Polyurethane cast elastomers made of NCO prepolymers based on 2,4'-MDI and a process for their preparation

Abstract

Polyurethane (PUR) cast elastomers are produced from NCO-functional prepolymers based on 2,4′-MDI satisfying specific compositional requirements and amine-based chain extenders and/or crosslinking agents.

1 . A polyurethane elastomer comprising the reaction product of 
 a.) an NCO prepolymer which is the reaction product of 
 (1) a diphenylmethane diisocyanate having 
 (i) a 2,4′ isomer content of at least 85 wt. % and  
 (ii) from at least 1 to 25 wt. %, based on total weight of the NCO prepolymer of free monomeric 2,4′-diphenylmethane diisocyanate and  
 
 (2) a polyol having an OH number of from 20 to 200 mg KOH/g and a functionality of from 1.95 to 2.40,  
   b.) an amine-based chain extender and/or crosslinking agent, and    c.) optionally, auxiliary substances and additives.    
   
   
       2 . The polyurethane elastomer of  claim 1  in which component b) is selected from diethyltoluenediamine, 3,3′-dichloro-4,4′-diaminodiphenylmethane, isobutyl 3,5-diamino-4-chlorobenzoate, 4-methyl-2,6-bis(methylthio)-1,3-diaminobenzene, trimethylene glycol di-p-aminobenzoate, 4,4′-diamino-2,2′-dichloro-5,5′-diethyldiphenylmethane and mixtures thereof.  
   
   
       3 . A process for the production of the polyurethane elastomer of  claim 1  comprising adding 
 A) the amine-based chain extender and/or crosslinking agent and any optional auxiliary substance or additive to    B) the NCO prepolymer.    
   
   
       4 . An adhesive or sealant comprising the polyurethane elastomer of  claim 1 .  
   
   
       5 . A molded article produced from the polyurethane elastomer of  claim 1.