Polycarbonate copolymer of spirobisindan and bisphenol-A, method of preparing such a copolymer and optical components of such a copolymer

摘要

A description is given of a polycarbonate copolymer (Fig. 3) of a spirobisindan (6,6'-dihydroxy-3,3,3',3'-tetramethyl-1,1'-spirobisindan) and bisphenol-A in which the mole fraction of the spirobisindan alpha ranges between 0.844 and 0.887. Such a copolymer has a stress-optical coefficient Cm in the melt which is equal to zero or substantially equal to zero, so that the sensitivity of the polymer to orientation birefringence is very small. Such a copolymer can be rendered optically isotropic and is very suitable for use in optical components in which birefringence is undesirable. Examples of such optical components are lenses and substrates for optical information media.