Application of stepwise temperature and pressure scanning thermal analysis in identifying retrograde vitrification in polymers and in foaming process development

摘要

Differential scanning calorimetry is the most widely used technique for establishing the glass transition temperature T_g of a polymer. We have extended this technique to measure the T_g of a two-phase polymer-gas system, where the polymer remains in contact with the high-pressure gas. Recently, a theoretical prediction was made that certain polymer-gas systems exhibit two glass transitions at a constant gas pressure. One of these transitions pertains to rubber-to-glass transition on heating, and is thus called retrograde vitrification. This rather unusual phenomenon has been verified by creep compliance measurements. However, such high pressure measurements, employing pressure sweep, are difficult to perform, are time consuming, and do not provide a precise control on the thermodynamic state of the system. This talk will describe a new technique based on high-pressure DSC to establish retrograde vitrification in polymer-gas systems. Examples will be given of the new morphologies that become accessible from the retrograde phase.