Patent Description:
Phthalonitrile (aka benezene-<NUM>,<NUM>-dicarbonitrile) is an organic compound with the formula C<NUM>H<NUM>(CN)<NUM> that is observed as an off-white crystal that is solid at room temperature. It has low solubility in water but it is soluble in common organic solvents. Phthalonitrile is typically used to prepare phthalocyanine, which is used as a dye or pigment. Phthalonitrile compounds, i.e. compounds that include a phthalonitrile moiety, can be used in the manufacture of composites, coatings, adhesives, and other speciality chemical materials. However many phthalonitrile derivatives, especially those containing silicon tend to have poor moisture stability.

It is known to prepare resins from certain phthalonitrile compounds however such resins tend to be poorly liquid processible, i.e. they are essentially incapable of being combined with fibres using liquid composite moulding techniques including resin infusion and resin transfer moulding. Such processes typically require a viscosity of <<NUM> cP (wherein <NUM> cP = <NUM> Pa. s) at the injection temperature, which is generally below <NUM> and ideally below <NUM>. Most historic phthalonitrile compounds do not fulfil these criteria. The feature of phthalonitriles that makes them most valuable compared to conventional thermoset resins is the thermal stability after polymerisation and in particular, their uniquely high thermal decomposition temperatures, which are usually in excess of <NUM> or even <NUM>. This stability is a direct product of the strong phthalocyanine and triazine units, which form the crosslinks in the cured material.

In addition to the thermal stability, the processing characteristics and stability of the uncured resin are also of fundamental importance. The polar, highly aromatic structure of phthalonitriles means that they usually have high melting points (><NUM>) and as such do not achieve a processible viscosity until they are raised above <NUM> or even <NUM>. This is particularly problematic because, when catalysed, most phthalonitriles begin curing at ~<NUM>. Crucially, high viscosity resins are not appropriate for liquid composite moulding techniques because fibre impregnation is greatly hindered. Poor impregnation results in a range of defects in the product fibre-reinforced composite, including dry fibres and voids. Accordingly, phthalonitriles should ideally be designed to be low-melting and low viscosity at common liquid resin injection temperatures (<NUM> to <NUM>). Furthermore, these uncured phthalonitriles should be stable prior to their cure. Although there is nothing intrinsically unstable about phthalonitriles themselves, strategies to decrease melting point and viscosity, can introduce groups that make the overall molecular structure unstable (e.g. to heat or moisture).

<NPL> discloses certain phthalonitrile compounds with siloxane bridges and discusses the influence of a multi-step curing pathway on the polymer matrix structure and properties using computer simulations at the mesoscale level. Coarse-grained dissipative particles dynamics (DPD) modelling is used to simulate the curing process at various conditions.

<NPL> studied certain low-melting siloxane- and phosphate-bridged phthalonitrile monomers. These include two diphthalonitrile compounds, namely bis(<NUM>-(<NUM>,<NUM>-dicyanophenoxy)phenyl)-phenyl phosphate (4a) and bis(<NUM>-(<NUM>,<NUM>-dicyanophenoxy)phenyl)phenylphosphonate (4b), which have a central phosphate group and a glass transition temperature of <NUM> and <NUM> respectively. It is understood that these glass transition temperatures can also be described as melting point temperatures.

<NPL> have disclosed certain low-melting siloxane-bridged phthalonitrile monomers. These include two diphthalonitrile compounds, namely <NUM>,<NUM>'-(((((diphenylsilanediyl)bis(oxy))bis-(methylene))bis(<NUM>,<NUM>-phenylene))bis(oxy))diphthalonitrile (<NUM>) and <NUM>,<NUM>'-(((((phenyl(methyl)-silanediyl)bis(oxy))bis(methylene))bis(<NUM>,<NUM>-phenylene))bis(oxy))diphthalonitrile (<NUM>), which have a central siloxane group and a glass transition temperature of <NUM> and <NUM> respectively. Once again it is understood that these glass transition temperatures can also be described as melting point temperatures.

European patent application <CIT>) discloses phthalonitrile monomers modified with organosilicon fragments and a method of obtaining them. The modified phthalonitriles can be used in aircraft and automobile manufacturing to produce polymer composite materials.

<NPL> have disclosed silicon-containing phthalonitrile monomers and self-catalyzed silicon-containing phthalonitrile resins. The monomers include three diphthalonitrile monomers, namely HSiPN (<NUM>,<NUM>'-((((methylsilanediyl)bis(azanediyl))bis(<NUM>,<NUM>-phenylene))bis(oxy))-diphthalonitrile), MeSiPN (<NUM>,<NUM>'-((((dimethylsilanediyl)bis(azanediyl))bis(<NUM>,<NUM>-phenylene))-bis(oxy))diphthalonitrile) and ViSiPN (<NUM>,<NUM>'-((((methyl(vinyl)silanediyl)bis(azanediyl))-bis(<NUM>,<NUM>-phenylene))bis(oxy))diphthalonitrile), which have a central diaminosilane group and a melting point of <NUM>, <NUM> and <NUM> respectively. Such compounds have however proved in use to be unstable, i.e. to the moisture in ambient air, and there of very limited utility.

It is therefore desirable to provide diphthalonitrile compounds, diphthalonitrile resin blends and diphthalonitrile resins with improved processability or to at least provide useful alternatives to known diphthalonitrile compounds, diphthalonitrile resin blends and diphthalonitrile resins.

In a first aspect the present invention provides a diphthalonitrile compound of formula I:.

Ar<NUM>(CN)<NUM>-O-Ar<NUM>-CH<NUM>-O-Si(R<NUM>)(R<NUM>)-O-[T-O-Si(R<NUM>)(R<NUM>)-O-]n-CH<NUM>-Ar<NUM>-O-Ar<NUM>(CN)<NUM>     (I).

in free or salt or solvate form, wherein:.

In certain embodiments the diphthalonitrile compound is a compound of formula I, wherein:.

In a second aspect the present invention provides a diphthalonitrile resin blend comprising one or more diphthalonitrile compounds of the first aspect, and an aromatic amine catalyst.

In a third aspect the present invention provides a diphthalonitrile resin comprising a cured diphthalonitrile resin blend of the second aspect.

In a fourth aspect the present invention provides a coating comprising a diphthalonitrile resin of the third aspect.

In a fifth aspect the present invention provides a process for preparing a diphthalonitrile compound of the first aspect.

In a sixth aspect the present invention provides a process for preparing a diphthalonitrile resin of the third aspect, the process comprising curing a diphthalonitrile resin blend of the second aspect to form a diphthalonitrile resin of the third aspect.

The term "phthalonitrile" as used herein means an organic compound with the formula C<NUM>H<NUM>(CN)<NUM> that is observed as an off-white crystal that is solid at room temperature. The IUPAC name for phthalonitrile is benezene-<NUM>,<NUM>-dicarbonitrile.

The term "phthalonitrile compound" as used herein means any organic compound that includes a C<NUM>H<NUM>(CN)<NUM> moiety.

The term "diphthalonitrile" as used herein means any organic compound that includes two C<NUM>H<NUM>(CN)<NUM> moieties.

The term "eutectic mixture" as used herein means a homogeneous mixture of a first phthalonitrile compound and a second phthalonitrile compound that melts or solidifies at a single temperature that is lower than the melting point of the first phthalonitrile compound or the second phthalonitrile compound.

The term "aromatic amine catalyst" as used herein means a catalyst that includes at least one aromatic group that substituted by at least one amino group. In some embodiments the aromatic amine catalyst is <NUM>,<NUM>'-((sulfonylbis(<NUM>,<NUM>-phenylene))-bis(oxy))dianiline (p-BAPS), <NUM>,<NUM>'-(<NUM>,<NUM>-phenylenebis(oxy))dianiline (m-APB), or <NUM>-(<NUM>-aminophenoxy)phthalonitrile.

The term "C<NUM>-C<NUM>-alkyl group" as used herein means as used herein denotes straight chain or branched alkyl having <NUM> to <NUM> carbon atoms. In some embodiments C<NUM>-C<NUM>-alkyl is methyl, ethyl, n-propyl, isopropyl, n-butyl, s-butyl, i-butyl, t-butyl, -C(CH<NUM>)<NUM>C<NUM>H<NUM>, -CH(CH<NUM>)C<NUM>H<NUM> or -CH(CH<NUM>)CH<NUM>C(CH<NUM>)<NUM>.

The term "C<NUM>-C<NUM>-alkylene group" as used herein means a straight chain or branched alkylene that contains one to ten carbon atoms, for example, methylene, ethylene, trimethylene, methylethylene, tetramethylene, -CH(CH<NUM>)CH<NUM>CH<NUM>-, -CH<NUM>CH(CH<NUM>)CH<NUM>-, straight or branched pentylene, straight or branched hexylene, straight or branched heptylene, straight or branched octylene, straight or branched nonylene, or straight or branched decylene. C<NUM>-C<NUM>-alkylene may be C<NUM>-C<NUM> alkylene, e.g. ethylene or methylethylene.

The term "C<NUM>-C<NUM>-aryl group" as used herein means a monovalent carbocyclic aromatic group that contains <NUM> to <NUM> carbon atoms and which may be, for example, a monocyclic group such as phenyl or a bicyclic group such as naphthyl. C<NUM>-C<NUM>-aryl may be C<NUM>-C<NUM>-aryl, e.g. phenyl.

The term "halo" as used herein means an element belonging to group <NUM> (formerly group VII) of the Periodic Table of Elements, which may be, for example, fluorine, chlorine, bromine or iodine. In some embodiments, halo is chloro.

The term "leaving group" as used herein means a molecular fragment that departs with a pair of electrons in heterolytic bond cleavage. Good leaving groups are typically weak bases. In some embodiments, the leaving group is halo, e.g. chloro, or the leaving group is a triflate group (OTt).

The term "solvate" as used herein denotes a molecular complex comprising a compound of the present invention and one or more solvent molecules, for example ethanol. The term "hydrate" is used when the solvent is water.

The term "processible" as used herein means, e.g. with respect to a resin, being capable of being combined with fibres using liquid composite moulding techniques including resin infusion and resin transfer moulding. Such processes typically require a viscosity of <<NUM> cP (wherein <NUM> cP = <NUM> Pa. s) at the injection temperature, which is generally below <NUM> and ideally below <NUM>.

Other than in the operating examples, or where otherwise indicated, all numbers expressing quantities of ingredients used herein are to be understood as modified in all instances by the term "about".

Throughout this specification and in the claims that follow, unless the context requires otherwise, the word "comprise" or variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other stated integer or group of integers.

Aspects and embodiments of the present invention will now be discussed with reference to the accompanying drawings.

The present invention concerns diphthalonitrile compounds or monomers, diphthalonitrile resin blends that include one or more of such diphthalonitrile compounds, diphthalonitrile resins that comprise such diphthalonitrile resin blends that have been cured, coatings that comprise such diphthalonitrile resins. The present invention also concerns a process for preparing such diphthalonitrile compounds and a process for preparing such diphthalonitrile resins.

These aspects of the present invention will be described separately.

In a first aspect there is provided a diphthalonitrile compound of formula I:.

While not wanting to be bound by theory, the poor moisture stability of known silicon-containing phthalonitriles (PNs) is overcome via incorporation of bulky, hydrophobic groups onto the Si centre, conferring stability both by sterically shielding the Si-O bonds from attacking water molecules and by strengthening the Si-O bonds by electronic induction. The bulky silicon units have the additional advantage of suppressing the melting point, conferring resins made therefrom with desirable processing characteristics.

Again while not wanting to be bound by theory, Si-groups can confer greater melting point suppression (improved processability) than phosphate groups, e.g. as per the compounds of the aforementioned <NPL>. The phosphate structure also offers less 'tuneability' or capacity for modification than the Si-groups of the compounds of the present invention. The siloxane structures of the aforementioned <NPL> are not air stable, i.e. they react with the moisture in the air and decompose over a relatively short period of time. And the aminosilane structures of the aforementioned <NPL> are not air stable and decompose rapidly when in contact with atmospheric moisture.

In some embodiments, Ar<NUM> is a C<NUM>-C<NUM>-aryl group, e.g. phenyl.

In some embodiments, R<NUM> is C<NUM>-C<NUM>-alkyl, e.g. propyl or butyl, In some embodiments, propyl is isopropyl and/or butyl is t-butyl.

In some embodiments, R<NUM> and R<NUM> are the same. In some embodiments, R<NUM> and R<NUM> are the different.

In some embodiments, T is a C<NUM>-C<NUM>-aryl group, e.g. phenyl.

In some embodiments, n is <NUM>, <NUM>, <NUM>, or <NUM>, or a mixture thereof.

In some embodiments the diphthalonitrile compound is a compound of formula I in free or salt or solvate form, wherein:.

The diphthalonitrile compound of formula I may be a compound of formula IIa:
<CHM>
in free or salt or solvate form.

This compound is a viscous liquid or oily solid at room temperature (dependent on purity) and is moisture stable. It is thus compatible with conventional composites processing techniques e.g. infusion, resin transfer moulding (RTM), prepreg/ATL/ATP (automated tape laying/automated fibre placement).

The diphthalonitrile compound of formula I may be a compound of formula Ilb:
<CHM>
in free or salt or solvate form, where n is <NUM>, <NUM>, <NUM> or <NUM>, or a mixture thereof.

In some embodiments the diphthalonitrile compound of formula I is a mixture of compounds of formula IIb with n = <NUM> as the modal species.

Oligomerisation enables one to modify or tune the material properties of resins made from the diphthalonitrile compounds, for example by varying the constituent ratio and/or substitution of different diols (e.g. resorcinol, bisphenol C2).

The diphthalonitrile compound of formula I may be a compound of formula llc:
<CHM>
in free or salt or solvate form.

Compounds of formula I, which includes compounds of formulae IIa, IIb and IIc, can be prepared using known procedures or using the process described below.

Compounds of formula I are useful as monomers from which diphthalonitrile resins can be prepared. Such resins have various applications including as coatings for aerospace components, e.g. gas turbine aircraft components.

In a second aspect there is provided diphthalonitrile resin blends that include one or more of diphthalonitrile compounds of the first aspect. The diphthalonitrile resin blends are formulated as to be curable diphthalonitrile resin blends. They may be so formulated in many ways that are known in the art.

In some embodiments the curable diphthalonitrile resin blend is free of any solvent, or at least substantially free of any solvent. This is desirable for several reasons. It reduces safety risks for those who manufacture and otherwise work with the materials. It is environmentally advantageous as it means using fewer chemicals, being less reliant on petroleum- based feedstocks, and minimising chemical waste. From a processing perspective, it avoids the need to remove any solvent from the final product thereby simplifying processing, maximising yield, and minimising the formation of voids in the product that could weaken the product. Furthermore, solvent systems generally cannot be processed by liquid composite moulding.

The curable diphthalonitrile resin blend can be formulated to fine-tune one or more properties of the resin produced by curing it. Such properties may include, for example, the process ability/fluidity/viscosity prior to curing, thermo-mechanical properties (e.g. glass-transition temperature), thermal and thermo-oxidative stability, reactivity, extremely low dielectric constant, and flame retardancy moisture absorption, and/or erosion performance.

The curable diphthalonitrile resin blend typically has a low viscosity that makes blending much easier than would be expected of high viscosity materials.

In some embodiments the curable diphthalonitrile resin blend includes a catalyst in order to lower the cure initiation temperature. This is useful when low temperature processing is needed. Curable diphthalonitrile resin blends of the present invention typically include a catalyst as curing/polymerisation typically occurs at <NUM> or higher.

The catalyst, when desired or necessary, catalyses the polymerisation of the monomers.

The catalyst can take many forms suitable for the required purpose. In some embodiments the catalyst is an aromatic amine catalyst.

Various aromatic amine catalysts are known in the art.

In some embodiments the aromatic amine catalyst is <NUM>,<NUM>'-((sulfonylbis(<NUM>,<NUM>-phenylene))-bis(oxy))dianiline (aka p-BAPS), <NUM>,<NUM>'-(<NUM>,<NUM>-phenylenebis(oxy))dianiline (aka m-APB), or <NUM>-(<NUM>-aminophenoxy)phthalonitrile.

In some embodiments the diphthalonitrile resin blend comprises a eutectic mixture of two or more compounds of formula I in free or salt or solvate form.

In some embodiments the diphthalonitrile resin blend comprises two or more of the group consisting of a compound of formula IIa, a compound of formula IIb, and a compound of formula IIc.

If desired, any further additives including alternative DPNs and/or toughening agents can be added to the blend, e.g. in proportions between <NUM> and <NUM> mol%, such that the proportion of IIa remains between <NUM> and <NUM> mol%.

In a third aspect there is provided diphthalonitrile resins that comprise diphthalonitrile resin blends of the second aspect that have been cured, i.e. cured diphthalonitrile thermosets.

The curing process can be performed by any art known curing method. Such methods may include autoclaving, hot pressing, or liquid moulding.

The resin comprises thermoset polymers with low viscosities (e.g. about <<NUM> mPa. s) at temperatures lower than about <NUM>, making liquid composite moulding feasible at temperatures below about <NUM>, and in some cases at ambient temperature. The low viscosity and fluidity of the blend facilitates suitably wetting and suitably covering the fibres when impregnating the fibrous reinforcement in the manufacture of laminates/composites.

The liquid processible diphthalonitrile resins of the present invention have desirable electrical, thermal, and other properties that enable useful applications in various industries including the aerospace and electronics industries.

In the aerospace industry for example, liquid processible diphthalonitrile resins of the present invention can be combined with a fibrous reinforcement, such as carbon or glass, to produce composite materials, which possess properties that provide weight, strength and other advantages over more traditionally used metals such as steel and aluminium.

Desirable properties of cured diphthalonitrile thermosets of the present invention as represented by those formed from diphthalonitrile compounds of formulae IIa, IIb and Ilc are demonstrated in the Examples, more particularly Example <NUM>.

The significant improvement in air stability exhibited by IIa, IIb and IIc indicates that a variety of structures related to these compounds would be expected to have both good processing characteristics (low melting point and viscosity) and high moisture stability. Accordingly, the structure of IIb could be tuned in one of at least three ways to affect the physical properties of both the liquid resin and the cured thermoset network:.

In a fourth aspect there is provided a coating that comprises a diphthalonitrile resin of the third aspect.

Such coatings have various applications including providing protective coatings for aerospace components, e.g. gas turbine aircraft components.

Such coatings enable aerospace components to maintain their required functionality when exposed to high temperatures, e.g. up to <NUM>.

The coating can be applied to the aerospace component using any suitable method known in the art. The thickness of the coating can be determined by the skilled person for the desired function.

In a fifth aspect there is provided a process for preparing diphthalonitrile compounds of the first aspect, i.e. diphthalonitrile compounds of formula I:.

where Ar<NUM>, Ar<NUM>, Ar<NUM>, Ar<NUM>, L, R<NUM>, R<NUM>, R<NUM>, R<NUM>, and n are as hereinbefore defined.

The process for preparing a diphthalonitrile compound of formula I, in free or salt or solvate form, comprises:.

Process variant (A) may be effected using known procedures of reacting alcohols with silanes or analogously, for example as hereafter described in the Examples. The reaction may be conveniently carried out in a solvent, e.g. tetrahydrofuran, and in the presence of a base, e.g. triethylamine.

Process variant (B) may be effected using known procedures of reacting alcohols with silanes or analogously, for example as hereafter described in the Examples. The reaction may be conveniently carried out in a solvent, e.g. tetrahydrofuran, and in the presence of a base, e.g. triethylamine.

Leaving groups are well known in the art and the skilled person can select suitable leaving groups. Good leaving groups are typically weak bases. In some embodiments, the leaving group is halo, e.g. chloro, or the leaving group is a triflate group (OTf).

Compounds of formula III are commercially available or may be prepared as demonstrated in the Examples.

Compounds of formula IV and V are commercially available or may be prepared by known procedures.

In a sixth aspect there is provided a process for preparing diphthalonitrile resins of the third aspect. The diphthalonitrile resins are prepared by curing diphthalonitrile resin blends of the second aspect.

As mentioned above, the curing process can be performed by any art known curing method. Such methods may include autoclaving, hot pressing or liquid moulding.

In some embodiments the diphthalonitrile resin blend is partially cured to prevent or minimise phase separation during the curing step.

The diphthalonitrile resin blend may be degassed after the partial curing, e.g. under vacuum at <NUM> for <NUM> minutes or until there are no visual bubbles in the mixture, to remove entrapped air before the curing step to prevent or at least minimise the formation voids in the cured product.

For example, the curing is performed at an elevated temperature, e.g. at <NUM> for about <NUM> hours, at <NUM> for about <NUM> hours and at <NUM> for about <NUM> hours.

An additional post curing step may be performed to increase the thermal stability of the resin.

The follow examples are provided to illustrate embodiments of the resin composition and resin blend of the present invention.

<NUM>-hydroxybenzaldehyde (<NUM>, <NUM> mmol) and K<NUM>CO<NUM> (<NUM>, <NUM> mmol) were added against a flow of N<NUM> to a flame-dried Schlenk flask equipped with magnetic stirrer. N,N-dimethylformamide (DMF, <NUM>) was then added and the reaction vessel cooled to <NUM>. In a separate flame-dried Schlenk flask, <NUM>-nitrophthalonitrile (<NUM>, <NUM> mmol) was added and then dissolved in DMF (<NUM>). The resulting <NUM>-nitrophthalonitrile solution was then added to the first Schlenk incrementally over the course of <NUM>-<NUM> minutes, producing an orange suspension that became dark brown with further addition. The reaction mixture was then heated to <NUM> and stirred for a further <NUM> hours. Thereafter, the reaction mixture was poured into ice water (~<NUM>), and the resultant brown precipitate isolated via Büchner filtration (<NUM> x <NUM> aqueous washes). The brown filtrand was then dissolved in CH<NUM>Cl<NUM> and washed with brine (<NUM> x <NUM>). The CH<NUM>Cl<NUM> solution was then dried through addition of MgSO<NUM> and filtered prior to rotary evaporation, resulting in intermediate X as an off-white solid (<NUM>, <NUM>%). <NUM>H NMR (DMSO-D6, <NUM>): <NUM> (s, <NUM>, (CO)H); <NUM> (d, <NUM>, JHH = <NUM>, (CN)ArH); <NUM> (d, <NUM>, JHH = <NUM>, <NUM>, (para)ArH); <NUM> (m, <NUM>, (CN)ArH); <NUM> (dd, <NUM>, JHH = <NUM>, <NUM>, (CN)ArH); <NUM> (d, <NUM>, JHH = <NUM>, (para)ArH). In agreement with literature data.

Intermediate X (<NUM>, <NUM> mmol) was added against a flow of N<NUM> to a flame-dried Schlenk flask equipped with magnetic stirrer. Tetrahydrofuran (THF, <NUM>) was added to the flask, the resultant suspension was then cooled to <NUM> prior to the addition of sodium borohydride (<NUM>, <NUM> mmol). Methanol (<NUM>) was then slowly (<NUM> minutes) added to the reaction mixture, resulting in the formation of an orange solution. The reaction was stirred for <NUM> hour and then quenched by pouring into ice water (<NUM>). The resultant aqueous suspension was then acidified to pH <NUM>-<NUM> via the careful addition of aqueous HCl. The crude product (a brown oil) was then extracted into diethyl ether (<NUM> x <NUM>). The combined organic fractions were washed with brine (<NUM> x <NUM>) and then treated with MgSO<NUM>. After filtration, the product was concentrated under vacuum, revealing an orange-brown oil, which was dried overnight and eventually formed intermediate Y as an off-white solid (<NUM>, <NUM>%). <NUM>H NMR (DMSO-D6, <NUM>): <NUM> (d, <NUM>, JHH = <NUM>, (CN)ArH); <NUM> (d, <NUM>, JHH = <NUM>, (CN)ArH); <NUM> (m, <NUM>, (para)ArH); <NUM> (dd, <NUM>, JHH = <NUM>, <NUM>, (CN)ArH); <NUM> (m, <NUM>, (para)ArH); <NUM> (t, <NUM>, OH), <NUM> (d, <NUM>, JHH = <NUM>, CH<NUM>). In agreement with literature data.

Intermediate Y (<NUM>, <NUM> mmol) was added against a flow of N<NUM> to a flame-dried Schlenk flask equipped with magnetic stirrer. THF (<NUM>) and triethylamine (<NUM>, <NUM> mmol) were added to the flask and the resultant solution was then cooled to <NUM>. Dichlorodiisopropylsilane (<NUM>, <NUM>, <NUM> mmol) was then added (dropwise over <NUM>) to the reaction mixture. The reaction was allowed to gradually warm to room temperature and stirred for <NUM> hours. At this stage, TLC (thin layer chromatography, <NUM>:<NUM> (ethyl acetate:hexane) was used to monitor the reaction via comparison with intermediate Y. The crude reaction mixture (an orange solution) was then filtered by cannula to another Schlenk and concentrated under vacuum, affording IIa as a red oil (<NUM>, <NUM>%). <NUM>H NMR (CDCl<NUM>, <NUM>): <NUM> (m, <NUM>, (CN)ArH); <NUM> (m, <NUM>, (para)ArH); <NUM> (m, <NUM>, (CN)ArH); <NUM> (m, <NUM>, (para)ArH); <NUM> (s, <NUM>, CH<NUM>); <NUM> (m, <NUM>, alkyl-H).

The compound of formula Ila is <NUM>,<NUM>'-((((diisopropylsilanediyl)bis(oxy))bis(methylene))-bis(<NUM>,<NUM>-phenylene))bis-(oxy))diphthalonitrile.

Intermediate Y (<NUM>, <NUM> mmol) and resorcinol (<NUM>, <NUM> mmol) were added to a flame-dried Schlenk flask equipped with a magnetic stirrer. THF (<NUM>) and triethylamine (<NUM>) were added and the solids dissolved. The solution was then cooled to <NUM> prior to the dropwise addition of dichlorodiisopropyl-silane (<NUM>, <NUM> mmol, <NUM>) over <NUM> minutes. The reaction was warmed to <NUM> and left to stir for <NUM> hours. Thin layer chromatography (<NUM>:<NUM> ethyl acetate:hexane) revealed a small quantity of residual intermediate Y. A further <NUM> of THF was added to the reaction, which was then left to stir for a further <NUM> hours. The reaction was then filtered and the residue washed with THF (<NUM> x <NUM>). The solvent was then removed under reduced pressure and the product dried overnight under vacuum at <NUM>, revealing IIb as a dark red oil (<NUM>, <NUM>%). <NUM>H NMR (CDCl<NUM>, <NUM>): <NUM> (m, <NUM>, ArH), <NUM> (m, <NUM>, ArH), <NUM> (m, <NUM>, ArH), <NUM> (m, <NUM>, ArH), <NUM> (m, <NUM>, ArH), <NUM> (m, <NUM>, CH<NUM>), <NUM> (m, <NUM>, iPrH). FTIR v(CN) / cm-<NUM>: <NUM>.

The compound of formula Ilb where n is <NUM> is <NUM>,<NUM>'-((((((<NUM>,<NUM>-phenylenebis(oxy))bis-(diisopropylsilanediyl))bis(oxy))bis(methylene))bis(<NUM>,<NUM>-phenylene))bis(oxy))-diphthalonitrile. However the procedure described above provides a mixture of compounds of formula IIb where n is <NUM>, <NUM>, <NUM> or <NUM>, or more particularly a mixture of compounds of formula IIb with n = <NUM> as the modal species.

Intermediate Y (<NUM>, <NUM> mmol) was added to a flame-dried Schlenk flask equipped with magnetic stirrer and dissolved in THF (<NUM>). Triethylamine (<NUM>, <NUM> mmol) was then added, and the combined solution cooled to <NUM>. tBu<NUM>Si(OTf)<NUM> (<NUM>, <NUM> mmol) was added dropwise over <NUM> minutes. The reaction mixture was then allowed to warm to room temperature and left to stir for <NUM> hours. Volatiles were removed under reduced pressure and then the crude product was dissolved in CH<NUM>Cl<NUM> (<NUM>). This solution was then washed with a combination of deionised water (<NUM> x <NUM>) and brine (<NUM>), which facilitated the separation of organic and aqueous layers. The organic fraction was separated, dried over MgSO<NUM>, filtered and then concentrated under reduced pressure, affording IIc as a golden-brown oil (<NUM>, <NUM>%). <NUM>H NMR (DMSO-d6, <NUM>): <NUM> (m, <NUM>, Ar(CN)H), <NUM> (m, <NUM>, Ar(para)H), <NUM> (m, <NUM>, Ar(CN)H), <NUM> (m, <NUM>, Ar(para)H), <NUM> (s, <NUM>, CH<NUM>), <NUM> (s, <NUM>, CH<NUM>). FTIR v(CN) / cm-<NUM>: <NUM>.

The compound of formula IIc is <NUM>,<NUM>'-(((((di-tert-butylsilanediyl)bis(oxy))bis(methylene))-bis(<NUM>,<NUM>-phenylene))bis(oxy))diphthalonitrile.

A diphthalonitrile compound of formula Ila was heated to approximately <NUM> in an aluminium pan. Thereafter, <NUM>-(<NUM>-aminophenoxy)phthalonitrile was added (<NUM> mol%) and manually stirred into the liquid resin until a homogeneous red-brown mixture was formed.

A diphthalonitrile compound of formula IIb was heated to approximately <NUM> in an aluminium pan. Thereafter, <NUM>-(<NUM>-aminophenoxy)phthalonitrile was added (<NUM> mol%) and manually stirred into the liquid resin until a homogeneous red-brown mixture was formed.

A diphthalonitrile compound of formula Ilc was heated to approximately <NUM> in an aluminium pan. Thereafter, <NUM>-(<NUM>-aminophenoxy)phthalonitrile was added (<NUM> mol%) and manually stirred into the liquid resin until a homogeneous red-brown mixture was formed.

<NUM> of the diphthalonitrile resin blend formed in Example <NUM> was poured into a mould, in which it was degassed for <NUM> minutes at <NUM> in a vacuum oven. Resin samples were cured in a muffle furnace (under an N<NUM> atmosphere) using the following cure cycle; <NUM> for <NUM> hours, <NUM> for <NUM> hours, and <NUM> for <NUM> hours, each yielding a thermally stable diphthalonitrile thermoset of the present invention.

<FIG> demonstrates that each of the diphthalonitrile compounds of formulae IIa, IIb and IIc have melting/softening points between -<NUM> and <NUM>, i.e. less than room temperature, <NUM>). This is in sharp contrast to most conventional diphthalonitrile compounds, which have melting points in excess of <NUM>.

Since the diphthalonitrile compounds are highly amorphous materials, they do not exhibit a sharp melting event, instead they exhibit second order transitions, i.e. step changes in the heat capacity. These transitions are labelled as ranges on <FIG>.

<FIG> shows the dynamic viscosities of the diphthalonitrile compounds of formulae IIa, IIb and Ilc (parallel plate, <NUM> gap, <NUM>% oscillatory strain, <NUM>/min). From these curves it can be seen that Ila and IIb reached an optimal viscosity (~<NUM> cP (wherein <NUM> cP = <NUM> Pa. s)) for infusion type composite moulding processes such as resin transfer moulding (RTM) at approximately <NUM>. The viscosity then dropped to a minimum of <NUM> cP (wherein <NUM> cP = <NUM> Pa. s), which gives an additional margin of viscosity that could be used to accommodate increased viscosity due to additives in the resin formulation. Although the minimum viscosity of Ilc is <NUM> cP (wherein <NUM> cP = <NUM> Pa. s), which makes it less appropriate for infusion type processes, this higher viscosity is well suited for alternative composites processing techniques such as prepregging. This marginally higher viscosity minimum also indicates suitably for coatings applications. The viscosity curves shown in <FIG> confirm that Ila/llb are compatible liquid infusion techniques. The slightly higher viscosity of IIc is more suitable for prepregging.

<FIG> shows that a cured blend of Ila exhibits the high thermal stability typical of diphthalonitrile thermosets. The onset of degradation ><NUM> and <NUM> char yield (><NUM>%) are in the expected region for phthalonitriles under a nitrogen atmosphere.

The good moisture stability of an uncured diphthalonitrile resin blend is demonstrated by the <NUM>H NMR spectra in <FIG>. Only <NUM> mol% of the 'IIa' sample (<FIG>, bottom) has hydrolysed to the related alcohol (an authentic sample is shown in <FIG>, top) after <NUM> days of exposure to air (at ca.

In contrast, the much poorer hydrolytic stability of a literature diphthalonitrile is shown in <FIG>. In this figure, two spectra are shown, which compare the diphthalonitrile before and after exposure to air for <NUM> days (at ca. In this time, almost half of the sample has hydrolysed to the alcohol.

Claim 1:
A diphthalonitrile compound of formula I:

        Ar<NUM>(CN)<NUM>-O-Ar<NUM>-CH<NUM>-O-Si(R<NUM>)(R<NUM>)-O-[T-O-Si(R<NUM>)(R<NUM>)-O-]n-CH<NUM>-Ar<NUM>-O-Ar<NUM>(CN)<NUM>     (I)

in free or salt or solvate form, wherein:
Ar<NUM> is a C<NUM>-C<NUM>-aryl group;
Ar<NUM> is a C<NUM>-C<NUM>-aryl group;
R<NUM> and R<NUM> are independently C<NUM>-C<NUM>-alkyl;
T is a C<NUM>-C<NUM>-aryl group; and
n is <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM>, or a mixture thereof.