COLLAPSE OF RANDOM COPOLYMERS

We propose a theoretical approach to the description of the coil-globu le transition of random copolymers having a fixed sequence of units. F or simplicity, we consider copolymers formed by two different units on ly, although the generalization to any other number is straightforward . The theory is based on self-consistent minimization of the intramole cular free energy, which includes two-body attractive interactions amo ng units of a given type, two- and three-body repulsive interactions a mong all the units, and configurational entropy. Chain connectivity is accounted for throughout. Considering copolymers with 20%-60% mutuall y attractive units, we predict in all cases a first-order coil-globule transition, unlike the analogous homopolymer. The monomolecular micel le formed by the collapsed copolymer consists of two basic conformatio ns: (a) stable compact globules, having the mutually attractive units clustered in a dense core, where from the other units are expelled; (b ) metastable open globules, where most attractive units are still with in the core, but a few of them are outside, interspersed with the othe r units. Possible connections with ionomer behavior in apolar solvents and with current results on globular proteins are also; discussed. (C ) 1998 American Institute of Physics.