Temperature Modulated Calorimetry of Glassy Polymers and Polymer Blends

Abstract

The theoretical modeling of the relaxation behavior of polymers in the glass transition region, advocated by Moynihan and co-workers, has been used to analyze the heat flow and the relaxation of polymer systems during isothermal modulated DSC experiments in the glass transition region. An analytic solution for the frequency dependent fictive temperature is obtained, which takes a particularly simple form in the high-frequency region. The maximal phase lag of the fictive temperature T f is π/2, where the exponent of the stretched-exponential characterizing the enthalpy relaxation, , is on the order of 0.1-0.7. The corresponding maximal phase lag in the heat flow is much smaller, on the order of 2-5 deg. It is once more iterated that, as observed long ago by Birge and Nagel, the loss heat capacity corresponds to the entropy production due to a redistribution of energy over the heat baths. The possibility of using specific-heat spectroscopy as a tool to determine miscibility in polymer blends whose constituents possess similar glass transition temperatures is discussed. Compared to conventional differential scanning calorimetry, the resolution is enhanced. However, in many cases an unambiguous conclusion still requires additional enthalpy relaxation of the blend induced by physical aging in the glassy state.

Determination of the Flory−Huggins Interaction Parameter of Styrene and 4-Vinylpyridine Using Copolymer Blends of Poly(styrene-co-4-vinylpyridine) and Polystyrene

“…Where necessary, i.e., if the respective glass transition temperatures were too close, this procedure has been applied to our blends. With the advent of modulated differential scanning calorimetry additional options became available, − which will be illustrated here by presenting reversing and nonreversing heat flow curves besides the usual total heat flow. For selected cases the phase behavior concluded from the thermal analysis procedure has furthermore been verified by optical microscopy using phase contrast.…”

Use of isoconversional methods to analyze the cure kinetics of isocyanate‐ended quasi‐prepolymers with water

“…At temperatures sufficiently far from the T g , the system will remain in equilibrium at all curing times and T f will be identical to the temperature of the system. However, during the T g the system will not respond structurally to the changing temperature and T f will differ from the temperature of the system 18…”

Effect of low‐temperature physical aging on the dynamic transitions of atactic polystyrene in the glassy state

“…Numerous studies have been done to examine the effect of physical aging on the macroscopic mechanical behavior of glassy polymers and similarly for the enthalpy changes upon aging . Most of the studies are trying to explain their results based on the free‐volume theory, in which the changes of the properties of the material are interpreted solely by the changes in free volume .…”