Vibrational and configurational heat capacity of poly(vinyl acetate) from dynamic measurements

摘要

The complex heat capacity C-p(*) of poly(vinyl acetate) has been measured at 20.95 mrad/s modulation frequency during the cooling as well as on heating at 24, 8, and 2 K/h and during cooling at 0.5 K/h. The study is complemented with (the rate-dependent) C-p,C-app measured during cooling and heating at 60, 24, and 8 K/h. At low temperatures, the real component of C-p(*) yields the unrelaxed C-p or C-p,C-vib, the vibrational part of C-p. It is found to be indistinguishable from C-p,C-glass and lies on a line extrapolated to its equilibrium melt's temperature. At T near T-g,Delta C-p(=C-p,C-melt-C-p,C-glass) shows no detectable contribution from C-p,C-vib. The finding conflicts with a modified entropy theory calculation [E. A. DiMarzio and F. Dowell, J. Appl. Phys. 50, 6061 (1979)], which had predicted that similar to 27% of Delta C-p of poly(vinyl acetate) at T near T-g is vibrational in origin and the remainder configurational. At T < T-g, the real component of C-p(*) varies more slowly with T than C-p,C-app.