Physical properties relating to chain stiffness are determined for a series of copolycarbonates of Bisphenol A and 1,1‘-spiro[bis(3,3‘-dimethyl-6-hydroxyindan)] (SBI) of varying composition. The entanglement molecular weight, M e, is derived from the rubbery plateau modulus. The recoverable compliance, is determined from the dynamic moduli as well as from steady shear creep and recovery experiments. It is found that all properties change in a nonlinear fashion with SBI content. For small SBI content the entanglement density is hardly affected, whereas T g and increase strongly. With further increase in SBI content the effect on T g is less pronounced. M e, however, starts increasing progressively to about 10 times that of pure Bisphenol A polycarbonate. The functional dependence of M e on composition is not predicted correctly from group contributions.
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Wimberger‐Friedl et al. (1996) studied this question.