Molar-mass dependence of the lamellar thickness in symmetric diblock copolymers

A homologous series of nine symmetric poly(styrene)-block-poly(butadieme) diblock copolymers was synthesized and characterized. The scaling of the lamellar thickness, D, with the chain length N(DαN ^δ ) was investigated with small-angle X-ray scattering. Different sample preparation methods were used: annealing, solvent-casting and shear alignment. We find that the lamellar thickness and thus the value of the exponent δ depends on the preparation method used, i.e. care must be taken to ensure that the samples investigated are in thermodynamic equilibrium.