Latent curing agent and epoxy compositions containing the same

Abstract

A latent curing agent obtained by the reaction of a coumarin compound with an amine.

1 . A latent curing agent obtained by the reaction of a coumarin compound of the general formula (1) 
       
         
           
           
               
               
           
         
       
       wherein X and Y can be independently H, an alkyl group, a heteroalkyl group, an aromatic group, a heteroaromatic group or an acetyl group, and Z can be H, OH, an alkyl group, a heteroalkyl group, an aromatic group, a heteroaromatic group, with an amine of the general formula (2)
   (H 2 N-A) a -B  (2)
 
 
       wherein “a” is 1 or 2,
 A can be an alkylene group, a heteroalkylene group, an aromatic group, a heteroaromatic group, 
 and B can be an alkyl group (if a=1), an alkylene group (if a=2), a heteroalkyl group (if a=1), a heteroalkylene group (if a=2), an aromatic group, a heteroaromatic group, a hydroxyl group (if a=1), a secondary amino group (if a=2), O or S (if a=2), whereby B has the valency “a”, 
 or wherein B alone or where A and B together form a ring system selected from an aliphatic ring system, a heteroaliphatic ring system, or an aromatic ring system. 
 
     
     
         2 . A latent curing agent according to  claim 1  wherein the amine is a primary monoamine which is reacted at a stoichiometric ratio of 2 equivalents of amine to 1 equivalent of the coumarin. 
     
     
         3 . A latent curing agent according to  claim 1  wherein the amine is a primary diamine which is reacted at a stoichiometric ratio of 1 equivalents of amine to 1 equivalent of the coumarin. 
     
     
         4 . A latent curing agent according to  claim 3  wherein the diamine is selected from the group consisting of tetramethylenediamine, hexamethylenediamine, 2-methylpentamethylene-diamine, nonamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4-trimethylhexamethylenediamine, 2,4,4-trimethylhexamethylenediamine, 5-methyl-nonamethylenediamine, 1,3-bis(aminomethyl)cyclohexane, 1,4-bis(aminomethyl)-cyclohexane, 1-amino-3-aminomethyl-3,5,5-trimethyl-cyclohexane, bis(4-aminocyclo-hexyl)methane, bis(3-methyl-4-aminocyclohexyl)methane, 2,2-bis(4-aminocyclohexyl)-propane, polyoxytetramethylenediamine, triethyleneglycoldiamine, polyoxyethylene-diamines, polyoxyethylenetriamines, polyoxypropylenediamines, m-xylylenediamine, p-xylylenediamine (XDA), 1,4-bis(aminopropyl)piperidine, 1-propanamine, 3,3′-(oxy bis(2,1-ethanediyloxy))bis-1-propan-amine, diaminopropylated diethylene glycol, 1,3-diaminocyclohexane, 1,4-diaminocyclohexane, di(aminomethyl)cyclohexane, 1-amino-3-aminomethyl-3,5,5-trimethylcyclohexane, 4,4′-diamino-3,3′-dimethyldicyclohexylmethane, cyclohexylenediamine, 4,4′-diamino-dicyclohexylmethane, 4,4′-isopropylidenedicyclohexyldiamine, and 3,3′-dimethyl-4,4′-isopropylidenedicyclohexyldiamine or mixtures thereof. 
     
     
         5 . A latent curing agent according to  claim 2  where the monoamine is selected from the group consisting of butylamine, pentylamine, hexylamine, heptylamine, octylamine, nonylamine, decylamine, dodecylamine, cyclohexylamine, aminomethylcyclohexane, N-aminoethyl-piperidine, 1-amino-3,5,5-trimethyl-cyclohexane, benzylamine, aminophenol, 2-aminoethanol, 3-amino-1-propanol, 4-amino-1-butanol, 5-amino-1-pentanol or mixtures thereof. 
     
     
         6 . A latent curing agent according to  claim 1  wherein the coumarin is 1-benzopyran-2-on. 
     
     
         7 . A curable composition comprising
 (a) at least one reactive epoxy resin,   (b) optionally a flexibilizing agent,   (c) optionally a reactive diluent,   (d) at least one finely divided filler,   (e) a latent curing agent according to  claim 1 ,   (f) optionally an accelerator,   (g) optionally a blowing agent.   
     
     
         8 . A method of making a curing agent according to  claim 1  comprising the steps of
 (a) mixing at least one of the mono- or diamine with the coumarin, optionally in the presence of an polar solvent, 
 (b) heating the reaction mixture to a temperature between room temperature and 70° C. until the monoamine or diamine has completely reacted with the coumarin, 
 (c) precipitating the reaction mixture into a nonsolvent for the coumarin amine reaction product, 
 (d) filtering the precipitate from the liquid phase and 
 (e) drying the coumarin amine reaction product. 
 
     
     
         9 . A method according to  claim 8  where the solvent is selected from methanol, ethanol, acetone, dimethylsulphoxide (DMSO), N,N-dimethylacetamide (DMA) and tetrahydro-furane (THF) or mixtures thereof. 
     
     
         10 . A method according to  claim 8  comprising the addition of a basic catalyst. 
     
     
         11 . A method according to  claim 9  wherein the basic catalyst is a heterocyclic compound having an amidine bonding.