Accelerated and depressed aging of PS blocks under 3D nanoconfinement in diblock copolymers

In this work, physical aging of polystyrene (PS) blocks in two representative diblock copolymers were investigated by a differential scanning calorimeter. Aging of PS blocks was remarkably accelerated in polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA), compared to the homo-PS. In addition, the enthalpy results demonstrate that the aging rate of PS blocks in PS-b-PMMA increases with larger PMMA/PS mole ratio. On the other hand, the aging rate of PS blocks in polystyrene-block-poly(n-butyl methacrylate) (PS-b-PnBMA) is lower than the relaxation rate of corresponding neat PS. Together with morphology in theses copolymers, the aging results imply that the hard three-dimensional confinement induced by the PMMA blocks accelerates the aging rate of relatively soft PS blocks in copolymer, while the sluggish aging of PS blocks in PS-b-PnBMA is attributed to the extremely soft confinement formed by PnBMA blocks, which was liquid in the aging process due to its low glass transition temperature.