Viscoelasticity and crystallization of poly(ethylene oxide) star polymers of varying arm number and size

We investigated the linear melt viscoelasticity and the crystallization kinetics of a series of model poly(ethylene oxide) stars with different functionalities (f=4-32 arms) and moderately entangled arms (their molecular masses ranging from 5.5 to 12 kg/mol). The limited data in the homogeneous state indicated that the zero-shear viscosity eta(0) was adequately described by the Milner-McLeish model for functionalities f < 32, where the core effect is insignificant; a similar behavior was observed for the recoverable compliance J(e)(0) which depended on both the molecular weight and the number of the arms. Below the melting point, the isothermal crystallization was measured with differential scanning calorimetry and rheology, and analyzed in terms of the Avrami theory, expanding over a wide range of temperatures. The results were supported by additional polarizing optical microscopy data and indicated a slower crystallization kinetics of the stars compared to their linear analogues. They showed a strong dependence of the crystallization rate on the arm molecular weight, whereas the available experimental evidence is suggestive of some functionality dependence as well. (c) 2007 The Society of Rheology. Journal of Rheology