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 $P>200000$, 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.