Computational Predictions of the Tensile and Compressive Properties of Rigid-Rod Polymers

Abstract

ABSTRACTThe Austin Model 1 (AM1) semiempirical molecular orbital method has been used to calculate tensile moduli and molecular tensile and compressive deformation for several rigid-rod polymers and a graphite model. The calculated moduli are an improvement over previous Modified Neglect of Differential Overlap (MNDO) calculations. These are the ultimate moduli or the perfectly aligned bulk systems. By analyzing the deformation of polymer molecules in tension and compression, the failure modes and weak points in the molecules can be determined. In compression, all the heterocyclic rigid-rod polymers exhibit a “bending” failure mode. In tension and compression, the phenyl group in the rods undergoes in-plane deformation more easily than the heterocyclic moiety, thus causing a lowering of the modulus. The hypothetical “ladder” polymer, polyacene, shows higher tensile and compressive resistance than any of the rods, suggesting that further study into the ladder polymers is warranted.