Time‐dependent morphologies and viscoelastic properties of block copolymers

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Abstract
Dynamic mechanical properties of block copolymers over a wide temperature range have been previously correlated with the phase‐separated microstructure of these systems. In the present work, the morphology of the block copolymer is altered by large tensile deformation at various temperatures. Upon removal of the applied stress, the morphological features of such stretched‐and‐released systems become functions of time, as the nonequilibrium microstructure reverts to a thermodynamically stable state. This reformation process is monitored by dynamic mechanical measurements, with a modified torsion pendulum capable of applying both tensile and torsional deformation. Experimental results are analyzed using a modified Nielsen model to obtain information on the time‐dependent structural state of the samples. These results are then compared with stress‐strain curves to provide further insight into the structure breakdown‐reformation mechanisms. Two competing mechanisms, domain fracture and block pull‐out, are proposed to explain these experimental observations.

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