Process for producing uretidione dimers of isocyanates using catalysts which are bound to inorganic matrices

A process for preparing a dimer by the steps of:

• (a) cyclodimerizing a polyisocyanate in the presence a dimerization catalyst which is covalently bound to an insoluble inorganic matrix by contacting said polyisocyanate with said catalyst at a temperature of between about 20.degree. and about 130.degree. C. in a reaction to form an uretidione-containing cyclodimerized isocyanate wherein a portion of the isocyanate moieties comprising said polyisocyanate are converted to uretidione groups, and
• b) separating said catalyst from said cyclodimerized isocyanate in order to stop said reaction after a desired amount of isocyanate moieties in said polyisocyanate have been converted to uretidione moieties.

A process for preparing a dimer by cyclodimerizing an isocyanate in the presence a dimerization catalyst which is covalently bound to an insoluble inorganic matrix to form an uretidione-containing cyclodimerized isocyanate wherein said dimerization catalyst which is covalently bound to an insoluble inorganic matrix consists essentially of an inorganic substrate and having dimerization catalyst moieties chemically bound to said substrate, said catalyst moieties being selected from the group consisting of:

• aromatic tertiary amines, alkyl- and alkylamino-phosphines;
• and combinations thereof.

A process for preparing a dimer by cyclodimerizing an isocyanate in a reaction medium in the presence a dimerization catalyst which is covalently bound to an insoluble inorganic matrix substrate, said catalyst having between 0.1 and 10 miliequivalents of catalytic sites attributable to said functional groups per gram of said insoluble matrix, and said insoluble inorganic matrix being essentially insoluble in said reaction medium and having a pore diameter of between 5 and 500 nanometer, and a surface area of between 5 and 600 square meters per gram and a pore volume of between 0.5 and 1.2 cubic centimeters per gram of said insoluble inorganic matrix.