Poly( isobutylene) (PIB) chains with a radical at the chain end were graft-copolymerized on the poly(tetrafluoroethylene) (PTFE) surface in, vacuo at 77 K. The PIE chains tethered on the PTFE surface in vacuo were regarded as isolated chains from neighboring tethered PIE chains. The molecular motion of the ends of the isolated PIE chains was observed by an electron spin resonance (ESR) spectrometer in the temperature range from 3 to 125 K, which was lower than T-g of PIB, 200 K,(1) and two motion modes were found : One is a quantum tunneling of the methyl group located at the chain end at 3 K, and the other is an interconformation transition with freely rotating methyl group at the end at 77 K, where the transition rate was estimated to be 15 MHz at that temperature. The transition rate increased with an increase in temperature. The activation energy of the transition was estimated to be 370 J/mol. The high mobility and low activation energy was attributed to the isolation of PIE chains in vacuo.