Two scaling regimes, D∼${\mathit{N}}^{\mathrm{\delta }}$ with δ=0.49±0.02 and 0.80±0.04, have been identified in a model set of nearly symmetric diblock copolymer melts, where D and N are the system peridocity and degree of polymerization, respectively. The crossover from δ=0.49 to 0.80 is identified as the Gaussian to stretched-coil transition (GST). Contrary to current theory, the GST occurs well below the order-disorder transition (ODT), ${\mathit{N}}_{\mathrm{GST}}$=0.57${\mathit{N}}_{\mathrm{ODT}}$. We associate δ=0.80 with the crossover from weak-segregation (δ=1/2) to strong-segregation (δ=2/3) behavior.

• Received 4 June 1990

DOI:https://doi.org/10.1103/PhysRevLett.65.1112