Fragility in amorphous blends of linear polymers

By analysing the specific heats and the mechanical characteristics of poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF) amorphous single-state blends in the glass transition region, it has been found that increasing PVDF content causes a small reduction of the fragility of these systems. The degree of fragility has been evaluated from ΔC_p /C_p,l, the normalized change of the heat capacity at T_g, and by modelling the mechanical α_a-relaxation. The observed behaviour has been ascribed to a more coherent structure of the blends due to strong specific interactions between PMMA and PVDF polymeric chains.