Diffusion of poly- p-phenyleneterephthalamide in concentrated sulphuric acid

Abstract

The translational diffusion of poly- p-phenyleneterephthalamide molecules of different molecular weights in 96% H 2SO 4 has been investigated with the aid of a new experimental technique. The diffusion coefficients D are not concentration dependent in dilute solutions, and show marked sensitivity to the length of macromolecules. The molecular weights of the specimens M obtained from the diffusion coefficients D in the light of the theory of translational friction of persistent chains are practically equal to those calculated in terms of a Tsvetkov-Klenin hydrodynamic parameter of A 0=3·78 × 10 −10 erg/deg. A slight divergence of the M values in question from those determined by the method of flow birefringence could stem from polydispersity of the specimens and from inconstancy of A 0. In the range of M=(4·−45) × 10 3 examined in this investigation relationships have bee found between the diffusion coefficients D and the intrinsic viscosity [η] and M: D=4·0 × 10 −5 M −0.80, [ η]=2·5 × 10 −5 M 1.7 M ⩽ 10,000) and [ η]=1·7 × 10 −2 M 1.0 ( M>20,000). In the light of a joint analysis of the diffusion and viscosimetric data a conclusion is reached as to the high equilibrium rigidity of poly- p-phenyleneterephthalamide molecules and as to their hydrodynamic properties in 96% H 2SO 4 which approximate to those of another rigid chain polymer, poly- p-benzamide, in the same solvent.