Melt Rheology of Ring Polystyrenes with UltrahighPurity.

The melt rheology of highly-purified ring polystyrenes in a wide rangeof molecular weights(10K ≤ Mw≤ 240K g/mol)was investigated. All the rings revealed no obvious rubbery plateauand faster terminal relaxation compared to the linear counterparts.The rheological data obtained were compared with some theoreticalmodels such as the Rouse ring model and the lattice-animal model.Moreover, two rheological parameters, zero-shear viscosities η0and the steady-state recoverable compliances Je, were estimated, and their Mwdependence was discussed. From these data analysis, it was foundthat relaxation mechanisms of ring chains can be divided into threecategories depending on their Mwas follows:(i) Smaller rings (Mw≤ 20K) exhibitfaster terminal relaxation than the predicted Rouse rings. This behavioris related to the difference of the local chain conformation fromlinear chains. (ii) Rings with the moderate molecular weight (40K≤ Mw≤ 90K) exhibit dynamicmoduli similar to the Rouse ring prediction. (iii) A larger ring (Mw> 90K) also shows deviant behavior fromtheRouse chain because its relaxation time is much longer than the Rousering prediction and also the lattice-animal model, where some intermolecularinteractions are considered to occur. [ABSTRACT FROM AUTHOR]