Cooperative rearranging regions in polymeric materials: Relationship with the fragility of glass-forming liquids

From measurements performed on different polymeric glass-forming liquids using differential scanning calorimetry (DSC), we determined the values of the fragility index m according to the concept proposed by Angell. We calculated the average size of a cooperative rearranging region (CRR) at the glass transition i.e. z( T g), according to the definition proposed by Solunov. This quantity is linked to the Kauzmann temperature which was determined from dielectric spectroscopy or viscosimetry measurements performed on different samples including three-dimensional polymeric networks and linear polymer families with variable lateral chain lengths. By using our experimental data and others collected in the literature in order to scan a large domain of fragility values, we show that the fragility index m, characterising the glass-forming liquid, can be correlated to z( T g) which characterises the glass formed.