The effects of polydispersity, additives, impurities, free top layer and of surface roughness on the nucleation are studied for poly(ethylene oxide) located inside self-ordered nanoporous aluminum oxide (AAO). AAO pore diameters ranged from 400 nm to 25 nm. With the exception of a surface layer, none of the above factors is able to induce heterogeneous nucleation under confinement. Homogeneous nucleation remains the sole mechanism in pores having diameters below 65 nm. The internal pore surface roughness is small, which explains the minor effects of AAO surfaces on inducing heterogeneous nucleation especially within the smaller pores. The presence of oligomers shifts the homogeneous nucleation temperature to lower temperatures, reflecting the plasticizing effect of the oligomers on the liquid-to-glass temperature. (C) 2016 Elsevier Ltd. All rights reserved.