GB2318787A - Unsymmetrical alkenyl cyanate oligomers - Google Patents

Abstract

Novel unsymmetrical oligomers comprising one alkenyl- and one cyanate-functional group of the general formula: in which X is an organic group containing an alkenyl double bond and Y is an organic group with a molecular weight of up to about 1000, have extensive applications in polymer technology in particular as modifiers for bis-maleimide polymer resins. Modified resins have improved high temperature performance while retaining other mechanical properties making them particularly suited to use in structural composites for use in aeronautical and automotive applications.

Description

UNSYMMETRICAL ALKENYL CYANATE OLIGOMERS This invention relates to alkenyl cyanate oligomers and their use in the modification of polymeric materials. In particular, the invention relates to use of these modified polymeric materials as matrix resins for composite structural materials.

UK Patent Application no. PCT/GB92100995 discloses alkenyl cyanate oligomers bis(3,5 dipropenyl4-cyanotidophenyl) and bis(3,5-dipropenyl4-cyanotidophenyl) having both cyanate and propenyl functionalisation. The possible polymerisation of these compounds by co-reaction with bis-maleimides, bis-citraconimides, aspartimides or compounds containing epoxide groups or other cyanate esters such as dicyanate ester prepolymers is also disclosed. A suitable combination of heat resistance, toughness, low dielectric loss and low moisture absorption enables use of these modified polymeric products in a multitude of applications. Such uses include as matrix resins for structural composites, commonly used in the aeronautical and automotive industries, or as laminating resins for micro-electronic applications.

Methods of synthesis for the propenyl cyanate oligomers disclosed in PCT/GB92/00995 limit the yield of oligomers which are obtainable. The syntheses disclosed in that application involve many processing steps resulting in the inefficient production of a high proportion of side products, and which consequently are not ideal for industrial scale production.

Additionally, the necessary use of high concentrations of potassium hydroxide required to bring about the allyl to propenyl isomerisation was found to cause cleavage of the oligomeric backbone giving undesirably low yields of the alkenyl cyanate product. When used as modifiers for polymeric materials, the symmetrical nature of these oligomers and the difunctional nature of each end group means that cross-link densities in the modified polymeric materials are high. Lower cross-link densities are preferred as they result in a tougher composite material when the modified polymeric material is used as a resin for a composite material.

The present invention aims to provide improved alkenyl cyanate oligomers for use as modifiers in polymeric materials which may be used as resins for structural composites. A further aim of the invention is to provide simpler and cheaper methods of preparation for the improved oligomers which involve fewer processing steps and higher yields of the desired product than the methods described in PCTIGB92/00995.

The present invention provides novel oligomers comprising one alkenyl- and one cyanatefunctional group of the general formula.

In which X is a group containing an alkenyl double bond and Y is an organic group with a molecular weight of up to about 1000.

Preferably, X is propenyl as this group is more reactive with polymers such as bismaleimide, more preferably X forms the trans isomer as this isomer is more easily isolated from the reactant mixture. Preferably, Y will not react with compounds of the group comprising bis-maleimides, bis-citraconimides, aspartimides, compounds containing epoxide groups, or other cyanate esters as this would limit the usefulness of the oligomer as a modifier for polymers containing these compounds.

Oligomers of the present invention are conveniently prepared using the following general method of synthesis: Initially. a di-phenolic compound with one of the OH groups protected is added to a bishalophenyl compound containing the desired group Y in solution in a polar aprotic solvent such as dimethylacetimide, at temperatures above 90"C. Secondly, a compound with an OH functional group and containing the desired group X is then added to the reaction mixture under similar processing conditions. This gives as the main product a compound with an alkenyl group at one end, and a protected hydroxyl group at the other. Deprotection of the hydroxy group with a cyanogen halide gives the required alkenyl cyanate compound.

It will be apparent to the person skilled in the art that the order of the first two steps is not critical to achieving the desired result.

For optimum yield of the oligomers, the bis-halophenyl compound will preferably comprise two different halo groups.

when added as modifiers to blends of commercial cyanate ester and/or bis-maleimide (BMI) monomers, the oligomers of the present invention provide modified polymers with improved mechanical properties over both the unmodifed polymers and polymers incorporating the oligomer modifiers of PCT1GB92100995. Further advantages can be obtained in co-reaction of these oligomers with bis-citraconimides, aspartimides or other cyanate compounds containing epoxide groups which may be present in commercial cyanate ester and/or bismaleimide blends. Significantly, glass transition temperature (Tg) of the resulting modified polymers can be increased with minimal effect on fracture toughness (Kc) making these polymers more reliable at high temperature operation than those of PCT/GB92/00995 in high temperature applications. Consequently, the modified polymers are of particular use as matrices in fibre reinforced plastics, in particular carbon fibre reinforced plastics (CFRP) for use in the aeronautical and automotive industries.

Use of the modified polymers of this invention in CFRPs can facilitate optimisation of both Tg and Kic with minimal effect on other mechanical properties of the composite. Furthermore these advantages can be obtained using processing techniques substantially similar to those required for the manufacture of the unmodified blend. It will occur to the skilled reader that suitable choice of Y will enable the manufacturer to produce long or short chain oligomers as required. When used as modifiers for polymeric materials, in general, longer chain oligomers will provide tougher composites where shorter chains will provide composites with higher glass transition temperatures. The proportion of modifier in the polymer blend will also affect the changes in mechanical and physical properties that the oligomer modifier causes in the polymeric material.

In addition to giving further improvements in modified polymers over known modified polymers, the oligomers of this invention can be manufactured more simply and more cheaply than the propenyl functionalised aromatic oligomers previously disclosed in PCT/GB92/00995.

There now follows descriptions of two methods of obtaining particular embodiments of this invention. Variations on these processes and embodiments will be apparent to the person skilled in the art.

EXAMPLES Example 1 The following describes the process steps taken in obtaining a source of a 4 ring alkenyl cyanate oligomer (4rOCN). The starting material in this case is bis-4-(fluorophenylsulphone) A 250ml 3-necked round bottomed flask equipped with a magnetic stirrer bar, dropping funnel and a Dean-Stark trap, was charged with bis-4-fluorophenylsulphone (25.49, 100mmol), 2-allyl phenol (13.49, 100mmol) and potassium carbonate (159, il0mmol). N,N' Dimethylacetimide (100ml) was added and the mixture heated at 1000C ovemight (approximately 16 hours), then at 1300C for 2 hours. After the reaction mixture had cooled to approximately 90"C, hydroquinone mono-tetrahydro-pyranyl (THP) ether potassium salt (309, 130 mmol) and toluene (30 ml) were added. The mixture was heated under reflux to remove water, then at 140"C overnight (16 hours). After the reaction mixture was cooled to room temperature, water (100ml) was added and the product extracted into di-ethyl ether (2 x 150ml). The ethereal fractions were washed with sodium hydroxide solution (2M, 2 x 100ml) and water (2 x 100ml), then dried over magnesium sulphate and combined. The solvent was removed by rotary evaporation to leave a light brown glassy solid. In laboratory experiments, the yield obtained using this method was 53.49 (98mmol, 98%).

51.49 (94.8mmol) of the product was dissolved in methanol (200ml) in a 500ml round bottomed flask fitted with a reflux condenser. 4-toluenesulphonic acid (1g, catalytic) was added and the mixture heated under reflux for two hours, then allowed to cool to room temperature. Water (200ml) was added, and the product extracted into diethyl ether (2 x 150ml) and washed with further water (2 x 100ml). The ethereal fractions were dried over magnesium sulphate, combined and the solvent removed by rotary evaporation to give a light brown solid. In laboratory experiments, the yield obtained by this method was 35.29 (77mmol, 81%).

A 250 ml round bottomed flask is charged with the second product (34.19, 74.5mmol) and cyanogen bromide (8.09, 75mmol) in solution in acetone (100ml). The solution was cooled to -100C and triethyl amine (7.69, 75mmol) was added dropwise at a rate such that the temperature of the reaction mixture is maintained between -5 C and -10 C. After the addition of the triethyl amine, the reaction mixture was allowed to warm to room temperature and the product extracted into dichloromethane (2 x 100ml) and washed with water (2 x 100ml). The extracts were dried over magnesium sulphate, combined and the solvent removed by rotary evaporation to give a light brown glassy solid. The yield of the final product, 4-(2-prn2-enyl-phenoxy)phenyl4'-(4-cyanatophenoxy)phenylsulphone, obtained by this method in laboratory experiments was 34.39 (71.0mmol. 95%).

Example 2 The following describes the process steps taken in obtaining a 5 ring alkenyl cyanate oligomer (5rOCN). A 1 litre 3-necked round bottomed flask, equipped with a Dean-Stark trap was charged with bis-phenol-A mono-THP ether/sodium salt (66.8g, 200mmol), bis-4chlorophenyl sulphone (57.49, 200mmol) and potassium carbonate (39, 22mmol). N,N' Dimethylacetamide 600ml) and toluene (200ml) were added, and the mixture heated under reflux with stirring until no more water was being removed (6ml collected). Toluene was distilled off until the temperature of the reaction mixture reached 1600C, the reactants were stirred, at this temperature for a further 2 hours. After the reaction mixture, had cooled to about 900C, potassium carbonate (289, 200mmol) and toluene (200ml were added. The mixture was heated under reflux until no more water was given off (3ml collected, after 1 hour). The toluene was distilled off and the reaction mixture heated to 1600C for a further 2 hours then allowed to cool to room temperature. The resulting mixture was poured into water (500ml) and the product extracted into di-ethyl ether (600ml + 300ml) and washed with sodium hydroxide solution (300ml, 2M), water (300ml) and brine (300ml). The ethereal solutions were dried over magnesium sulphate combined and the solvent was removed by rotary evaporation to give a light brown, glassy solid. The yield obtained was 127.49 (193mmol, 97%).

127.49 (193mmol) of the intermediate compound was then dissolved in methanol (500ml) in a 1 litre round bottomed flask. 4-toluene sulphonic acid (29, catalytic) iwas added and the solution heated under reflux for 2 hours then allowed to cool to room temperature. The product was extracted into di-ethyl ether (600ml + 300ml) and washed with water (2 x 300ml). The ethereal solutions were dried over magnesium sulphate and combined. The solvent was removed by rotary evaporation to give a light brown, glassy solid. The yield of this second intermediate product was 114.09 (192mmol, 99.5%).

A 250ml round bottomed flask was charged with the second intermediate (26.249, 44.4mmol) and cyanogen bromide (4.719, 44.4mmol), dissolved in acetone (100ml). The solution was cooled to -10 C and triethylamine (4.50g, 44.4mmol) was added dropwise with stirring to a rate such that the temperature was kept between -5 C and -10 C (this took approximately 30 minutes). The reaction mixture was allowed to warm to room temperature, then the product was extracted into dichloromethane (2 x 100ml) and washed with water (2 x 100ml). The extracts were dried over magnesium sulphate combined and the solvent removed by rotary evaporation. This gave a light brown, glassy solid. The yield of the final product 4-(2-prop-2-enyl-phenoxyphenyl) 94'-(2-(4-cynatophenyl) propa ne) phenoxyphenyl sulphone was 25.59 (99%).

RESINS AND COMPOSITES COMPRISING THE INVENTION For the purposes of the following comparative trials, an epoxy sized fibre was chosen as the reinforcing fibre for the composite comprising the invention. The resin systems were based on blends of a commercially available low molecular weight prepolymer of bis-phenol A dicyanate (Arocym B-30)and a commercially available low melting point blend of 3 bismaleimide components (Compimide TM 353) with varying concentrations of different custom modifiers. A catalyst combination of 300ppm of copper(ll) naphthenate 300ppm and 4 parts per hundred resin (phr) nonyl phenol was used in all cases.

The modifiers used in the blends tested were the 4 and 5 ring unsymmetrical propenyl cyanante oligomers of the present invention and a 6-ring symmetrical propenyl cyanate oligomers of the known art.

The resin monomers and oligomer modifiers were first melt blended at approximately 80"C, then catalyst and acetone (approximately 100ml per 80g resin) were added. The resins were then solution impregnated onto the fibre using a drum-winding type pre-pregger. The resulting pre-preg (900mm x 290mm sheets) was used to prepare 10 or 18 ply unidirectional panels which were then cured in a low pressure autoclave.

Two thicknesses of panel were used routinely: 10 ply unidirectional for all tests except GIC fracture toughness, and 18 ply unidirectional with PTFE insert for Ge fracture toughness tests. The following resinicure cycle combinations were found to give the best results.

The panels were heated from room temperature to 22 C at 1 Klmin, with a 60 minute soak at 90 C or 70 C (for the more reactive system containing modifier 4rOCN). A vacuum was applied to the panel ovemight prior to cure to help remove any residual volatiles. A pressure of 100psi was applied at the start of the cure cycle and the vacuum was vented as the pressure reached 30psi.

Table 1 describes the actual blends tested.

TABLE 1. Blends used In composite samples by weight Blend ID %ArnCyB-30 % Compimide % Modifier Modifier ID 353 2/1 65 35 0 none 4r/2/2 50 35 15 4rOCN 4r1213 35 35 30 4rOCN 5r/2 50 35 15 5rOCN 5r/3 35 35 30 5rOCN 6r12'2 50 35 15 6rOCN* 6r1213 35 35 30 6rOCN* * A 6 ring symmetrical Propenyl cyanate oligomer of the type disclosed in PCT/GB92/0995 On completion of the tests, density and fibre content of the panels tested were calculated.

Density was calculated by the displacement method, by immersion in water. Fibre content was determined by the digestion of the resin with sulphuric acid and hydrogen peroxide.

The test methods used were those recommended in "CRAG Test Methods for the Measurement of the Engineering Properties of Fibre Reinforced Plastics", RAE Technical Report No. 88012, ed P.T. Curtis 1988.

Results of the tests carried out are tabulated below. Where appropriate values normalised to 60% Vf are given, in addition to the raw data.

TABLE 2: Interlaminar Shear Strength (ILSS) Blend ILSS Standard Fibre Volume Density (MPa) Deviation (MPa) Vf (%) gcm-3 211 104 6 33 1.47 4r/2/2 115 2 40 1.49 4rl213 101 4 54 1.58 5r/2 113 5 45 1.55 5r/3 92 5 55 1.59 6r/2/2 113 3 45 1.52 6r/2/3 110 7 44 1.57 TABLE 3. Flexural Data (normalised to 60% V) Blend Normalised Standard Normalised Standard Flexural Deviation (GPa) Flexural Deviation Strength(GPa) Modulus (MPa) (MPa) 211 1.89 0.27 133 11 4r/2/2 1.94 0.23 161 14 4r/2/2 2.03 0.09 135 11 5r/2 2.24 0.36 143 1 5r/3 1.81 0.04 131 4 6rl212 1.88 0.21 125 1 6r213 1.45 0.09 110 2 TABLE 4. Compressive Strength (normalised to 60% V Blend Normalised Standard Compressive Deviation (MPa) Strength (MPa) 211 1064 111 4r1212 1200 42 4rl213 1006 150 5r/2 1301 83 5r/3 1104 60 6rl212 1169 101 6r213 1073 160 TABLE 5. Mode 1 Fracture Toughness Blend GIC Fracture Standard Fibre Volume Density Energy (Jm-2) Deviation Fraction Vf (%) gcm-3 2/1 372 50 36 1.48 4rl212 367 52 62 1.63 4rl213 337 114 55 1.60 5r/2 513 90 60 1.58 5r/3 not measured n/a n/a n/a 6r1212 346 36 42 1.49 6rl213 271 30 43 2.48 In addition to the mechanical tests detailed above, dynamic thermal analysis was used to determine the glass transition temperature (Tg) of the modified resins. Table 6 illustrates the comparative TgS of the various blends tested. Tg was taken as the temperature intersection of extrapolated tangents drawn to the storage modulus (E') curve before and after the transition event, where E' is rapidly decreasing. The maximum peak value for tan a is also given as a measure of the mid-point of the glass transition region, where E' is significantly reduced.

TABLE 6: Glass transition temperatures (composite samples) Blend Modifier TgatE'onset Ivan a 2/1 0 165 190 4rl212 15 190 225 4r1213 30 175 255 5r/2 15 170 200 5r/3 30 145 250 6rl212 15 175 203 6r2/3 30 165 200 Of the blends tested. blend 5r/2 proved to give optimum benefit of improved glass transition temperature and fracture toughness with minimal compromising of the other mechanical properties tested. Table 7 compares the properties of this blend with an unmodified blend 211.

TABLE 7: Mechanical properties of blends tested Resin: Blend 211 Resin: Blend 5r/2 ILSS 104 MPa 113 MPa Flexural Modulus* 133 MPa 143 MPa Flexural Strength* 1.89 GPa 2.24 GPa Compressive Strength* 1064 MPa 1104 MPa Fracture Energy. GIC 372 Jm-2 513 Jm-2 Tg (composite. tana) 1900C 200 C * normalised to 60% fibre volume fraction

Claims (16)

1. CLAIMS 1. An alkenyl cyanate oligomer characterised in that it is unsymmetrical and comprises the general formula:

   in which X is an organic group containing an alkenyl double bond and Y is an organic group with a molecular weight of upto about 1000.
2. 2. An alkenyl cyanate oligomer as claimed in claim 1 characterised in that Y does not react with compounds from the group comprising bis-maleimides, bis-citraconimides, aspartimides, compounds containing epoxide groups and other cyanate esters.
3. 3. An alkenyl cyanate oligomer as claimed in claim 1 or claim 2 characterised in that X is a propenyl functional group.
4. 4. An alkenyl cyanate oligomer as claimed in any one of the preceding claims characterised in that X contains an alkenyl group which forms the trans isomer.
5. 5. An alkenyl cyanate oligomer of the formula: 4-(2-prop-2-enyl-phenoxyphenyl)-4'-(4- cyanatophenoxy)phenylsulphone.
6. 6. An alkenyl cyanate oligomer of the formula: 4-(2-prop-2-enyl-phenoxyphenyl)-4-4'-(2-(4- cyanatophenyl)propane)phenoxyphenylsulphone.
7. 7. An alkenyl cyanate oligomer of the formula: 4-(2-prop-2-enyl-phenoxyphenyl)A'-(4- cyanatophenoxy)phenylacetone.
8. 8. An alkenyl cyanate oligomer of the formula 4-(2-prop-2-enyl-phenoxyphenyl)-4-4'-(2-(4- cyanatophenyl)propane) phenoxyphenylacetone.
9. 9. A method of making a polymeric resin comprising polymerising an oligomer as claimed in any one of the preceding claims alone or by co-reaction with one or more polymers from the group comprising bis-maleimides, bis-citraconomides, aspartimides, compounds containing epoxide groups, and compounds containing other cyanate ester groups.
10. 10. A method as claimed in claim 9 characterised in that the compounds co-polymerised are 4- (2-prop-2-enyl-phenoxyphenyl) 4'4- (2-(4-cyanatophenyl)propane) phenoxyphenyl sulphone, a bismaleimide and a cyanate ester approximately in the molar ratio 15% to 35% to 50%.
11. 11. A polymerised resin characterised in that it is made according to the method of claim 9 or claim 10.
12. 12. A composite material characterised in that it comprises a polymerised resin according to claim 11.
13. 13. A composite according to claim 12 characterised in that the resin is reinforced with fibres from the group comprising carbon, glass and aramid.
14. 14. A composite according to claim 12 characterised in that the fibres are carbon fibres.
15. 15. A composite according to claim 13 or 14 characterised in that it is laminated.
16. 16. Novel propenyl-functionalised aromatic compounds and polymerised products thereof substantially as herein described with reference to the examples.