Glass-Transition Temperature and Characteristic Temperatures of α Transition in Amorphous Polymers Using the Example of Poly(methyl methacrylate)

Abstract

The glass-transition temperatures of poly(methyl methacrylate) measured by 20 different physical methods are analyzed. At equal impact frequencies and heating rates of the samples, the values of glass-transition temperatures measured by different methods are equivalent. As follows from the analysis, for atactic PMMA with Mw > 1 × 105 without additives, crosslinking agents, and plasticizers at a standard heating rate of 10°С/min, the most probable values of the extrapolated onset temperature of the α transition Tf as a point of intersection of the first baseline and a line extrapolating linear decrease in heat flow in the region of the α transition are 105 ± 5°С; inflection temperatures corresponding to the temperature of a peak on the temperature derivative of heat flow in the region of the α transition Ti and the temperature of the midpoint determined at the half jump of normalized heat flow Tm are observed at 125 ± 5°С; and the values of the extrapolated end temperature of the α transition Te as the points of intersection of the line extrapolating the linear decrease in heat flow in the region of the α transition and the second baseline in the region of the rubbery state and the temperature of the last return to the second baseline Tr attain 140 ± 5°С.