Viscoelastic properties of poly(propylene glycols)

Abstract

The relaxational and retardational properties of poly(propylene glycol) liquids, of nominal molecular weights 400 and 4000, are described. The viscoelastic behaviour of each liquid has been determined over a wide temperature range, using high frequency shear wave techniques operating at 30 and 454 MHz. It is found that the complex compliance J∗(jω) is described in terms of the viscosity ν, the limiting high frequency compliance J ∞, the retardational compliance J r and a characteristic retardation time т r by: J ∗(jω)=J ∞+ 1 jωη + j r (1+jωτ r) β where β is a parameter of the retardation time distribution. For the lower molecular weight liquid, J r J ∞ = 17.4 , β = 0.45 and т r т m increases with decreasing temperature, reaching a limit of 170 near 0°C. This liquid shows no evidence of polymeric behaviour. For the other, J r J ∞ , β = 0.76, т r т m = 15.4 and is constant over the temperature range investigated. The main difference between the two liquids appears as an additional retardational or relaxational process for the higher molecular weight material which occurs in the initial or low frequency part of the relaxation region. This process is characterized by a single time, but with relaxation time 1 7 and a stiffness 7 times the values calculated for the first Rouse mode of polymer chain motion.