Proton Magnetic Relaxation in Polyethylene Oxide Solutions

Abstract

Proton magnetic relaxation times have been measured in solutions of polyethylene oxide. Molecular weight, temperature, and solution concentration have been systematically varied. Several low‐molecular‐weight oligomers have been studied as well as polymers which vary in molecular weight from 4 × 103 to 4 × 106. The results show that in dilute solution both T 1 and T 1 are independent of molecular weight. T 1 decreases with increasing concentration for concentrations greater than 0.2 g per ml of polymer, but is independent of concentration for more dilute solutions. T 2 is independent of concentration in the limit of low concentration, but decreases rapidly with increasing concentration. The concentration dependence of T 2 is a sensitive function of molecular weight. The relaxation mechanism has been analyzed using a model of rotameric transitions and the molecular geometry calculated from the known crystal structure of the polymer. The most important term is that arising from a conformational change about the C‐C bond, in which the oxygen atoms move from a gauche to a gauche′ position. The relaxation times (T 1 ) of water in aqueous polyethylene oxide solutions decrease with increasing polymer concentration, and are independent of the molecular weight of the polymer.