UNUSUAL RETARDATION AND ENHANCEMENT IN POLYMER DISSOLUTION - ROLE OF DISENGAGEMENT DYNAMICS

This work addresses the issue of resolution of some unusual observatio ns in the swelling-dissolving problem in polymers. There are observati ons showing several fold increase in the rate of dissolution when the residual solvent content is increased only marginally. Additionally, b y using an in situ NMR technique to study dissolution, we have found t he existence of an intermediate plateau in the dissolution curve indic ating an unusual retardation in the rate of dissolution under certain conditions. Interestingly, this plateau disappears on either increasin g the molecular weight of the polymer or on doing dissolution under sh earing rather than under stagnant conditions. An improved model is pro posed to explain these results, which cannot be explained by the exist ing models. The new feature is the incorporation of a kinetic model to relate the disengagement rate to the swelling rate, through the chang ing mobility of the disengaging macromolecule at the gel-liquid interf ace. The present study thus enables a clearer elucidation of the role of disengagement dynamics in the dissolution process.