The glass transition kinetics in bulk polymers and ultrathin films and reaction kinetics for cyclopentadiene demerization
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The glass transition behavior under nanoconfinement has been extensively studied in the last two decades and the glass transition temperature (Tg) is found to decrease, increase, or remain the same compared with the bulk values. The leading explanation for the Tg changes is the mobility changes at the interface/free surface. However, prior nanocalorimetry results did not show any depression, and in addition, some researchers have suggested that the Tg changes result from sample degradation or plasticization. In this dissertation, the glass transition temperature of the single polystyrene thin films is investigated using a rapid scanning chip calorimeter. The Tg values for thin films are found to decrease as cooling rate decreases, as well with decreasing film thickness. The importance of the interface between the thin film and substrate on Tg depression is also investigated. The suggestion that degradation or plasticization is the cause of the Tg depression is shown to be inconsistent with annealing and morphological experiments. The structural recovery of polystyrene is also investigated using the rapid scanning chip calorimeter. Intrinsic isotherms for different jump sizes are performed and compared with Kovac’s seminal aging experiments in volume space. The departure from equilibrium for the enthalpic intrinsic isotherms decreases smoothly and monotonically without any intermediate plateau. The dependence of the relaxation time in the glassy state on the fictive temperature is obtained from the induction period at the initial stages of structural recovery. The rapid scanning chip calorimeter is also used to show that the limiting fictive temperature, Tf', does not depend on heating rate. Cyclopentadiene (CPD) dimerization is a common Diels-Alder reaction and the reaction kinetics have been previously studied using different techniques. However, the reaction kinetics for this reaction have never been investigated incorporating the effect of pressure when reacted in the closed system. Here, we performed both experimental calorimetry and modeling work for CPD reaction, and for the first time, have incorporated the pressure effects to model the reaction.