Bonded composite structures

A bonded, composite structure comprising at least one polymeric substrate selected from the group consisting of polyester polymers and polyolefin polymers, said substrate having a solid material adhered thereto by an interposed bonding material which is a thin polymer zone having a thickness of up to about 500 Angstroms and consisting essentially of an organic polycarbodiimide polymer containing at least two carbodiimide groups, each linked directly to an aromatic nucleus through a carbodiimide nitrogen, said polycarbodiimide polymer containing about 1 to 35 weight percent carbodiimide groups.