Ternary blends of PEN with PEI and PEEK were investigated in order (i) to eliminate the neck formation that occurs during deformation in the rubbery state while maintaining the strain induced crystallizability, (ii) to increase the glass transition temperature. For this purpose, we investigated the uniaxial deformation behaviour of miscible and immiscible PEN rich ternary blend films stretched above their glass transition temperatures. The increase of PEI concentration increased glass transition temperature and eliminated the neck formation while decreasing crystallizability. In order to compensate for the latter, the concentration of PEEK was increased which recovered the strain hardening (crystallization) and associated self levelling behaviour while boosting the glass transition temperatures of the final films. PEN crystallization is hindered in blends containing 40% PEI. In these blends, although PEEK can be crystallized at concentrations as low as 10%, PEN remains amorphous. Upon annealing both PEEK and PEN separate from PEI and crystallize into their own domains.
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