MXPA99008932A - Polyisocyanate based xerogels - Google Patents

Abstract

Process for making polyisocyanate based xerogels by trimerisation of an organic polyisocyanate in an organic solvent in the presence of a (co)polymer containing an isocyanate-reactive group, gellation and drying of the obtained sol-gel.

Description

XEROGELS BASED ON POLI I SOC IANATOS DESCRIPTION OF THE INVENTION The present invention relates to xerogels based on polyisocyanates and methods for their preparation. Xerogels based on polyisocyanate chemistry are described in DE 19505046. They are prepared by mixing a polyisocyanate and a catalyst in a suitable solvent and maintaining said mixture in a quiescent or quiescent state for a sufficiently long period to form a polymer gel and then removes the solvent from the gel by means of drying by evaporation. The densities of the obtained xerogels are quite high due to shrinkage in volume during drying. In addition, the drying times are prolonged. Therefore, one of the objectives of the present invention is to provide a method for preparing organic xerogels based on polyisocyanates of lower density, reduced shrinkage with retention of the two-dimensional shape and having a fast drying time.

Accordingly, the present invention provides a method for preparing an organic xerogel based on polyisocyanates comprising the steps of: a) mixing an organic polyisocyanate and an isocyanate trimer catalyst in a suitable solvent, b) maintaining said mixture in a quiescent or resting state for a period of time sufficiently long to allow for the formation of a polymeric gel and c) to dry the obtained gel, in which a (co) polymer containing at least one isoc group is mixed i ana to-r eac ti vo with the other ingredients in step a). The group i o cyan t o - r e a c t i vo present in the copolymer is an OH, COOH, NH2 or NHR group, it is preferred that it be an OH group. Examples of the suitable classes of (co) or 1, which can be used in the present invention are: po 1 a 1 a, po 1 esters, polyketones, biphenol A resins, hydrocarbon resins, polyesters, polyaldehyde-ketone resins, resoles, novolaks, neutral phenolic resins, po 1 ime tacri 1 atos, polyacrylonitrile, polyvinylacetate, PET derivatives, polyesters, cellulose, polyethers, polyethylene and modified polypropylene, po 1 ibu t adi ene and alkyl resins.

A particularly preferred class of (co) po 1 is those which are derived from ethylenically unsaturated monomers; Preferred are styrenes, acrylic acid and ester derivatives of acrylic acid, such as methyl esters, hydrolytic esters and partially fluorinated acrylate esters. Another preferred class of (co) polymers are those obtained by condensation of aldehydes (preferably formaldehyde) and / or ketones such as phenolic resins, in particular neutral phenolic resins, polyaldehyde-ketone resins, polyketones, novolaks and resoles. . The (co) polymer that can be used in the present invention has an OH value between 30 and 800 mg KOH / g, preferably between 100 and 500 mg KOH / g and a vitreous transition temperature between -50 and ~ 150 ° C. , preferably between 0 and 80 ° C. The molecular weight of the (co) polymer is preferably between 500 and 10,000, more preferably between 4000 and 6000. The (co) polymer preferably has a melting range of 60 to 160 ° C. Optimal results are generally obtained when the aromaticity of the (co) polymer is at least 15%; the aromaticity is calculated as 7200 x the amount of aromatic groups in the polymer / average molecular weight number. Preferred (co) polymers for the present invention are copolymers of styrene and hydroxyl acrylate, and optionally also acrylate. Such copolymers are commercially available, for example, as Reactol 180, Reactol 255 and Reactol 100 (all from Laster International). Other preferred (co) polymers that are commercially available from Laster Intern tional are K 1717 (a polyketone), Biresol (a biphenol resin A), K 2090 (a polyester), K 1717B (a resin of a 1 deh í do - c on t) and K 1111 (a neutral phenolic resin). The amount of (co) po 1 i that is used in the present process is such that the ratio between the functional groups in the polyisocyanate (NCO) and in the (co) polymer (OH) is between 1: 1 and 10: 1, preferably between 3: 1 and 7: 1. The use of the previous (co) p or 1 i r in the preparation process allows to obtain xerogels of lower density. The densities of the xerogels obtained by using the process of the present invention are generally in the range of 1 to 1000 kg / m 3, more preferably in the range of 10 to 800 kg / m 3 and more preferably even in the range from 20 to 400 kg / m3 or even from 100 to 300 kg / m3. The xerogels prepared according to the process of the present invention consist of agglomerated particles with a diameter of 0.1 to 10 μm, generally 1 to 3 μm. The surface areas of the xerogels prepared according to the process of the present invention are generally in the range of 1 to 500 m2 / g, more preferably in the range of 5 to 100 m2 / g. The polyisocyanates that can be employed in the present method for preparing the xylogels based on polyisocyanates include aliphatic, cyclo-lifatic, araliphatic and aromatic polyisocyanates known in the art for their exclusive use in the production of materials -da-polyurethane / polyisocyanurate. Of particular importance are the aromatic polyisocyanates t_aies_ as diphenylmethane diisocyanate and toluene in their pure, modified and crude forms, in particular diphenylmethane diisocyanate (MDI) in the form of their 2,4'-, 2,2'- and 4,4'- (pure DI) and mixtures thereof known in the art as "crude" or polymeric MDI (polyphenylene po 1 ime ti 1 e no) polyisocyanates possessing an isocyanate functionality greater than 2 and the so-called variants of MDI (MDI modified by the introduction of residues of urethane, allophanate, urea, biuret, carbodiimide, uretonimine oisoci anur ato). The polyisocyanate is used in amounts ranging from 0.5 to 30% by weight, preferably from 1.5 to 20 by weight and more preferably from 3 to 15% by weight based on the total reaction mixture. The trimerization catalysts which may be employed in the present preparation method include any isocyanate trimerization catalyst known in the art, such as quaternary ammonium hydroxides, alkali metal and alkaline earth metal hydroxides, alkoxides and Examples are potassium acetate and potassium 2-ethylhexoate, certain tertiary amines and non-basic metal carboxylates, for example lead octoate, and symmetrical triazine derivatives. which can be employed in the present method are Policat 41, available from Abbott Laboratories, and DABCO TMR, TMR-2, TMR-4 and T 45 available from Air Products, and potassium salts such as potassium octoate. and potassium hexanoate. In addition to the urethane catalyst, a urethane catalyst known in the art can be used. The weight ratio between po 1 iiso ci ana to / ca ta 1 izador varies between 5 and 1000, preferably between 5 and 500, more preferably between 10 and 80. The preferred weight ratio between pol iis oci ana to / The amount of polyisocyanate used depends on the amount of polyisocyanate used, the temperature of the reaction / cured, the solvent used, the additives used. The solvent that can be used in the preparation method according to the present invention must be a solvent suitable for the (co) po i i r o, the catalyst and the monomeric polyisocyanate (unreacted) as well as for the polymeric polyisocyanate (reacted). The power of the solvent must be such as to allow the formation of a homogeneous solution with the unreacted compounds and the dissolution of the reaction product or at least to prevent the flocculation of the product of the reaction. Solvents with a solubility parameter d between 0 and 25 MPa + and with a hydrogen bonding parameter dH between 0 and 15 MPa + are the most suitable. Volatile solvents having a boiling point below 150 ° C at room temperature are preferably used. Solvents suitable for use in the method according to the present invention include hydrocarbons, dialkyl ethers, cyclic ethers, ketones, at 1 to 1 to 1 years, hydropluorocarbons aliphatic and cycloaliphatic, hydrochloro-fluorone , c 1 orof luor oca rbur os, hydrochlorocarbons, ethers containing fluorine and halogenated aromatics. Mixtures of said compounds can also be used. Suitable hydrocarbon solvents include lower aliphatic or cyclic hydrocarbons, such as ethane, propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane, neopentane, hexane and cyclohexane. Suitable dialkyl ethers that can be employed as a solvent include those compounds having 2 to 6 carbon atoms. Examples of suitable ethers are dimethylether, methyl ether, diethyl ether, methylprietal ether, methyl ether, ethylpropether, et al. read, dip r opi 1 é ter, propil-i s op rop i 1 é ter, di op op i 1 é ter, i ti lbu ti 1 é ter, me ti 1 is obu ti 1 é ter, methyl t-butyl ether, ethylbutethylether, eti 1 is obu ti 1 é er and ethyl t-butyl ether. Suitable cyclic ethers include tetrahydrofuran. Suitable diols which can be employed as solvents include acetone, cyclohexanone, methyl t-butyl ketone and methylethyl ketone. Suitable carriers which can be used as a solvent include me t i 1 m ore, me t i 1 a c e t t a, e t i 1 f or rmi a t, butyl acetate and ethylacetate. Suitable hydrofluorocarbons, which can be used as a solvent, include lower hydrofluoroalkanes, for example, di-fluorine, 1,2-difluoroethane, 11,1,4,4,4 -hexafluorobutane, pentafluoroethane, 1,1,1,2-tetrafluoroethane, 1, 1, 2, 2 - t e t r a f 1 or o t a t e n t, f o u r t a r t u u r t and its isomers, t e t r a f lor op o m e r and its isomers and pen t a f o u r op no and its isomers. It is also possible to employ substantially fluorinated or perfluorinated (ci c 1 o) to 1 o-ones having 2 to 10 carbon atoms. Suitable hydrophobicizers that can be used as a solvent include a fluoride, 1, 1 - dic 1 gold - 2, 2, 2 - trif - 1 - oethane, 1, 1 - di cl oro - 1 - f 1 uo roet an e, l-chloro-1,1-di f 1 oo roo taño, 1 - cl or o - 2 - f 1 uo r oe t y 1.1, 1,2-tetraf luor or -2-cl oroe t ano. Suitable chlorofluorocarbons that can be used as a solvent include a chlorofluorocarbon, a diuretic, an orbital, a triclo-r otrif, and a tetrahydrofloxane. c 1 Oroethane. Suitable hydrophobicizers that can be used as a solvent include 1- and 2-chloropropane and dichloromethane. Suitable halogenated aromatics include mono c 1 or r oben z e n and d i c 1 o r ob e n e. Suitable fluorine-containing ethers which can be used as a solvent include bi- (trifluoromethyl) ether, trifluoromethyl-difluoro-methyl ether, methyl 1-1-one-1-ether, methyltrifluo-rometylether, bi (di f luor orne) ti 1) é ter, f 1 uo r orne ti 1 di -f 1 uo roe t ilé ter, I gave you 1, 1, 2, 2, 2, 2-trifluoroethyl, diflubb orb, ether, pentaf, 1o, or 1, or 1 1-ether, penta-fluoroethyldifluoromethyl ether, 1, 1, 2, 2-tetrafluoroethyl-di-fluorine orne-1-methyl ether, 1, 2, 2, 2-tetraf-1-or-111-f-1-n-1, and 1, 2, 2-trifluoro-di-trifluoride 1-ether, 1, 1-trifluoroethyl ether, 1,1,1,3,3,3-hexafluoroprop-2-yl-fluoromethylether. Preferred solvents for use in the method according to the present invention are acetone, cyclohexanone, methyl t-ethyl ketone, methyl t-butyl ketone and bu t-lacerate. The polyisocyanate, the (co) polymer, the catalyst and the solvent are mixed by simple stirring of the reaction vessel or by slow stirring the mixture or by strong mixing, with static in-line mixers or continuous deposition in preforming molds. Alternatively, the polymer and the solvent are first mixed and then the catalyst is added to the mixture. Some catalyst can also be added after gelling to improve post-curing. The mixing can take place at room temperature or at somewhat higher temperatures. The solids content of the reaction mixture is preferably between 2 and 30% by weight, more preferably between 5 and 20% by weight. The use of the previously specified co-polyols in the xerogels processing process allows a higher solids content to be used, and still obtain xerogels of lower density with less volume shrinkage, where rapid drying maintains the form two-dimensional The mixture is then allowed to stand for a certain period of time to form a polymer gel. This period varies from 5 seconds to several weeks depending on the system and the density and size of gaps sought. Temperatures in the range of -55 ° C to 50 ° C, preferably 0 to 45 ° C, can be used. While the mixture gels within a few hours, it has been found to be advantageous to cure the gels for a minimum of 24 hours in order to obtain a solid gel that can be handled with ease in subsequent processing. A post-curing cycle may be included at elevated temperatures. The solvent is removed from the gel obtained either by drying in the air (drying by evaporation) (cold or hot air), by drying under vacuum (for example, in an oven or on a Buchner), by drying in a microwave, by drying with radiofrequency, by sublimation, by drying with freezing or any combination of the mentioned methods. The drying step can take from 10 minutes to a few days, but in general it is less than 6 hours. During drying, the xerogel can be given the proper shape by applying mechanical pressure to the gel. In order to further improve the structural integrity and the handling of the xerogels, a reinforcing material can be incorporated in the sol-gel process, preferably in amounts between 0.05 and 30% in polymer weight. Examples of suitable reinforcing materials include glass fiber, glass mat, plush, glass wool, carbon fiber, boron fiber, ceramic fiber, rayon fiber, nylon fiber, olefin fiber, alumina fiber, asbestos fiber, zirconium fiber, alumina, clay, mica, silica, calcium carbonate, talc, zinc oxide, barium sulphates, wood and shell flour, polystyrene, Tyvec (available from Dupont). Other suitable additives that can be used in the process of the present invention and other suitable processing methods are described in WO 95/03358, WO 96/36654 and WO 96/37359, the contents of which are incorporated in full herein. as a reference. The obtained xerogels can be used for thermal insulation, for example in construction, or in sound insulation applications and / or appliances. The present invention is illustrated, but not limited, by the following examples in which the following ingredients were used: Reactol 180: a (hi dr ox i) acri 1 ato / co-styrene polymer available from La ter International, which has an OH value of 180 mg KOH / g. K 1717: a polyketone resin with an OH value of 270 mg KOH / g, available from Lawter International. K 2090: a polyester resin with an OH value of 320 mg KOH / g, available from Lawter International. SUPRASEC X2185: a polymeric isocyanate available from Imperial Chemical Industries.

SUPRASEC ONE: a polymeric isocyanate available from Imperial Chemical Industries. Dabco TMR: a catalyst available from Air Products. Policat 41: a catalytic converter available from Air Products. acetone: degree of distillation, Ra t hbu r n - g 1 a s s. SUPRASEC is a trademark of Imperial Chemical Industries.

EXAMPLE 1 In a vessel, 4.74 grams of Reactol 180 were dissolved in 208.7 grams of acetone. In this mixture 6.26 grams of SUPRASEC X2185 were incorporated until a homogeneous solution was obtained. This solution was injected with 0.313 ml of Dabco TMR by means of a syringe. The vessel was sealed and vigorously stirred to ensure a good distribution of the catalyst throughout the liquid. The solution was then isolated at ambient conditions for 1 hour to allow the formation of a sol gel. Once the reaction was complete, the sol gel was removed from the vessel and brought to the ambient atmosphere. This allowed the acetone to evaporate spontaneously. This process took 1 day for a 3.5 cm thick sample. The dried specimen was then treated for four hours in a vacuum oven at 90 ° C to allow the evaporation of residual amounts of acetone. The obtained xerogel monolith has the following properties: density 303 kg / m3, surface area 11 m2 / g, initial lambda 11 mW / mK, air lambda 32 mW / mK, critical pressure 20 mBar. The density (envelope density) was measured in a Mi crome re t i c s Geopyc 1360 equipment. The surface area was measured in a Gemini i c rnene r equipment (BET adsorption of N2). The lambda value was measured in accordance with ASTM C519 standards; the initial lambda value at a pressure lower than 0.1 mbar, the value of air lambda at atmospheric pressure. The critical pressure is the pressure at which the lambda / log curve of the pressure deviates from a straight line.

EXAMPLE 2 In a container, they were dissolved 3.44 grams of Reactol 180 in 208.6 grams of acetone. In this mixture, 7.56 grams of SUPRASEC X2185 were incorporated until a homogeneous solution was obtained. This solution was injected with 0.378 ml of Dabco TMR by means of a syringe. The vessel was hermetically sealed and vigorously stirred to ensure a good distribution of the catalyst throughout the liquid. The solution was then isolated under ambient conditions and the gel formed in 25 minutes. Once the reaction was completed, the sol gel was removed from the vessel and taken to ambient atmosphere. This allowed the acetone to evaporate spontaneously. This process took 1 day for a 3.5 cm thick sample. The dried specimen was then treated for four hours in a vacuum oven at 90 ° C to allow the evaporation of residual amounts of acetone. The xerogel obtained has the following properties: density 109 kg / m3, surface area 5 m2 / g, initial lambda 5 mW / mK, air lambda value 38 mW / mK, critical pressure 2 mBar.

EXAMPLE 3 In a container, they were dissolved 6.63 grams of Reactol 180 in 204.4 grams of acetone. In this mixture, 8.77 grams of SUPRASEC X2185 were incorporated until a homogeneous solution was obtained. This solution was injected with 0.219 ml of Dabco TMR by means of a syringe. The vessel was sealed and vigorously stirred to ensure a good distribution of the catalyst throughout the liquid. The solution was then isolated under ambient conditions for 20 minutes to allow the formation of a sol gel. Once the reaction was completed, the sol gel was removed from the vessel and taken to ambient atmosphere. This allowed the acetone to evaporate spontaneously. This process took 1 day for a 3.5 cm thick sample. The dried specimen was then treated for four hours in a vacuum oven at 90 ° C to allow the evaporation of residual amounts of acetone. The xerogel obtained has the following properties: density 256 kg / m3, surface area 26 m2 / g, initial lambda 16 mW / m: K, air lambda 32 mW / mK, critical pressure 30 mBar.

EXAMPLE 4 In a vessel, 4.81 grams of Reactol 180 were dissolved in 204.3 grams of acetone. In this mixture, 10.6 grams of SUPRASEC X2185 were incorporated and a homogeneous solution was obtained. This solution was injected with 0.265 ml of Dabco TMR by means of a syringe. The vessel was sealed and vigorously stirred to ensure a good distribution of the catalyst throughout the liquid. The solution was then isolated under ambient conditions for 10 minutes to allow the formation of a sol gel. Once the reaction was completed, the sol gel was removed from the vessel and taken to ambient atmosphere. This allowed the acetone to evaporate spontaneously. This process took 1 day for a 3.5 cm thick sample. The dried specimen was then treated for four hours in a vacuum oven at 90 ° C to allow the evaporation of residual amounts of acetone. The xerogel obtained has the following properties: density 174 kg / m3, surface area 9 m2 / g, initial lambda 7 mW / mK, air lambda 31 mW / mK, critical pressure 8 mBa r.

EXAMPLE 5 In a vessel, 3.77 grams of Reactol 180 were dissolved in 2C9.3 grams of acetone. In this mixture, 11.63 grams of SUPRASEC X2185 were incorporated until a homogeneous solution was obtained. This solution was injected with 0.291 ml of Dabco TMR by means of a syringe. The vessel was sealed and vigorously stirred to ensure a good distribution of the catalyst throughout the liquid. The solution was then isolated under ambient conditions for 5 minutes to allow the formation of a sol gel. Once the reaction was completed, the sol gel was removed from the container and taken to the ambient atmosphere. This allowed the acetone to evaporate spontaneously. This process took 1 day for a 3.5 cm thick sample. The dried specimen was then treated for four hours in a vacuum oven at 90 ° C to allow the evaporation of residual amounts of acetone. The xerogel obtained has the following properties: density 94 kg / m3, surface area 6 m2 / g, initial lambda 5 mW / mK, air lambda 37 mW / mK, critical pressure 2 mBa r.

EXAMPLE 6 In a vessel, 13.55 grams of Reactor 12C were dissolved in 197.8 grams of acetone. In this mixture 8.45 grams of SUPRASEC X2185 were incorporated until a homogeneous solution was obtained. This solution was injected with 0.169 ml of Dabco TAR by means of a syringe. The vessel was sealed and vigorously stirred to ensure a good distribution of the catalyst throughout the liquid. The solution was then isolated under ambient conditions for 20 minutes to allow the formation of a sol gel. Once the reaction was completed, the sol gel was removed from the vessel and taken to ambient atmosphere. This allowed the acetone to evaporate spontaneously. This process took 1 day for a 3.5 cm thick sample. The dried specimen was then treated for four hours in a vacuum oven at 90 ° C to allow the evaporation of residual amounts of acetone.

EXAMPLE 7 In a container, 7.66 grams of Reactol 180 were dissolved in 197.7 grams of acetone.In this mixture, 14.33 grams of SUPRASEC X2185 were incorporated until a homogeneous solution was obtained. They injected 0.287 ml of Dabco TMR by means of a syringe.The container was sealed and vigorously agitated to ensure a good distribution of the catalyst throughout the liquid.The solution was then isolated under ambient conditions for 10 minutes to allow the formation of a Once the reaction was completed, the sol gel was removed from the container and brought to the ambient atmosphere, which allowed the acetone to evaporate spontaneously, which took 1 day for a 3.5 cm thick specimen. dry was then treated for four hours in a vacuum oven at 90 ° C to allow the evaporation of residual amounts of acetone.The xerogel obtained has the following properties : density 249 kg / m3, surface area 49 m2 / g, initial lambda 25 mW / mK, air lambda 33 mW / mK, critical pressure 30 mBar.

EXAMPLE 8 In a vessel, 5.34 grams of Reactol 180 were dissolved in 197.7 grams of acetone. In this mixture, 16.66 grams of SUPRASEC X2185 were incorporated until a homogeneous solution was obtained. This solution was injected with 0.333 ml of Dabco TAR by means of a syringe. The vessel was sealed and vigorously stirred to ensure a good distribution of the catalyst throughout the liquid. The solution was then isolated under ambient conditions for less than 5 minutes to allow the formation of a sol gel. Once the reaction was complete, the sol gel was removed from the vessel and brought to the ambient atmosphere. This allowed the acetone to evaporate spontaneously. This process took 1 day for a 3.5 cm thick sample. The dried specimen was then treated for four hours in a vacuum oven at 90 ° C to allow the evaporation of residual amounts of acetone. The xerogel obtained has the following properties: density 197 kg / m3, surface area 9 m2 / g, initial lambda 6 mW / mK, air lambda 31 mW / mK, critical pressure 8 mBa r.

COMPARATIVE EXAMPLE 9 In a vessel, 135 grams of acetone were mixed with 15 grams of SUPRASEC X2185 until a homogeneous solution was obtained. To this solution 0.3 ml of Dabco TMR was injected by means of a syringe. The vessel was sealed and vigorously stirred to ensure a good distribution of the catalyst throughout the liquid. The solution was then isolated under ambient conditions for 24 hours to allow the formation of a sol gel. Once the reaction was completed, the sol gel was removed from the vessel and taken to ambient atmosphere. This allowed the acetone to evaporate spontaneously. This process took 1 day for a 3.5 cm thick sample. The dried specimen was then treated for four hours in a vacuum oven - at 90 ° C to allow the evaporation of residual amounts of acetone. The air-dried xerogel has a density of 178 kg / m3, surface area 3 m2 / g, initial lambda 5 mW / mK, air lambda 3z5 mW / mK, critical pressure 2 mbar.

COMPARATIVE EXAMPLE 10 __ Seven grams of SUPRASEC X2185 were dissolved in 93 grams of acetone. To this solution was added 0.175 g of Dabco TMR. The polymer began to flocculate and it was not possible to obtain a monolithic sol-gel.- COMPARATIVE EXAMPLE 11 _ _ _ _ ^ _ 5 g of SUPRASEC X2185 were dissolved in 95 g of acetone. To this solution was added 5 g of Dabco _TMR. The reaction mixture was completely precipitated and no sol-gel was formed. ~ zr EXAMPLE 12 Example 2 was repeated. After the formation of the sol-gel the sol-gel monolith was placed on a filter.

Buchner The solvent was removed under moderate vacuum for 1 hour for a 3.5 cm thick sample. The resulting monolith had the following properties: density 170 kg / m3, initial lambda 4 mW / mK, air lambda 29 mW / mK, critical pressure 3 mbar.

EXAMPLE 13 A reaction mixture containing 8.8 g of SUPRASEC X2185, 155 g of acetone, 2.86 g of Reactol R180, 0.22 g of Dabco TMR and glass wool (0.5% by weight of solids) converted into a sol-gel and then subjected to drying air. The density of the obtained xerogel was 220 kg / m3.

EXAMPLE 14 A catalyst solution was prepared by successively mixing 0.271 ml of Policat 41 and 0.271 ml of Dabco TMR in 22.96 g of acetone (technical grade). The addition of the catalysts was carried out by means of a micrometer syringe. A second solution was prepared in two steps. First, 2.93 g of the polyketone resin K1717 were dissolved in 70.0 g of acetone (technical grade) and then 13.57 g of SUPRASEC DNR were added. Both solutions were mixed vigorously and for a very short time (a few seconds) before mixing together. The obtained mixture was allowed to stand for gelation and cured for 24 hours at room temperature.

The sol-gel obtained was removed from the container where it was prepared and dried by a natural evaporation process. A xerogel with a density of 181 kg / rrr was obtained EXAMPLE 15 A catalyst solution was prepared by consecutively mixing 0.326 ml of Policat 41 and 0.326 ml of Dabco TMR in 23.95 g of acetone (technical grade). The addition of the catalysts was effected by means of a syringe mi c romé t r i ca. A second solution was prepared in two steps. First 2.37 g of the polyester resin K2090- were dissolved in 70.0 g of acetone (technical grade) and then 13.03 g of SUPRASEC DNR were added.

Both solutions were mixed vigorously and for a very short time (a few seconds) before mixing with each other. The obtained mixture was left to stand for gelation and cured for 24 hours at room temperature. The sol-gel obtained was removed from the container where it was prepared and dried by a natural evaporation process. - A xerogel with a density of 3 was obtained.

Claims (18)

1. Method for preparing a polyisocyanate-based xerogel comprising the steps of a) mixing an organic polyisocyanate, a copolymer containing at least one isocyanate reactive group and an isocyanate trimerization catalyst in a suitable solvent, b) maintaining mixing in a quiescent state for a sufficiently long period of time to form a polymer gel, and c) removing the solvent from the gel obtained by air drying, vacuum drying, microwave drying, radio frequency drying, sublimation, drying by freezing or any combination thereof, characterized in that the copolymer is derived from the ethylene monomers neither unsaturated or obtained by the condensation of aldehydes and / or ketones.

2. The method according to the claim 1, wherein the isocyanate reactive group is OH.

3. The method according to the claim 1 or 2, wherein the monomers are selected from the group consisting of styrene, acrylic acid ester and hydroxyl acid ester i cr.

4. The method according to claim 1 or 2 wherein the copolymer is selected from the group consisting of phenolic resins, potassium resins, aldehyde s ketones, polyketones novolaks and resols.

5. The method according to any of the preceding claims wherein the copolymer is used in an amount such that the ratio between the functional groups in the polyisocyanate and the functional groups in the copolymer is between 1: 1 and 10: 1.

6. The method according to any of the preceding claims, wherein the density of xerogel is between 100 and 300 kg / m3.

7. The method according to any one of the preceding claims wherein the organic polyisocyanate is diphenyl methane diisocyanate or polyphenyl polymethyl polyisocyanate.

8. The method according to any of the preceding indications wherein the organic polyisocyanate is used in amounts ranging from 1.5 to 20% by weight based on the total reaction mixture.

9. The method according to any of the preceding claims wherein the isocyanate catalyst is a triazine derivative or a quaternary ammonium salt or a potassium carboxylate.

10. The method according to any one of the preceding claims wherein the weight ratio of c a t a 1 i z a to r / po 1 i i s or c a a n a t o is between 10 and 80.

11. The method according to any of the preceding precedents where the solvent is acetone. _

12. The method according to any of the preceding claims wherein the solid contents of the reaction mixture is between 5 to 20% by weight.

13. The method according to any of the preceding claims wherein the mechanical pressure is applied to the gel during step c) of drying.

14. The method according to any of the preceding claims wherein step c) of drying takes less than 6 hours.

15. The method according to any of the preceding claims wherein the drying step c) involves vacuum draining and / or evaporative drying.

16. The method according to any of the preceding claims wherein the reinforcing material is incorporated in the sol-gel process.

17. Xerogel based on polyisocyanate obtainable by the method as defined in any of the preceding claims.

18. The use of a xerogel as defined in rei indication 17 by thermal insulation and / or sound isolation.