HEAT-CAPACITY SPECTROSCOPY AT THE GLASS-TRANSITION IN POLYMERS

A heat capacity spectroscopy HCS setup (3 omega method) adapted to mea sure glass transitions in polymers is described. Sample contacting and signal sensitivity are improved so that the relevant complex heat cap acity in a (0.2-2000) Hz frequency region can be recorded down to rela tive heat capacity steps Delta c(p)/c(p) of a few percent. Linearity a nd Kramers-Kronig consistency tests are described. The influence of he ater width and sample thickness is discussed. The possibilities of the instrument are demonstrated for the glass transition in natural rubbe r, polystyrene, and a random copolymer of n-butyl methacrylate and sty rene. (C) 1997 Elsevier Science B.V.