A thermodynamic study on molecular motion of the peroxide ends of isolated single polymer chains tethered to the surface of poly(tetrafluoroethylene) in vacuo

摘要

A thermodynamic study on the molecular motion of peroxide ends of isolated single polymer chains tethered to the surface of poly(tetrafluoroethylene) (PTFE) in vacuo is discussed. The five kinds of isolated single polymer chains were produced by a block copolymerization of PTFE with five kinds of monomers at the PTFE surface in vacuo. Copolymerized polyethylene (PE), polypropylene (PP), polyisobutylene (PIB), polybutadiene (PBD), and poly(methyl methacrylate) (PMMA) have radicals at the free ends of their chains. The end radicals were converted to peroxide radicals by contact with oxygen. The peroxide radicals were used as labels for detecting the molecular motion of the peroxide ends of isolated single polymer chains tethered to the PTFE surface in vacuo. A "train-tail" (immobile-mobile) transition of the peroxide ends of the isolated single polymer chains was analyzed using a new model in which the motional relaxation is due to the rotational relaxation of a "rotmer". The rotmer is the smallest rotational unit in the repeat unit forming an isolated single polymer chain and has a reduced molecular weight (M-ro). If the ratio of a population of freely rotating rotmers in the tail state to that of frozen rotmers in the train state can be expressed by Boltzmann statistics with transition free energy (Delta G), the transition enthalpy (Delta H-ro) and the transition entropy (Delta S-ro) of rotmers due to the train-tail transition can be estimated. These thermodynamic values and their linear relationships among Delta H-ro, transition temperature (T-ro), and M-ro were found. In contrast, Delta S-ro was constant in relation to both T-ro and M-ro. These relationships were interpreted to mean that the rotmers, which form isolated single polymer chains, are free from the neighboring rotmers which form neighboring isolated single polymer chains. [References: 18]