SOLUTION PROPERTIES OF PERFLUOROPOLYETHER POLYMERS

Solution properties of fractions of a perfluoropolyether copolymer (PFPE Z) having the structure CF3-(OC2F4)(p)-(OCF2)(q)-O-CF3 have been studied 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 pressure osmometry and viscosimetry, were found to be narrow. The coefficients of the Mark-Houwink-Sakurada equation, [eta] = KM(a), were determined for both solvents in the molecular weight range between 8000 and 200 000. CFC 113 turned out to be a theta solvent (the Flory polymer-solvent interaction parameter (chi) is close to 0.5) while perfluoroheptane behaves as a good solvent (chi = 0.28). The coil expansion factor alpha(3) in perfluoroheptane was also measured. The relationship between the hydrodynamic radius and the molecular weight was determined from dynamic light scattering. Finally, a parameter related to the chain stiffness, the characteristic ratio C-infinity, was also determined. In the molecular weight range explored it was found that the stiffness is independent of the p/q ratio. PFPE Z polymer has a chain flexibility similar to that of poly(oxyethylene) and larger than that of poly(tetrafluoroethylene).