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SUMh4ARYCharacterization of methylalumoxane (MAO) by gel permeation chromatography reveals the presence of different oligomeric products. Using suitable series of columns and alkylaluminium compounds with known molecular weight, it is possible to obtain the average molecular weights of most species which are present in a sample of MAO. The study of the chromatograms reveals modifications in composition of the MA0 oligomers in relation to the time of residence in solution at given temperatures.CCC 0025-1 16X/90/$03.00 _''

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.

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