Limits of Reptation in Polymer Melts

Abstract

Tracer diffusion coefficients $D^{*}$ of deuterated polystyrene of molecular weight $M$ diffusing into polystyrene of molecular weight $P$ are measured by means of an ion-beam analysis method. While for $P>\mathrm{}200\mathrm{}000$, these $D^{*}$ values are independent of $P$, consistent with a reptation mechanism ($D^{*}=D_R$) for the diffusion of $M$ chains, $D^{*}$ increases rapidly as $P$ is decreased, in quantitative agreement with $D^{*}=D_R+D_{\mathrm{CR}}$, where $D_{\mathrm{CR}}$ is the diffusion coefficient of the $M$ chain by constraint release.