm (m, 2H), 6.9 - 7.3 ppm (m, 4H).

Example El (according to the invention). Synthesis of a para-aromatic cyclic PEKK oligomer.

In a 250 ml double-jacket reactor under N2 were charged successively 1,2- dichloroethane (100 ml), AlCb (2 g, 15 mmol, 6 eq.), 1,2-dichloroethane again (25 ml) and N-methyl-2-pyrrolidone (0.248 g, 0.241 ml, 2.5 mmol, 1 eq.), so as to form a yellow mixture 21. The yellow mixture 21 was stirred at 300 rpm at 25 °C for 10 min. Then, a mixture 22 of terephthaloyl chloride (0.508 g, 2.5 mmol, 1 eq.) and diphenyl ether (0.426 g, 0.397 ml, 2.5 mmol, 1 eq.) in 1,2-dichloroethane (25 ml) was added slowly over a period of time of 8 hours to the yellow mixture 21, so as to form a reactive mixture 23. The addition rate of terephthaloyl chloride and diphenyl ether was kept approximately constant during this 8-hour period of time, and equal to about 1.058 mg/min of terephthaloyl chloride and about 0.8875 mg/min of diphenyl ether. During the 8-hour period of time, the mixture 23 turned progressively from yellow to deep red, and an insoluble solid by-product 24 appeared during this period. Then, IN HC1 (50 ml) was added to the deep red mixture 23, which comprised cyclic oligo(phenylene ether ketone)s and unreacted AlCh, so as to form a new reactive mixture 25. The reactive mixture 25 was stirred at 50°C for 4 hours, so as to allow for the quenching of unreacted AlCh. After 4 hours, a triphasic mixture 26 consisting of an organic phase 26a comprising cyclic oligo(phenylene ether ketone)s, an aqueous phase 26b comprising quenched AlCh, and the insoluble solid by-product 24 was obtained. The triphasic mixture 26 was cooled to 25 °C and filtered to remove the insoluble solid by-product 24. The filtrate recovered after filtration consisting of the organic phase 26a and the aqueous phase 26b was left to settle during 5 min in a separating funnel, with the organic phase 26a at its bottom and the aqueous phase 26b at its top. The phases 26a and 26b were separately drawn off from the separating funnel. About 20 ml of dichloromethane were added to the aqueous phase 26b under stirring to form a biphasic mixture 27. The biphasic mixture 27 was left to settle during 5 min in a separating funnel, with the organic phase 27a at its bottom and the aqueous phase 27b at its top. The phases 27a and 27b were separately drawn off from the separating funnel. Again, about 20 ml of dichloromethane were added to the aqueous phase 27b under stirring to form a new biphasic mixture 28 comprising an organic phase 28a and an aqueous phase 28b. The biphasic mixture 28 was in turn left to settle during 5 min in a separating funnel, with the organic phase 28a at its bottom and the aqueous phase 28b at its top. The phases 28a and 28b were separately drawn off from the separating funnel. The organic phases 26a, 27a and 28a were mixed together so as to form an organic phase 29. The organic phase 29, which contained cyclic oligo(phenylene ether ketone)s and HC1, was washed with about 20 ml of water under stirring to form a biphasic mixture 30 with an organic phase 30a and an aqueous phase 30b. The biphasic mixture 30 was left to settle during 5 min in a separating funnel, with the organic phase 30a at its bottom and the aqueous phase 30b at its top. The pH of the aqueous phase 30b was measured; it was well below 4. Again, about 20 ml of water were added to the organic phase 30a under stirring to form a biphasic mixture 31 with an organic phase 31a and an aqueous phase 31b. The biphasic mixture 31 was in turn left to settle during 5 min in a separating funnel, with the organic phase 31a at its bottom and the aqueous phase 31b at its top. The pH of the aqueous phase 31b was measured; it was substantially above 4. Should the pH had still been below 4, a further wash with H2O could have been desirable to remove further HC1 residues from the organic phase 31a. Then, 5 g of anhydrous MgSCh were added under stirring to the organic phase 31a which comprised a residual amount of water. The so-obtained MgSCh-organic phase admixture 32 was then filtered using a sintered filter, which retained hydrated MgS04 on the filter. An organic filtrate 33 essentially free of water was recovered; it comprised cyclic oligo(phenylene ether ketone)s, 1,2-dichloroethane and di chi orom ethane as main components. The 1,2-dichloroethane and dichloromethane were then evaporated from the organic filtrate 33 using a Buchi rotary evaporator at a temperature of 40°C and under reduced pressure (300 mbar), so as to afford 325 mg of a green solid 34 comprising cyclic oligo(phenylene ether ketone)s, corresponding to a yield of 43%, as defined by the ratio of the weight of the green solid 34 to the theoretical weight of oligo(phenylene ether ketone) repeat units obtainable by the full conversion of terephthaloyl chloride and diphenyl ether starting reagents into such oligo(phenylene ether ketone) repeat units.

Surprisingly, the Applicant was able to synthesize a para-aromatic cyclic PEKK oligomer with a yield as high as 43%, which was barely 12% less than the yield achieved when synthesizing a meta-aromatic cyclic PEKK oligomer under the same operating conditions. This quite minor decrease in yield was unexpected because of the deemed extremely poor bond geometry of para-phenyl ene rings of cyclic oligomers. It was indeed commonly understood by the skilled person that para-phenylene rings form cyclics much less readily than meta-phenylene ones, in the same way as meta-phenylene rings are known to form cyclics much less readily than ortho-phenylene ones: this would be a matter of a bond angle between the diacid chloride, which is alleged to be disadvantageous for isophthaloyl chloride (too high, over 120°) when compared to orthophthaloyl chloride, resulting in the high decrease in yield observed by Changchun (and the even higher decrease in yield obtained by Guo et ah, as commented in the background art section), and would thus have been expected to be even more disadvantageous in case terephthaloyl chloride is used as the acylating agent.

More surprisingly, the yield of example El in accordance with the present invention was achieved for the synthesis of para-aromatic PEKK cyclic oligomers, while the global assessment of Changchun’s experimental data suggest rather to the skilled person that PEKK cyclic oligomers would be especially difficult-to-synthesize cyclic oligo(phenylene ether ketone)s: among all ortho-aromatic cyclic oligo(phenylene ether ketone)s prepared by Changchun, the lowest yield was achieved with ortho- aromatic cyclic PEKK (see comparative example CE15) and no synthesis of meta aromatic cyclic PEKK was (even) reported by Changchun.

Characterization of the green solid 34

HPLC

The HPLC chromatogram showed the presence of cyclic oligo(phenylene ether ketone)s, more precisely of cyclic PEKK trimer having a retention time of 3.7 min, and cyclic PEKK tetramer having a retention time of 6.1 min.

The distribution of the cyclic PEKK oligomers, estimated from the respective surface areas they develop on the HPLC chromatogram, was as follows:

84% of cyclic PEKK trimer, and 16% of cyclic PEKK tetramer.

On the other hand, no cyclic PEKK dimer, which would have had a retention time of about 1.9-2.2 min, was identified. Also, no cyclic PEKK higher oligomers, such as pentamer, hexamer and heptamer, were identified.

Example E2 (according to the invention). Synthesis of a para-aromatic cyclic PEKK oligomer.

Example E2 was a reproducibility test of example El. Thus, the reactants and operating conditions were exactly the same as in example El. The compositions which were used or formed in E2 are hereinafter labeled using the same numbers as those of El but followed with a ’ character, so as to distinguish them from those used or formed in El.

When conducting the experiment E2, the same visual or other observations were made as in experiment El : mixture 21’ (corresponding to mixture 21 of El) was also yellow; after the 8-hour period of time, mixture 23’ turned progressively from yellow to deep red, and an insoluble solid by-product 24’ appeared; after the 4-hour quenching period, a triphasic mixture 26’ was obtained; pH of aqueous phase 30b’ was well below 4; pH of the aqueous phase 31b’ was above 4.

Finally, 315 mg of a green solid 34’ comprising cyclic oligo(phenylene ether ketone)s were obtained, corresponding to a yield of 42%, as defined by the ratio of the weight of the green solid 34’ to the theoretical weight of oligo(phenylene ether ketone) repeat units obtainable by the full conversion of terephthaloyl chloride and diphenyl ether starting reagents into such oligo(phenylene ether ketone) repeat units.

Thanks to example E2, the Applicant could thus confirm the unexpectedly high yield in para-aromatic cyclic PEKK of example El.

Characterization of the green solid 34’

HPLC

As for the green solid 34 of example El, the HPLC chromatogram of the green solid 34’ of example E2 established the presence of cyclic PEKKs, more precisely of cyclic PEKK trimer and cyclic PEKK tetramer. Their distribution, estimated from the respective surface areas they develop on the HPLC chromatogram, was as follows:

87% of cyclic PEKK trimer, and

13% of cyclic PEKK tetramer.

On the other hand, as for the green solid 34 of El, no cyclic PEKK dimer was identified for the green solid 34’ of E2. Also, no cyclic PEKK higher oligomers, such as pentamer, hexamer and heptamer, were identified for the green solid 34’ of E2.

NMR

Green solid 34’ (1H, CDCh): 7.92 - 7.88 (m), 7.85 (s), 7.18 - 7.14 (m). Examples E3 to E7 (according to the invention). Additional syntheses of para-aromatic cyclic oligo(arylene ether ketone)s

Various aromatic compounds other than diphenyl ether are caused to undergo an acylation reaction with terephthaloyl chloride so as to obtain para-aromatic cyclic oligo(arylene ether ketone)s.

The operating modes used for examples E3 to E7 differ from the one used for examples El and E2 only by the nature of the aromatic compound monomer. In each of the examples in accordance with the invention, the aromatic compound monomer, whatever it is, is used in the same molar amount as in El and E2 (2.5 mmol). The same molar amount of terephthaloyl chloride is also used, and the same reaction conditions and treatment steps are applied.

Approximate yields are provided in table 3 here below. Table 3

Various para-aromatic cyclic oligo(arylene ether ketone)s, including para- aromatic cyclic PESEKK, PEKEKK and PEEKK oligomer s, are obtained with a yield of at least about 45%, typically barely minus 10-15% lower than the yield obtained when isophthaloyl chloride was used as acylating agent.

Examples E8 to E10 (according to the invention). Ring-opening polymerization of para-aromatic cyclic oligo(arylene ether ketone)s 250 mg of the para-aromatic cyclic oligo(arylene ether ketone)s obtained through example E3, E4 or E7 are weighed and well mixed with 5 mg of cesium fluoride, heated in a test tube filled with nitrogen, and reacted at about 300-350°C (e.g. about 325°C) for about 40 min in a melt state so as to obtain a linear poly(arylene ether ketone) with high molecular weight. Example E8 provides that, starting from the para-aromatic cyclic PESEKK oligomer of example E3, a linear para-aromatic PESEKK polymer with a high molecular weight is obtained. Example E9 provides that, starting from the para-aromatic cyclic PEKEKK oligomer of example E4, a linear para-aromatic PEKEKK polymer with a high molecular weight is obtained.

Example E10 provides that, starting from the para-aromatic cyclic PEEKK oligomer of example E7, a linear para-aromatic PEEKK polymer with a high molecular weight is obtained.

Examples Ell to E15 (according to the invention). Ring-opening polymerization of mixtures of meta-aromatic and para-aromatic cyclic PEKK oligomers

In accordance with example Ell, 170 mg of the para-aromatic cyclic PEKK oligomer obtained through example El and 80 mg of the meta-aromatic cyclic PEKK obtained through comparative example CE12 are weighed, and well mixed with 5 mg of cesium fluoride, heated in a test tube filled with nitrogen, and reacted at about 300- 350°C (e.g. at about 325°C) for 40 min in a melt state so as to obtain an acyclic PEKK polymer with high molecular weight comprising about 68 wt% of straight repeat units (derived from the para oligomer) and 32 wt% of kinked repeat units (derived from the meta oligomer).

The operating mode for example E12 is identical to the one as above detailed for example Ell, except that 212 mg of the para-aromatic cyclic PEKK oligomer obtained through example El and 38 mg of the meta-aromatic cyclic PEKK obtained through comparative example CE12 are caused to undergo a ring opening polymerization, thereby obtaining an acyclic PEKK polymer with about 85 wt% of straight repeat units and 15 wt% of kinked repeat units.

The operating mode for example El 3 is identical to the one as above detailed for example Ell, except that 125 mg of the para-aromatic cyclic PEKK oligomer obtained through example El and 125 mg of the meta-aromatic cyclic PEKK obtained through comparative example CE12 are caused to undergo a ring opening polymerization, thereby obtaining an acyclic PEKK polymer with about 50 wt% of straight repeat units and 50 wt% of kinked repeat units.

The operating mode for example E14 is identical to the one as above detailed for example Ell, except that cesium fluoride is replaced weight pro weight by potassium 4,4’-biphenoxide as nucleophilic initiator. As in example Ell, an acyclic PEKK polymer with high molecular weight comprising about 68 wt% of straight repeat units (derived from the para oligomer) and 32 wt% of kinked repeat units (derived from the meta oligomer) is obtained.

In accordance with example El 5, 170 mg of the para-aromatic cyclic PEKK oligomer obtained through example El and 80 mg of the meta-aromatic cyclic PEKK obtained through comparative example CE12 are dissolved in a minimum amount of methylene chloride. The so-obtained solution is then mixed with 0.5 mL of a solution comprising potassium 4,4’-biphenoxide at a concentration of 2.5 mg/mL. The resulting mixture is then dried at 80°C under vacuum for 12 h so as to get a dry powder. The dry powder is placed in a test tube equipped with a nitrogen inlet and outlet. The ring opening polymerization of the cyclic PEKK oligomers is carried out in melt state under nitrogen atmosphere for 40 min at about 300-350°C (e.g. at about 325°C) to afford an acyclic PEKK polymer with about 68 wt% of straight repeat units and 32 wt% of kinked repeat units.