The surface-modified diamond and PET film underwent photopolymerization rapidly with a binder agent to afford coating films of interpenetrating network (IPN) structure. The coating films thus formed exhibit higher tensile strength, thermal stability, and adhesion strength to the PET film. The inert surfaces of pristine diamond (PD) and PET film were modified by different chemicals and procedures to introduce epoxide and methacryloyl groups, respectively, on their surfaces. A coating agent consisting of an epoxide group containing modified diamond (called ED), a binder agent, and photoinitiators was prepared. After applying the coating agent to the substrate (a glass plate or a methacryloyl group containing PET film, MMA-PET) and degassing under reduced pressure, the thin film of the coating agent was exposed to UV light (lambda(max); 365 nm) at room temperature to yield a coating film of IPN-structure. The tensile strength and thermal properties of the ED-containing free coating film (called free film) increased with the amount of ED embedded, whereas the strength of the PD-containing free film decreased with the amount of PD embedded. The adhesion strength of the coating film on the MMA-PET improved significantly by the free radical polymerization of the methacryloyl groups on the MMA-PET and the acrylate resin in the binder agent. The surface photoreactions of ED and MMA-PET with the binder agent were confirmed by modeling. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 119: 693-701, 2011