Abstract
Abstract Electric birefringence (EB) in solutions of a series of fractions of polybutylisocyanate (PBIC) in tetrachloromethane in the range of molecular weights (M) from 5 × 103 to 8 × 105 was investigated by using sinusoidal and rectangular pulse fields. Dispersion relaxation times (τ) were determined from dispersion of EB in a sinusoidal field. The times of free relaxation (〈τ0〉) and the times (QR) of the rise in EB were determined from the rise and decay of EB. It is shown that, for M ⩽ 105, EB in PBIC solutions is entirely determined by the large-scale orientation of kinetically rigid polar molecules whereas, for M ⩾ 2 × 105, the EB phenomenon reveals the kinetic flexibility of polymer chains. By using the theory of rotational friction and the dependence of τ on M, the persistence length of PBIC molecules was found as (40 ± 5) nm. The number of monomer units in the Kuhn segment, S = 360, was determined from the dependence of the Kerr constant K on M. The longitudinal component of the dipole moment of the monomer unit, μ011 = 1.9D, was determined from the comparison of data on EB with those on flow birefringence. This value agrees with the dipolar structure of PBIC chain. Apart from the conjugation effect, an important role in the hindrance to rotation in the PBIC chain is also played by the interaction between side groups.
Published Version
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