Calorimetric studies on poly(ethylene glycol) Mn = 400 g mol(-1), encapsulated in polystyrene fibers show non-trivial crystallization behavior. Analysis, assuming constant Avrami exponent n, is unsuitable. Approach allowing for changes in the exponent n, requires assumption of the crystallization rate function, derived from the nucleation theory. Changes in Avrami exponent n, follow the changes in geometry of crystal growth and in nucleation mechanisms. Crystallization in micrometer fibers starts from heterogeneous nucleation with three-dimensional crystal growth - as in bulk - but changes to two and one-dimensional, terminated by homogenous nucleation. For bulk and in I and 0.6 mu m thick fibers, the approach evidences similar thermodynamic parameters. In 0.6 pm thick fibers, crystallization rate is lower due to higher energy barrier for diffusion, E-D = 10 kJ mol(-1) versus 8.7 kJ mol(-1) for bulk and 1 pm thick fibers. Additionally, fiber thickness depends not only on parameters of the electrospinning process but also on the thermal history. (C) 2016 Elsevier Ltd. All rights reserved.