Composition and Temperature Dependence of Terminal and Segmental Dynamics in Polyisoprene/Poly(vinylethylene) Blends

Abstract

The frequency-dependent shear moduli were measured over a range of temperature for polyisoprene (PI, M = 22 000 and 78 000), poly(vinylethylene) (PVE, M = 10 000 and 120 000), and their blends. The longest relaxation times of each component in the blends were extracted by a modified Tsenoglou mixing rule, and converted to monomeric friction factors via the reptation model. Dielectric relaxation and pulsed field gradient NMR were used to follow the terminal relaxation and diffusion, respectively, of a low molecular weight PI (M = 1300) in blends with perdeuterated PVE (M = 2300), for a range of temperature and composition. In this case monomeric friction factors were extracted via the Rouse model. The friction factors for PI via all three techniques agreed quantitatively, and the friction factors for both components were independent of molecular weight. Segmental dynamics of each component in PI/PVE blends by NMR methods, reported in the literature, could be compared directly with the terminal relaxation data. In all cases, the segmental and terminal dynamics exhibited equivalent dependences on temperature and composition. The predictions of the model of Lodge and McLeish were compared to the combined data, by calculating component self-concentrations and effective glass transition temperatures using a single temperature-independent length scale. As anticipated in the original model, this length scale is close to the Kuhn length of the particular component. In the case of PI, the model provides a quantitative description over the entire composition and temperature range studied. For PVE the agreement is not as quantitative, but it is still quite satisfactory.