We report measurements of chain diffusion in macroscopically oriented, well-entangled lamellar block copolymers. Diffusion in the lamellar plane is proposed to occur by an ``activated reptation'' mechanism when the composition profile is roughly sinusoidal. At higher degrees of segregation a crossover to an entropically limited ``block retraction'' mechanism is apparent. Diffusion through the layers reflects a thermodynamic barrier determined by the combination of temperature and molecular weight.
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Lodge et al. (1995) studied this question.
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