Reaction-induced strain in rigid-rod polymeric fibers

The thermomechanical behavior of several rigid-rod polymeric fibers has bee n investigated. Up to 300 degreesC, all fibers exhibited the expected axial shrinkage on heating (CTE approximate to -6 x 10(-6) degreesC(-1)). Howeve r, a pronounced increase in thermal contraction was observed at temperature s where polymer degradation cr cleaving of the pendant group occurred. A de gradation mechanism has been proposed that accounts for the evolved gases i n PBZT and MePBZT. The accelerated shrinkage in these rigid-rod polymers is a result of decrease in the c-axis lattice parameter as measured via WAXD. The enhanced axial shrinkage and accompanying decrease in lattice paramete r are attributed to chemical changes, and consequent cross-linking taking p lace within these systems which, in turn, serves to perturb the crystalline structure. The implications of this phenomenon of accelerated axial contra ction, with, regards to morphology, are discussed.