We introduced methacrylic acid (MAA) into 80/20 trifluoroethyl methacrylate (TFEMA)-methyl methacrylate (MMA) copolymer in order to prepare heat-resistant cladding materials for plastic optical fiber based on poly(methyl methacrylate) (PMMA). As the content of MAA in the terpolymers increases, their T$_{g}$s increase to be higher values than those predicted by the Fox equation. Moreover, the interfacial adhesion between PMMA and the terpolymers, evaluated from the cross cut tape test, also increases from 1B to 4B classification. The results show that the MAA units, introduced in order to induce a specific intermolecular interaction, effectively contribute to increase the interfacial adhesion with PMMA as well as the thermal stability of the resultant copolymers.s.