Thermoset resins containing sterically hindered alkyne groups for reduced crosslink density

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AbstractA series of thermoset matrix materials with phenylethynyl and phenoxyphenylethynyl end groups were prepared to assess the extent of crosslinking in the cured resins by thermoanalytical and thermomechanical methods. These novel materials with varying flexibility and thermal stability of both the end group and backbone were evaluated against a group of materials known to contain a substantial number of primary acetylenic thermal crosslinking sites. The evaluation indicated increased thermooxidative stability of the secondary acetylenic materials over the primary acetylenic systems at or below 600°F (312°C). However, above 600°F, the secondary systems were less thermooxidatively stable than the primary structures due to the thermal decomposition of the phenyl pendants near 400–450°C (750–842°F). Cure exotherms for the monomers exhibited typical Gaussian behavior with discernable cure onsets and maxima. Cure maxima for the secondary acetylene quinoxalines were close to their thermal decomposition temperature (450°C). Percentages of weight retained varied from 64 to 92% after isothermal aging at 600°F for 200 h in circulating air. Glass transition temperatures of the secondary systems more closely approximated the values calculated for linear homopolymers of similar structure. The increased linearity of the cured secondary systems is further verified by fracture analysis which indicated a 20% increase over the room temperature value of the observed KQ for its comparable primary system analog.