Methods for enhancing the bonding strength of thermoset adhesives and sealants via disulfide dynamic chemistry

Abstract

Curable compositions for dynamic epoxy-based thermoset adhesives and/or sealants are provided. Methods of applying the compositions to form strong, low-stress, cured adhesive polymer films are also provided. The cured polymer films use crosslinkers that include disulfide and carbon-nitrogen bonds, wherein the disulfide bonds impart dynamic chemistry to the polymer network structure in order to the achieve adaptable thermoset adhesives and sealants.

What is claimed is: 
     
         1 . An adhesive composition comprising:
 a polymer having the structure:   
       
         
           
           
               
               
           
         
         where R is a hydrogen atom or a methyl group and n represents the number of repeat units in the polymer; and 
         a crosslinker comprising at least two reactive amine groups and a disulfide bond. 
       
     
     
         2 . The composition of  claim 1 , wherein the polymer is poly[(phenyl glycidyl ether)-co-formaldehyde]. 
     
     
         3 . The composition of  claim 1 , wherein the poly[(phenyl glycidyl ether)-co-formaldehyde] has a number average molecular weight of at least 320. 
     
     
         4 . The composition of  claim 2 , wherein the poly[(phenyl glycidyl ether)-co-formaldehyde] has a number average molecular weight in the range from 320 to 6000. 
     
     
         5 . The composition of  claim 1 , wherein the crosslinker has the structure H 2 N—X—S—S—X—NH 2 , wherein X represents an aliphatic or aromatic hydrocarbon group having from one to ten carbon atoms. 
     
     
         6 . The composition of  claim 5 , wherein the crosslinker is cystamine. 
     
     
         7 . The composition of  claim 1 , wherein the at least two reactive amine groups are hydrazine groups. 
     
     
         8 . The composition of  claim 1 , wherein the crosslinker is cystamine. 
     
     
         9 . The composition of  claim 1 , wherein the mole ratio of amine groups on the crosslinker to epoxy groups on the polymer is at least 1:2. 
     
     
         10 . A crosslinked polymer film comprising the product of crosslinking epoxy groups of a polymer having the structure: 
       
         
           
           
               
               
           
         
         where R is a hydrogen atom or a methyl group and n represents the number of repeat units in the polymer, with the reactive amine groups of a crosslinker comprising at least two reactive amine groups and a disulfide bond. 
       
     
     
         11 . The polymer film of  claim 10 , wherein the polymer is poly[(phenyl glycidyl ether)-co-formaldehyde]. 
     
     
         12 . The polymer film of  claim 11 , wherein the poly[(phenyl glycidyl ether)-co-formaldehyde] has a number average molecular weight in the range from 320 to 6000. 
     
     
         13 . The polymer film of  claim 10 , wherein the crosslinker has the structure H 2 N—X—S—S—X—NH 2 , wherein X represents an aliphatic or aromatic hydrocarbon group having from one to ten carbon atoms. 
     
     
         14 . The polymer film of  claim 10 , wherein the crosslinker is cystamine. 
     
     
         15 . The composition of  claim 12 , wherein the crosslinker is cystamine. 
     
     
         16 . A method of forming a film on a substrate, the method comprising:
 applying a composition comprising a polymer having the structure:   
       
         
           
           
               
               
           
         
         where R is a hydrogen atom or a methyl group and n represents the number of repeat units in the polymer, and a crosslinker comprising at least two reactive amine groups and a disulfide bond to a surface of the substrate; and 
         annealing the applied composition at a temperature that induces epoxy groups of the polymer to react with amine groups of the crosslinker to form a covalent bond and that further induces the cleavage and reformation of the disulfide bonds. 
       
     
     
         17 . The method of  claim 16 , wherein the polymer is poly[(phenyl glycidyl ether)-co-formaldehyde]. 
     
     
         18 . The method of  claim 17 , wherein the poly[(phenyl glycidyl ether)-co-formaldehyde] has a number average molecular weight in the range from 320 to 6000. 
     
     
         19 . The method of  claim 16 , wherein the crosslinker has the structure H 2 N—X—S—S—X—NH 2 , wherein X represents an aliphatic or aromatic hydrocarbon group having from one to ten carbon atoms. 
     
     
         20 . The method of  claim 16 , wherein the crosslinker is cystamine.