Phase behaviour of rigid-rod/coil/solvent ternary systems with rod—coil interaction

Abstract

This paper reports the phase diagrams of PBZT/nylon/MSA, PBZT/NaAMPS polymer/MSA, PBZT/HAMPS monomer/MSA and PBZT/PPTA-PS/MSA, with PBZT = poly( p-phenylene benzobisthiazole), MSA = methanesulphonic acid, NaAMPS = sodium 2-acrylamido-2-methylpropanesulphonate, HAMPS = 2-acrylamido-2-methylpropanesulphonic acid and PPTA-TS = poly( p-phenyleneterephthalamido)propanesulphonate). The ternary phase diagram of rigid-rod polymer PBZT and amorphous nylon in MSA solvent was found to follow Flory's prediction of a rod/coil/solvent ternary system very well. Flory's theory assumes no interaction between the rod and the coil, and the PBZT/nylon system fits this model nicely. When sulphonated polymers, such as NaAMPS polymer and PPTA-PS, were used instead of nylon in a ternary solution, it was found that the phase behaviour deviated from Flory's theory. This deviation could be due to the possible coil—rod intermolecular interaction in the ternary solution. Flory's formalism was used to analyse these data. It was found that for the PBZT/nylon/MSA system, the X 3 value was consistent with the contour length of the coil molecules as predicted by Flory's theory. However, both PBZT/HAMPS monomer/MSA and PBZT/NaAMPS polymer/MSA systems showed an X 3 value of unity. The ternary phase diagram of the PPTA-PS system showed an X 3 value between 1 and 5. This suggests that the degree of intermolecular interaction between rod and coil plays an important role in determining the phase behaviour of a rod/coil/solvent ternary system.