Thermovolumetric properties versus glass transition temperature of diolic perfluoropoly(oxyethylene-ran-oxymethylene) oligomers

The specific volume v from – 20 to 60°C and the glass transition temperature Tg was measured of a homologous series of linear diolic oligomer fractions constituted by a random perfluoro‐poly(oxyethylene‐ran‐oxymethylene) chain of fairly uniform composition and two CH2OH end units, with a degree of polymerization x̄n from 5,4 to 165,9 (M̄n from 400 to 14900). An empirical parabolic v = v(T, wE) equation of state is found as satisfactory, wE being the end copolymeric composition expressed as weight fraction of end units, inversely proportional to M̄n. A predictive bridge is then established between thermovolumetric parameters and Tg, through a highly reliable linear relation vg – Tg between experimental Tg and calculated specific volume at Tg, which leads with measurable parameters to a Tg – wE relation, in very good agreement with experimental results. For the range of M̄n above 1500–2000, simpler relations can also be used to a good approximation, which are discussed in their physical meaning and validity.