The hydrodynamic and optical properties of solutions of the molecular-homologous series of oligomers of aspartic acid N,N′-piperazine-N″,N‴-hexamethylenebisimide

The structure and rigidity of a new polymer, the N,N′-piperazinohexamethylenebisimide of aspartic acid, has been studied. It is shown that the hexamethylene groups are the factors that control the conformation of the molecules of this aminoimide, while the rigid, cyclic groupings do not alter the flexibility of the molecules appreciable (the length of the Kuhn segment A=23 A), nor its optical properties. A study has been made of the flow birefringence of some monomers (models of the lowest members of corresponding molecular-homologous series). It is shown that by using the usual expression for the reduced birefringence when the intrinsic viscosity is not very low ([η]≳0·02), good agreement can be obtained between the experimental results and the orientation theory of persistent chains of finite thickness. Possible methods of calculating the reduced birefringence are discussed for the case of solutions of monomeric compounds, which do not explicitly obey the laws of macroscopic hydrodynamics ([η]⩽0). Measurement of the Maxwell constant Km ≡ Δn/η of the low molecular substances (in bulk) is regarded as being less suitable for comparison with the orientation theory of persistent chains of finite thickness.