Intrinsic Birefringence of Poly(butylene terephthalate)

Abstract

Theoretical refractive indices were calculated by summarizing bond polarizabilities for α and β form crystal of poly (butylene terephthalate). The principal direction at which the polarizability indicates minimum was almost parallel to the normal direction of phenylene ring. The principal refractive indices revealed 1.411, 1.713, 1.760 for α form crystal, and 1.398, 1.708, 1.768 for β form crystal. The resulting intrinsic birefringences for c-axis orientation of α and β form crystals were 0.153 and 0.215, respectively. © 1993, The Society of Fiber Science and Technology, Japan. All rights reserved.