A Slip-Link Model of Branch-Point Motion in Entangled Polymers

Abstract

In melts of asymmetric three-arm star polymers in which a short arm is attached to two long, equal-length arms, the existing “tube” theory fails to predict how rapidly the motion of the branch-point becomes quenched when the length of the third, short, arm grows from zero length, for which the two other arms form a reptating linear chain, to a length equal to the other two arms, for which reptation is quenched. We use a simulation method that represents entanglements between two chains as “slip-links” that allow local relaxation of both chains when an end of either chain passes through the slip-link. We include an extreme form of branch-point motion in this algorithm and find that it can explain the anomalously rapid quenching of the branch-point if we assume that the time scale of the branch-point motion is set by the time required for the short arm to escape all entanglements, including those newly created while others are destroyed. The algorithm successfully predicts the linear viscoelasticity of H-po...