DYNAMIC-MECHANICAL PROPERTIES OF POLY(OXYPROPYLENEDIOL) AND POLY(OXYPROPYLENETRIOL)

Oscillatory shear measurements were done on linear poly(oxypropylenedi ol) and star-shaped poly(oxypropylenetriol) with three arms of equal l ength. Internal relaxation modes are observed in addition to the local segmental relaxation (alpha-relaxation) for all molar masses investig ated between 500 and 8000 g/mol. The alpha-relaxation is well describe d by a generalized exponential relaxation time distribution in which t he parameters have been chosen to give a close correspondence with a s tretched exponential decay in the time domain. The corresponding stret ched exponent beta = 0.49 +/- 0.01 and is the same for the diol and tr iol and independent of the molar mass. The temperature dependence of t he internal modes is the same for the diol and triol and independent o f the molar mass but is weaker than that of the alpha-relaxation close to the glass transition temperature. The shape of the internal modes' relaxation fits well to the Rouse model, and the molar mass dependenc e of the slowest relaxation time is stronger than expected from the Ro use model. At a given arm length, taking the linear diol as consisting of two arms, the internal modes of the triol and diol are the same wi thin experimental error. A triol with weight average molar mass 260 g/ mol, which corresponds to, on average, less than one POP segment per a rm, does not show internal modes and has a significantly broader alpha -relaxation.