NOVEL BISMALEIMIDE COMPOUNDS HAVING IMPROVED SOLUBILITY AND THEIR USE IN CURABLE COMPOSITIONS

Abstract

Specific bismaleimide compounds are made, and curable compositions are made that include at least one of these bismaleimides and at least one specific polyimide. A process is developed for the manufacture of these curable compositions, and crosslinked polymers are obtainable by this process. A process is developed for the manufacture of a composite material by curing a mixture of a fibrous or particulate reinforcement and the curable composition or the crosslinked polymer as well as the obtained composite material.

Claims

1. A bismaleimide according to formula (I) ##STR00026## wherein R is a substituted or unsubstituted C.sub.3-7 cycloaliphatic ring; or is a group of formula (II) ##STR00027## wherein R.sup.1 and R.sup.2 can be the same or different and are independently selected from the group consisting of C.sub.2-12 and alkenyl groups.

2. The bismaleimide of claim 1, wherein R is a cyclohexyl group of formula (III) ##STR00028## wherein R.sup.3 to R.sup.6 can be the same or different and are independently selected from the group consisting of H and C.sub.1-3 alkyl groups.

3. The bismaleimide of claim 1, wherein the bismaleimide is 2-(3,3,5-trimethylcyclohexyl)propane-1,3-bismaleimide having formula (IV) ##STR00029##

4. A curable composition, comprising: (i) at least one bismaleimide according to claim 1; (ii) at least one polyimide of general formula (V) ##STR00030## wherein B is a difunctional group containing a carbon-carbon double bond, A is a y-functional group; and y is an integer 2; and (iii) at least one co-monomer or a combination of at least two co-monomers selected from the group consisting of: (a) a compound of formula (VI) ##STR00031## wherein R.sup.7 is a difunctional group, and R.sup.8 and R.sup.9 can be the same or different and are independently selected from alkenyl groups with 2 to 6 carbon atoms; (b) a compound of formula (VII) ##STR00032## wherein R.sup.10 is a difunctional group, and R.sup.11 and R.sup.12 can be the same or different and are independently selected from alkenyl groups with 2 to 6 carbon atoms; (c) a compound of formula (VIII) ##STR00033## wherein R.sup.13 is a difunctional group, and R.sup.14 and R.sup.15 can be the same or different and are independently selected from alkenyl groups with 2 to 6 carbon atoms; (d) a compound of formula (IX) ##STR00034## wherein R.sup.16 is a difunctional group, and R.sup.17 and R.sup.18 can be the same or different and are independently selected from alkenyl groups with 2 to 6 carbon atoms; (e) a compound of formula (X) ##STR00035## wherein R.sup.19 is a y-functional group, R.sup.20 is an alkenyl group with 2 to 6 carbon atoms, and y is an integer 2; and (f) a compound of formula (XI) ##STR00036## wherein R.sup.21 is a y-functional group, R.sup.22 is alkenyl group with 2 to 6 carbon atoms, and y is an integer 2.

5. Curable The curable composition according to claim 4, wherein B in the polyimide of formula (V) is a difunctional group selected from the group consisting of: ##STR00037##

6. The curable composition according to claim 4, wherein the A in the polyimide of formula (V), is a difunctional group selected from the group consisting of: a) an alkylene group with 2 to 12 carbon atoms; b) a cycloalkylene group with 5 to 6 carbon atoms; c) a heterocyclic group with 4 to 5 carbon atoms and at least one nitrogen, oxygen, or sulphur atom in the ring; d) a mono-or dicarbocyclic group; e) a bridged multicyclic group consisting of at least two groups selected from the following: group consisting of monocarbocyclic aromatic groups, dicarbocyclic aromatic groups, and cycloalkylene groups; wherein these groups are linked to each other by direct carbon-carbon bonds or by divalent groups; f) a group defined by formula (XII) ##STR00038## wherein R.sup.31 is one of the following groups ##STR00039##

7. The curable composition according to claim 4, wherein the polyimide of formula (V) is a bisimide of formula (Va) ##STR00040## wherein R.sup.32 is one of the following groups ##STR00041##

8. The curable composition according to claim 4, wherein the at least one polyimide of formula (III) is a bismaleimide selected from the group consisting of 4,4-bismaleimidodiphenylmethane, bis(3-methyl-5-ethyl-4-maleimidophenyl)methane, bis(3,5-dimethyl-4-maleimidophenyl)methane, 4,4-bismaleimidodiphenylether, 4,4-bismaleimidodiphenylsulfone, 3,3-bismaleimidodiphenylsulfone, bismaleimidodiphenylindane, 2,4-bismaleimidotoluene, 2,6-bismaleimidotoluene, 1,3-bismaleimidobenzene, 1,2-bismaleimidobenzene, 1,4-bismaleimidobenzene, 1,2-bismaleimidoethane, 1,6-bismaleimidohexane, 1,6-bismaleimido-(2,2,4-trimethyl)hexane, 1,6-bismaleimido-(2,4,4-trimethyl)hexane, 1,4-bis(maleimidomethyl)cyclohexane, 1,3-bis(maleimidomethyl)cyclohexane, 1,4-bismaleimidodicyclohexylmethane, 1,3-bis(maleimidomethyl)benzene, 1,4-bis(maleimidomethyl)benzene and a mixture thereof.

9. A process for the manufacture of curable compositions according to claim 4, comprising: blending the at least one polyimide and the at least one bismaleimide using a powder-, melt-, or solvent assisted blending process to obtain the curable composition.

10. A crosslinked polymer obtainable from the curable composition according to claim 4 by heating the curable composition to a temperature in a range of from 70 C. to 280 C.

11. A process for the manufacture of a composite material, comprising: mixing the curable composition according to claim 4, with a fibrous or particulate reinforcement. and curing the mixture.

12. A composite material obtainable by the process according to claim 11.

13. The curable composition according to claim 6, wherein the divalent groups are selected from the group consisting of oxy-groups, thio-groups, alkylene-groups with 1 to 3 carbon atoms, sulfone-groups, methanone-groups, and the following groups: ##STR00042## wherein R.sup.23 to R.sup.28 are independently selected from alkyl groups with 1 to 6 carbon atoms; and R.sup.29 and R.sup.30 are independently selected from alkylene groups with 1 to 6 carbon atoms.

14. A process for the manufacture of a composite material, comprising: mixing the crosslinked polymer according to claim 10 with a fibrous or particulate reinforcement, and curing the mixture.

Description

EXAMPLES

[0151] The following examples are intended to illustrate but not to limit the invention.

EXAMPLES

A. Preparation of 2-(3,3,5-trimethylcyclohexyl)propane-1,3-bismaleimide

Example 1

[0152] The 2-(3,3,5-trimethylcyclohexyl)propane-1,3-bismaleimide was produced according to the following reaction scheme:

##STR00025## [0153] 120 ml of N,N-dimethylacetamide were charged under nitrogen into a glass reactor equipped with mechanical stirrer, thermometer, and dropping funnel. 100 g of maleic anhydride were added and the mixture was stirred until dissolution was complete. Then, 99.2 g of 2-(3,3,5-trimethylcyclohexyl)propane-1,3-diamine were added dropwise so that the temperature did not exceed 60 C. After addition, the mixture was stirred for 1 hour at 50-55 C. Then, 128 g of acetic anhydride were added, followed by 200 g of triethylamine. The reaction mixture was heated up to 90 C., stirred for 1 hour, and cooled down to 60 C. The mixture was then stirred for 20 min at 60 C. and poured into 2 l of water under vigorous stirring. The precipitate was filtered off and washed by slurrying in distilled water. Finally, the product was filtered off and dried at 60 C. under reduced pressure. For analytical purposes, the product was purified by column chromatography using silica gel as a solid phase and methyl ethyl ketone as an eluent. M.p. 119 C. (DSC, 10 C./min).

[0154] .sup.1H NMR (CDCl.sub.3) 0.91/0.93* (s/s, 6H), 0.98 (d, 3H), 1.08 (t, 1H), 1.18 (dd, 1H), 1.30 (dd, 1H), 1.35 (d, 1H), 1.37-1.47 (m, 2H), 1.71 (m, 1H), 1.97 (m, 1H), 2.05 (m, 1H), 3.31/3.32* (d/d, 2H), 3.58* (m, 2H), 6.69/6.69* (s/s, 4H).

[0155] The resulting 2-(3,3,5-trimethylcyclohexyl)propane-1,3-bismaleimide is highly soluble in different organic solvents in comparison to other aliphatic bismaleimides:

TABLE-US-00001 TABLE 1 Solubilities of aliphatic bismaleimides in organic solvents, Solubility at 25 C. in 1,3- Ethyl Methyl BMI Acetone DMF.sup.a Dioxolane acetate MEK.sup.b proxitol.sup.c Toluene 1,6-Bismaleimidohexane* 2.6 6.1 8.7 2.1 2.6 3.3 1.5 1,3-Bismaleimidomethyl(cyclohexane) 9.1 11.4 30.4 5.7 7.9 5.2 5.9 1,5-Bismaleimido(2-methylpentane) 30.2 30.1 42.9 16.7 19.8 11.9 10.4 1,6-Bismaleimido-(2,2,4-/2,4,4,-trimethylhexane)* 23.0 38.3 38.3 22.9 26.3 15.8 22.8 mixture of isomers 2-(3,3,5-trimethylcyclohexyl)propane-1,3-bismaleimide 43.7 42.6 54.6 34.6 47.9 38.0 40.4 *Commercial product; .sup.aN,N-dimethylformamide; .sup.bMethyl ethyl ketone; .sup.c1-Methoxy(2-propanol)

[0156] The solubility of the example and comparative examples was determined as follows: [0157] 10 g of a sample were weighed into a 100 ml conical flask. 50 ml of a solvent were added to the flask and the mixture was stirred with magnetic bar for 1 h at 25 C. to assure the formation of a saturated solution. If the entire sample was dissolved, additional portion of the sample should be added and the mixture should be stirred further for 1 h. In the end, a portion of undissolved material should be clearly seen at the bottom of the flask. After that, the supernatant was filtered through a folded filter. Some 15 g of the filtrate are weighed into a tared round-bottom flask, and the solvent was evaporated to dryness on a rotary evaporator at 90 C. under reduced pressure. Finally, the flask was dried in a vacuum drying cabinet at 120 C. for 2 h under reduced pressure, cooled down to room temperature in a desiccator and weighed.

[0158] The solubility value is then calculated as:

[00002]$\mathrm{Solubility}\left[\%\right]=\frac{\left[\mathrm{Output}\mathrm{weight}\right]100}{\left[\mathrm{Original}\mathrm{sample}\mathrm{weight}\right]}$

B. Preparation of Curable Mixtures according to the Invention Based on Bismaleimide of Formula (I), Polymaleimide of Formula (V), and a Co-Mononmer

[0159] The curable mixtures according to the invention can be obtained according to the following general processes:

(a) Solvent-Assisted Process

[0160] At least one polymaleimide of formula (V) and at least one bismaleimide of formula (I) and, if required, at least one additional co-monomer component and an organic solvent, preferably toluene or methylene chloride, in a weight ratio solid-to-solvent of 1:1 are heated to 90-100 C. until a clear solution is obtained. Subsequently, the solvent is stripped off under reduced pressure, and the temperature is simultaneously increased to between 100-120 C. Finally, the mixture is degassed for 2-10 minutes under reduced pressure of 20 hPa [15 mm Hg] to obtain a curable mixture. The resin/solvent ratio may vary, depending on the solubility of components. Other solvents or diluents, as mentioned in the patent, may also be used.

(b) Melt Process

[0161] At least one polymaleimide of formula (V), at least one bismaleimide of formula (I) and, if required, at least one additional co-monomer component are melt-blended in a temperature range of 100-120 C. until a homogeneous mixture is obtained. Subsequently, the melt thus obtained is further heated in the same temperature range for a time sufficient to obtain a stable melt. Finally, the melt is degassed under reduced pressure of 20 hPa [15 mm Hg] for 2-10 minutes to obtain the curable mixture.

(c) Reactivity Measurements

(c.1) Differential Scanning Calorimetry (DSC)

[0162] Differential scanning calorimetric (DSC) traces, obtained at a defined heating rate (10 C./min) in the temperature range from 20 to 380 C., are used to characterize the cure kinetics of curable compositions of the present invention. The cure exothermic maximum, T.sub.MAX, represents the temperature of maximum heat release due to polymerization at the specified heating rate. The growth onset of the exothermic peak represents the temperature of polymerization onset, T.sub.ONSET. The higher are T.sub.ONSET and T.sub.MAX the slower is the cure of a resin.

(c.2) Hot-Plate Gel Time

[0163] Being a standard measure of resin reactivity, the gel time is measured by placing 1 g of the resin on an electrically heated metal block with a polished surface, which is capable of being maintained at temperatures between 130 C. and 230 C., and continuous stirring and probing the molten sample with a wooden rod, as described in the ISO 8987:2005-12 and ASTM D4217-07 (2017) norms.

C. Curable Polymaleimide/Asymmetric Substituted Bis-Alkenyl Diphenyl Ether Mixtures

Example 2

[0164] Curable mixture comprising 60 wt.-% bismaleimide of formula (IV), and 40 wt.-% 2,2-bis(3-allyl-4-hydroxyphenyl)propane prepared by a solvent-assisted process (a) with the use of toluene as a solvent. [0165] Gel time: 54 min. [0166] Dynamic viscosity at 90 C.: 487 mPa.Math.s; at 110 C.: 122 mPa.Math.s. [0167] DSC Polymerization onset (T.sub.ONSET): 150 C. [0168] DSC Polymerization maximum (T.sub.MAX): 279 C.

Example 3

[0169] Curable mixture comprising 35 wt.-%, bismaleimide of formula (IV), 35 wt.-% meta-xylylene bismaleimide, and 30 wt.-% 4,4-bis(ortho-propenylphenoxy)benzophenone, prepared by a solvent-assisted process (a) with the use of toluene as a solvent. [0170] Gel time: 48 min [0171] Dynamic viscosity at 90 C.: 867 mPa.Math.s; at 110 C.: 194 mPa.Math.s. [0172] DSC Polymerization onset (T.sub.ONSET): 136 C. [0173] DSC Polymerization maximum (T.sub.MAX): 253 C.

Example 4

[0174] Curable mixture comprising 30 wt.-% bismaleimide of formula (IV), 30 wt.-% 4,4-bismaleimidodiphenylmethane, 26.7 wt.-% 4,4-bis(ortho-propenyiphenoxy)benzophenone, and 13.3 wt.-% 2,2-bis(3-allyl-4-hydroxyphenyl)propane, prepared by a solvent-assisted process (a) with the use of toluene as a solvent. [0175] Gel time: 27 min [0176] Dynamic viscosity at 90 C.: 2043 mPa.Math.s; at 110 C.: 3302 mPa.Math.s. [0177] DSC Polymerization onset (T.sub.ONSET): 135 C. [0178] DSC Polymerization maximum (T.sub.MAX): 260 C.

Example 5

[0179] A mixture comprising 21 g of bismaleimide of formula (IV), 9 g of 2,2-bis(3-allyl-4-hydroxyphenyl)propane, and 30 g of methyl ethyl ketone was stirred at 60 C. for 10 min, filtered, and cooled down to room temperature, providing a resin solution containing 50 wt.-% of solids. No crystallization was observed after six weeks at room temperature. [0180] Gel time: 62 min [0181] Dynamic viscosity: 17 mPa.Math.s