Anomalous domain spacing difference between AB diblock and homologous A(2)B(2) starblock copolymers

Based on weak- and strong-segregation theories, symmetric AB diblock copoly mers and the homologous A(2)B(2) starblock copolymers formed by joining pai rs of diblocks together by their junctions should have identical order-diso rder transitions (ODT's) and lamellar periods. However, recent experiments report that the starblock melts have elevated ODT's and domain spacings. Th e ODT shift has been attributed to the increase in chain stretching, but th ere is still no convincing explanation for the larger domain size. Here, we show that this latter effect is correctly predicted by self-consistent fie ld theory (SCFT) and that it results due to a reduction in translation entr opy of the junctions. Furthermore, we derive a strong-segregation based app roximation for this anomalous domain spacing difference. (C) 2000 American Institute of Physics. [S0021-9606(00)51029-0].