R e f r a c t i v e

I n d i c e s

o f

P o l y m e r s

James C. Seferis Polymeric Composites Laboratory, Department of Chemical Engineering, University of Washington, Seattle, VVA, USA

A. B. C. D. E.

Introduction Molar Refraction Refractive Indices of Heterogeneous Polymers Optical Anisotropy Applications Table 1. Intrinsic Optical Properties of Selected Polymers Table 2. Average Refractive Indices of Polymers (in Order of Increasing n) Table 3. Average Refractive Indices of Polymers (in Alphabetical Order) F. References A.

VI-571 VI-571 VI-572 VI-572 VI-573 VI-573 VI-574 VI-578 VI-582

INTRODUCTION

The refractive indices of polymers provide fundamental physical property information that can be used in characterization, processing, and usage analyses. In-depth description of refractive indices based on classic electromagnetic theory can be found in basic texts (1,2). The purpose of this monograph is to provide a convenient reference of values and some general remarks in approximating and utilizing refractive indices of polymers. The refractive index, reported as the velocity of light in a vacuum relative to the velocity in the polymer, depends on the wavelength of light. All values reported in this chapter refer to the sodium spectral line A = 5893A, referred to as HD in this literature. However, for simplicity, the subscript D is omitted here in the subsequent discussion and tables. In general, it should be kept in mind that for any polymer, the refractive index represents an average property of its aggregate state (3,4). Orientation, conformation, as well as phase changes may all contribute to variations in the index of refraction of a polymer with a given chemical structure. Thus, the refractive index may not be expected to be equal along all axes of the molecule (5). Consequently, the measured refractive index is an average value, with contributions from the refractions of the molecule's different chemical bonds. It can be shown from classic electromagnetic theory that the square of the refractive index (n2) is the appropriate form to use in molecular descriptions of refractive indices since it is related to the dielectric tensor, having a magnitude as well as a

directional description (1,4). However, since 1.3