Relaxation during polymerization on slow heating and the vibrational heat capacity of the polymers

Year: 2007

Authors: Ferrari C., Tombari E., Salvetti G., Johari G.P.

Autors Affiliation: Istituto per i Processi Chimico-Fisici, CNR, via G. Moruzzi 1, 56124 Pisa, Italy; Department of Materials Science and Engineering, McMaster University, Hamilton, Ont., Canada

Abstract: The real and imaginary components of the complex heat capacity, C-p(\’) and C-p(\’), and C-p,C-app have been measured in real time during the linear chain polymerization on 12 K/h heating of six different (partially) polymerized states of a stoichiometric mixture of cyclohexylamine and diglycidyl ether of bisphenol A. Their C-p,C-app shows a sigmoid shape rise with different onset temperatures T-onset, which is followed by a deep exotherm as the viscosity decreases and further polymerization occurs at different rates. The rates of their enthalpy decrease on polymerization determined by subtracting C-p(\’) from C-p,C-app differ but C-p(\’) and C-p,C-app of their final states are the same. The relaxation time increases with polymerization and decreases with an increase in T. C-p(\’) rises in a sigmoid shape manner, and C-p(\’) shows a peak when the relaxation time of the polymerized state is equal to the inverse of the temperature modulation frequency, whether polymerization occurs or not. The unrelaxed or vibrational heat capacity C-p,C-vib of the polymers at T>T-onset is close to C-p of their glassy state at T < T-onset, showing that C-p difference between the equilibrium liquid and its glass is mostly configurational. This contradicts a calculation showing that C-p,C-vib change of a polymer at T-g is generally similar to 20% of the total C-p change. Journal/Review: JOURNAL OF CHEMICAL PHYSICS

Volume: 127 (2)      Pages from: 024903-1  to: 024903-9

KeyWords: DIFFERENTIAL SCANNING CALORIMETRY; DIEPOXIDE-DIAMINE COMPOSITIONS; NARAYANASWAMY-MOYNIHAN MODEL; GLASS-TRANSITION; STRUCTURAL RELAXATION
DOI: 10.1063/1.2752169

Citations: 4
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