The effect of saturation on thermodynamic interactions in polystyrene-
polyisoprene (SI) diblock copolymers is examined by small-angle neutro
n scattering (SANS) and birefringence. Experiments were conducted on a
n SI sample in which both blocks had molecular weights of 7.5 x 10(3)
and its saturated product-a poly(vinylcyclohexane)-poly(methylbutylene
) block copolymer (HSHI). The SANS data show a reversal in miscibility
in the vicinity of 96-degrees-C. Above this temperature, the Flory-Hu
ggins interaction parameter, chi, is higher in the HSHI polymer than i
n the SI polymer, while the reverse is true at temperatures below 96-d
egrees-C. The high-temperature result is consistent with published dat
a of Gehlsen and Bates, while the low-temperature result is confirmed
by birefringence measurements presented here.