Maleimide resins

Abstract

A curable polymer composition comprising: (A) a thermoset maleimide resin precursor component; and further comprising one or both of: (B) an arylsulphone-containing maleimide component; and (C) a polyarylpolymer thermoplastic toughening agent component, wherein in the absence of component (B), said component (C) comprises one or more maleimide pendant and/or end groups, and thermoset resins and composites derived therefrom.

Claims

1. A curable polymer composition comprising: (A) a thermoset maleimide resin precursor component; (B) an arylsulphone-containing maleimide component; and (C) a polyarylpolymer thermoplastic toughening agent which comprises at least one SO.sub.2 group in the polymer chain but does not comprise maleimide pendant or end-groups, wherein the weight proportions, based on the total weight of components (A), (B) and (C), are from 20% to 45% by weight of component (B) and from 5% to 20% by weight of component (C).

2. The curable polymer composition according to claim 1 further comprising one or more additional toughening agent(s), wherein at least one of said additional toughening agent(s) is/are in particulate form.

3. The curable polymer composition according to claim 1, wherein said maleimide resin precursor component is a bismaleimide resin precursor.

4. The curable polymer composition according to claim 1, wherein said arylsulphone-containing maleimide component (B) is an arylsulphone-containing bismaleimide component.

5. The curable polymer composition according to claim 1, wherein said thermoset maleimide component comprises one or more polymerisable bismaleimide compound(s), optionally with a mono-functional or tri-functional or tetra-functional maleimide.

6. The curable polymer composition according to claim 1 further comprising one or more co-reactants selected from the group consisting of: allylnadicimide resins; epoxy resins; di- and poly-amines; cyanate resins; unsaturated polyester resins; alkenylphenol-terminated compounds; comonomers characterized by the presence of one or more CHCH.sub.2, >CCH.sub.2, or CCH groups polymerizable with the carbon-carbon double bonds of the maleimide groups; and silicone rubbers terminated with maleimide, epoxy, vinyl or amino groups.

7. The curable polymer composition according to claim 1 further comprising one or more co-reactants selected from alkenyloxyphenols and alkenylphenols.

8. The curable polymer composition according to claim 1 further comprising one or more co-reactants selected from: o,o-diallybisphenols; o,o-dipropenylbisphenols; allylphenoxy; propenylphenoxy; allylphenyl; propenylphenyl-terminated oligomeric compounds; and alkenylphenol- or alkenyloxyphenyl terminated dicyclopentadienes.

9. The curable polymer composition according to claim 1 further comprising at least one radical inhibitor or catalyst.

10. The curable polymer composition according to claim 1, wherein the polyarylpolymer thermoplastic toughening agent comprises sequences of phenylene groups linked either as fused rings, through a single chemical bond or through a divalent group selected from SO.sub.2, CO, O, S and a divalent hydrocarbon.

11. The curable polymer composition according to claim 1, wherein said arylsulphone-containing maleimide component (B) is a bismaleimide group of formula (III): ##STR00014## wherein Z.sup.2 is a sulfone [SO.sub.2] group or comprises one or more arylsulphone unit(s), [ArSO.sub.2Ar], and optionally further comprises one or more arylene unit(s) [Ar], wherein said arylsulphone unit(s) and arylene unit(s) are linked either as fused rings, through a single chemical bond or through a divalent group selected from SO.sub.2, CO, O, S and a divalent hydrocarbon.

12. The curable polymer composition according to claim 11 wherein Ar is phenylene.

13. The curable polymer composition according to claim 1, wherein said arylsulphone-containing maleimide component (B) is selected from m-ESEDA-bismaleimide, 3,3-DDS-bismaleimide and 4,4-DDS-bismaleimide represented by the following structures (a)-(c), respectively: ##STR00015##

14. The curable polymer composition according to claim 1, wherein the number average molecular weight of the arylsulphone-containing maleimide component (B) is less than 2000.

15. The curable polymer composition according to claim 1, wherein the thermoset maleimide resin precursor component (A) comprises a bismaleimide, wherein the arylsulphone-containing maleimide component (B) is selected from m-ESEDA-bismaleimide, 3,3-DDS-bismaleimide and 4,4-DDS-bismaleimide, and wherein the polyarylpolymer thermoplastic toughening agent (C) is an amine-ended PES:PEES polyarylsulphone.

16. The curable polymer composition according to claim 1, wherein the polyarylpolymer thermoplastic toughening agent (C) comprises a combination of polyethersulphone (PES) and polyetherethersulphone (PEES) ether-linked repeating units.

17. A composite comprising reinforcing fibers and the curable polymer composition of claim 1, wherein said fibers are present at a concentration of 30 to 70% by weight.

18. The composite according to claim 17 wherein said fibers are selected from the group consisting of: glass, alumina, zirconia, silicon carbide, compound ceramics, aluminum, titanium, boron, carbon, graphite, poly paraphenylene terephthalamide, poly(benzothiazole), poly(benzimidazole) and poly(benzoxazole) fibers.

Description

EXAMPLES

(1) Synthesis of the maleimides follows several different procedures, for the m-ESEDA BMI, one method is based on the use of DMAc as a solvent, the other based on the use of DMF as a solvent. For 33-DDS BMI the solvent was MIBK, for 44-DDS BMI the solvent was DMF. For BMI ended PES/PEES polymers the solvent was DMAc.

(2) Described are the synthetic procedures for bismaleimides based on the diamines m-ESEDA, 33-DDS, 44-DDS and PES:PEES co-polymer, having the structures below in Schematic 2 below.

(3) ##STR00008##
Synthesis of m-ESEDA Based Bismaleimide (BMI) Via DMF Route

(4) ##STR00009##

(5) To a 5 L 4-neck round bottom flask, equipped with a reflux condenser, a thermo-couple, an over-head stirrer and a nitrogen inlet was added 0.78 mol of m-ESEDA and 600 mL DMF. To this stirred solution was added 1.78 mol of maleic anhydride in several parts; at first a drop in temperature was observed, followed by a sharp rise in temperature. To control this temperature rise the round bottomed flask was placed in an ice bath. Within 15 minutes a brownish solution was formed; LC showed no unreacted m-ESEDA remained. The solution was stirred for 120 minutes and 5.51 mol of acetic anhydride and 0.32 mol of sodium acetate were added to the reaction mixture. It was heated to 35 C., turning dark brown in colour. After 3 hours of stirring at 35 C., LC showed the absence of acid intermediate product. The mixture was poured over 1 Kg of ice and the mixture was stirred overnight. A tan coloured solid was observed in the flask, which was filtered and washed with water followed by a 1:1 mixture of water and methanol. To further purify the compound, it was re-slurried in water at ambient temperature, stirred for 3 hours, filtered, washed and dried in vacuum oven.

(6) Synthesis of m-ESEDA Based Bismaleimide (BMI) Via DMAc Route

(7) ##STR00010##

(8) m-ESEDA (39.21g, 0.091 moles) was placed into a 500 ml glass beaker. DMAc (400 ml, 4.316 moles) was added to the beaker along with a stirring bar and the solutions were then stirred using a stirrer hot plate until the m-ESEDA was fully dissolved (approximately 15 minutes). The solutions were stored in glass jars and put in the fridge overnight to cool. The cooled solution was then added to an 800 ml glass beaker along with a stirring bar. A salt-ice bath and dry ice was placed under the glass beakers and the solution was stirred until it reached 0 C.2 C. Maleic anhydride (17.781 g, 0.182 moles) was added to the solution and stirred until the maleic anhydride was dissolved (approximately 15 minutes). The ice bath was removed and replaced with cold water and the solutions were left to stir at 15 C. for one hour. Triethylamine (34.5 ml, 0.248 moles) and acetic anhydride (37 ml, 0.392 moles) were added dropwise to the maleic anhydride/m-ESEDA/DMAc solution, keeping the temperature below 20 C. The solutions were warmed to 20 C. and stirred for a further four hours. The solution was then placed in an oil bath and heated to 60 C. whilst stirring for a further two hours. The solutions were allowed to cool overnight prior to workup.

(9) The solution was precipitated into a 5 L glass beaker containing 3.5 L of cold water. This was done whilst stirring using a PTFE air stirrer. The precipitate was stirred for an additional 20 minutes. The product was allowed to settle and the majority of the water was decanted off. The water level was then raised to 3.5 L again and stirred for a further 20 minutes. The solid was then allowed to settle and the water was again decanted off. This procedure was repeated several times over the course of one day. The precipitate was vacuum filtered on a sintered funnel and then covered with IPA. The solid was then vacuum filtered again and then air dried overnight. The tacky solid product was removed from the sintered funnel and stirred into 500 ml of isopropyl alcohol for 1 hour. The solid was then vacuum filtered again, and redispersed into another 500 ml IPA. After a final vacuum filtration the solid was dried in a vacuum oven at 25 C. for anything upto 3 days. The solid was broken up by hand twice a day whilst vacuum drying to speed the drying process and ensure homogeneity in the sample. The solid was ground in a pestle and mortar to ensure that a fine powder was produced prior to Soxhlet extraction.

(10) The product was placed into a Soxhlet extraction thimble (12 cm4.5 cm) and a filter paper was placed loosely over the top of the thimble. A 500 ml capacity round bottom flask with 300 ml capacity Soxhlet extractor was set up and the product was extracted with 420 ml of isopropyl alcohol. The extraction was run for 24 hours, over 3 days, giving approximately 40 extraction cycles. At the end of each day, the Soxhlet thimble was removed from the equipment and the product was examined. If it had solidified into a solid plug, the Soxhlet thimble was cut off and all traces of the paper thimble were scrapped off the solid product. The plug was then broken up, dried and then re-ground prior to the next day's extraction. The extraction was then repeated until it had been extracted for a total of 24 hrs. The product was then dried in a vacuum oven at 80 C. for 6 hours. If any traces of the Soxhlet thimble got into the product an additional step was needed prior to drying, involving dissolving the product, filtering, removing the solvent in vacuo then re-grinding the solid. The product was then dried as mentioned previously.

(11) The final purification step involved washing with 1 l of 0.1M sodium bicarbonate solution and agitating the solution with a PTFE air stirrer for 30 minutes. The product was filtered using a Buchner funnel and then washed with 1 l of water, again with 30 minutes of agitation before being filtered via Buchner funnel and dried in vacuo at 80 C.

(12) Synthesis of 3,3-DDS Based Bismaleimide (BMI)

(13) ##STR00011##

(14) To a 5 L 4-neck round bottom flask, equipped with a reflux condenser, a thermo-couple, an over-head stirrer and a nitrogen inlet was added 0.58 mol of 3,3-diaminodiphenyl sulfone and 2.5 L MIBK. To this stirried solution was added 1.32 mol of maleic anhydride in several parts; at first a drop in temperature was observed, followed by a sharp rise in temperature. To control this temperature rise the round bottomed flask was placed in an ice bath. Within 15 minutes the solids went into solution and the reaction mixture became faintly yellow. This was followed by the appearance of an off white solid; LC showed no unreacted m-ESEDA remained. The solution was stirred for 120 minutes, by which time a large quantity of fluffy white solid could be observed. LC showed no 3,3-DDS remaining. 4.4 mol of acetic anhydride and 0.3 mol of sodium acetate were added to the reaction mixture and it was heated to 65 C. The reaction mixture contained a large quantity of solid but could be stirred. The white solid then started to turn bright yellow, then an off white. turning dark brown in colour. After 5 hours of stirring at 65 C., LC showed the absence of acid intermediate product. The mixture was cooled to room temperature and filtered; the off-white solid obtained was washed with MIBK, and dried in vacuum oven. Once MIBK was completely removed, the solid was re-slurried in water for 3 hours at room temperature then filtered and washed with additional water. The solid was filtered and re-slurried again, this time in water at 50 C. for 3 hours. The material was filtered, washed with additional water and dried in vacuum oven.

(15) Synthesis of 4,4-DDS Based Bismaleimide (BMI)

(16) ##STR00012##

(17) To a 5 L 4-neck round bottom flask, equipped with a reflux condenser, a thereto-couple, an over-head stirrer and a nitrogen inlet was added 1.36 mol of 44-DDS and 1400 mL DMF. To this stirred solution was added 3.5 mol of maleic anhydride in several parts; at first a drop in temperature was observed, followed by a sharp rise in temperature. To control this temperature rise the round bottomed flask was placed in an ice bath. Within 15 minutes all the solid had gone into solution; LC showed no unreacted 44-DDS remained. The solution was stirred for 120 minutes and 10.4 mol of acetic anhydride and 0.61 mol of sodium acetate were added to the reaction mixture. It was heated to 35 C., turning off white in colour. After 3 hours of stirring at 35 C., LC showed the absence of acid intermediate product. The mixture was poured over 1.5 Kg of ice and the mixture was stirred overnight. An off white coloured solid was observed in the flask, which was filtered and washed with water followed by a 1:1 mixture of water and methanol. To further purify the compound, it was re-slurried in water at ambient temperature, stirred for 3 hours, filtered, washed and dried in vacuum oven.

(18) Synthesis of Amine Ended PES/PEES Based Bismaleimide (BMI) Via DMAc Route

(19) ##STR00013##
PES/PEES-BMI-Mn8400

(20) The procedure was identical to that used for the m-ESEDA BMI synthesis in DMAc, although the amine ended PES/PEES polymer replaced the m-ESEDA and the amounts were as follows. 0.225 g (2.3 mmol) of maleic anhydride was reacted with 9.904 g (1.2 mmol) of amine ended PES/PEES polymer (M.sub.w=8400 g mol.sup.1) in 50 ml of DMAc. Cyclisation was carried out using 1 ml of acetic anhydride and 1 ml triethylamine.

(21) Precipitation was carried out by adding the water dropwise to the DMAc solution until in excess followed by quick addition of the remaining 400 ml. 8.43 g of a fine grey powder was obtained after drying giving a crude yield of 84%.

(22) PES/PEES-BMI-Mn6600

(23) The procedure was identical to that used for the m-ESEDA BMI synthesis in DMAc, although the amine ended PES/PEES polymer replaced the m-ESEDA and the amounts were as follows. 0.296 g (3.0 mmol) of maleic anhydride was reacted with 9.879 g (1.5 mmol) of KM (M.sub.w=6554 g mol.sup.1) in 50 ml of DMAc. Cyclisation was carried out using 1 ml of acetic anhydride and lml triethylamine. 8.59 g of a fine grey powder was obtained after drying giving a crude yield of 86%.

(24) PES/PEES-BMI-Mn3500

(25) The procedure was identical to that used for the m-ESEDA BMI synthesis in DMAc, although the amine ended PES/PEES polymer replaced the m-ESEDA and the amounts were as follows. 0.765 g (7.8 mmol) of maleic anhydride was reacted with 9.360 g (3.9 mmol) of KM (M.sub.w=2400 g mol.sup.1) in 50 ml of DMAc. Cyclisation was carried out using 1 ml of acetic anhydride and 1 ml triethylamine. 6.88 g of a fine grey powder was obtained after drying giving a crude yield of 69%.

(26) General Blendinga Curing Procedure

(27) Resin blends were prepared by first mixing diallylbisphenol-A (DBA) with t-butyl hydroquinone (THQ) in a glass jar for 15 min at 120 C. in an oil bath. Once there was complete mixing the jar was removed from the heat and BMI-H was added with the blend being stirred until homogeneous. At this point any m-ESEDA BMI was added in small portions and again stirred until homogeneous. Any thermoplastic toughening agent (a PES:PEES co-polymer of formula I or II herein) was added in a small portion, the blend was stirred until homogeneous and then another portion was added and blended until homogeneous. This was continued until all of the thermoplastic was added (normally around 5 portions). Any powder sticking to the sides of the jar was scraped into the blend. The jar was then returned to the oil bath and stirred at high speed at 120 C. for 45 minutes.

(28) The thick solution was then poured into a mould, degassed at 100 C. for 2-3 h (2 h for DMTA sized dishes and 3 h for 64 mechanical plaques) before being cured. The curing cycle was that of 5250-4, 121 C. to 177 C. at 3 C./min, followed by a hold for 6 h.

(29) Cooldown was at 3 C./min to room temperature. A postcure was then applied at 25 C. to 227 C. for 6 h, with a cooldown of 3 C./min.

(30) BMI Blends

(31) PES/PEES Polymer Toughening Agents

(32) A number of different blends prepared with PES/PEES polymer are summarised in Table 1.

(33) TABLE-US-00001 TABLE 1 Blends of BMI's with PES/PEES polymer BMI ratio PES/PEES BMI-H m-ESEDA BMI Polymer (wt %) 100 0 0 100 0 10 100 0 20 70 30 0 70 30 10 70 30 20

(34) The PES/PEES polymer described in Table 1 is amine-ended with a Mn 8200. THQ was present at 1% in all blends.

(35) Mechanical Properties

(36) Note that the 20% PES/PEES containing specimens were not analysed for their mechanical properties as they showed a phase inverted morphology, a morphology unsuitable for the desired use of the material. Mechanical properties are given in Table 2.

(37) TABLE-US-00002 TABLE 2 Mechanical properties K.sub.1C G.sub.1C E modulus K.sub.1C (MPa m.sup.0.5) G.sub.1C (Jm.sup.2) E modulus (GPa) Plaque Formulation (MPa m.sup.0.5) SD (Jm.sup.2) SD (GPa) SD High Tg commercial epoxy resin 0.69 0.02 145 10 3.54 0.08 BMI-H/DBA/1% THQ 0.7 0.02 150 9 3.78 0.15 BMI-H/DBA/10% KM-177/1% THQ 0.92 0.04 259 23 3.79 0.08 BMI-H/BDA/m-ESEDA BMI/1% THQ 0.7 0.03 150 13 3.75 0.5 BMI-H/DBA/m-ESEDA BMI/10% KM-177/1% THQ 0.86 0.07 224 36 3.59 0.49 0.88 0.04 236 22 3.78 0.15
Thermomechanical Properties

(38) The DMTA Peak Tan delta for blends of BMI-H, DBA, THQ and/or m-ESEDA BMI and/or amine ended PES/PEES polymer is shown in FIG. 1. Note that there is a 26 C. drop between the unmodified system and the compatibilised, toughened system.

(39) Solvent Uptake

(40) Studies on the level of solvent uptake using MEK and water have also been undertaken. These solvent uptake studies involved refluxing the solvents for 6.5 h per day, then leaving the samples to soak in the solvent overnight. This process was repeated for >30 days. The results are shown in FIG. 2 (MEK) and FIG. 3 (water).

(41) FIG. 2 shows that the toughened systems do pick up more solvent than the non-toughened systems but only by 1% over 36 days. The compatibilised systems also pick up more MEK, by around 0.4%-0.5% over 36 days.

(42) Thermo-Oxidative Stability

(43) The therm-oxidative stability of the toughened and non-toughened samples have been examined for their thermo-oxidative stability. Samples were held at 200 C. and measured for weight loss over time. This data has been plotted graphically in FIG. 4.

(44) FIG. 4 shows that all of the blends, toughened, non-toughened, compatibilised and non-compatibilised have very similar weight loss over time. A comparison sample based on a commercial epoxy resin system is included for reference.

(45) Rheology

(46) Rheology studies on the blends of resins to determine if the addition of toughening agents gave a level of flow control. This flow control would be an additional benefit to the processing of BMI systems. The rheology trace for blends of BMI with and without compatibiliser and toughening agent are shown in FIG. 5. It can be seen from FIG. 5 that the viscosity of the toughened blends is indeed higher than the non-toughened systems. The addition of 10% PES/PEES polymer raises the viscosity from around 100 cP to around 420-830 cP. As a comparison, a commercial BMI resin, has a viscosity around 40 cP, a high flow epoxy resin, 1000 cP. This increase in viscosity may lead to less resin bleed out during composite manufacture.

(47) High-Tg Sulfone-containing Toughening Agents

(48) A higher Tg polymer containing sulfone units was prepared so that the effective use temperature of the cured blend was raised. The modulus of the cured systems dropped off above the Tg of the thermoplastic toughener and so a toughener with a Tg close to that of the neat BMI resin was sought. This polymer is described in Schematic 1 and formula II herein. A number of blends containing high-Tg sulfone containing polymers were also examined. These are detailed in Table 3.

(49) TABLE-US-00003 TABLE 3 Blends of BMI's with PES:Biphenyl polymer of formula II 6500 Mn polymer-Amine ended BMI ratio Polymer backbone ratio m-ESEDA (PES:Biphenyl) % wt BMI-H BMI 50:50 25:75 0:100 polymer 100 0 x 10 100 0 x 10 100 0 x 10 70 30 x 10 70 30 x 10 70 30 x 10 100 0 x 20 100 0 x 20 100 0 x 20 70 30 x 20 70 30 x 20 70 30 x 20
Morphology

(50) The morphology of the cured and toughened samples were analysed by scanning electron microscopy (SEM).

(51) FIG. 6 shows the 10% PES/PEES toughened BMI-H, DBA, THQ system, which shows some fine particulate morphology but some gross, phase inverted areas, predominantly close to edges, suggesting demixing.

(52) FIG. 7 shows the SEM images of a resin system compatibilised with m-ESEDA BMI, and in particular the 10% PES/PEES, 70:30 BMI-H:m-ESEDA BMI, DBA and THQ system. The fine particulate morphology is present and consistent throughout the resin and no large, phase inverted areas are present. Thus, FIG. 7 shows a highly homogenous fine particulate morphology, as well as extremely fine particulate morphology.