Degradable hydrazone curing agents and applications thereof

Abstract

This invention provides, among others, curing agents of Formulae (I) and (II), methods for preparing these curing agents, prepreg materials, degradable cross-linked polymers and reinforced composites made from these curing agents and epoxy resins, and methods for degrading and/or recycling the degradable polymers and reinforced composites.

1 . A curing agent comprising a compound of Formula I or a salt thereof: 
       
         
           
           
               
               
           
         
       
       wherein
 n is an integer greater than 1; 
 A is alkylene, alkylene-hetero-alkylene, alkenylene, alkenylene-hetero-alkenylene, alkylene-hetero-alkenylene, alkynylene, cycloalkylene, alkylene-cycloalkylene, alkylene-cycloalkylene-alkylene, alkenylene-cycloalkylene, alkenylene-cycloalkylene-alkenylen, alkylene-cycloalkylene-alkenylene, alkynylene-cycloalkylene, alkynylene-cycloalkylene-alkynylene, heterocycloalkylene, alkylene-heterocycloalkylene, alkylene-heterocycloalkylene-alkylene, alkenylene-heterocycloalkylene, alkenylene-heterocycloalkylene-alkenylene, alkylene-heterocycloalkylene-alkenylene, alkynylene-heterocycloalkylene, alkynylene-heterocycloalkylene-alkynylene, cycloalkenylene, alkylene-cycloalkenylene, alkylene-cycloalkenylene-alkylene, alkenylene-cycloalkenylene, alkenylene-cycloalkenylene-alkenylene, alkylene-cycloalkenylene-alkenylene, alkynylene-cycloalkenylene, alkynylene-cycloalkenylene-alkynylene, heterocycloalkenylene, alkylene-heterocycloalkenylene, alkylene-heterocycloalkenylene-alkylene, alkenylene-heterocycloalkenylene, alkenylene-heterocycloalkenylene-alkenylene, alkylene-heterocycloalkenylene-alkenylene, alkynylene-heterocycloalkenylene, alkynylene-heterocycloalkenylene-alkynylene, arylene, arylene-X-arylene, alkylene-arylene, alkylene-arylene-alkylene, alkenylene-arylene, alkenylene-arylene-alkenylene, alkylene-arylene-alkenylene, alkynylene-arylene, alkynylene-arylene-alkynylene, heteroarylene, heteroarylene-X-heteroarylene, heteroarylene-X-arylene, alkylene-heteroarylene, alkylene-heteroarylene-alkylene, alkenylene-heteroarylene, alkenylene-heteroarylene-alkenylene, alkylene-heteroarylene-alkenylene, alkynylene-heteroarylene, or alkynylene-heteroarylene-alkynylene; 
 X is alkylene, alkenylene, oxygen, sulfur, nitrogen, sulfoxide, sulfone, carbonyl, —C(O)O—, —OC(O)O—, —OC(O)NH—, —C(O)NH—, or —HNC(O)NH—; 
 each B independently is hydrogen, alkyl, cycloalkyl, heterocyclic, heterocycloalkyl, alkenyl, cycloalkenyl, aryl, arylalkyl, heteroaryl, heteroarylalkyl, alkyl-hetero-alkyl, alkyl-hetero-alkenyl, or alkynyl; 
 or, A and at least one B, together with the carbon atom to which they are bonded, form a saturated or unsaturated ring optionally containing at least one hetero ring atom of O, S, N, or P; 
 or, at least two B groups, together with A and carbon atoms to which A and B groups are bonded, form a saturated or unsaturated ring optionally containing at least one hetero ring atom of O, S, N, or P. 
 
     
     
         2 . The curing agent of  claim 1 , wherein n is 2, 3, or 4. 
     
     
         3 . The curing agent of  claim 2 , wherein n is 2. 
     
     
         4 . The curing agent of  claim 1 , wherein A is alkylene, alkylene-hetero-alkylene, alkenylene, alkenylene-hetero-alkenylene, alkylene-hetero-alkenylene, cycloalkylene, heterocycloalkylene, arylene, arylene-X-arylene, alkylene-arylene, alkylene-arylene-alkylene, alkenylene-arylene, alkenylene-arylene-alkenylene, alkylene-arylene-alkenylene, alkynylene-arylene, alkynylene-arylene-alkynylene, heteroarylene, heteroarylene-X-heteroarylene, heteroarylene-X-arylene, alkylene-heteroarylene, alkylene-heteroarylene-alkylene, alkenylene-heteroarylene, alkenylene-heteroarylene-alkenylene, alkylene-heteroarylene-alkenylene, alkynylene-heteroarylene, or alkynylene-heteroarylene-alkynylene. 
     
     
         5 . The curing agent of  claim 4 , wherein A is alkylene, arylene, heteroarylene, arylene-X-arylene, heteroarylene-X-heteroarylene, or heteroarylene-X-arylene. 
     
     
         6 . The curing agent of  claim 5 , wherein A is alkylene, arylene, or arylene-X-arylene. 
     
     
         7 . The curing agent of  claim 6 , wherein A is methylene, ethylene, propylene, phenylene, or phenylene-X-phenylene. 
     
     
         8 . The curing agent of  claim 1 , wherein X is alkylene, oxygen, sulfur, nitrogen, sulfoxide, sulfone, or —OC(O)O—. 
     
     
         9 . The curing agent of  claim 8 , wherein X is oxygen, sulfur, nitrogen, sulfoxide, or sulfone. 
     
     
         10 . The curing agent of  claim 1 , wherein each B independently is hydrogen, alkyl, alkyl-hetero-alkyl, alkenyl, alkenyl-hetero-alkenyl, alkenyl-hetero-alkyl, alkyl-hetero-alkenyl, or alkynyl. 
     
     
         11 . The curing agent of  claim 10 , wherein each B independently is hydrogen or alkyl. 
     
     
         12 . The curing agent of  claim 1 , wherein the compound of Formula I is: 
       
         
           
           
               
               
           
         
         
           
           
               
               
           
         
       
     
     
         13 . The curing agent of  claim 1 , wherein A and at least one B, together with the carbon atom to which they are bonded, form a 3- to 8-membered saturated or unsaturated ring optionally containing at least one hetero ring atom. 
     
     
         14 . (canceled) 
     
     
         15 . (canceled) 
     
     
         16 . (canceled) 
     
     
         17 . (canceled) 
     
     
         18 . (canceled) 
     
     
         19 . (canceled) 
     
     
         20 . (canceled) 
     
     
         21 . (canceled) 
     
     
         22 . A degradable cross-linked polymer comprising a cleavable cross-linking group derived from a curing agent of  claim 1  and an epoxy resin, wherein at least one amino group in the curing agent is fully reacted to lose both hydrogen atoms and form two bonds with the epoxy resin. 
     
     
         23 . The degradable cross-linked polymer of  claim 22 , wherein the epoxy resin comprises a glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl epoxy amine epoxy resin, trifunctional epoxy resin, tetrafunctional epoxy resin, novolac epoxy resin, o-cresol formaldehyde epoxy resin, aliphatic epoxy resin, alicyclic epoxy resin, or nitrogen-containing epoxy resin. 
     
     
         24 . The degradable cross-linked polymer of  claim 22 , wherein the cleavable cross-linking group is derived from 
       
         
           
           
               
               
           
         
       
       and at least one amino group of which is fully reacted to lose both hydrogen atoms. 
     
     
         25 . A recyclable prepreg composition or reinforced composite material, comprising a curing agent of  claim 1 , an epoxy resin, an auxiliary material, and a reinforcing material, wherein:
 the epoxy resin comprises glycidyl ether epoxy resin, glycidyl ester epoxy resin, glycidyl epoxy amine epoxy resin, trifunctional epoxy resin, tetrafunctional epoxy resin, novolac epoxy resin, o-cresol formaldehyde epoxy resin, aliphatic epoxy resin, alicyclic epoxy resin, or nitrogen-containing epoxy resin;   the reinforcing material comprises carbon nanotube, boron nitride nanotube, carbon black, metal nano-particle, metal oxide nanoparticle, organic nanoparticle, iron oxide, glass fiber, carbon fiber, natural fiber, synthetic fiber, or fabrics made therefrom; and   the auxiliary material comprises accelerator, diluent, plasticizer, toughening agent, thickening agent, coupling agent, defoamer, flatting agent, ultraviolet absorber, antioxidant, brightener, fluorescent agent, pigment, or filler.   
     
     
         26 . A method for degrading a degradable cross-linked polymer of  claim 24  or a recyclable prepreg composition or reinforced composite material of  claim 25 , comprising the steps of:
 (1) under the heating and stirring conditions, immersing the polymer in a mixed acid and solvent system to obtain a degradation solution; and 
 (2) using an alkaline solution to control the pH of the degradation solution. 
 
     
     
         27 . The method of  claim 26 , further comprising a step of washing and drying the precipitate and degradation solution after pH adjustment in step (2). 
     
     
         28 . The method of  claim 26 , wherein the acid comprises a hydrochloric acid, hydrobromic acid, hydrofluoric acid, acetic acid, trifluoroacetic acid, lactic acid, formic acid, propionic acid, citric acid, methanesulfonic acid, p-toluenesulfonic acid, nitric acid, sulfuric acid, sulfurous acid, phosphoric acid, perchloric acid, benzoic acid, salicylic acid, or phthalic acid; the alkali comprises lithium hydroxide, sodium hydroxide, potassium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate, potassium carbonate, potassium bicarbonate, or ammonia; each of the solvent for immersing the polymer in step (1) and the solvent for the alkaline solution in step (2) independently comprises methanol, ethanol, ethylene glycol, propanol, isopropanol, butanol, isobutanol, t-butanol, pentanol, hexanol, heptanol, octanol, nonanol, benzyl alcohol, phenethyl alcohol, p-hydroxymethyl benzene, m-hydroxymethyl benzene, o-hydroxy benzene, p-hydroxyethyl benzene, m-hydroxyethyl benzene, o-hydroxyethyl benzene, water, N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, dimethyl sulfoxide, tetrahydrofuran, methyl tetrahydrofuran, glycerol, or dioxane. 
     
     
         29 . The method of  claim 26 , wherein in step (1), the heating temperature is in the range of 80˜150° C., and the heating time is 4˜8 hours, and the mass concentration of the acid in the solvent system is 0.5˜20% (w/w); and in step (2), the temperature is in the range of 5˜50° C., the final pH is 6˜12, and the mass concentration of the alkali in the solvent is 5˜30% (w/w). 
     
     
         30 . A method for preparing a curing agent of  claim 1 , comprising reacting a compound of Formula I-a with hydrazine, wherein A and B in Formula I-a are the same as defined in  claim 1 . 
       
         
           
           
               
               
           
         
       
     
     
         31 . (canceled) 
     
     
         32 . The method of  claim 30 , wherein the mole ratio of the compound of Formula I-a or the compound of Formula II-a to hydrazine is 1:2˜100, and the reaction is conducted at a temperature of −20˜150° C.