Atactic polystyrenes of narrow molar mass distribution with average molar masses larger than the critical molar mass Mc were mixed with similar polystyrenes of molecular masses lower than M c. Linear viscoelastic melt properties of these binary blends were measured with a dynamic viscometer of the concentric cylinder type. One of the experimental findings is that the time-temperature shift factors ar are dependent on the composition of the samples. This can be understood, if free volume due to chain-ends is taken into account. A computer-fitted WLF-equation being modified in a proper way leads to the following results: At the glass-transition-temperature the fraction of free volume in polystyrene of infinite molar mass is only 0.015. At a temperature of 180 °C the mean value of the free volume at a chain end is 0.029 nm 3 for the polystyrene investigated.
Abstract." The influence of short chain molecules (with M < M c ) on the rheology of the melts of binary blends of long and short chain polymers was studied. For this purpose, the complex moduli as functions of circular frequency were examined for these melts and also for melts of unblended long chain samples. For pertinent blending a set of standard polystyrenes with narrow molar mass distribution was used.The short chain component causes a typical diluent effect. This is clearly revealed from the lowering of the plateau modulus of the long chain component. This lowering is found to be proportional to the square of the weight fraction w2 of the long chain component, as theoretically predicted. The reduction of the relaxation times of the long chain molecules turns out to be proportional to w~ '8, when the influence of an increased contribution of chain ends to the free volume is separately taken into account according to the results of the first paper of this series. As the power of w2 in the latter relation is not critical, one can formulate equations for the first normal-stress coefficient and for the zero-shear viscosity as functions of w2M~.~, which merge into the respective M 6'8-and M34-1aws well-established for undiluted high polymers (w2 = 1).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.