HK1084961B - Low-viscosity polyurethane prepolymers based on 2,4'-mdi - Google Patents

Description

Low-viscosity polyurethane prepolymers based on 2, 4' -diphenylmethane diisocyanate

Cross Reference to Related Applications

The present application claims priority to german application De 102004035764 filed 7, 23/2004 in accordance with 35u.s.c. § 119.

Technical Field

The invention relates to low-viscosity, low-monomer-content, moisture-curing sealants based on 2, 4' -MDI prepolymers, to a process for their preparation and to their use. Moisture-curing sealants based on polyurethane essentially comprise, in addition to fillers, pigments and flow assistants, NCO-containing polyurethane prepolymers which crosslink by reaction of urea groups with moisture.

Background

At present, prepolymers with ultra low intrinsic viscosity are of particular importance. This makes it possible to dispense with viscosity-reducing additives such as solvents in the synthesis, further processing and/or use of the PU systems, completely or in part, so that high VOC contents or poor material properties caused by additive residues in the polyurethanes can be avoided. Irrespective of the viscosity, low residual amounts of di-or triisocyanate monomers are generally also desired in systems based on the prepolymers and PU described above from an occupational health standpoint.

Because of their outstanding properties, flexible, moisture-curing polyurethane-based sealants have very important applications in the automotive and construction sectors.

EP-B0425694 describes moisture-curing sealants which contain polyether polyurethane prepolymers. Although only toluene diisocyanate is specifically mentioned and used in the examples, aliphatic, cycloaliphatic and aromatic polyisocyanates are generally listed as the isocyanate building blocks of these prepolymers. Owing to the relatively high vapor pressure of the monomeric TDI (2, 4-TDI is 1.3.10 at 20 ℃)^-2mbar; 2, 6-TDI is 1.3.10 at 20 DEG C^-2mbar) which must be completely removed after the prepolymer has been prepared. This step is undesirable for cost reasons. There have thus been increasing attempts to replace TDI based systems with similar MDI based systems. MDI except low steam pressure (4.0.10 at 20℃)^-6mbar), similar systems as described above have the advantage of faster curing speeds.

However, the 4, 4' -MDI-based prepolymers known from the prior art have disadvantages with respect to viscosity compared to TDI systems of similar structure. Thus, the viscosity of the MDI-based prepolymer containing 98% by weight of 4, 4' -MDI at 23 ℃ was 70000 mPas, whereas the viscosity of the similar TDI-based prepolymer at 23 ℃ was only 11000 mPas. Although increasing the 2, 4' -MDI content to 25% by weight had no significant effect on the viscosity and elongation at break, the tensile strength, stress value (100% modulus) and Shore A strength (Lay et al, world representative polyurethane record; 1991, p.319 ff) were deteriorated.

EP-A0693511 describes NCO-containing hotmelt systems prepared from MDI, in which the 2, 4' isomer content is at least 70% by weight, preferably at least 85% by weight. In addition to i) polyols containing ester and/or ether groups and having an average functionality of from 1.95 to 2.2, polyols of higher functionality may also be used as the hydroxyl component. Preference is given to using polyols containing ester groups in i). However, such groups are not stable to hydrolysis and are therefore unsuitable for use in the field of sealants. WO 93/09158 discloses prepolymers preferably containing 2, 4-TDI, MDI and/or IPDI isocyanate components, wherein the MDI contains at least 90% by weight of 2, 4-MDI. The polyol component used for the synthesis has a functionality of from 2.05 to 2.5 and consists of polyesters, polyethers and/or polyether esters having a molecular weight of 200-6000 g/mol. The examples disclose prepolymers synthesized from MDI having a 2, 4' -MDI content of greater than 92% by weight and polyether diols and triols having a molecular weight of 1000g/mol or less. Because of the short polyether chains, such prepolymers are not suitable for the preparation of elastomeric sealants from one-component, moisture-curing formulations.

WO 03/006521 and WO 03/033562 describe low-monomer-content, NCO-containing MDI-based prepolymers in which the 2, 4' -MDI content is greater than 97.5% by weight. The polyols used include polyether diols having a molecular weight of 2000g/mol or less. Due to the short chain length of the polyols, the prepolymer products obtained are solid at room temperature or have an extremely high viscosity (shear viscosity > 100000 mPas at 23 ℃), and are therefore unsuitable for use in low-solvent sealants which can be used at room temperature.

WO 03/055929 describes NCO-containing prepolymers which are preferably prepared from 2, 4 '-MDI and polyols, the 4, 4' -and 2, 2 '-MDI content of the 2, 4' -MDI preferably being less than 1% by weight. Suitable polyols are preferably liquid at room temperature or amorphous or crystalline compounds having 2 or 3 OH groups per molecule and an average molecular weight of 400-20000 g/mol. In the present application, a large number of polyether, polyester and polyacrylate polyols are listed non-specifically. In other formulations, one-or two-component adhesives/sealants can be prepared from these prepolymers. For this purpose they are used in mixtures with high molecular weight polyisocyanates. These high molecular weight isocyanates are likewise based on 2, 4' -MDI, but contain polyols having a molecular weight of from 60 to 2000 g/mol. 2, 4' -MDI prepolymers containing exclusively polyether diols having a number average molecular weight of > 2000g/mol, low monomer content, low viscosity and moisture-curing sealants are not described.

WO03/051951 discloses a process in which an asymmetric diisocyanate is first reacted with a polyol having an average molecular weight of 60 to 3000g/mol to form an NCO-functional prepolymer, which is subsequently reacted with at least one further polyol. For the preparation of the prepolymer, TDI, IPDI or 2, 4' -MDI is preferably used. The polyols which can be used in the first step include not only low molecular weight alcohols containing 2 to 4 OH groups but also polyether, polyester, or polyacrylate polyols. Prepolymers or sealants based only on polyether polyols having a number average molecular weight of 2000g/mol or more and MDI having a 2, 4' -MDI content of more than 95% by weight are not described.

Disclosure of Invention

We have now surprisingly found that, in order to prepare moisture-curing sealants having an elongation at break of > 100%, measured in accordance with DIN53504 in the case of sealant curing, suitable MDI-based prepolymers which are free of carboxylate groups and have a shear viscosity of < 100000 mPas at 23 ℃ can be used and, when preparing the prepolymers, using a mixture of MDI isocyanate containing at least 95% by weight of 2, 4' -MDI and polyether polyol, the polyether polyol mixture comprises at least one polyether polyol having a number average molecular weight of 2000g/mol to 20000g/mol and an average OH functionality of 3 to 8, if desired, polyether polyols having a number-average molecular weight of more than 2000g/mol, in particular difunctional polyether polyols, in addition to a composition such that the total functionality of the OH groups is > 2 and the number-average molecular weight Mn is from 3000 to 20000 g/mol.

Such prepolymers and moisture-curing sealants comprising such prepolymers have not been described to date in the prior art.

Moisture-curing sealants based on such prepolymers have comparable or improved properties compared to TDI-based systems.

The present invention accordingly provides a process for preparing MDI-based prepolymers which are free of carboxylate groups and have a shear viscosity of < 100000 mPas at 23 ℃, wherein

Reacting A) an MDI-type isocyanate containing at least 95% by weight of 2, 4' -MDI with B) a polyether polyol mixture,

the polyether polyol mixture comprises:

b1) at least one number average molecular weight M_nA polyether polyol having from 2000 to 20000g/mol and an average OH functionality of from 3 to 8, and

b2) one or more optional polyether polyols having a number average molecular weight of greater than 2000g/mol,

wherein B1) is present in B) in an amount of at least 20% by weight, and B1) and B2) in B) are of such a composition that the total OH functionality is > 2 and the number-average molecular weight M_nFrom 3000 to 20000 g/mol.

The invention likewise provides prepolymers obtainable in this way and sealants and/or adhesives prepared from the prepolymers having an elongation at break of > 100% measured in accordance with DIN 53504.

Detailed Description

The abbreviation "MDI" is used herein to denote diphenylmethane diisocyanate.

The present invention accordingly provides a process for preparing MDI-based prepolymers which are free of carboxylate groups and have a shear viscosity of < 100000 mPas at 23 ℃, wherein

Reacting A) an MDI-type isocyanate containing at least 95% by weight of 2, 4' -MDI with B) a polyether polyol mixture,

the above polyether polyol mixture comprises:

b1) at least one number average molecular weight M_nA polyether polyol having from 2000 to 20000g/mol and an average OH functionality of from 3 to 8, and

b2) one or more optional polyether polyols having a number average molecular weight of greater than 2000g/mol,

wherein B1) is present in B) in an amount of at least 20% by weight, and B1) and B2) in B) are such that the total OH functionality is > 2 and the number-average molecular weight M_nFrom 3000 to 20000 g/mol.

The invention likewise provides prepolymers obtainable in this way and sealants and/or adhesives prepared from the prepolymers having an elongation at break of > 100% measured in accordance with DIN 53504.

The ratio of components A) and B) to one another is preferably such that the NCO/OH ratio is less than 2.0, more preferably from 1.4 to 1.9.

The proportions of components A) and B) relative to one another are preferably such that the NCO content of the resulting prepolymer is less than 4% by weight.

A) The MDI-type isocyanate used in (1) preferably contains at least 97% by weight, more preferably at least 97.5% by weight, of 2, 4' -MDI.

A) The MDI-type isocyanate used in (1) preferably contains not more than 0.5% by weight, more preferably not more than 0.25% by weight, of 2, 2' -MDI.

Such methylene diisocyanates containing 95% by weight or more of 2, 4' -MDI are generally obtained by distillation or crystallization of the bicyclic fraction from the industrial preparation of MDI.

The polyether polyols used in B) are known per se to the skilled worker in polyurethane chemistry. These polyether polyols are usually obtained starting from low molecular weight compounds containing a plurality of OH or NH functions by reaction with cyclic ethers or mixtures of different cyclic ethers. Catalysts used include alkaline or double metal cyanide systems such as KOH. The skilled worker is familiar with the following polyether first moieties, polyalkylene oxides and other polyethers from, for example, US-B6486361 or l.e.st.pierre, editor: norman g.gaylord; high polymer volume XIII; intersciences press; newark 1963; and p.130ff.

Suitable starters preferably contain from 2 to 8, more preferably from 2 to 6, hydrogen atoms capable of addition polymerization with the cyclic ethers. Examples of such compounds include water, ethylene glycol, 1, 2 or 1, 3-propanediol, 1, 3-butanediol, 1, 4-butanediol, 1, 6-hexanediol, bisphenol A, neopentyl glycol, glycerol, trimethylolpropane, pentaerythritol and sorbitol.

Suitable cyclic ethers include alkylene oxides such as ethylene oxide, 1, 2-propylene oxide or butylene oxide, 3-chloro-1, 2-propylene oxide or styrene oxide or tetrahydrofuran.

Preference is given to using polyethers based on the abovementioned starting materials and containing 1, 2-propylene oxide, ethylene oxide and/or tetrahydrofuran units, preferably comprising propylene oxide and/or ethylene oxide units, in B).

b1) The number average molecular weight of the polyether polyol in the component (A) is preferably 2000 to 15000 g/mol. The preferred average OH functionality is from 3 to 6, more preferably from 3 to 4.

b2) The number average molecular weight of the polyether polyol in the component (A) is preferably 2000 to 25000g/mol, more preferably 2000 to 18000 g/mol. The preferred average OH functionality is from 2 to 6, more preferably from 2 to 4, and especially preferably 2. The ethylene oxide content of the polyether polyols of components b1) and b2) amounts to from 0 to 25% by weight, preferably from 0 to 20% by weight, more preferably from 0 to 15% by weight.

The content of component B1) in the polyether polyol mixture B) is preferably at least 30% by weight.

The polyurethane prepolymers containing NCO end groups are prepared in a manner known from polyurethane chemistry.

The above-mentioned preparation is preferably carried out in a one-step process. The polyols of component B) are in this case mixed individually or in mixtures with an excess of component A), and the homogeneous mixture is stirred until the NCO value has stabilized. The reaction temperature chosen is from 50 ℃ to 120 ℃, preferably from 50 ℃ to 100 ℃. Preferably, both the reactants and the product are liquid at the reaction temperature chosen so that homogenization can be carried out without the use of additional solvents and the viscosity of the reaction mixture can be reduced.

The above preparation can also be carried out in a two-step procedure. In this case, the precursor is prepared in a first step from B1) and/or B2) of the B) component and an excess of the isocyanate component A). The reactants in the homogeneous mixture are stirred until a constant NCO value is obtained, at a temperature of from 50 ℃ to 120 ℃, preferably from 50 ℃ to 100 ℃. The precursor has a high content of unreacted monomeric diisocyanate. This precursor is then reacted in a second reaction step with the remaining polyol of component B) to give the finished sealant prepolymer. The reactants in the homogeneous mixture are stirred at a temperature of from 50 ℃ to 120 ℃, preferably from 50 ℃ to 100 ℃, until a constant NCO value is obtained. Preferably, the reactants and the product of both reactions are liquid at the reaction temperature chosen so that homogenization can be carried out without the use of additional solvents and the viscosity of the reaction mixture can be reduced.

It is of course also possible to prepare the NCO-terminated polyurethane prepolymers continuously in a stirred tank cascade or in a suitable mixing apparatus, for example a high-speed mixer operating according to the rotor/stator principle. The NCO content is determined by the NCO titration method customary in polyurethane chemistry.

When synthesizing the prepolymer, a suitable catalyst and/or solvent for accelerating the NCO/OH reaction can be added, if necessary.

Suitable catalysts are amine compounds or organometallic compounds known from polyurethane chemistry.

For example, the following compounds may be used as catalysts: triethylamine, tributylamine, dimethylbenzylamine, dicyclohexylmethylamine, dimethylcyclohexylamine, N, N, N ', N ' -tetramethyldiaminodiethyl ether, bis- (dimethylaminopropyl) urea, N-methyl-and N-ethylmorpholine, N, N ' -dimorpholinodiethyl ether (DMDEE), N-cyclohexylmorpholine, N, N, N ', N ' -tetramethylethylenediamine, N, N, N ', N ' -tetramethylbutanediamine, N, N, N ', N ' -tetramethyl-1, 6-hexanediamine, pentamethyldiethylenetriamine, dimethylpiperazine, N-dimethylaminoethylpiperidine, 1, 2-dimethylimidazole, N-hydroxypropylimidazole, 1-azabicyclo [2.2.0] octane, 1, 4-diazabicyclo [2.2.2] octane (Dabco) and alkanolamine compounds such as triethanolamine, Triisopropanolamine, N-methyl-and N-ethyldiethanolamine, dimethylaminoethanol, 2- (N, N-dimethylaminoethoxy) ethanol, N, N ', N-tris (dialkylaminoalkyl) hexahydrotriazines such as N, N ', N ' -tris (dimethylaminopropyl) -s-hexahydrotriazine), iron (II) chloride, zinc chloride, lead octoate, and preferred are tin salts such as tin dioctoate, tin diethylhexanoate, dibutyltin dilauryl and/or dibutyltin mercaptide, 2, 3-dimethyl-3, 4, 5, 6-tetrahydropyrimidine, tetraalkylammonium hydroxides such as tetramethylammonium hydroxide, alkali metal hydroxides such as sodium hydroxide, alkali metal alkoxides such as sodium methoxide and potassium isopropoxide, and/or alkali metal salts of long chain fatty acids containing 10 to 20 carbon atoms and optionally OH side groups. Other compounds which have been found to be suitable as catalysts include Ti compounds, in particular Ti (VI) -O-alkyl compounds, where the alkyl group is, for example, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, n-pentyl, 2-pentyl, 3-pentyl, preferably ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, particularly preferably titanium (VI) butoxide.

Also suitable are, for example, organometallic compounds of tin, lead, iron, titanium, bismuth, zirconium, such as tetraisopropyl titanate, lead phenylethyldithiocarbamate, tin (II) carboxylates, for example tin (II) acetate, tin ethylhexanoate and tin diethylhexanoate. Yet another class of compounds is represented by dialkyltin (IV) carboxylates. The carboxylic acids mentioned above contain at least 2, preferably at least 10, in particular 14 to 32 carbon atoms. Dicarboxylic acids may also be used. Specific acids which may be mentioned include the following: adipic acid, maleic acid, fumaric acid, malonic acid, succinic acid, pimelic acid, terephthalic acid, phenylacetic acid, benzoic acid, acetic acid, propionic acid, and 2-ethylhexanoic acid, octanoic acid, decanoic acid, lauric acid, myristic acid, palmitic acid, and stearic acid.

Tin oxides and sulfides and tin mercaptides may also be used. Specific compounds include the following: bis- (tributyltin) oxide, bis- (trioctyltin) oxide, dibutyltin bis- (2-ethylhexyl mercaptan) and bis- (2-ethylhexyl sulfideAlcohols) dioctyltin, dibutyltin bis and dioctyltin bis dodecanethiolate, bis- (beta-methoxycarbonylethyl) tin bis dodecanethiolate, bis- (2-ethylhexylmercaptan) bis- (beta-acetylethyl) tin bis dodecanethiolate and dioctyltin bis dodecanethiolate, butyltin tris- (thioglycolic acid-2-ethylhexanoic acid) and octyltin tris- (thioglycolic acid-2-ethylhexanoic acid), dibutyltin bis- (thioglycolic acid-2-ethylhexanoic acid) and dioctyltin bis- (thioglycolic acid-2-ethylhexanoic acid), (thioglycolic acid-2-ethylhexanoic acid) tributyltin and trioctyltin (thioglycolic acid-2-ethylhexanoic acid), butyltin tris- (thioglycol-2-ethylhexanoic acid) and octyltin tris- (thioglycol-2-ethylhexanoic acid), dibutyltin tris- (thioethylene glycol 2-ethylhexanoate) and dioctyltin tris- (thioethylene glycol 2-ethylhexanoate) with the general formula R_n+1S_n(SCH₂CH₂OCOC₈H₁₇)_3-nTributyltin thioglycol 2-ethylhexanoate and trioctyltin thioglycol 2-ethylhexanoate, wherein R is an alkyl group having 4 to 8 carbon atoms, bis- (thioglycol 2-ethylhexanoate) bis- (β -methoxycarbonylethyl) tin, bis- (2-ethylhexanoate thioglycolate) bis- (β -methoxycarbonylethyl) tin, and bis- (2-ethylhexanoate) bis- (β -acetylethyl) tin and bis- (2-ethylhexanoate thioglycol) bis- (β -acetylethyl) tin.

The organobismuthates used are in particular bismuth carboxylates, the carboxylic acids having from 2 to 20 carbon atoms, preferably from 4 to 14 carbon atoms. Acids which may be explicitly mentioned include the following: butyric acid, caproic acid, caprylic acid, capric acid, lauric acid, myristic acid, palmitic acid, stearic acid, arachidic acid, isobutyric acid and 2-ethylhexanoic acid. It is also possible to use mixtures of bismuth carboxylates with other metal carboxylates such as tin carboxylates.

In the synthesis of the prepolymers of importance according to the invention, preference is given to using catalysts, particularly preferably organometallic compounds. By using such catalysts prepolymers with a particularly low residual free MDI monomer content and a low viscosity can be prepared.

If a catalyst is used, it is present in an amount of from 0.01 to 8% by weight, preferably from 0.1 to 5% by weight, relative to the total amount of components A) and B) to be reacted. Preferred organometallic catalysts are selected from tin (IV) compounds. Preferred catalysts from the group of tin (IV) compounds are dibutyltin diacetate and dioctyltin diacetate, dibutyltin maleate and dioctyltin maleate, dibutyltin bis (2-ethylhexanoate) and dioctyltin bis (2-ethylhexanoate), dibutyltin dilaurate and dioctyltin dilaurate, dibutyltin dichloride and dioctyltin dichloride, dibutyltin dilaurate and dioctyltin dilaurate, tributyltin acetate, bis (. beta. -methoxycarbonylethyl) tin dilaurate and bis (. beta. -acetylethyl) tin dilaurate.

One particularly preferred organometallic catalyst is dibutyltin dilaurate.

Suitable organic or inorganic acids may be added to terminate the reaction, for example hydrochloric acid, sulphuric acid, phosphoric acid or derivatives thereof, formic acid, acetic acid or other alkanoic acids or components capable of liberating acid, such as organic acids or acid halides. Examples of suitable acid chlorides are formyl chloride, acetyl chloride, propionyl chloride and benzoyl chloride. The termination reaction is very beneficial when the above-mentioned known amine or organometallic catalysts have been used in the preparation of the prepolymer.

Benzoyl chloride is preferably used as a terminator.

The products obtainable according to the invention preferably have a residual content of methylene diphenyl diisocyanate of less than 0.3% by weight, more preferably less than 0.15% by weight, based on the solvent-free NCO-functional prepolymer. The shear viscosity of the prepolymer obtained according to the invention, measured in the solvent-free state at 23 ℃, is preferably 5000-.

The present invention also provides polyurethane polymers, coatings, adhesives and/or sealants prepared using the prepolymers obtained according to the present invention, preferably moisture-curing sealants and/or adhesives based on the prepolymers of the present invention.

The moisture-curing sealants and/or adhesives obtained from such prepolymers generally have an elongation at break of > 100%, preferably > 200%, more preferably > 300%, measured in accordance with DIN 53504.

To produce such moisture-curing sealants and/or adhesives, the NCO-containing polyurethane polymers according to the invention can be formulated with the customary plasticizers, fillers, pigments, drying agents, additives, light stabilizers, antioxidants, thixotropic agents, catalysts, adhesion promoters and other auxiliaries and additives which are suitable for the known sealant production processes.

Suitable fillers which may be mentioned include, for example, carbon black, precipitated silica, pyrogenic silica, mineral chalk and precipitated chalk.

Suitable plasticizers which may be mentioned include, for example, phthalates, adipates, alkyl sulfonates or phosphonates of phenol.

Examples of suitable thixotropic agents include fumed silica, polyamides, hydrogenated castor oil related products, or polyvinyl chloride.

Examples of catalysts suitable for accelerating the cure include tertiary amines not incorporated into the prepolymer chain, such as diazabicyclooctane (Dabco), triethylamine, dimethylbenzylamine(s) ((R))DB, Bayer MaterialScienceAG, levikusen, DE), bis-dimethylaminoethyl ether, tetramethylguanidine, bis-dimethylaminomethylphenol, 2 '-dimorpholinodiethyl ether, 2- (2-dimethylaminoethoxy) ethanol, 2- (dimethylamino) ethyl 3- (dimethylamino) propyl ether, bis- (2-dimethylaminoethyl) ether, N-dimethylpiperazine, N- (2-hydroxyethoxyethyl) -2-azanorbornane, N' -tetramethyl-1, 3-butanediamine, N '-tetramethyl 1, 3-propanediamine or N, N' -tetramethyl 1, 6-hexanediamine or any desired mixtures of two or more of these compounds.

The catalyst may also be present in oligomeric or polymeric form, such as in the form of N-methylated polyaziridine.

Suitable catalysts also include 1-methylimidazole, 2-methyl-1-vinylimidazole, 1-allylimidazole, 1-phenylimidazole, 1, 2, 4, 5-tetramethylimidazole, 1- (3-aminopropyl) imidazole, pyrimidazole, 4-dimethylaminopyridine, 4-pyrrolidinopyridine, 4-morpholinopyridine, 4-methylpyridine or N-dodecyl-2-methylimidazole or any desired mixtures of two or more of the above compounds.

In addition to or instead of tertiary amines, organometallic compounds, for example carboxylic acids, organotin compounds such as strong bases, for example alkali metal hydroxides, alkali metal alkoxides and alkali metal phenoxides, for example di-n-octyltin mercaptide, dibutyltin maleate, dibutyltin diacetate, dibutyltin dilaurate, dibutyltin dichloride or dibutyltin didodecylmercaptide, tin (II) acetate, tin ethylhexanoate and tin diethylhexanoate or lead phenylethyldithiocarbamate, can also be added to such moisture-curing polyurethane sealants.

The drying agents mentioned are generally prepared from alkoxysilyl compounds (e.g.vinyltrimethoxysilane, methyltrimethoxysilane, isobutyltrimethoxysilane, hexadecyltrimethoxysilane), inorganic substances such as calcium oxide (CaO) and compounds containing isocyanate groups (e.g.isocyanatotosylate).

The adhesion promoters used are known silanes containing functional groups, for example aminosilanes of the type mentioned above, but also N-aminoethyl-3-aminopropyltrimethoxysilane and/or N-aminoethyl-3-aminopropylmethyldimethoxysilane, epoxysilanes and/or mercaptosilanes.

Sealants, adhesives and coatings based on the NCO-containing moisture-curing prepolymers of the invention can be used for different purposes. They are widely used in coatings, joints or seals for metals, ceramics, glass, plastics, wood, concrete and other building materials.

Examples

All percentages are by weight unless otherwise noted.

The viscosity was measured at a measurement temperature of 23 ℃ with a Viscotester VT550 rotary viscometer from Thermo Haake, Karlsruhe, DE, using an SV measuring cup and an SV DIN2 measuring instrument.

The content of free diisocyanato monomer was determined by Gel Permeation Chromatography (GPC). The measurement was performed at room temperature. The eluent used was THF, the flow rate was 1mL/min, and the injection volume was 50. mu.l. The separation column used is packed with 5 μm separation material and hasA porosity GPC column is available, for example, from MZ-Analyzenchnik, Mainz, DE under the trade name MZ-Gel SD-plus. The total length of the separation column was 120 cm. The detector used was a refractive index detector.

The NCO content of the prepolymer and the reaction mixture was determined in accordance with DIN EN 1242.

Shore A hardness was determined in accordance with DIN 53505 and tensile strength, elongation at break and stress value were determined in accordance with DIN 53504.

Polyether A:

a polyether polyol having a nominal functionality of 3 and a hydroxyl number of 35mgKOH/g, which is prepared by propoxylating glycerol and then terminating it by ethoxylation. The ethylene oxide content was 13% by weight and the product contained 80 to 85 mol% primary alcohol groups.

Polyether B:

a polyether polyol having a nominal functionality of 2 and a hydroxyl number of 28mgKOH/g, which is prepared by propoxylating glycerol and then terminating it by ethoxylation. The ethylene oxide content was 13% by weight and the product contained 70 to 80 mol% primary alcohol groups.

Polyether C:

push buttonPolypropylene glycol prepared by DMC catalysis having a nominal functionality of 2 and a hydroxyl number of 28mgKOH/g (4200, available from Bayer MaterialScience AG, Leverkusen, DE).

Polyether D:

push buttonThe polypropylene glycol obtained by DMC catalysis has a nominal functionality of 3 and a hydroxyl number of 28mgKOH/g (6300, available from Bayer MaterialScience AG, Leverkusen, DE).

Polyether E:

a polyether polyol having a nominal functionality of 2 and a hydroxyl number of 260mgKOH/g, prepared by propoxylation of propylene glycol.

Polyether E:

a polyether polyol having a nominal functionality of 2 and a hydroxyl number of 147mgKOH/g, prepared by propoxylation of propylene glycol.

Diisocyanate I:

44M (4, 4' -diphenylmethane diisocyanate), Bayer MaterialScience AG, Lecerkusen, DE

Diisocyanate II:

diphenylmethane diisocyanate having the following isomer distribution:

99.10% of 2, 4' -diphenylmethane diisocyanate

4, 4' -diphenylmethane diisocyanate 0.88%

2, 2' -diphenylmethane diisocyanate 0.02%

Diisocyanate III:

diphenylmethane diisocyanate having the following isomer distribution:

2, 4' -diphenylmethane diisocyanate 96.93%

4, 4' -diphenylmethane diisocyanate 3.05%

2, 2' -diphenylmethane diisocyanate 0.02%

Diisocyanate IV:

diphenylmethane diisocyanate having the following isomer distribution:

99.92 percent of 2, 4' -diphenylmethane diisocyanate

4, 4' -diphenylmethane diisocyanate 0.04%

2, 2' -diphenylmethane diisocyanate 0.04%

: plasticizers based on phenol alkylsulfonates, Bayer MaterialScience AG, Leverkusen, DE

DBTL：

Dibutyl tin dilaurate, Goldschmidt TIB GmbH, Mannheim, DE, trade name218。

Example 1:

in a heatable glass flask equipped with stirrer device and dropping funnel, 266.73g (1.07mol) of diisocyanate II were melted at 85 ℃. The molten diisocyanate was first mixed with 0.157g of benzoyl chloride with stirring and then with a mixture of 1160.25g (0.29mol) of polyether B and 556.87g (0.116mol) of polyether A, previously dehydrated under a vacuum of 15mbar and at a temperature of 100 ℃ at a mixing rate such that the temperature was kept constant at 85 ℃. The reaction mixture was then stirred further at 85 ℃ until after 12 hours of reaction the NCO content had reached a constant value of 2.51% (theoretical 2.56%). The temperature is then lowered to 50 ℃ and 15.99g of tosyl isocyanate are added, the mixture is stirred for a further 15 minutes and the product is decanted off. The NCO content of the end product was 2.52%.

Example 2:

in a heatable glass flask equipped with stirrer device and dropping funnel, 298.75g (1.195mol) of diisocyanate II were melted at 50 ℃. The molten diisocyanate was first mixed with 0.12g of benzoyl chloride with stirring and then with 1687.85g (0.352mol) of polyether A dehydrated beforehand under a vacuum of 15mbar and a temperature of 100 ℃ at a rate such that the temperature was kept constant at 50 ℃. After complete addition of the polyether, the reaction mixture was heated to 70 ℃ and stirring was continued at this temperature until after 19 hours of reaction the NCO content had reached a constant value of 2.81% (theoretical 2.83%). The temperature was then lowered to 60 ℃ and 13.27g of tosyl isocyanate were added first, followed by 497.89The mixture was then stirred for more than 15 minutes and the product decanted. The NCO content of the end product was 2.24%.

Practice ofExample 3:

in a heatable glass flask equipped with stirrer and dropping funnel, 181.94g (0.728mol) of diisocyanate II were melted at 50 ℃. The molten diisocyanate was mixed with stirring with a mixture of 659g (0.165mol) of polyether C and 659g (0.11mol) of polyether D, previously dehydrated under a vacuum of 15mbar and at a temperature of 100 ℃ at such a rate that the temperature was kept constant at 50 ℃. After the polyether mixture had been completely added, the reaction mixture was heated to 70 ℃ and stirring was continued at this temperature until after 20 hours of reaction the NCO content had reached a constant value of 2.27% (theoretical 2.24%). The temperature is then lowered to 60 ℃ and 10g of tosyl isocyanate are added, the mixture is stirred for a further 15 minutes and the product is decanted off. The NCO content of the end product was 2.20%.

Example 4:

in a heatable glass flask equipped with stirrer device and dropping funnel, 151.08g (0.604mol) of diisocyanate III were melted at 50 ℃. The molten diisocyanate was first mixed with 0.15g of DBTL under stirring and then with a mixture of 674.5g (0.169mol) of polyether C and 674.5g (0.112mol) of polyether D, previously dehydrated under a vacuum of 15mbar and at a temperature of 100 ℃, at such a rate that the temperature was kept constant at 50 ℃ without rising. After the polyether mixture had been completely added, the reaction mixture was heated to 70 ℃ and stirring was continued until the NCO content reached a constant value of 1.44% (theoretical value 1.50%) after 5 hours of reaction. The temperature is then lowered to 60 ℃ and 120ppm of benzoyl chloride are added to deactivate the catalyst, 12g of tosyl isocyanate are added and the mixture is stirred for a further 15 minutes and the product is decanted off. The NCO content of the end product was 1.50%.

Example 5:

in a heatable glass flask equipped with stirrer device and dropping funnel, 202.25g (0.809mol) of diisocyanate IV were melted at 50 ℃. The molten diisocyanate was first mixed with 0.2g of DBTL with stirring and then with a mixture of 1797.75g (0.3mol) of polyether D dehydrated beforehand under a vacuum of 15mbar and at a temperature of 100 ℃ at a rate such that the temperature was kept constant at 50 ℃. After the polyether addition was complete, the reaction mixture was heated to 70 ℃ and stirring was continued at this temperature until after 3 hours of reaction the NCO content had reached a constant value of 1.49% (theoretical 1.51%). The temperature was then lowered to 60 ℃ and 120ppm of benzoyl chloride was added to deactivate the catalyst. 15.76g of tosyl isocyanate were then added and the mixture was stirred for a further 15 minutes and the product was decanted off. The NCO content of the end product was 1.49%.

Example 6.

The sealant prepolymer was prepared in a two-step procedure.

The first stage is as follows: preparation of precursors containing NCO functional groups.

395g (1.58mol) of diisocyanate IV were melted at 50 ℃ in a heatable glass flask equipped with a stirrer device and a dropping funnel. The molten diisocyanate was first mixed with 0.14g of DBTL with stirring and then with 1000g (0.25mol) of polyether C dehydrated beforehand under a vacuum of 15mbar and at a temperature of 100 ℃ at a rate such that the temperature was kept constant at 50 ℃. After the addition of the polyether mixture was complete, the reaction mixture was heated to 70 ℃ and stirring was continued at this temperature until after 4 hours of reaction the NCO content had reached a constant value of 7.58% (theoretical 8.0%). The precursor was then cooled to room temperature and poured out.

And a second stage: preparation of sealant prepolymer using the precursor prepared above: 712.9g of the precursor prepared in the first stage were introduced at 50 ℃ into a heatable glass flask equipped with stirrer device and dropping funnel. 0.13g of DBTL were initially introduced with stirring and then a mixture of 387.7g (0.097mol) of polyether C and 899.4g (0.15mol) of polyether D dehydrated beforehand at 100 ℃ under a vacuum of 15mbar were added at such a rate that the temperature was kept constant at 50 ℃ without increasing. After the addition of the polyether mixture was complete, the reaction mixture was heated to 70 ℃ and stirring was continued at this temperature until the NCO content reached a constant value of 1.26% (theoretical 1.50%) after 3.5 hours of reaction. The temperature was then lowered to 60 ℃ and 240ppm of benzoyl chloride was added to deactivate the catalyst and the product was decanted. The NCO content of the end product was 1.26%.

Comparative example 1:

in a heatable glass flask equipped with stirrer device and dropping funnel, 133.37g (0.533mol) of diisocyanate I were melted at 85 ℃. The molten diisocyanate was first mixed with 0.075g of benzoyl chloride with stirring and then with a mixture of 580.13g (0.145mol) of polyether B and 278.44g (0.058mol) of polyether A, previously dehydrated under a vacuum of 15mbar and at a temperature of 100 ℃ at a mixing rate such that the temperature was kept constant at 85 ℃. The reaction mixture was then stirred further at 85 ℃ until after 8 hours of reaction the NCO content had reached a constant value of 2.48% (theoretical 2.56%). The temperature is then lowered to 50 ℃ and 8g of tosyl isocyanate are added, the mixture is then stirred for a further 15 minutes and the product is decanted off. The NCO content of the end product was 2.48%.

Comparative example 2:

149.75g (0.599mol) of diisocyanate I were melted at 50 ℃ in a heatable glass flask with stirrer device and dropping funnel. The molten diisocyanate was first mixed with 0.06g of benzoyl chloride with stirring and then with 843.93g (0.176mol) of polyether A dehydrated beforehand under a vacuum of 15mbar and a temperature of 100 ℃ at a rate such that the temperature was kept constant at 50 ℃. After complete addition of the polyether, the reaction mixture was heated to 70 ℃ and stirring was continued at this temperature until after 14 hours of reaction the NCO content had reached a constant value of 2.84% (theoretical 2.83%). Then the temperature was lowered to 60 ℃ and 6.64g of tosyl isocyanate and then 248.95g were addedThe mixture was then stirred for a further 15 minutes and the product was decanted off. The NCO content of the end product was 2.24%.

Comparative example 3:

in a heatable glass flask equipped with stirrer device and dropping funnel, 181.94g (0.728mol) of diisocyanate I were melted at 50 ℃. The molten diisocyanate was mixed with stirring with a mixture of 659g (0.165mol) of polyether C and 659g (0.11mol) of polyether D, previously dehydrated under a vacuum of 15mbar and at a temperature of 100 ℃ at such a rate that the temperature was kept constant at 50 ℃. After the addition of the polyether mixture was complete, the reaction mixture was heated to 70 ℃ and stirring was continued at this temperature until after 15 hours of reaction the NCO content had reached a constant value of 2.24% (theoretical 2.24%). The temperature was then lowered to 60 ℃ and 10g of tosyl isocyanate and then 377.5g were addedThe mixture was then stirred for a further 15 minutes and the product was decanted off. The NCO content of the end product was 1.86%.

Comparative example 4:

in a glass flask which can be cooled by heating and is equipped with a stirrer device and a dropping funnel, 40.29g (0.161mol) of diisocyanate I are melted at 50 ℃. The molten diisocyanate was first mixed with 4mg of DBTL with stirring and then with a mixture of 179.86g (0.045mol) of polyether C and 179.86g (0.03mol) of polyether D which had been dehydrated beforehand under a vacuum of 15mbar and at a temperature of 100 ℃ at such a rate that the temperature was kept constant at 50 ℃ without increasing. After the addition of the polyether mixture was complete, the reaction mixture was heated to 70 ℃ and stirring was continued at this temperature until the NCO content reached a constant value of 1.41% (theoretical 1.50%) after 2 hours of reaction. The temperature was then reduced to 60 ℃ and 120ppm of benzoyl chloride was added to deactivate the catalyst. 3.04g of tosyl isocyanate are then added, the mixture is stirred for a further 15 minutes and the product is decanted off. The NCO content of the end product was 1.41%.

Comparative example 5:

in a glass flask which can be cooled by heating and is equipped with a stirrer device and a dropping funnel, 40.29g (0.161mol) of diisocyanate I are melted at 50 ℃. The molten diisocyanate was mixed with stirring with a mixture of 179.86g (0.045mol) of polyether C and 179.86g (0.03mol) of polyether D, previously dehydrated under a vacuum of 15mbar and at a temperature of 100 ℃ at such a rate that the temperature was kept constant at 50 ℃. After the addition of the polyether mixture was complete, the reaction mixture was heated to 70 ℃ and stirring was continued at this temperature until after 28 hours of reaction the NCO content had reached a constant value of 1.52% (theoretical 1.50%). The temperature is then lowered to 60 ℃ and 2.64g of tosyl isocyanate are added, the mixture is then stirred for a further 15 minutes and the product is decanted off. The NCO content of the end product was 1.52%.

Comparative example 6.

101.7g (0.407mol) of diisocyanate IV are melted at 70 ℃ in a heatable glass flask with stirrer device and dropping funnel. The molten diisocyanate was first mixed with 22mg of DBTL with stirring and then with a mixture of 94.64g (0.22mol) of polyether E and 23.66g (0.0039mol) of polyether D which had been dehydrated beforehand under a vacuum of 15mbar and a temperature of 100 ℃ at a rate such that the temperature was kept constant at 70 ℃ without increasing. After the addition of the polyether mixture was complete, the reaction mixture was stirred further at this temperature until the NCO content reached a constant value of 6.7% (theoretical 6.9%) after 4.5 hours of reaction. The temperature was then lowered to 60 ℃ and 33ppm of benzoyl chloride was added to deactivate the catalyst and the product was decanted. The NCO content of the end product was 6.7%.

Comparative example 7:

in a heatable glass flask equipped with stirrer device and dropping funnel, 490.09g (1.96mol) of diisocyanate IV were melted at 70 ℃. The molten diisocyanate was first mixed with 0.15g of DBTL with stirring and then with a mixture of 807.95g (1.105mol) of polyether F and 201.95g (0.034mol) of polyether D at such a rate that the temperature remained stable at 70 ℃ without rising, the mixture of polyether F and polyether D having been dewatered beforehand at 100 ℃ under a vacuum of 15 mbar. After the addition of the polyether mixture was complete, the reaction mixture was stirred further at this temperature until the NCO content reached a constant value of 4.74% (theoretical 4.87%) after 4.5 hours of reaction. The temperature was then lowered to 60 ℃ and 120ppm of benzoyl chloride was added to deactivate the catalyst and the product was decanted. The final product had an NCO content of 4.74%.

Comparative example 8:

197.5g (0.79mol) of diisocyanate II were melted at 50 ℃ in a heatable glass flask with stirrer device and dropping funnel. The molten diisocyanate was mixed with stirring with a mixture of 1042g (0.261mol) of polyether C and 260.5g (0.0434mol) of polyether D, previously dehydrated under a vacuum of 15mbar and at a temperature of 100 ℃ at such a rate that the temperature was kept constant at 50 ℃. After the addition of the polyether mixture was complete, the reaction mixture was heated to 70 ℃ and stirring was continued at this temperature until after 20 hours of reaction the NCO content had reached a constant value of 2.57% (theoretical 2.61%). The temperature is then lowered to 60 ℃ and 12g of tosyl isocyanate are added, the mixture is then stirred for a further 15 minutes and the product is decanted off. The NCO content of the end product was 2.60%.

Production of samples for determination of mechanical properties:

under dynamic vacuum, 240g of the mixture is mixed405g of Omya BLP3 (calcium carbonate (filler), Omya GmbH, Cologne, DE) and 170g of adhesive from the corresponding examples with 21g of adhesiveVH20 (MDI-based polyisocyanate semiprepolymer, Bayer MaterialScience AG, Leverkusen, DE) and 45g of Wacker HDK N20 (fumed silica, Wacker Chemie Gmbh, Munich, DE) were kneaded in a cross-arm kneader for 30 minutes. 100g of the respective binder, 5.4g of Dynasylan GLYMO (glycidyl 3- (trimethoxysilyl) propyl ether, Degussa AG, Frankfurt amMain, DE) and 2.7g ofDabco T-12N (dibutyltin dilaurate, Air Products, 3502 GD Urrecht, NL). The mixture was kneaded under static vacuum for 20 minutes and then degassed with a brief dynamic vacuum. The resulting mixture was dispensed into aluminum cylinders and processed the next day into films of approximately 2mm thickness. The film was then cured at room temperature for 14 days.

Discussion of the results:

from the results summarized in tables 1 and 2, it is evident that the viscosity of the prepolymers prepared on the basis of pure 2, 4 '-MDI (examples 1, 2 and 3) is comparable to that of the prepolymers prepared on the basis of 4, 4' -MDI (II)44M) (comparative examples 1, 2 and 3) was about half the reduction in product. In this comparison it should be remembered that example 3 differs from comparative example 3 in that example 3 does not contain Mesamoll. While the mechanical properties of sealants prepared with different prepolymers vary only slightly. Thus, 2, 4' -MDI based sealants have a slightly higher elongation at break, while still having equivalent stress values (100% modulus) and equivalent Shore A hardness.

If an NCO/OH equivalent ratio of < 2.0 is chosen and DBTL is also used as catalyst in the preparation of the prepolymer (example 4), an NCO-containing prepolymer results. With 4, 4' -MDI (B)44M) (comparative examples 4 and 5), this prepolymer not only had a greatly reduced viscosity (20 and 3 times reduction, respectively), but also a residual monomer content of < 0.3%. Using this prepolymer, it is possible to prepare no-indicating (labeling) moisture-curing sealants with residual monomer contents of < 0.1%. The mechanical properties of these sealants are at a similar level to example 3, the prepolymer in example 3 being prepared with the same polyol mixture, but with an NCO/OH equivalent ratio > 2.0 and without the use of DBTL catalyst, so that the residual monomer content is greater than 0.3%.

When a prepolymer was prepared with a polyol mixture containing more than 70% short-chain polyethers (molecular weight < 1000g/mol), the product obtained was solid at room temperature (comparative example 6) or had a very high viscosity compared to the product according to the invention (comparative example 7). In addition, the free monomeric MDI content is clearly greater than 0.3% by weight when the NCO/OH ratio is 1.8 and a DBTL catalyst is used, whereas the residual monomer content is < 0.3% by weight in the product according to the invention using the same NCO/OH ratio and DBTL catalyst. And the mechanical properties of the sealant prepared with the prepolymer in comparative example 7 were unsatisfactory. The Shore A hardness is too high compared to sealants prepared with prepolymers of the present invention, and the elongation at break is only 21%, completely failing the sealant (the elongation at break of the sealant of the present invention is between about 330% and about 530%). In addition, the sealant prepared in comparative example 7 largely bleeds out the plasticizer in the sealant formulation, thereby obtaining a very viscous product. In contrast, sealants prepared with the prepolymers of the present invention do not bleed plasticizer. These products were completely tack-free within 1 to 7 days. The sealant prepared in comparative example 7 has poor mechanical properties not due to the high content of trifunctional polyether but due to the high content of hard segments (caused by the small molecular weight polyether), as shown in inventive example 5 based on trifunctional polyether only. . A mechanically good sealant can be formulated with the prepolymer of example 5. Thus, prepolymers prepared with polyol mixtures containing more than 70% by weight of short-chain polyethers (molecular weight < 1000g/mol) are unsuitable for formulating sealants.

When the content of trifunctional polyethers in the polyol mixture is less than 20% by weight (comparative example 8), the mechanical properties are impaired, so that higher functionality (functionality > 2) polyethers with a content > 20% are advantageous.

Table 1: viscosity comparison at 23 ℃ in mPas

Table 2: comparison of mechanical Properties

Although the invention has been described in detail in the foregoing for the purpose of illustration, it is to be understood that such detail is solely for that purpose and that variations can be made therein by those skilled in the art without departing from the spirit and scope of the invention except as it may be limited by the claims.

Claims (9)

1. A process for the preparation of diphenylmethane diisocyanate-based prepolymers which are free from carboxylate groups and have a shear viscosity at 23 ℃ of < 100000 mPa.s, characterized in that

Reacting A) a diphenylmethane diisocyanate-based isocyanate containing at least 95% by weight of 2, 4' -diphenylmethane diisocyanate with B) a polyether polyol mixture,

the polyether polyol mixture comprises the following components:

b1) at least one number average molecular weight M_n2000 to 20000g/mol and an average OH functionality of3 to 8 of a polyether polyol, and

b2) one or more optional polyether polyols having a number average molecular weight of greater than 2000g/mol,

wherein B1) is present in B) in an amount of at least 30% by weight, and the compositions of B1) and B2) in B) are such that the total functionality of the OH groups is > 2 and the number average molecular weight M is_nFrom 3000 to 20000 g/mol.

2. The method for preparing a diphenylmethane diisocyanate-based prepolymer containing no carboxylate groups, as claimed in claim 1, wherein the NCO/OH ratio is in the range of 1.4 to 1.9.

3. The method for preparing a diphenylmethane diisocyanate-based prepolymer containing no carboxylate groups as claimed in claim 1, wherein the isocyanate used in a) has a 2, 4 '-diphenylmethane diisocyanate content of at least 97.5% by weight and a 2, 2' -diphenylmethane diisocyanate content of not more than 0.25% by weight.

4. The process for the preparation of diphenylmethane diisocyanate-based prepolymers containing no carboxylate groups according to claim 1, wherein the at least one polyether polyol in b1) has a number average molecular weight of from 2000 to 15000g/mol and an average OH functionality of from 3 to 4.

5. The process for the preparation of diphenylmethane diisocyanate-based prepolymers containing no carboxylate groups according to claim 1, wherein the one or more polyether polyols in b2) have a number average molecular weight of from 2000 to 18000 g/mol.

6. The method for preparing a diphenylmethane diisocyanate-based prepolymer containing no carboxylate groups according to claim 1, wherein the ethylene oxide content of the polyether polyol in b1) and b2) is from 0% to 15% by weight.

7. Diphenylmethane diisocyanate-based prepolymer free of carboxylate groups, obtainable by the process according to claim 1.

8. The diphenylmethane diisocyanate-based prepolymer containing no carboxylate groups as claimed in claim 7, having a residual diphenylmethane diisocyanate content of less than 0.15% by weight and a shear viscosity at 23 ℃ of 5000-.

9. A moisture-curable adhesive or sealant comprising the diphenylmethane diisocyanate-based prepolymer prepared in accordance with the process of claim 1.