SOLUTION PROPERTIES OF PERFLUOROPOLYETHER POLYMERS

Solution properties of fractions of a perfluoropolyether copolymer (PF PE Z) having the structure CF3-(OC2F4)(p)-(OCF2)(q)-O-CF3 have been st udied in two solvents, 1,1,2-trichloro-1,2,2-trifluoroethane (CFC 113) and perfluoroheptane, over a large molecular weight range. Two series of fractions having pig ratio equal to 0.54 and 1.27 were considered. The fractions, which were characterized by light scattering, vapour p ressure osmometry and viscosimetry, were found to be narrow. The coeff icients of the Mark-Houwink-Sakurada equation, [eta] = KM(a), were det ermined for both solvents in the molecular weight range between 8000 a nd 200 000. CFC 113 turned out to be a theta solvent (the Flory polyme r-solvent interaction parameter (chi) is close to 0.5) while perfluoro heptane behaves as a good solvent (chi = 0.28). The coil expansion fac tor alpha(3) in perfluoroheptane was also measured. The relationship b etween the hydrodynamic radius and the molecular weight was determined from dynamic light scattering. Finally, a parameter related to the ch ain stiffness, the characteristic ratio C-infinity, was also determine d. In the molecular weight range explored it was found that the stiffn ess is independent of the p/q ratio. PFPE Z polymer has a chain flexib ility similar to that of poly(oxyethylene) and larger than that of pol y(tetrafluoroethylene).