Stiffness parameter of brush-like polymers with rod-like side chains

The stiffness parameter lambda(-1) of brush-like polymers having rod-like side chains with the hard core potential was calculated. Side chains are, first, assumed to be connected with a free joint to the main chain. The free energy per molecule F was calculated invoking the single contact approximation in which only the interaction between two side chains is considered and the higher interactions are ignored. In the calculation, the contact is assumed to occur when the two side chains are in a plain and the condition for the angles between the side chain and the main chain to make a triangle by two side chains and the main chain was exactly taken into account. The change of F after bending the main chain with a certain curvature from the straight state was calculated to obtain lambda(-1). The resulting lambda(-1) came close to the experimental value for brush-like polymers with a poly( methacrylate) main chain and poly(hexylisocyanate) (PHIC) side chains if we add a constant as the intrinsic stiffness of the main chain, lambda(-1)(0), to it. By considering the potential function having a minimum when the angle between the side and main chains equals pi/2, the data for brush-like polymers with a poly( styrene) main chain and PHIC side chains were also closely fitted by the theoretical values with an appropriate value of lambda(-1)(0) and the force constant of the angle. Published by AIP Publishing.