MICROPHASE SEPARATION IN TOPOLOGICALLY CONSTRAINED RING COPOLYMERS

This paper presents results of the Monte Carlo simulation of dense mel ts of symmetric diblock copolymer rings using the cooperative motion a lgorithm. Due to topological constraints, i.e., the entire absence of entanglements prevents the self-avoiding ring melts from adopting Gaus sian statistics, and the scaling exponent nu is found to be nu = 0.45 +/- 0.01, where the radius of gyration R(g) scales with chain length N as R(g) approximately N(nu). The loss of entropy due to the missing c hain ends of the rings reduces the microphase separation transition te mperature in block copolymer rings with respect to dense melts of line ar diblock copolymers by almost 40%. This compares surprisingly well t o random phase approximation calculations. With decreasing temperature the copolymer rings strongly stretch in the direction of the axis con necting the two centers of mass of the block. The symmetric diblock co polymer rings undergo a microphase separation transition into a lamell ar structure with a wavelength smaller than that for linear diblock co polymers by a factor 0.51-0.55.