Polyurethane elastomers made using mixtures of aliphatic diol chain extender and secondary amine
Polyurethane elastomers are formed by curing a reaction mixture containing at least one polyisocyanate at least one polyol, an aliphatic diol chain extender and a small amount of a secondary amino compound that may have none or one or more hydroxyl groups. The reaction is catalyzed with a metal catalyst. In certain embodiments, the catalyst is an organozirconium, organotitanium or tertiary amine-based catalyst. The presence of the secondary amine compound in those cases provides for a good surface appearance and good physical properties.
1. A process for preparing a noncellular or microcellular polyurethane elastomer, comprising 1) forming a reaction mixture containing a) one or more aliphatic diols having a hydroxyl equivalent weight of from about 30 to about 100, b) one or more secondary amine compounds selected from the group consisting of 2-(methylamino)ethanol, 2-(ethylamino)ethanol, 2-(propylamino)ethanol, 1-methyl-2-(methylamino) ethanol, 1-methyl-2-(ethylamino) ethanol, 1-methyl-2-(propylamino)ethanol, 1-ethyl-2-(methylamino)ethanol, 1-ethyl-2-(ethylamino)ethanol, 1-ethyl-2-(propylamino)ethanol, N-hydroxyethylbenzylamine, N-hydroxypropylbenzylamine, or a mixture of any two or more thereof and at least one of c-1) and c-2), wherein c-1) includes one or more organic polyisocyanates having an isocyanate content of at least 15% by weight and one or more polyols having a hydroxyl equivalent weight of at least 250 and c-2) includes one or more isocyanate-terminated prepolymers or quasi-prepolymers having an isocyanate content of less than 15% formed in a reaction of an organic polyisocyanate with one or more polyols having a hydroxyl equivalent weight of at least 250 and 2) curing the reaction mixture in the presence of a catalyst to form the polyurethane elastomer, wherein:
A) the reaction mixture contains no more than 0.25% by weight of a chemical blowing agent;
B) the secondary amine compound contains one or two secondary amino groups, is devoid of primary amino groups, and the combined number of secondary amino groups and hydroxyl groups is from one to two;
3) the weight ratio of component a) to component b) is from 60:40 to 95:5;
3) the hard segment content of the polyurethane elastomer is from 30 to 60% by weight; and
4) the isocyanate index is from 70 to 125.
2. The process of claim 1 , wherein component a) constitutes from 6 to 15% of the weight of the reactive materials in the reaction mixture.
3. The process of claim 1 , wherein components a) and b) are present in a weight ratio of from 80:20 to 95:5.
4. The process of claim 1 , wherein the reaction mixture contains no mercury-containing catalyst.
5. The process of claim 1 , wherein the catalyst includes at least one organozirconium or organotitanium compound.
6. The process of claim 1 , wherein the catalyst includes at least one tertiary amine-based catalyst.
7. The process of claim 1 , wherein the reaction mixture contains less than 0.5% by weight of a crosslinker and less than 0.25% by weight of compounds that contain one or more primary amino groups.