Intrinsic viscosity‐molecular weight relationships for dextran

Intrinsic viscosities of dextrans of known branching ratio were measured in water formamide, and in a water‐methanol mixture at two temperatures. Weight‐average molecular weights (sedimentation equilibrium) ranged from 1.1 × 10 4 to 1.7 × 10 6 . A model for the hydrolyzed dextran molecule was assumed. Using the methods of Zimm and Stockmayer, the g factor calculated from this model was compared with the g factor obtained from the intrinsic viscosity‐molecular weight data through the use of the Flory‐Fox theory ( g = ratio of squares of radii of gyration of branched to unbranched polymer). The calculated branch lengths required to make consistent the g factors obtained by two different routes were of the same order of magnitude as those found by classical organic chemical methods for other dextran preparations. The intrinsic viscosity‐molecular weight relation at 25°C. in water for linear dextran was predicted from the data. It is suggested that investigations of branched polymers of known constitution be carried out by these methods.