Dynamics of irregular copolymers.

Reptation dynamics of AB copolymers with irregular chemical structure are considered theoretically. It is shown that interactions between A and B monomers could result in a significant slowdown of copolymer dynamics in the disordered (macroscopically homogeneous) state. The dynamical copolymer length N* showing the crossover to the strongly retarded dynamics is calculated. It is shown that contour-length fluctuations (internal reptation modes) give rise to a strong reduction of the slowdown effect and to a strong increase of N* which becomes unrealistically high in the case of a genuinely random chemical structure. The following scaling dependence of N* is predicted for irregular block copolymers: N* proportional, variant delta(-8)chi(-8)n(-8)(0)N(3)(e), where delta is the degree of block polydispersity, chi the Flory AB interaction parameter, and n(0) the mean block length. The strongest dynamical effect of AB interactions is predicted for correlated random copolymers near the critical point related to the formation of microdomain superstructures.