Cooperativity range and fragility in vitreous polymers

Abstract In this work, dielectric and viscosimetric investigations were performed on three different kinds of polymeric structures, i.e. three samples of poly[oxy(2,2 dialkylpropane-1,3-diyl)carboxylbisphenyl-4,4′ dicarbonyl], three samples of poly-methyl (α-n-alkyl) acrylate, and four samples of unsaturated polyester resins. Using the strong-fragile concept, we characterized the glass-forming liquid by means of the fragility index m. From the random walk model (RWM), it is possible to define the quantity ΔT = (Tc − Tk), which characterizes the cooperative range, Tc being a critical temperature and Tk being the Kauzmann temperature. In this work, we show that the cooperative range and the fragility index are correlated, and more precisely that the greater the quantity (Tc − Tk), the smaller the fragility index m.