Sandwich structures including hybrid adhesives and methods thereof

A method of making an epoxy-phthalonitrile copolymer, comprising:

• combining an epoxy-functional monomer and an amino-phthalonitrile functional monomer, wherein the amino-phthalonitrile functional monomer contains a single phthalonitrile functional group;
• heating the epoxy-functional monomer and the amino-phthalonitrile functional monomer to a first melting temperature to form a solution;
• mixing the solution until it is homogenous;
• and
• heating the solution at a second temperature to cure the epoxy-phthalonitrile copolymer.

A sandwich panel composition, comprising:

• a honeycomb core;
• a first facesheet panel affixed to a first outer edge of the honeycomb core;
• a second facesheet panel affixed to a second outer edge of the honeycomb core;
• a first phthalonitrile-epoxy adhesive layer between the first facesheet panel and the first outer edge of the honeycomb core, wherein the first phthalonitrile-epoxy adhesive layer comprises an amino-phthalonitrile monomer or amino-phthalonitrile polymer containing a single phthalonitrile functional group;
• and
• a second phthalonitrile-epoxy adhesive layer between the second facesheet panel and the second outer edge of the honeycomb core, wherein the second phthalonitrile-epoxy adhesive layer comprises an amino-phthalonitrile monomer or amino-phthalonitrile polymer containing a single phthalonitrile functional group.