Dielectric and Viscoelastic Behavior of Low-M Linear Polyisoprene Blended in Long Matrix

Abstract

Cis-polyisoprene (PI) has the type-A dipole parallel along the chain backbone thereby exhibiting slow dielectric relaxation that reflects the global chain motion (end-to-end vector fluctuation). For linear PI probes having the molecular weights M1 in a range between 21.4× 103 and 179 × 103 (M1/Me = 4-36) and being blended with a longer PI matrix (M2 = 1.12 × 106), a recent dielectric experiment revealed that the probe relaxation is moderately retarded on blending and this retardation is enhanced with decreasing M1 in this range; cf. Matsumiya et al., Macromolecules, 46, 6067 (2013). Those dielectric data were analyzed within the context of the tube model to suggest that the probe relaxation in monodisperse bulk occurs through reptation along a partially dilated tube that wriggles in a fully dilated tube. However, this mechanism of relaxation is expected to vanish on a further decrease of M1 because the tube itself loses its sound meaning for small M1. This expectation was examined in this study. Dielectric and viscoelastic tests revealed that the retardation of the probe relaxation on blending becomes minor (though not negligible) on a decrease of M1 to 7.8× 103 (≈ 1.6Me), as expected.