This paper composes the dynamic mechanical and dielectric relaxation properties for Poly (5-indanyl methacrylate) (P51M), a polymer with a bulky side chain. Measurements were carried out from about -100 degrees C to near 250 degrees C. A secondary loss peak was observed in dielectric measurements at room temperature (20 degrees C at 0.1 Hz.), whereas nothing was resolved in the mechanical spectrum, A prominent alpha relaxation associated with the glass transition was also observed near 107 degrees C at 0.1 Hz. in the dielectric and the mechanical spectra. Dipolar dielectric loss overlapped with conductivity at high temperatures and low frequencies. A new method to split the conductive, interfacial, and dipolar contributions to the spectrum is proposed.