Epoxy network thermal expansion

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

Figure 5 (a, b) shows typical heat capacities and thermal expansion coefficient curves for some epoxy-aromatic amine networks. Table 1 gives some numerical values for networks with different component ratios P Cp and P values for the glassy state do not practically depend on the chemical composition of networks and are very... 

Fig. 6a and b. Heat capacity ACP(TS) and cubic thermal expansion coefficient jumps AP(Tg) for some epoxy-amine systems.. Experimental results O DGER-mPhDA networks of different P, completely cured and annealed (T = 0.5°/min) DGEBA-mPhDA networks of different P, completely cured and annealed DGEBA-mPhDA unreacted mixture (P = 1) DGER-mPhDA unreacted mixture (P = 1) solid lines — the best fit... 

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