Three copolymeric perfluoroethers with the structure CF3[(OCF2CF2)p(OCF2)q] OCF3, having different p/q ratios, have been fractionated. The fractions obtained have been characterized by Gel Permeation Chromatography and 19F‐NMR. The viscosity η the specific volume v and the glass transition temperature, Tg have been measured by standard techniques for all the above samples as well as for some other perfluorinated polyethers.The temperature dependence of viscosity of the unfractionated samples is described by the W.L.F. equation. The values of fg (fractional free‐volume at Tg) and of af (free‐volume expansion coefficient) are independent of composition, for p/q ratios from 0.53 to 1.15. The critical molecular weight, Mc, is of the order of 8–9,000. From the molecular weight dependence of specific volume, the contribution to the molar volume of the in‐chain CF2 group and the excess molar free volume of the chain ends have been determined. The limiting value of Tg for an infinite molecular weight polymer was found to depend linearly on the compositional ratio O/C and the extrapolated values for polytetrafluoroethylene and for the homopolymer (CF2O)n were found to be respectively 200 K and 120 K.

Processing of virgin and recycled polytethylene terephthalate) (PET) in a twin screw extruder evidences the degradative effect caused by thermal decomposition of polytvinyl chloride) (PVC) and other impurities, e.g. adhesives, at the processing temperature. Lower melt viscosity and molecular weight, along with higher carboxylic end group concentration, were observed for recycled PET, the extent depending on PET purity. In an attempt to investigate the correlation between the kinetics of degradation phenomena and the level of thermomechanical stress, a novel dynamic method of evaluating thermal stability in processing conditions was developed. Such a method allows the achievement of long equivalent residence times while using lab-scale extruders. As a result of these experiments, PVC-rich recycled PET was shown to reach very low melt viscosity after less than 10 min in processing conditions, while virgin PET retained high viscosity even after 30 min. 5 10 15 20 25 90 Residence time (min) Rg. 4. Effmt of CLE on intrinsic viscosity. 50(1oO, 5 . . . . 0 5 10 i s Po 25 90 35 Residence time (min) Rg. 5. E f f ' t o f CIE on weight-average molecular weight

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Solution characterization of the thermotropic liquid–crystalline copolyester synthesized from terephthalic acid, phenyl hydroquinone, and (1‐phenylethyl) hydroquinone (2 : 1 : 1) has been performed. Viscometry, size exclusion chromatography, and light scattering have been carried out under the optimal conditions found for measurement: 85°C in a 50/50 mixture by weight of phenol/1,2,4‐trichlorobenzene. The absolute weight‐average molecular weight from light‐scattering measurements served for calibration of indirect methods of charac‐terization (e.g., the limiting viscosity number [η] is related to the molecular weight by [η] = 5.10 × 10−4 Mw0.72), and the molecular weight per unit chain length, \documentclass{article}\pagestyle{empty}\begin{document}$ \bar M_L * $\end{document}, from light scattering and size exclusion chromatography (SEC) is found to be 28 Å−1, consistent with theoretical expectations. The calculated persistence length q is 28 Å. Moreover, the meth‐odology of SEC characterization enables the kinetics of solid‐state postpolymerization of this liquid‐crystalline copolyester to be studied. © 1993 John Wiley & Sons, Inc.