Microphase separation in topologically constrained ring copolymers

This paper presents results of the Monte Carlo simulation of dense melts of symmetric diblock copolymer rings using the cooperative motion algorithm. Due to topological constraints, i.e., the entire absence of entanglements prevents the self-avoiding ring melts from adopting Gaussian statistics, and the scaling exponent ν is found to be ν=0.45±0.01, where the radius of gyration ${\mathit{R}}_{\mathit{g}}$ scales with chain length N as ${\mathit{R}}_{\mathit{g}}$∼${\mathit{N}}^{\nu }$. The loss of entropy due to the missing chain ends of the rings reduces the microphase separation transition temperature in block copolymer rings with respect to dense melts of linear diblock copolymers by almost 40%. This compares surprisingly well to random phase approximation calculations. With decreasing temperature the copolymer rings strongly stretch in the direction of the axis connecting the two centers of mass of the block. The symmetric diblock copolymer rings undergo a microphase separation transition into a lamellar structure with a wavelength smaller than that for linear diblock copolymers by a factor 0.51–0.55.