Conformation of a Diblock or Random Square-Well Copolymer in Dilute Solution

Combined with an approximation suggested by Taylor and Lipson for the third-order correlation function and the translational invariance approximation, the BGY equation is used to calculate the conformation and thermodynamic properties of a diblock square-well copolymer or a random square-well copolymer. The BGY results for the end-to-end distribution of copolymers are in good agreement with Monte Carlo simulations when the attractive interaction between segments is not strong. BGY calculations semi-quantitatively predict the conformations of a copolymer when the attractive interaction is strong. At low temperatures, one block comprised of attractive segments of the diblock copolymer collapses while the other block, comprised of repulsive segments, dominates the scaling behavior. The end-to-end-distance distribution function for a random copolymer is similar to that for an AB...AB copolymer when the temperature is at least moderate.