Effect of architecture on the tensile properties of triblock copolymers in a lamellar phase

We have used self-consistent field theory to calculate the tensile moduli of triblock copolymers in lamellar microstructures prepared from linear and star architectures. The extensional moduli K₃₃ are the main contributors to the tensile moduli, and the contribution of K₃₃^U (the internal energy contribution to K₃₃) is the main component of the value of K₃₃. We find that the tensile moduli of ABC three-miktoarm star terpolymers are smaller than those of ABC linear triblock copolymers having identical components, presumably for two main reasons. First, for the ABC three-miktoarm star terpolymers, the contributions of K₃₃^U are larger than those of the linear triblock copolymers; we attribute this phenomenon to the star terpolymers having smaller lamellar domain sizes at equilibrium relative to those of the linear triblock copolymers. Second, conformational entropies play an important role in affecting the tensile moduli, mainly because of the different degrees of freedom of the various chains. In contrast, the shear moduli contribute negligibly to the tensile moduli.