From small molecules to polymers: Relaxation behavior of n-butyl methacrylate based systems

Calorimetric and dielectric data for a series of n-butyl methacrylate (nBMA) based systems are presented. Dynamic glass transition (α) and secondary relations (β, β′, γ) are studied for monomer, dimer, oligomers as well as polymers with a narrow molecular weight distribution. Fragility m and cooperativity N_α increase with decreasing degree of polymerization P indicating that the cooperative character of the α motions increases. All glass transition parameters change smoothly with P without clear peculiarities that would indicate a transition from small molecules to polymers. Relations between α dynamics and the different secondary relaxations in these series are discussed. The results are compared with the predictions of different approaches aimed to understand the nature of the dynamic glass transition and the interaction between localized and cooperative dynamics in glass-forming liquids.