Dilute solution properties of poly(1,4-phenylene terephthalamide) in sulfuric acid

The intrinsic viscosity [η] of dilute solutions of poly(1,4-phenylene terephthalamide) (PPPT) is found to depend strongly on sulfuric acid strength, exhibiting a maximum at about 100% H₂SO₄. This behavior instigated measurements of [η] and light scattering from dilute solutions of unfractionated PPPT in concentrated (≈96%) and 100% H₂SO₄. From [η] and weight-average molecular weight M _w relationships, Mark-Houwink exponents a were determined to be 1.36 in 96.6% and 1.62 in 100.2 ± 0.2% H₂SO₄, indicating that the PPPT molecule can undergo considerable expansion in 100% H₂SO₄. For the case of 100% H₂SO₄, a noticeable polyelectrolyte effect is observed in the reduced viscosity versus concentration curves. This result suggests that the repulsive charges generated along the PPPT backbone may be responsible for the change in configuration of PPPT upon increasing the acid strength from 96.6% to 100% H₂SO₄. It is pointed out that there is considerable experimental difficulty in measuring consistent values of M _w, and this may be the reason for the variation among published data.