Viscosity-molecular weight relationships, intrinsic chain flexibility, and dynamic solution properties of guar galactomannan

Abstract Molecular theories of the viscosity of dilute and more concentrated solutions of random-coil polymers have been applied to five molecular-weight fractions of guar galactomannan. The variation in intrinsic viscosity ([η]; dL.g−1) with molecular weight (Mr) followed the relationship [η] = 3.8 × 10−4) Mr0.723, consistent with random-coil behaviour. The intrinsic stiffness of the galactomannan backbone was estimated by evaluating the “characteristic ratio” C∝, which is ∼ 12.6 and agrees well with results for carboxymethylcellulose, which has a closely similar, β-(1→4)-linked polymer backbone. At intermediate concentrations (c), up to specific viscosities of ∼ 10, ηsp was proportional to c1.3, while at higher concentrations, ηsp was ∼c5.1. This exponent is higher than is usually observed for polymers interacting purely by physical entanglement, and is evidence for more specific polymer-polymer interactions (“hyperentanglements”). The concentration dependence and the time-scale of entanglement coupling have been monitored by both steady-shear and oscillatory measurements, and a generality of response has been demonstrated.