Swelling studies of crosslinked poly(p-phenylene terephthalamide) copolymers in sulfuric acid |
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Authors: | Jennifer Rigney Monica D. Little David C. Martin |
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Abstract: | In an attempt to improve the mechanical properties of extended chain polymers such as poly(p-phenylene terephthalamide) (PPTA), a crosslinkable terephthalic acid derivative (XTA) has been developed which can be incorporated into copolymers in various concentrations and activated after polymerization. The crosslinking of PPTA-co-XTA copolymer particles was investigated through a series of swelling experiments in concentrated H2SO4. The data show a systematic decrease in equilibrium swelling with increasing XTA content, indicating the XTA units are in fact acting as crosslink sites. Values for crosslink density were calculated from the Flory-Rehner theory of polymer swelling and compared with previous findings on crosslinked rigid polymer network systems. The effective number of crosslinks per XTA unit (efficiency) predicted by the Flory-Rehner theory increases and then decreases with % XTA. The decrease in crosslinking efficiency at high XTA concentrations is consistent with differential scanning calorimetry data which show the enthalpy of XTA reaction decreasing slightly with % XTA. The deviations at low % XTA may represent a failure of the Flory-Rehner theory to properly describe the rubbery elasticity of extended chain polymers. © 1994 John Wiley & Sons, Inc. |
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Keywords: | Poly(p-phenylene terephthalamide) benzocyclobutene swelling, crosslink density |
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