The Influence of Solvent and Temperature Upon the Aggregation of Poly(ethylene glycol)

A viscometric method was used to investigate the influence of solvent and temperature upon the aggregation of poly(ethylene glycol) (PEG) in dilute solution. While no obvious change in the value of the intrinsic viscosity [η] and the Huggins coefficient kH was observed for PEG in benzene solutions upon increasing the temperature from 15°C to 40°C, for the same increase in temperature, the [η] values in aqueous solutions and aqueous potassium sulfate (0.45 mol/l K2SO4) solutions showed a substantial decrease, kH values showed a substantial increase. Especially for 0.45 mol/l K2SO4 solutions, at high temperatures (35°C and 40°C), deviation from the Huggins law and a much higher value of kH are obtained, which presents the occurrence of polymer aggregation. These facts imply that intersegment attraction (cohesive interaction) gets gradually important relatively to intersegment repulsion, due to the salt out effect and the hydrogen bond breaking action of thermal energy added to the solution. As a consequence, in aqueous K2SO4 solutions at higher temperatures, polymer-polymer contacts are favored. Then above a critical concentration, the phenomenon of aggregation occurs. However, there is no obvious aggregation in PEG/water solution and PEG/benzene solutions in the temperature range by our viscometric measurement, although in PEG/water solutions, the intersegment cohesion causes that the polymer coil shrinks gradually as the temperature increases. The results show that aggregation of polymer is possible to occur only in poor solvent.