Time and Temperature as Key Parameters Controlling Dynamics and Properties of Spatially Restricted Polymers

The annealing behavior of poly(propylene glycol) (PPG, M-W = 4000 g/mol) incorporated into the nanoporous aluminum oxide (AAO) membranes of different pore diameter was investigated by broadband dielectric spectroscopy (BDS) and differential scanning calorimetry (DSC). The presence of two subsets of molecules of different dynamics (interfacial and core) allows to produce conditions, where only one fraction (interfacial) is vitrified. Upon these conditions, annealed samples undergo continuous changes reflected in a shift of dielectric processes (segmental and normal mode). This unusual behavior was observed to be a reversible effect strictly governed by chain diffusion, indicated by the coupling between the equilibration constant (tau(anneal)) and the relaxation times of normal mode (tau(NM)). Despite the similarity in macroscopic changes observed upon the annealing of 2D and 1D materials [Napolitano, S.; et al. Nat. Commun. 2011, 2, 260], the examined behavior occurs accordingly to a totally different mechanism than the one reported for thin polymer films. Nevertheless, on the other hand, it reveals the possibility of exploring aging effects up to now not accessible for bulk materials.