CONFIGURATION OF A THERMOTROPIC POLYESTER FROM SMALL-ANGLE NEUTRON-SCATTERING

Small-angle neutron scattering has been used to ascertain the configuration of a random thermotropic terpolyester at three temperatures between the glass transition and the melting point on four fractions of different molecular weight. Specimens were prepared by casting films from solutions and subsequent annealing at selected temperatures for 1 h. All samples have a small amount of crystallinity, but at the lowest annealing temperature, 448 K, the molecules have a random-coil configuration. At the two higher annealing temperatures, 493 and 523 K, the molecules become increasingly stiff. This is observed as an increase in the persistence length from 9 angstrom at 448 K to ca. 44 angstrom at 523 K. The variation of the ratio <S2>w/M(w) with M(w) for the two higher temperatures displayed the characteristics of a Kratky-Porod wormlike chain. Persistence lengths and shift factors were obtained from an extrapolation procedure based on an approximation for the dependence of the radius of gyration of a wormlike chain on the contour length and persistence length. The value of the persistence length obtained at 523 K is in good agreement with a value obtained from scanning tunneling microscopy elsewhere. These data suggest that the transformation to the nematic mesophase at temperatures above the melting point is aided by stiffening of the molecule at lower temperatures.