Polyurethane prepolymer containing NCO groups

Details Polyurethane prepolymer containing NCO groups Polyurethane prepolymer containing NCO groups

1998-02-10

2002-03-19

Geist, Gary (Department: 1621)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Cellular products or processes of preparing a cellular...

C521S107000, C521S156000, C521S172000, C521S173000, C521S129000, C521S157000, C524S100000, C524S247000, C524S251000, C524S096000, C528S073000, C528S074500, C560S330000

Reexamination Certificate

active

06359023

ABSTRACT:

This invention relates to a moisture-curing polyurethane prepolymer of oleochemical polyols and polyisocyanates. The invention also relates to the use of this prepolymer in moisture-curing adhesives and foams, more particularly in foams produced from non-reusable pressurized containers using blowing gases liquefied under pressure.
BACKGROUND OF THE INVENTION
Polyurethane prepolymers of the type in question are known. Thus, in EP 125 579, the oleochemical polyols are obtained from epoxidized triglycerides by reaction with low molecular weight monoalcohols, for example by reaction of epoxidized soybean oil with methanol or ethanol. This ring-opening reaction is accelerated by acidic catalysts which, on completion of the reaction, are neutralized with a basic substance, preferably with an amine. Together with polyisocyanates, these oleochemical polyols form NCO prepolymers with a considerable, but not always adequate storage stability when known tertiary amines are added as accelerators for the reaction of the NCO groups with water.
Corresponding polyurethane prepolymers are described in DE 36 26 223. The polyols used in this document are preferably ring opening products of epoxidized oils with monoalcohols. In this case, however, the epoxide groups are completely reacted. In addition, the triglyceride obtained, which contains secondary OH groups and OR groups, is additionally reacted with excess monoalcohol. A mixture of partial glycerides with unreacted triglyceride is formed in this transesterification reaction. These polyols are also produced in the presence of acid catalysts. Finally, the catalyst is again neutralized with an amine. These oleochemical polyols also form polyurethane prepolymers with inadequate stability in storage, particularly when the usual catalysts are present in relatively high concentrations for the moisture curing process.
Polyether polyols obtained by addition of alkylene oxides to low molecular weight diols or triols in the presence of alkaline compounds also form moisture-curing polyurethane prepolymers with limited stability in storage after reaction with polyisocyanates. This applies, for example, to polyols of propylene oxide and/or ethylene oxide and glycerol or trimethylol propane in the presence of NaOH, KOH, MeONa and MeOK in concentrations of more than 10 ppm metal content. Accordingly, to obtain satisfactory storage stability with polyols such as these, the alkali metal content of the polyols is reduced by additional purification measures to concentrations of about 5 ppm Na or K.
Accordingly, there is a need for polyurethane polymers having improved stability in storage for otherwise the same production and performance properties.
DETAILED DESCRIPTION OF THE INVENTION
The solution provided by the invention is defined in the claims and consists essentially in the use of basic lithium compounds in the production of polyols, more particularly oleochemical polyester polyols.
Accordingly, the polyurethane prepolymer containing NCO groups according to the invention of oleochemical polyols and polyisocyanates is characterized in that it contains up to 14 ppm of lithium and 0.1 to 2.0% by weight of a tertiary amine to accelerate the moisture curing process and is free from Na, K and other amines, particularly salts thereof with strong acids.
N-substituted morpholines above all are suitable for accelerating the reaction of water with NCO groups. Specific examples include 2,2′-dimorpholinodiethyl ether, N-ethyl morpholine, 2,2-bis-(dimethylaminodiethyl)-ether or mixtures of the compounds mentioned. 2,2′-dimorpholinodiethyl ether (DMDEE) is preferably used. These catalysts are particularly suitable because they catalyze above all the curing reaction and, to a lesser extent, the polymerization of the NCO groups (trimerization) or the urethanization reaction. The catalysts are used in a concentration of 0.1 to 2.0% by weight, preferably in a concentration of 0.2 to 1.2% by weight and more preferably in a concentration of 0.5 to 1.0% by weight, based on the prepolymer as a whole. They are generally added to the polyol or to the polyisocyanate before the prepolymerization.
The lithium is used as a basic lithium compound. Basic lithium compounds in the context of the invention are understood to be the hydroxides and alcoholates. However, compounds, such as lithium acetate, lithium oxides and Li metal, may also be used. They are employed in a concentration of 0.1 to 4.0 and preferably 0.5 to 2.0 mmole/kg polyol. This corresponds to a concentration of 0.35 to 14 and preferably 1.75 to 7.0 ppm of lithium in the polyurethane prepolymer. The lithium compound may be added to the reaction mixture as a basic transesterification catalyst either before or during the transesterification reaction. However, where the transesterification is acid-catalyzed, the acid may be neutralized with the lithium compound.
The oleochemical polyols preferably used are polyols containing ester groups which are derived from natural fats and oils. Accordingly, they contain structural elements of fatty acids and fatty alcohols. Starting materials for the oleochemical polyols of the polyurethane prepolymers according to the invention are fats and/or oils of vegetable and/or animal origin with preferably unsaturated fatty acid residues. Specific examples are castor oil, rapeseed oil and soybean oil. However, beef tallow, palm oil, peanut oil, sunflower oil and fish oil may also be used. These starting fats are preferably epoxidized and transesterified. Of the epoxidized triglycerides, epoxidized soybean oil is preferably used. The epoxidation and the reaction with alcohols or carboxylic acids is known (see, for example, EP 125 579 and DE 36 26 223). The polyols formed contain ether groups besides the ester groups.
To produce the polyester polyols according to the invention, polyhydric alcohols with a functionality of 2 to 4 are required in addition to the fats and oils. They have a molecular weight below 400. Suitable polyhydric alcohols are, for example, glycol, glycerol, pentaerythritol and trimethylol propane. Besides these polyhydric alcohols, dicarboxylic acids may also be used in small amounts. Specific examples are adipic acid, phthalic acid, isophthalic acid, terephthalic acid, glutaric acid, succinic acid, azelaic acid, dimer fatty acid and mixtures thereof.
The esterification is carried out under conditions known per se.
After the transesterification, the oleochemical polyols to be used in accordance with the invention have an OH value of 100 to 400 and preferably in the range from 150 to 350.
Besides these oleochemical polyols, the polyisocyanates are the second important structural element for the polyurethane prepolymers according to the invention.
Particularly suitable isocyanates are aromatic polyisocyanates based on MDI (methylene-bis-diphenyl isocyanate or diphenylmethane-4,4′-diisocyanate). Mixtures of MDI with relatively high molecular weight homologs having an average isocyanate functionality of 2.3 to 2.8 are particularly suitable. Other aromatic isocyanates include NDI and TDI. Cycloaliphatic isocyanates, such as IPDI, H
12
-MDI, and aliphatic diisocyanates, such as tetramethylene diisocyanate and hexamethylene diisocyanate, are also suitable.
The oleochemical polyol and the polyisocyanate are used in a quantity ratio which corresponds to a molar ratio of OH to isocyanate groups of 1:3 to 1:11 and, more particularly, 1:4 to 1:6.
The reaction between the oleochemical polyol and the polyisocyanate is normally carried out at a temperature of 0 to 100° C. and preferably at a temperature of 15 to 50° C. Catalysts for the reaction of the isocyanate groups with the OH groups are generally not necessary. However, catalysts may be added in small quantities to control the reaction, accelerating the reaction of the isocyanate group with the OH group, but not the trimerization thereof. Specific examples are dimorpholinodiethyl ether, bis-(dimethyl-aminoethyl)-ether, Dabco X-DM (Air Products) and N-ethyl morpholine. However, other catalysts may also be used prov

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