Polyisoprene Diblock Research Articles

Electron energy-loss chemical imaging of polymer phases

Transmission electron energy-loss spectrum-imaging investigations of a low-density polyethylene blend with polystyrene show that chemical imaging is possible with high spatial resolution for polymers in a dedicated scanning transmission electron microscope. Spectrum-imaging provides highly accurate phase identifications without staining. This polymer blend also contains a small amount of styrene-hydrogenated polyisoprene diblock copolymer (Kraton G 1701) as a compatibilizer. Detection of this compatibilizer at interfaces was expected to be difficult because of its chemical similarity to the pure components. We were unable to detect the copolymer with EELS imaging unambiguously, but were able to accurately map regions rich in either polyethylene or polystyrene. Chemical imaging techniques that we develop here are of use for polymer mixtures that exhibit variations in either carbon bonding or distribution of heteroatoms.

Collective dynamics of tethered chains: Breathing modes.

Polystyrene (PS)-polyisoprene (PI) diblock copolymers dissolved in n-decane aggregate into spherical micelles with a PS core and a corona of tethered PI chains. The PI corona may be considered as a brush on the surface of a sphere or as the outer part of a many-armed polymer star. The thermal density fluctuations of the PI corona have been observed by neutron spin-echo spectroscopy. The peculiar multi-decay time relaxation behavior can be described remarkably well by a model based on an idea of de Gennes for treating the corona as a semidilute polymer solution with varying concentration profile.

Small-Angle X-Ray Scattering from Bulk Block Polymers in Disordered State. Estimation of χ-Values from Accidental Thermal Fluctuations

Small-angle X-ray scattering (SAXS) from accidental thermal concentration fluctuations of block polymers in bulk and in the disordered state was studied for a polystyrene–polyisoprene diblock polymer as a function of temperature. It was shown that the experimental SAXS profiles are predictable by Leibler’s theory based on the random phase approximation. Temperature dependence of χ-parameter between polystyrene and polyisoprene was estimated by fitting the experimental and theoretical SAXS profiles. An effect of glass transition on the thermal concentration fluctuations was also predicted.

The influence of diblock copolymers on the structure and properties of polybutadiene‐polyisoprene blends

AbstractThe structure and properties of a ternary polymer system comprised of 1, 4 polybutadiene, cis 1, 4 polyisoprene, and the corresponding 1, 4 polybutadiene/cis 1, 4 polyisoprene diblock copolymer have been investigated. Dynamic mechanical properties were measured as a function of frequency (3.5 to 110 Hz) and temperature (−135 to 40°C). Thermomechanical analysis and transmission electron microscopy provided additional information on the, phase relationships in the various specimens. The blends studied covered the entire triangular composition diagram; both slow solvent evaporation and rapid spin casting techniques were employed in the sample preparation. Results indicate that the BI diblock is a single phase material whereas binary blends of the two homopolymers are two‐phase in nature. Ternary blends of the two homopolymers with diblock and binary blends of a single homopolymer with diblock can be one or two phase materials depending on the sample composition and the ratio of B to I units in the diblock. All evidence From the dynamic, thermomechanical and microscopic experiments is used to elucidate the influence of the diblock in these polymer blends.