Reaction kinetics and chemo-rheology of poly( p-phenylenebenzobisthiazole) polymerization in the ordered phase

The phenomenon of mesophase-enhanced polymerization of the rodlike polymer poly( p-phenylenebenzobisthiazole) at 15% by weight in polyphosphoric acid has been investigated. The reacting mixture becomes anisotropic at an early stage of the polymerization. The reaction rate increases significantly at the isotropic-nematic phase transition as the rods are aligned in positions more favourable for the condensation reaction to occur. The chemo-rheological properties at high shear rates (⩾ 10 s −1), but not at low shear rates (⩽ 5 s −1), also indicate the occurrence of the phase change. A systematic study of the effects of shear rate and temperature suggests that initial mixing of the monomer mixture below the polymerization temperature greatly influences the final achievable molecular weight of the polycondensation reaction.