The phase behaviour and gelation of a rod-like polymer in solution and implications for microcellular foam morphology

Abstract

The phase separation and gelation of the rod-like macromolecule, poly(γ-benzyl- l-glutamate), were studied in an effort to understand the mechanism by which microcellular materials are made via thermally induced phase separation processes. Previous workers have studied similarly prepared materials from molecules which exist as random coils in solution. The microcellular materials were formed by lowering the solution temperature until phase separation and solvent freezing occurred. The solvent was removed by vacuum sublimation. An emphasis was placed on dilute isotropic solutions (<5 wt%) which yield low-density materials or ‘foams’. Both one- (e.g. benzene) and two-component (e.g. dioxane/water) solvent systems were employed. The morphology produced by liquid-liquid phase separation and gelation was an open-celled, fibrous structure, which resembles a three-dimensional lattice. The cell diameters were in the range of 1–10 μm and the fibres which comprise the struts were 0.2 to 2.0 μm thick. Various experimental observations are discussed in terms of the theories and proposed mechanisms of phase separation in solutions of rod-like macromolecules. Calculations of the spinodal for the Flory theory of rod-like particles were also made to assess the possibility of placing the isotropic solutions into an unstable region.