WO1995007309A1

WO1995007309A1 - Resin compositions of phenolic cyanate esters and polyepoxide compounds

Info

Publication number: WO1995007309A1
Application number: PCT/GB1994/001989
Authority: WO
Inventors: Zhou Zhiming
Original assignee: University Of Leeds
Priority date: 1993-09-11
Filing date: 1994-09-12
Publication date: 1995-03-16
Also published as: AU7619394A; GB9318872D0

Abstract

A resin blend is provided comprising an epoxy component of general formula (I) and a cyanate component of general formula (II) wherein E represents epoxide groups, Y represents cyanate groups, R represents hydrogen atoms or substituents, n represents 0 or an integer of 1 or more, m represents an integer of 1 or more, and M represents a divalent organic radical, for example methylene. The resin blend may be cured by heat alone and offers excellent properties in relation to manufacturing processes and high temperature applications, the latter demonstrated in part by the three point bend test results shown in the figure.

Description

RESIN COMPOSITIONS OF PHENOLIC CYANATE ESTERS AND POLYEPOXIDE COMPOUNDS

This invention relates to a polymer resin of the cured epoxy type.

To make a cured epoxy resin, typically, a relatively low molecular weight linear polymer is formed with very reactive epoxy groups at the end. This compound may for example be formed by a -isphenol and epichlorohydrin. Then a cross-linking agent is added. It may be a dicarboxylic anhydride but is commonly a polyfunctional amine such as diethylenetria ine, which cross-links the epoxidised linear polymer.

Whilst such cross-linked epoxy resins of traditional type generally have good adhesive properties and structural characteristics, they have relatively low deflection temperatures and are sensitive to oxidation. Furthermore, they have relatively poor fire retardancy properties, s. much so that within the last 10-20 years they have lost favour in certain applications such as seating for underground trains, aerospace, and the older phenolic resin systems have re-gained favour.

Recently, dicyanates have been used to cross-link epoxy resins and much work has been done on the curing systems for epoxy resins and bisphenol-A-dicyanate. Although the thermal and thermooxidative stability of cross-linked epoxide/dicyanate systems has been enhanced compared to the traditionally cured epoxy resins, the improvement is not very significant.

The present invention provides a resin blend comprising an epoxy component of general formula

wherein at least half of the groups X represent epoxide groups of formula:

each group R independently represents a hydrogen atom or a substituent, n represents 0 or an integer of 1 or more, and M represents a divalent organic radical;

and a polyfunctional cyanate of general formula

wherein at least half of the groups Y represent a group of formula

-OCN

each group Q independently represents a hydrogen atom or a substituent, m represents an integer of 1 or more; and W represents a divalent organic radical. When a group R represents a substituent, it may suitably be a halogen, cyano, C_M alkoxy or, especially, a C alkyl group.

Preferably a group R represents a methyl group or, most preferably, a hydrogen atom.

Suitably, at least 80%, and preferably substantially all, of the moieties X in the compound of general formula I are epoxide groups of the formula defined above.

Suitably, the compound of general formula I contains at least 2 epoxide groups X, on average.

Suitably M may comprise an optionally substituted alkylene, cycloalkylene or (hetero)arylene group.

A suitable alkylene group M may be a C,.₁₀ alkylene group. Illustrative are methylene, ethylmethylene, m e t h y 1 e t hy 1 e n e , d i m e thy 1 m e t hy 1 ene , 2- ethylpentylmethylene , isopropylmethylene , isobutyl ethylene and pentylmethylene. A suitable cycloalkylene group M may be a C₃.₁₂ cycloalkylene group. Illustrative are cyclohexylene, cyclooctylene, 1,3- cyclohexanedimethylene and dicyclopentylene (i.e. the divalent radical derived from dicyclopentadiene) .

Optional substituents of alkylene or cycloalkylene groups M are preferably selected from halogen atoms, for example fluorine, chlorine or bromine atoms. Preferably, however, an alkylene or cycloalkylene group, when present, is unsubstituted.

A suitable (hetero)arylene group M may have 5 or 6 ring atoms. Furylene and phenylene are preferred. Illustrative are furylenemethylene, phenylenemethylene, 1,3-phenylenedimethylene, 1,4-phenylenedimethylene and 2,2-bis-(4-phenyl)propane. In more general terms a preferred arylene group M may be represented by the definition optionally substituted C alkylene - phenylene - C alkylene.

Optional substituents of a (hetero)arylene group M are suitably selected from C alkyl, C alkoxy, cyano, C haloalkyl, and halogen, for example fluorine, chlorine or bromine. Preferably, however, a (hetero)arylene group, when present, is unsubstituted.

Particularly preferred groups M are 1,4- phenylenedi ethylene, dimethylmethylene and, especially, methylene.

Preferably a group Q represents a methyl group or, most preferably, a hydrogen atom.

In the compound of general formula II, suitably at least 80%, and preferably substantially all, of the moieties Y are cyanato groups, and/or the moieties are substantially all comprised by a majority of cyanato groups and a minority of hydroxyl groups.

Preferably the compound of general formula II contains at least 3 cyanato groups Y, on average.

Suitably W may comprise an optionally substituted alkylene, cycloalkylene or (hetero)arylene group.

A suitable alkylene group W may be a C,.,₀ alkylene group. Illustrative are methylene, ethylmethylene, e thy 1 methy 1 e n e , di ethylmethylene, 2- ethylpentylmethylene , isopropylmethylene, isobutyl ethylene and

-methylene. A suitable cycloalkylene group W may be a C_3.I2 cycloalkylene group. Illustrative are cyclohexylene, cyclooctylene, 1,3- cyclohexanedimethylene and dicyclopentylene (i.e. the divalent radical derived from dicyclopentadiene) .

Optional substituents of alkylene or cycloalkylene groups W are preferably selected from halogen atoms, for example fluorine, chlorine or bromine atoms. Preferably, however, an alkylene or cycloalkylene group, when present, is unsubstituted.

A suitable (hetero)arylene group W may have 5 or 6 ring atoms. Furylene and phenylene are preferred. Illustrative are furylenemethylene, phenylenemethylene, 1,3-phenylenedimethylene, 1,4-phenylenedimethylene and 2,2-bis-(4-phenyl)propane. In more general terms a preferred arylene group W may be represented by the definition optionally substituted C alkylene - phenylene

- C alkylene.

Optional substituents of a (hetero)arylene group W are suitably selected from C alkyl, C alkoxy, cyano, C_M haloalkyl, and halogen, for example fluorine, chlorine or bromine. Preferably, however, a (hetero)arylene group, when present, is unsubstituted.

Particularly preferred groups W are 1,4- phenylenedimethylene, dimethylmethylene and, especially, methylene.

For further information about compounds of general formula II, including their preparation, reference may be made to US Patent No. 4831036, which relates to their use per se to form cross-linked phenolic triazine resins.

The resin blend of the present invention may be hardened solely by the application of heat; it does not require a hardening agent (although it should be noted that a resin of the present invention in which a hardening agent has been used is not excluded from the scope of the present invention as herein defined) .

Suitably n is in the range 0-50, preferably 0-8, most preferably 0-4, inclusive.

Preferably the mean molecular weight of the compound of general formula I is in the range 300-10000, preferably 300-2000, more preferably 300-1200, inclusive (i.e. n is in the range 0-4) .

Suitably m is in the range 1-50, preferably 1-8, most preferably 1-4, inclusive.

Preferably the mean molecular weight of the phenolic cyanate is in the range 370-8000, more preferably 370- 1000, inclusive (i.e. n is in the range 1-4) .

Preferably the compounds of formulae I and II have the same or similar main chain structure and are of similar molecular weights i.e. the epoxide compound is within about 100%, preferably within about 60%, most preferably within about 20% of the molecular weight of the cyanate compound. This aids compatibility and good dissolution of the components in the uncured blend.

Suitably a resin blend of the present invention is hardened by being heated to a temperature in the range 60- 300°C, preferably 100-250°C, suitably from 0.1-5 hours. The exact temperature is a matter of choice. Empirically it has been found that time of curing also appears to be important. A longer curing time appears to enable a lower curing temperature to be employed and this appears to have the advantage that a lighter colour product can be obtained. Higher temperatures have been found to produce darker colour products, though in all cases observed the cured products have been transparent, and preferable in appearance to the normally dark brown opaque phenolic resins.

During curing pressure may or may not be applied, but it may be desirable to apply pressure during curing of a resin composite product, in order to optimise its mechanical properties.

If desired resin modifiers may be included, for example to modify the cross-linking density. Such resin modifiers may, for example, be molecules designed to "cap off" a molecule at a potential cross-linking site. One example is 1,4-butanediol glycidylether, which has end epoxide groups to bond to available cyanate groups, to reduce the cross-linking density of the cyanate compound of general formula II, with the epoxy compound of general formula I, thereby to reduce both the viscosity of uncured resin and cross-linking density of cured resin.

Tests on cured hybrid resins of the present invention have shown them to have much better high temperature performance, including under wet conditions, than traditionally cured epoxy resins. The glass transition temperature of experimental resins of the present invention has been high, around 300°C or higher. Thermogravimetry (TGA) has shown that the thermal stability of the hybrid resins is very good up to at least 330°C, compared to about 200°C for standard epoxy resins. Furthermore they appear to show no diminution in properties when cycled between low and high temperatures.

Unidirectional carbon fibre reinforced composites have been made using the novel hybrid resins. The longitudinal elastic modulus of such composites is extremely stable up to at least 300°C, measured using the three point bend test, compared to 120°C for a typical traditionally (a ine) cured epoxy composite.

Furthermore the phenolic cyanate dissolves very well in the epoxide compound and the uncured resin blend has low viscosity making it ideal for fibre impregnation. It follows that, whilst solvent can be used, often it need not be, and this reduces the cost and is environmentally preferable. If both resins are in the solid state, depending on the molecular weight, some solvent is necessary to prepare a homogeneous mixture. However, if one or both of the resins is in the liquid state or both are in the liquid state at ambient temperature, solvent is not necessary because both resins preferably have the same main chain structure and they are generally found to be miscible. In addition, solid phenolic cyanate is dissolved in the liquid epoxy resin and they can form a very homogeneous mixture.

The blend does not cure until heat is applied, so freeing manufacturing processes, such as the manufacture of composites, from time constraints. Further, there are no volatile components evolved during curing, making it easy to fabricate void-free components. Preliminary tests on long-term high temperature stability look very promising. Furthermore, the cured hybrid resins have good fire retardancy and char forming properties.

The cured hybrid resins of the present invention appear to have high temperature properties which compete well with those of current high temperature resin systems, for example polyimides, but to offer substantial advantages in respect of ease of processing and cost.

In accordance with a further aspect of the present invention there is provided a hybrid resin as defined above, and which has been cured, preferably by heat, and preferably without addition of a hardening agent.

In accordance with a further aspect of the present invention there is provided a method of making a resin blend or a cured hybrid resin, as defined or described herein.

In accordance with yet further aspects of the present invention there is provided a polymer composite comprising a cured hybrid resin in accordance with the present invention, and a structural or filler material; and a method of making such a composite. The structural or filler material may suitably be a high modulus fibre material, for example graphite fibre, aramid fibre, glass or ceramic fibre or metallic fibre. The structural or filler material may suitably additionally comprise, for modification of mechanical properties, for example toughness, crack-arresting and/or energy absorbing particles, for example of engineering thermoplastics (one example being High Impact Polystyrene - HIPS) , or of elastomeric materials. The cured hybrid resins of the present invention may be used in many situations, and will be used with great advantage in applications requiring good high temperature mechanical properties, for example aerospace, good fire- retardancy properties, for example aerospace, trains, ships, cars, coaches, public auditoria and stadia, and good dimensional stability during curing. For example the resins of the present invention could be used in RIM (Reaction Injection Moulding) applications. It may be used as a high temperature composite matrix resin, in adhesives, laminates, cast plastics, and coating and moulding materials. It is also believed that the new resins have low dielectric constants and so may be suitable for use in the electronics industry, for example for printed circuit boards and encapsulation.

It is believed that the cured hybrid resins have a cross-linked structure in which epoxy groups react with cyanato groups.

The ratio by number of epoxy groups to cyanato groups is preferably in the range 0.4-1:1-0.4, more preferably 0.8-1:1-0.8, most preferably substantially 1:1.

The invention will now be further described, by way of example, with reference to the accompanying drawings, which comprise Figures 1-8 of graphs which relate to the Samples and Tests described below. SAMPLE 1

A novolac resin believed to be of formula

with a number average molecular weight believed to be in the range 500-600 was chosen to make the required phenolic cyanate. In this novolac resin the position of the hydroxyl groups is believed to be predominantly ortho or para, relative to the chain linkages. The method of US Patent No. 4831086 was used. Thus the novolac resin and a triethylene amine (TEAM) in tetrahydrofuran (THF) at ambient temperature were reacted to form a triethyl ammonium salt of novolac. This was followed by reacting the triethyl ammonium salt with cyanogen bromide in THF at -45°C to -55°C to form phenolic cyanate. The dried product was an off-white powder.

28.9g of the phenolic cyanate powder was added to 71.1 g of an epoxy resin of similar backbone structure, believed to have a molecular weight of several hundred

(LY1927 from Ciba-Geigy, mole ratio epoxy resin/phenolic cyanate =2/1) with mechanical stirring. The mixture was further stirred at ambient temperature for about one hour and then left in a bottle overnight. The phenolic cyanate was by then completely dissolved in the epoxy resin, and the resin blend was ready for preparing fibre reinforced composite, casting materials etc. This mixed resin was stable at ambient temperature. Only heat was needed to cross-link the resin.. Typical curing temperature was from 100°C to 250°C. For fibre reinforced composite material, a certain level of moulding pressure (usually 10 Kg/cm² to 50 Kg/cm²) was usually necessary to reduce the void content and optimise the mechanical properties of the composite.

SAMPLE 2

To prepare a homogeneous mixture of both resins quickly, the preparation for Sample 1 was repeated except that the phenolic cyanate powder was first dissolved in 2- butanone (MEK) to prepare 50-70% (wt) of phenolic cyanate solution and then mixed at ambient temperature with the epoxy resin with mechanical stirring. Then MEK was removed by vacuum. In this case, more phenolic cyanate could be evenly mixed with the epoxy resin. The composition ratio of the resin was epoxy resin/phenolic cyanate=62.1/37.9 (wt) (mole ratio=4/3) .

SAMPLE 3

The preparation for Sample 2 was repeated except that the compos it i on rat i o wa s epoxy res i n / pheno l i c cyanate=55. 2/44 . 9 (wt) (mole ratio=l/ l) .

SAMPLE 4

The preparation for Sample 2 was repeated except that the epoxy resin was replaced by bisphenol-A epoxy (from Dow Chemicals, product DER 351, epoxy equivalence of 170- 183).

SAMPLE 5

The preparation for Sample 3 was repeated except that the epoxy novolac was replaced by bisphenol-A epoxy (from Dow Chemicals, product DER 351, epoxy equivalence of 170- 183) .

SAMPLE 6

The preparation for Sample 5 was repeated except that 10% of the bisphenol-A epoxy was replaced by an equal weight of reactive diluent 1,4-butanediol gylcidylether, to reduce the viscosity.

ANALYSIS AND TESTING

1. Differential Scanning Calorimetrv

Differential scanning calori etry (DSC) was used to study the curing characteristics of phenolic cyanate, epoxy resin without hardener and the epoxy resin/phenolic cyanate of Sample 3. A DSC Series 7 Perkin-Elmer machine was used. From the graph of Fig. 1, it can be seen that phenolic cyanate has a very sharp exothermal peak at 325°C but the epoxy resin without hardener has no cure exotherm produced up to 335°C. It should be noted that with addition of phenolic cyanate, the epoxy resin has a single broad exothermal peak at 308°C and that a much larger cure exotherm was produced in the novel resin then in phenolic cyanate. This indicates that phenolic cyanate is not only able to cure with the epoxy resin at lower temperature but also forms a very stable cross-linked structure.

2. Thermoσravimetrv (TGA.

A standard TGA test was conducted respectively in air

(50 ml/min) and N₂ (100 ml/min) atmosphere to measure the weight loss of cured Sample 3, as a function of temperature and char yield. The results are shown in Figs. 2 and 3. The y-axis of these graphs show both weight as a percentage of starting weight, and weight loss per rise in temperature of 1°C (called deriv weight) . Additionally, the excellent char forming characteristics of the products were observed by eye.

3. High Temperature Performance - three point bend test

Unidirectional carbon fibre reinforced composites, using unsized graphite fibres, of volume ratio 65% (35% volume resin) have been made using the novel hybrid resin of Scale 3. The longitudinal elastic modulus of the new resin composites is extremely stable up to 300°C measured using the three point bend test (carried out according to ASTM D790-80) , compared to 120°C for the traditionally cured epoxy resin composite (Fig. 4) .

All of the following tests on composites also used unsized graphite fibres, 65% vol. fibres/35% vol. resin.

4. Flexural Property Testing - ambient temperature

Unidirectional carbon fibre reinforced specimens have been made with the new hybrid resin of Sample 3 and with traditional epoxy resin cured with the traditional hardener and the flexural properties of them were measured at ambient temperature, using the three point bend method. The results are set out in Table 1 below. TABLE 1

The Flexural Properties of the Unidirectional Carbon Fibre Composite

Longitudinal Transverse

Traditional Hybrid Epoxy Traditional Hybrid Epoxy

Epoxy Composite Epoxy Composite

Composite Composite

Flexural 96.40+9.20 103.80+0.50 6.74+0.31 5.19±0.31 Modulus (GPa)

I

Flexural 1075+82 1049+77 41.70+6.12 42.75+7.67 Strength (MPa)

5. Glass transition temperature

The glass transition temperature (Tg) of the cured resins of Samples 1 to 6 was measured by DMTA (Dynamic Mechanical Thermal Analysis) and the results are set out in Table 2 below.

TABLE 2

Sample 1 2 3 4 5 6

Tg (°C) >320 >330 >330 >300 >300 >280

6. Interlaminar Shear Strength (ILSS.

The ILSS of unidirectional, unsized graphite/resin composites was assessed at 20°C by the method of ASTM D2344-76. A corresponding epoxy resin cured by standard amine curing agent HY1927 was included.

The results are set out in Table 3 below. It will be seen that the traditional amine cured product and the epoxy/cyanate products of the invention have closely comparable interlaminar shear strength. The epoxy/cyanate resins therefore perform quite adequately in this respect and can be expected to have very good adhesion properties. TABLE 3

Matrix Composition ILSS (MPa)

Max. Min. Mean

Amine cured epoxy resin 89.4 74.9 83.6

Sample 3 88.2 69.4 76.8

Sample 1 89.2 79.3 85.2

The ILSS was then tested on the same samples at different temperatures. All measurements were carried out after the samples were held at the desired temperature for 15 to 20 minutes. The results are set out in Figure 5, and indicate that, at elevated temperatures, the epoxy/cyanate resin composites of the present invention hav much better retention of their interlaminar shear strength, than does the amine cured resin composite. This may be because the amine cured resin has a glass transition temperature of 140°C, above which the resin has very low shear modulus and poor shear strength, whilst the epoxy/cyanate resin has no detectable glass transition temperature up to 320°C.

Flexural strength - temperature dependence

Flexural strength of the first two composite samples set forth in Table 3 above was assessed by test method ASTM D790-86. The results are set out in Figure 6. It can be seen that at ambient temperature the flexural strength of the samples is nearly the same, but that at high temperature the epoxy/cyanate composites showed much better performance than the traditional amine cured product. Again, an important factor is thought be to the higher glass transition temperature of the product in accordance with the invention. 8. Hot-Wet tests

It is well known that epoxy resin composites have relatively poor hot-wet performance because of their moisture absorbtion. One of the effects of the absorbed moisture is to lower the glass temperature of the resin matrix, thereby leading to poor temperature-related properties. Reductions in the glass transition temperature of 29-43°C, due to absorbed moisture, have been reported in the literature. Other effects of absorbed water are to reduce the interlaminar shear strength of fibre composites, to reduce their flexural strength, and to diminish adhesion/soldering properties.

To assess hot-wet strength, the methodology was based on method ASTM F-520 1991. However, the tests were in fact more severe than this standard test because the samples were boiled in water for 210 hours, instead of being held at 45-70°C, at 84% relative humidity.

The samples tested were the first and third set forth in Table 3 above, that is, composites whose matrices were, respectively, the amine cured resin, and the resin of Sample 1. The results for each are set out in Figures 7 and 8 respectively.

From Figure 7 it is clear that absorbed water has lowered the glass transition temperature, but beyond that it is also seen that the glass transition temperature range is widened, as shown by the wider tan delta peak, and more gradual decrease in elastic modulus.

For Figure 8 it is in clear that the composite in accordance with the present invention has much better hot- wet performance. There is still no glass transition temperature detectable up to 330°C and only at very high temperatures does absorbed water significantly affect the mechanical properties of the composite.

Moreover, further testing showed that, after the water absorbed into the composite having the epoxy/cyanate resin was removed by drying in a vacuum oven, the high temperature performance of the dried sample was completely recovered - there appears to be no detectable hysteresis if the sample is taken from dry, to wet, to dry conditions.

The effect of absorbed water on the interlaminar sheet strength (ILSS) of the composite whose matrix was the equimolar epoxy/cyanate resin of Sample 3 was studied by short beam shear testing and the result compared with that o the above-mentioned amine cured epoxy/graphite composite as recorded in Table 4 below. The experimental results demonstrate that hydrothermal environment had very significant effect on the interlaminar shear strength of the amine cured epoxy/graphite composite but had an insignificant influence on that of : ...αxy/cyanate/graphite composite. After the samples were ooiled in distilled water for 118 hours, the absorbed water lead to a reduction in the interlaminar shear strength of epoxy/cyanate/graphite composite by only 7%, compared to 23% for the amine cured epoxy/graphite composite. In addition, when the composite samples were further boiled in distilled water, although no more gained weight is found for both amine cured and epoxy/cyanate composite from 188 hours of boiling to 210 hours of boiling, a slight decrease in the ILSS of the amine cured epoxy/graphite composite is observed but no further effect on that epoxy/cyanate/graphite composite. A further interesting result was that moisture-induced property degradation of amine cured epoxy/graphite composite could not be completely recovered after the absorbed water was removed by drying at 210°C (under vacuum) for 10 hours but resulted in about 15% permanent loss of its original ILSS, whereas the epoxy/cyanate/graphite composite regained all of its ILSS loss caused by absorbed water after the sample was redried; and the redried composite samples have even slightly higher ILSS than the original samples. This may have resulted from some further post-curing reaction taking place when the samples were dried at 210°C for 10 hours.

TABLE 4

Tested at room Composite with Composite with temperature amine cured matrix Sample l

ILSS (MPa) ILSS (MPa)

Max. Min. Mean Max. Min. Mean before boiled 89.4 74.9 83.6 88.2 69.4 76.8 in water after boiled 64.7 63.2 64.3 73.1 68.8 71.3 in water for

118 hours

ILSS retention 76.9% 92.8% boiled in 63.4 61.5 62.3 73.5 68.5 71.8 water for 210 hours

ILSS retention 74.5% 93.4% redried under 73.1 70.3 71.7 93.5 79.0 85.3 vacuum at 210°C for 10 hours The effect of absorbed water on the flexural strength of the graphite composites has also been studied by measuring and comparing their flexural strength before and after they are boiled in distilled water. The results are recorded in Table 5 from which is can be seen that epoxy/cyanate/graphite composite has far better hot-wet performance than the amine cured epoxy/graphite composite. In fact, in this test water absorbed into the epoxy/cyanate/graphite composite hardly influenced its flexural strength after the sample was boiled in distilled water for 210 hours. It had 99.2% retention of its original flexural strength, compared to 74.5% for the amine HY1927 cured epoxy/graphite composite.

TABLE 5

Effect of Absorbed Water on Flexural Strength of

Epoxy/Graphite Composites

Tested at Room Unboiled Boiled Sample

Temperature Sample (210 hours)

0° Flexural Strength 2118 1577 of Amine Cured (74.5% retention)

Epoxy/Graphite (MPa)

0° Flexural Strength 2210 2194 of Epoxy/Graphite (99.2% retention)

(MPa)

The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) , may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment(s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings) , or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

1. A resin blend comprising an epoxy component of general formula

wherein at least half of the groups X represent epoxide groups of formula:

\

-0-CH₂-CH-CH₂

and a polyfunctional cyanate of general formula

wherein a least half of groups Y represent groups of formula

-OCN each group Q independently represents a hydrogen atom or a substituent, m represents an integer of 1 or more; and W represents a divalent organic radical.

2. A resin blend as claimed in Claim 1, wherein M comprises an optionally substituted alkylene, cycloalkylene or (hetero)arylene group.

3. A resin blend as claimed in Claim 2, wherein M represents a 1,4-phenylenemethylene, dimethylmethylene or methylene group.

4. A resin blend as claimed in Claims 1, 2 or 3, wherei: each group R independently represents a hydrogen atom or a methyl group.

5. A resin blend as claimed in any preceding claim, wherein n is in the range 0-50, inclusive.

6. A resin blend as claimed in Claim 5, wherein n is in the range 0-8, inclusive.

7. A resin blend as claimed in any preceding claim, wherein W comprises an optionally substituted alkylene, cycloalkylene or (hetero)arylene group.

8. A resin blend as claimed in Claim 7, wherein W represents a 1,4-phenylenemethylene, dimethylmethylene or methylene group.

9. A resin blend as claimed in any preceding claim, wherein each group Q independently represents a hydrogen atom or a methyl group.

10. A resin blend as claimed in any preceding claim, wherein m is in the range 1-50, inclusive.

11. A resin blend as claimed in Claim 10, wherein m is in the range 1-8, inclusive.

12. A method of curing a resin blend as claimed in any preceding claim, comprising the step of heating the resin blend to a curing temperature.

13. A resin blend as claimed in any of Claims 1 to 11, cured.

14. A resin composite, comprising a cured resin blend as claimed in Claim 13, serving as a matrix material, and a structural or filler material therein.

15. A resin composite as claimed in Claim 14, wherein the structural or filler material comprises carbon fibres.