The structural aspects of polyacrylamide thin films annealed at degradationthreshold temperature have been studied as a function of annealing time usingin situ X-ray reflectivity technique in vacuum. We observe significant decreaseof thickness and increase of density with annealing time for all the films. Thedynamical behavior of the changes was modeled in terms of two distinctexponential decay functions, following our earlier observation of two differenttime scales for the chemical modification pathways, and was found to be inexcellent agreement with the data. The diffusion coefficients of the polymerchains corresponding to the two modes are found to be different by an order ofmagnitude. It was found that the two dynamical modes correspond to theformation of two degradation products at two different rates. The larger timeconstants for both the modes in case of thickness reduction compare to thechemical changes was explained in terms of inter-chain entanglement andattachment of the polymer with the substrate.
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