Effect of etherification reaction on extraction and photoelastic and dynamic mechanical behavior of diepoxide–diamine networks

✍ Scribed by A. Vazquez; M. Ilavský; K. Dušek

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 238 KB
• Volume: 74
• Category: Article
• ISSN: 0021-8995
• DOI: 10.1002/(sici)1097-4628(19991213)74:12<2877::aid-app11>3.0.co;2-v

✦ Synopsis

Sol fraction and equilibrium photoelastic and dynamic mechanical behavior of epoxide networks based on bisphenol A diglycidyl ether (DGEBA) and poly(oxypropylene diamine) (Jeffamine D-400) with four initial molar ratios of epoxy (E) and amine ( A) groups, r E ϭ [E] 0 /(2[A] 0 ) ϭ 1.2, 1.5, 2.0, and 2.3 were investigated. Networks with different extents of total epoxy group conversions (including etherification), ␣ E , were prepared for each r E value. Both the ratio r E and the conversion ␣ E affected the value of the equilibrium modulus, G, and the weight fraction of the gel, w g . As expected, decreasing the r E ratio (at constant ␣ E ) and increasing ␣ E (at constant r E ) were accompanied by an increase in the modulus, G, and gel fraction, w g . The stress optical coefficient, C, is independent of ␣ E decreasing with increasing r E . The frequency- temperature superposition could be performed for all networks; the temperature dependence of the horizontal shift factor, a To , satisfied the WLF equation. The temperature and time positions of viscoelastic functions predominantly depend on the overall concentration of elastically active network chains e , regardless of the values of r E and ␣ E . While the shape of viscoelastic functions at the beginning of the main transition region depended on the detailed structure of the chain (number and length of pendant chains), the shape at the end of the transition was determined mainly by the concentration of elastically active network chains. An unexpected universal increase was found in the half-width of the maximum in the dependence of the superimposed loss compliance, J Љ p , on reduced frequency a T with increasing crosslinking density.