The effect of blend composition and deformation history on the development of structural hierarchy in crystallizable PET rich blends of PET/PEI from amorphous precursors was investigated. PET/PEI films are melt miscible consequently the addition of PEI to PET increases the glass transition temperature while slightly broadening it as a result of partial micro phase separation. The crystallization in these films were found to be affected by two main factors: I) blend composition ii) the extent of deformation imposed on the films leading to preferential orientation. In the absence of orientation, the increase of PEI fraction leads to decrease of crystallizability as expected from the dilution effect that spatially prevents the crystallizable polymer chains from coming together. Stretching process and resulting stress levels and crystallinity depend on the blend concentration. The increase of PEI at a given temperature increase the stress levels during stretching due to both the increase of Tg and its breadth. The increase PEI concentration lead to increase in highly defective crystallites due to intrusion of bulky PEI chains into the PET crystalline regions. Above 30% PEI, the blend crystallizability disappears. (C) 2016 Elsevier Ltd. All rights reserved.