Process for producing porous materials

Abstract

The present invention relates to a process for producing porous materials, which comprises providing a mixture comprising a composition (A) comprising components suitable to form an organic gel and a solvent mixture (B), reacting the components in the composition (A) in the presence of the solvent mixture (B) to form a gel and drying of the gel, wherein the solvent mixture (B) is a mixture of at least two solvents and the solvent mixture has a Hansen solubility parameter ?.sub.H in the range of 3.0 to 5.0 MPa-.sup.1, determined using the parameter ?.sub.H of each solvent of the solvent mixture (B). The invention further relates to the porous materials which can be obtained in this way and the use of the porous materials as thermal insulation material and in vacuum insulation panels.

Claims

1. A process for preparing a porous material, comprising: a) providing a mixture (I) comprising (i) a composition (A) comprising components suitable to form an organic gel and (ii) a solvent mixture (B), b) reacting the components in the composition (A) in the presence of the solvent mixture (B) to form a gel, and c) drying of the gel obtained in step b), wherein: the solvent mixture (B) is a mixture of at least two solvents; the solvent mixture (B) comprises propylene carbonate as one of the at least two solvents; and the solvent mixture (B) has a Hansen solubility parameter ?.sub.H in the range of 3.0 to 5.0 MPa.sup.?1, determined using the parameter ?.sub.H of each solvent of the solvent mixture (B).

2. The process according to claim 1, wherein the composition (A) comprises at least one polyfunctional isocyanate as component (a1).

3. The process according to claim 1, wherein the composition (A) comprises at least one polyfunctional isocyanate as component (a1), and at least one aromatic amine as component (a2), optionally comprises water as component (a3), and optionally comprises at least one catalyst as component (a4).

4. The process according to claim 3, wherein the at least one aromatic amine is a polyfunctional aromatic amine.

5. The process according to claim 3, wherein the at least one aromatic amine (a2) has the general formula I ##STR00008## where R.sup.1 and R.sup.2 can be identical or different and are each selected independently from among hydrogen and linear or branched alkyl groups having from 1 to 6 carbon atoms and all substituents Q.sup.1 to Q.sup.5 and Q.sup.1 to Q.sup.5 are identical or different and are each selected independently from among hydrogen, a primary amino group and a linear or branched alkyl group having from 1 to 12 carbon atoms, where the alkyl group can bear further functional groups, with the proviso that the compound having the general formula I comprises at least two primary amino groups, where at least one of Q.sup.1, Q.sup.3 and Q.sup.5 is a primary amino group and at least one of Q.sup.1, Q.sup.3 and Q.sup.5 is a primary amino group.

6. The process according to claim 1, wherein composition (A) comprises: (a1) from 25 to 94.9% by weight of at least one polyfunctional isocyanate, and (a2) from 0.1 to 30% by weight of at least one polyfunctional aromatic amine having the general formula I ##STR00009## where R.sup.1 and R.sup.2 can be identical or different and are each selected independently from among hydrogen and linear or branched alkyl groups having from 1 to 6 carbon atoms and all substituents Q.sup.1 to Q.sup.5 and Q.sup.1 to Q.sup.5 are identical or different and are each selected independently from among hydrogen, a primary amino group and a linear or branched alkyl group having from 1 to 12 carbon atoms, where the alkyl group can bear further functional groups, with the proviso that the compound having the general formula I comprises at least two primary amino groups, where at least one of Q.sup.1, Q.sup.3 and Q.sup.5 is a primary amino group and at least one of Q.sup.1, Q.sup.3 and Q.sup.5 is a primary amino group, (a3) from 0 to 15% by weight of water, and (a4) from 0.1 to 30% by weight of at least one catalyst, in each case based on the total weight of the components (a1) to (a4), where the % by weight of the components (a1) to (a4) add up to 100% by weight.

7. The process according to claim 3, wherein the amine component (a2) comprises at least one compound selected from the group consisting of 3,3,5,5-tetraalkyl-4,4-diaminodiphenylmethane, 3,3,5,5-tetraalkyl-2,2-diaminodiphenylmethane and 3,3,5,5-tetraalkyl-2,4-diaminodiphenylmethane, where the alkyl groups in the 3,3,5 and 5 positions can be identical or different and are selected independently from among linear or branched alkyl groups which have from 1 to 12 carbon atoms and can bear further functional groups.

8. The process according to claim 3, wherein component (a4) is selected from the group consisting of primary, secondary and tertiary amines, triazine derivatives, metal-organic compounds, metal chelates, oxides of phospholenes, quaternary ammonium salts, ammonium hydroxides and alkali metal and alkaline earth metal hydroxides, alkoxides and carboxylates.

9. The process according to claim 3, wherein component (a4) is selected from the group consisting of dimethylcyclohexylamine, bis(2-dimethylaminoethyl) ether, N,N,N,N,N-pentamethyldiethylenetriamine, methylimidazole, dimethylimidazole, aminopropylimidazole, dimethylbenzylamine, 1,6-diazabicyclo[5.4.0]undec-7-ene, trisdimethylaminopropylhexahydrotriazine, triethylamine, tris(dimethylaminomethyl)phenol, triethylenediamine (diazabicyclo[2.2.2]octane), dimethylaminoethanolamine, dimethylaminopropylamine, N,N-dimethylaminoethoxyethanol, N,N,N-trimethylaminoethylethanolamine, triethanolamine, diethanolamine, triisopropanolamine, diisopropanolamine, methyldiethanolamine, butyldiethanolamine, metal acetylacetonates, ammonium ethylhexanoates and metal ethylhexanoates.

10. The process according to claim 3, wherein the catalyst catalyzes the trimerization to form isocyanurate groups.

11. The process according to claim 3, wherein component (a4) comprises at least one tertiary amino group.

12. The process according to claim 1, wherein no water is used.

13. The process according to claim 1, wherein at least 0.1% by weight of water is added.

14. The process according to claim 1, wherein the solvent mixture (B) has a Hansen solubility parameter ?.sub.P in the range of 7.5 to 10.0 MPa.sup.?1, determined using the parameter ?.sub.P of each solvent of the solvent mixture (B).

15. The process according to claim 1, wherein the solvent mixture (B) has a Hansen solubility parameter ?.sub.D in the range of 15.0 to 18.0 MPa.sup.?1, determined using the parameter ?.sub.D of each solvent of the solvent mixture (B).

16. The process according to claim 1, wherein the drying according to step c) is carried out by converting the liquid comprised in the gel into the gaseous state at a temperature and a pressure below the critical temperature and the critical pressure of the liquid comprised in the gel.

17. The process according to claim 1, wherein the drying according to step c) is carried out under supercritical conditions.

Description

EXAMPLES

1. Methods

1.1 Determination of Hansen Solubility Parameters (HSP)

(1) The values for Hansen solubility parameters (HSP) ?.sub.D (Van-der-Waals interactions), ?.sub.P (polar interactions) and ?.sub.H (hydrogen-bonding interactions) for organic solvents are obtained from the handbook on Hansen solubility parameters by Charles M. Hansen (Hansen Solubility Parameters: A User's Handbook Second Edition, Charles M. Hansen, CRC Press Taylor & Francis Group 2007).

(2) The value of the Hansen solubility parameter OH of the solvent mixture (B) is determined following the procedure described in Hansen Solubility Parameters: A User's Handbook, CRC Press 2007, p. 205-206. Generally, the parameter ?.sub.H of the solvent mixture depends on the parameters ?.sub.H of the single solvents in a linear fashion according to the volume fraction of all the solvents in the mixture:
?.sub.H,mix=(?.sub.H,solvent 1?volume fraction 1)+(?.sub.H,solvent 2?volume fraction 2)+ . . .

(3) The parameters ?.sub.D and ?.sub.P of the solvent mixture are determined accordingly. Generally, the parameter ?.sub.D of the solvent mixture depends on the parameters ?.sub.D of the single solvents in a linear fashion according to the volume fraction of all the solvents in the mixture:
?.sub.D,mix=(?.sub.D,solvent 1?volume fraction 1)+(?.sub.D,solvent 2?volume fraction 2)+ . . .
and generally, the parameter ?.sub.P of the solvent mixture depends on the parameters ?.sub.P of the single solvents in a linear fashion according to the volume fraction of all the solvents in the mixture:
?.sub.P,mix=(?.sub.P,solvent 1?volume fraction 1)+(?.sub.P,solvent 2?volume fraction 2)+ . . .

(4) The parameters of the single solvents used to calculate the parameters of the mixture are found in Table A.1 of the handbook, which lists most common solvents. The available methods for their determination are described in Chapter 1 of the handbook.

1.2 Determination of Thermal Conductivity

(5) The thermal conductivity was measured according to DIN EN 12667 with a heat flow meter from Hesto (Lambda Control A50).

1.3 Solvent Extraction with Supercritical Carbon Dioxide

(6) One or several gel monoliths were placed onto sample trays in an autoclave of 25 l volume. Subsequent to filling with supercritical carbon dioxide (scCO.sub.2), the gelation solvent was removed (drying) by flowing scCO.sub.2 through the autoclave for 24 h (20 kg/h). Process pressure was kept between 120 and 130 bar and process temperature at 45? C. in order to maintain carbon dioxide in a supercritical state. At the end of the process, the pressure was reduced to normal atmospheric pressure in a controlled manner while maintaining the system at a temperature of 45? C. The autoclave was opened, and the obtained porous monoliths were removed.

2. Materials

(7) Component a1: oligomeric MDI (Lupranat M200) having an NCO content of 30.9 g per 100 g accordance with ASTM D-5155-96 A, a functionality in the region of three and a viscosity of 2100 mPa.Math.s at 25? C. in accordance with DIN 53018 (hereafter M200) Component a2: 3,3,5,5-Tetramethyl-4,4diaminodiphenylmethane (hereinafter MDMA) Catalyst: Dabco K15 (potassium ethylhexanoate dissolved in diethylene glycol (85%))

3. Examples

(8) Thermal conductivity values for all examples as well as the HSP are shown in Table 1.

3.1 Example 1 (Comparative)

(9) In a polypropylene container, 48 g M200 were dissolved under stirring in 220 g MEK at 20? C. leading to a clear solution. Similarly, 12 g MDMA, 4 g Dabco K15 and 4 g water were dissolved in 220 g MEK to obtain a second solution. The solutions were combined in a rectangular container (20?20?5 cm height) which led to a clear, homogeneous mixture of low viscosity. The container was closed with a lid and the mixture was gelled at room temperature for 24 h. The resulting monolithic gel slab was dried through solvent extraction with sc-CO.sub.2 in a 25 l autoclave leading to a porous material.

3.2 Example 2 (Comparative)

(10) Example 2 was carried out as Example 1 with the difference that DEK was used as solvent; the reactants do not completely dissolve in the solvent.

3.3 Example 3 (Comparative)

(11) Example 3 was carried out as Example 1 with the difference that ethyl acetate was used as solvent.

3.4 Example 4 (Comparative)

(12) Example 4 was carried out as Example 1 with the difference that acetone was used as solvent.

3.5 Example 5 (Comparative)

(13) Example 5 was carried out as Example 1 with the difference that PC was used as solvent. No gel is formed.

3.6 Example 6 (Comparative)

(14) Example 6 was carried out as Example 1 with the difference that acetone/DEK 85:15 (v/v) was used as solvent.

3.7 Example 7 (Comparative)

(15) Example 7 was carried out as Example 1 with the difference that acetone/DEK 70:30 (v/v) was used as solvent.

3.8 Example 8 (Comparative)

(16) Example 8 was carried out as Example 1 with the difference that acetone/DEK 50:50 (v/v) was used as solvent.

3.9 Example 9 (Comparative)

(17) Example 9 was carried out as Example 1 with the difference that acetone/DEK 39:61 (v/v) was used as solvent.

3.10 Example 10 (Comparative)

(18) Example 10 was carried out as Example 1 with the difference that acetone/MEK 20:80 (v/v) was used as solvent.

3.11 Example 11

(19) Example 11 was carried out as Example 1 with the difference that MEK/DEK 72:28 (v/v) was used as solvent.

3.12 Example 12

(20) Example 12 was carried out as Example 1 with the difference that DEK/PC 89:11 (v/v) was used as solvent.

3.13 Example 13

(21) Example 13 was carried out as Example 1 with the difference that DEK/PC 86:14 (v/v) was used as solvent.

3.14 Example 14

(22) Example 14 was carried out as Example 1 with the difference that DEK/PC 83:17 (v/v) was used as solvent.

4. Results

(23) Results of the thermal conductivity measurements in relation to ?.sub.P and ?.sub.H of the gelation solvent or solvent mixture are shown in Table 1.

(24) Within a certain boundary of ?.sub.P, the thermal conductivity seems to be mostly independent or only weakly dependent on ?.sub.P (DEK likely displays a deviating thermal conductivity due to solubility problems of the starting materials). However, the thermal conductivity depends on ?.sub.H, with lower ?.sub.H leading to lower thermal conductivities within the tested solvents and solvent mixtures. Limits are set by reagent solubility, i.e. reagents do not dissolve in mixtures with too low ?.sub.P or ?.sub.H.

(25) TABLE-US-00001 TABLE 1 Results Thermal conductivity [mW/m*K] ?.sub.D ?.sub.P ?.sub.H Density (p = 1 bar, [MPa.sup.?1] [MPa.sup.?1] [MPa.sup.?1] [g/l] T = 10? C.) Comparative Example 1 16.00 9.00 5.10 139 17.0 (MDMA, K15, H.sub.2O, MEK) Comparative Example 2 15.80 7.60 4.70 18.2 (MDMA, K15, H.sub.2O, DEK) Comparative Example 3 15.80 5.30 7.20 26.6 (MDMA, K15, H.sub.2O, EtOAc) Comparative Example 4 15.50 10.40 7.00 20.6 (MDMA, K15, H.sub.2O, Aceton) Comparative Example 5 20.00 18.00 4.10 no gelation (MDMA, K15, H.sub.2O, PC) Comparative Example 6 15.55 9.98 6.66 124 19.0 (as 1, but in acetone/DEK 85:15) Comparative Example 7 15.59 9.56 6.31 126 18.0 (as 1, but in acetone/DEK 70:30) Comparative Example 8 15.65 9.00 5.85 129 17.6 (as 1, but in acetone/DEK 50:50) Comparative Example 9 15.69 8.66 5.57 123 17.1 (as 1, but in acetone/DEK 38:62) Comparative Example 10 15.90 9.28 5.48 119 17.2 (as 1, but in acetone/MEK 20:80) Example 11 15.94 8.61 4.99 119 17.0 (as 1, but in MEK/DEK 72:28) Example 12 16.25 8.71 4.64 16.2 (as 1, but in DEK/PC 89:11) Example 13 16.39 9.06 4.62 16.3 (as 1, but in DEK/PC 86:14) Example 14 16.51 9.37 4.60 16.2 (as 1, but in DEK/PC 83:17)

5. Abbreviations

(26) DEK Diethyl ketone

(27) EtOAc Ethyl acetate

(28) H.sub.2O Water

(29) K15 Dabco K15 (PUR catalyst)

(30) PC Propylene carbonate

(31) M200 Lupranate M200 (polyisocyanate)

(32) MEK Methyl ethyl ketone

(33) MDMA 4,4-Methylene-bis(2,6-dimethylanilin)