Rheology of a twin liquid crystalline polymer

Phase transitions of a twin liquid crystalline polymer (TLCP), which was synthesized from 4-((4'-alkoxybenzoyl)oxy)benzoyl chloride and alpha , omega -dihydroxy-telechelic polytetrahydrofuran, have been determined by measurements of linear viscoelastic properties. In the phase-separated mesophase state, the TLCP displayed high elasticity to small-amplitude deformation, due to mesogen-induced physical cross-linking. As the strain amplitude increased, shear thinning affected both dynamic and steady flow properties. This effect is assumed to be due to a reduction of tie molecules and an increase of loops in the physical network. If the average shear rate of oscillatory flow was defined as < gamma > sub d = 4 gamma sub 0 omega /2 pi , a good agreement of eta *( < gamma > sub d ) approx eta ( gamma ) was found in the shear thinning region and the high shear rate plateau. After shear thinning a TLCP, structural recovery took several days, unless the sample was temporarily heated to the isotropic state. However, above the clearing temperature of approx 65 deg C, the polymer became single phased and showed rheological behavior typical for a polymeric melt of low molecular weight. 18 ref.--AA