Network structure in gels of rod-like polypeptides.

The formation of a mechanically self-supporting, macromolecular gel or network is understood on a molecular scale in terms of cross-links or branch points, either of a permanent nature by covalent bond formation, or of a reversible nature, such as in the gelation of gelatin. In thermally reversible gels each branch point may contain numerous monomeric units, indicative of local crystallite or aggregate formation, as in cellulose acetate or gelatin, or only two monomeric units as in polyacrylylglycinamide. The formation of reversible networks in nonionic, rod-like polypeptide homopolymers, particularly at low concentrations (<0.1 wt%), is surprising in that the molecular origin of the branch points is not obvious. We have suggested previously that this network constitutes a thermodynamic phase resulting from a particular kinetic mechanism of phase formation made favourable by the unusual polymerdiluent phase equilibria occurring with stiff-chain polymers. Here, the network is visualized by electron microscopy, and shown to be compatible with the proposed mechanism.