Epoxy resins having reversible crosslinks

A method for the preparation of insoluble, infusible epoxy resins containing reversible crosslinks comprising the steps of:

• (a) forming a reaction mixture of
• (i) an epoxy compound having two or more epoxy groups, and
• (ii) a crosslinking agent containing two or more epoxy-reactive groups and further containing a disulfide bond, said crosslinking agent being selected from compounds having the formula
• Q--X--S--S--X--Q
• where Q is an epoxy-reactive functional group selected from ##STR22## and X is a divalent aromatic or aliphatic hydrocarbon radical of one to ten carbon atoms, and
• (b) curing said reaction mixture under conditions conducive to the formation of a crosslinked resin.

A method for the preparation of insoluble, infusible epoxy resins containing reversible crosslinks and for the recovery of soluble polymers therefrom comprising the steps of:

• (a) forming a reaction mixture of
• (i) an epoxy compound having two or more epoxy groups, and
• (ii) a crosslinking agent containing two or more epoxy-reactive groups and further containing a disulfide bond,
• (b) curing said reaction mixture under conditions conducive to the formation of a crosslinked resin, and
• (c) cleaving the disulfide bonds in said resin by reducing said resin in the presence of solvent and a reducing agent and thereby forming a soluble polymer.

A method for the preparation of insoluble, infusible epoxy resins containing reversible crosslinks and for the recovery of soluble polymers therefrom comprising the steps of:

• (a) forming a reaction mixture of
• (i) an epoxy compound having two or more epoxy groups, and
• (ii) a crosslinking agent containing two or more epoxy-reactive groups and further containing a disulfide bond, said crosslinking agent being selected from compounds having the formula
• Q--X--S--S--X--Q
• where Q is an epoxy-reactive functional group selected from ##STR29## and X is a divalent aromatic or aliphatic hydrocarbon radical of one to ten carbon atoms,
• (b) curing said reaction mixture under conditions conducive to the formation of a crosslinked resin, and
• (c) cleaving the disulfide bond in said resin by reducing said resin in the presence of a solvent and a reducing agent selected from the group consisting of trialkyl and triaryl phosphine, alkali metal borohydride, alkali metal aluminum hydride and alkali metal trialkyl borohydride, and thereby forming a soluble polymer.

A method for preparing insoluble, infusible epoxy resins containing reversible crosslinks, recovering soluble polymers therefrom and reforming the insoluble, infusible resin, comprising the steps of:

• (a) forming a reaction mixture of
• (i) an epoxy compound having two or more epoxy groups, and
• (ii) a crosslinking agent containing two or more epoxy-reactive groups and further containing a disulfide bond,
• (b) curing said reaction mixture under conditions conducive to the formation of a crosslinked resin,
• (c) cleaving the disulfide bonds in said resin by reducing said polymer in the presence of a solvent and a reducing agent, and
• (d) reforming the said disulfide bonds by oxidizing the cleaved product formed in step (c).

A method for preparing insoluble, infusible epoxy resins containing reversible crosslinks, recovering soluble polymers therefrom and reforming the insoluble, infusible resin, comprising the steps of:

• (a) forming a reaction mixture of
• (i) an epoxy compound having two or more epoxy groups, and
• (ii) a crosslinking agent containing two or more epoxy-reactive groups and a disulfide bond, said crosslinking agent being selected from compounds having the formula
• Q--X--S--S--X--Q
• where Q is an epoxy-reactive functional group selected from ##STR30## and X is a divalent aromatic or aliphatic hydrocarbon radical of one to ten carbon atoms,
• (b) curing said reaction mixture under conditions conducive to the formation of a crosslinked resin,
• (c) cleaving the disulfide bonds in said resin by reducing said resin in the presence of a solvent and a reducing agent selected from the group consisting of trialkyl and triaryl phosphine, alkali metal borohydride, alkali metal aluminum hydride and alkali metal trialkyl borohydride and thereby forming a soluble polymer containing thiol groups, and
• (d) reforming the said disulfide bonds by oxidizing the soluble, thiol-containing polymer formed in step (c) in the presence of an oxidizing agent selected from iodine, hydrogen peroxide, potassium iodide, air, and oxygen.

A method for preparing insoluble, infusible epoxy resins containing reversible crosslinks, recovering soluble polymers therefrom and modifying those soluble polymers comprising the steps of:

• (a) forming a reaction mixture of
• (i) an epoxy compound having two or more epoxy groups, and
• (ii) a crosslinking agent containing two or more epoxy-reactive groups and further containing a disulfide bond,
• (b) curing said reaction mixture under conditions conducive to the formation of a crosslinked resin,
• (c) cleaving the disulfide bonds in said resin by reducing said resin in the presence of a reducing agent and thereby forming a soluble, thiol-containing polymer, and
• (d) modifying the soluble, thiol-containing polymers obtainded in step (c).

A method for preparing insoluble, infusible epoxy resins containing reversible crosslinks, recovering soluble polymers thereform and reforming the insoluble, infusible resin, comprising the steps of:

• (a) forming a reaction mixture of
• (i) an epoxy compound having two or more epoxy groups, and
• (ii) a crosslinking agent containing two or more epoxy-reactive groups and a disulfide bond, said crosslinking agent being selected from compounds having the formula
• Q--X--S--S--X--Q ,
• where Q is an epoxy-reactive functional group selected from ##STR31## and X is a divalent aromatic or aliphatic hydrocarbon radical of one to ten carbon atoms,
• (b) curing said reaction mixture under conditions conducive to the formation of a crosslinked resin,
• (c) cleaving the disulfide bond in said resin by reducing said resin in the presence of a reducing agent selected from the group consisting of trialkyl and triaryl phosphine, alkali metal borohydride, alkali metal aluminum hydride and alkali metal trialkyl borohydride and thereby forming a soluble, thiol-containing polymer;
• and
• (d) modifying the soluble, thiol-containing polymer obtained in step (c) by
• (i) crosslinking with bis-maleimides of aromatic diamines or with other bifunctional activated vinyl crosslinking agents;
• or
• (ii) crosslinking with dihalides to form stable thioether linkages in the resin;
• or
• (iii) reacting, in base-catalyzed reactions, with diepoxides or virgin epoxy resins to optimize the properties of the polymer and obtain interpenetrating polymer networks (IPN);
• or
• (iv) grafting of rubber particles which can become covalently bound to the resin and impart enhanced toughness.

A method for the conversion to a polymer of a crosslinked, insoluble, infusible epoxy resin formed by curing

• (i) an epoxy compound having two or more epoxy groups, and
• (ii) a crosslinking agent containing two or more epoxy-reactive groups and further containing a disulfide bond, comprising the steps of
• (a) cleaving the disulfide bonds in said resin by reducing said resin in the presence of a solvent and a reducing agent, and
• (b) reforming the disulfide bonds by oxidizing the cleaved mixture formed in step (a).

A method for the conversion to a polymer of a crosslinked, insoluble, infusible epoxy resin formed by curing

• (i) an epoxy compound having two or more epoxy groups, and
• (ii) a crosslinking agent containing two or more epoxy-reactive groups and further containing a disulfide bond, comprising the steps of
• (a) cleaving the disulfide bonds in said resin by reducing said resin in the presence of a solvent and a reducing agent selected from the group consisting of trialkyl and triaryl phosphine, alkali metal borohydride, alkali metal aluminum hydride and alkali metal trialkyl borohydride, and thereby forming a soluble thiol-containing polymer, and
• (b) reforming the disulfide bonds by oxidizing the cleaved mixture formed in step (a) in the presence of an oxidizing agent selected from iodine, hydrogen peroxide, potassium iodide, air, and oxygen.

A method for conversion to a polymer of a crosslinked, insoluble, infusible epoxy resin formed by curing

• (i) an epoxy compound having two or more epoxy groups,
• (ii) a crosslinking agent containing two or more epoxy-reactive groups and further containing a disulfide bond, comprising the steps of:
• (a) cleaving the disulfide bonds in said crosslinked resin by reducing said resin in the presence of a solvent and a reducing agent;
• and
• (b) modifying the soluble polymer obtained in step (a).

A method for conversion to a polymer of a crosslinked, insoluble, infusible epoxy resin formed by curing

• (i) an epoxy compound having two or more epoxy groups, and
• (ii) a crosslinking agent containing two or more epoxy-reactive groups and further containing a disulfide bond, comprising the steps of
• (a) cleaving the disulfide bonds in said crosslinked resin by reducing said resin in the presence of a solvent and a reducing agent selected from the group consisting of trialkyl and triaryl phosphine, alkali metal borohydride, alkali metal aluminum hydride and alkali metal trialkyl borohydride, thereby forming a soluble, thiol-containing polymer, and
• (b) modifying the soluble, thiol-containing polymer obtained in step (a) by
• (i) crosslinking with bis-maleimides of aromatic diamines or with other bifunctional activated vinyl crosslinking agents;
• or
• (ii) crosslinking with dihalides to form stable thioether linkages;
• or
• (iii) reacting, in base-catalyzed reactions, with diepoxides or virgin epoxy resins to optimize the properties of the resin and obtain interpenetrating polymer networks (IPN);
• or
• (iv) grafting of rubber particles which can become covalently bound to the resin and impart enhanced toughness.

An insoluble, infusible epoxy resin containing reversible crosslinks formed by curing

• (i) an epoxy compound having two or more epoxy groups, and
• (ii) a crosslinking agent containing two or more epoxy-reactive groups and a disulfide bond, said crosslinking agent being selected from compounds having the formula
• Q--X--S--S--X--Q ,
• where Q is an epoxy-reactive functional group selected from ##STR32## and X is a divalent aromatic or aliphatic hydrocarbon radical of one to ten carbon atoms, under conditions conducive to the formation of a crosslinked polymer.

A solubilized, thiol-containing epoxy polymer obtained from an insoluble, infusible epoxy resin containing reversible crosslinks, said resin having been formed by curing

• (i) an epoxy compound having two or more epoxy groups, and
• (ii) a crosslinking agent containing two or more epoxy-reactive groups, said crosslinking agent being selected from compounds having the formula
• Q--X--S--S--X--Q,
• where Q is an epoxy-reactive functional group selected from ##STR37## and X is a divalent aromatic or aliphatic hydrocarbon radical of one to ten carbon atoms, under conditions conducive to the formation of a crosslinked resin and said resin having been solubilized by cleaving the disulfide bonds in said resin by reducing said bonds in the presence of a reducing agent selected from the group consisting of trialkyl and triaryl phosphine, alkali metal borohydride, alkali metal aluminum hydride and alkali metal trialkyl borohydride.