Segmental mobility in the vicinity of Tg in PS/SBR blends: Nanodomain size prediction of the dispersed phase

Abstract

AbstractThe blends of polystyrene (PS) and styrene‐butadiene rubber (SBR) are melt‐blended at different ratios to form physical thermoplastic elastomers. This polymeric blend is expected to behave more or less similar to chemically synthesized block copolymers such as styrene‐butadiene block copolymers (SBS). In this study, mechanical and the thermomechanical properties of this blend are investigated and compared to those of SBS copolymer. As far as morphology is considered, the blend shows a two‐phase morphology with an interface, which shows very weak interactions. According to the observed morphology and the domain size of dispersed phase the blends are of good integrity. The mechanical properties of the blends confirm the integrity of the blend and effective interface stress transfer. The tensile and Izod impact properties of the blends shows improvements upon increase in SBR content of the blend. As SBR content augments the elongation at break increases, whereas tensile dissipated energy and impact resistance go through a maximum. Therefore, blend with SBR‐content in 60–75% range can be considered as preferred one. In a wide range of concentration a phase inversion was observed and Tg‐depression was detected also for the SBR phase. This Tg‐depression was correlated to the changes in dynamics of segments (segmental mobility) near the surfaces. Using the proposed relationships between Tg‐depression and the thickness of the thin films, it was tried to calculate domain size of SBR inclusions in PS matrix. A rough correlation between SBR domain sizes in SEM images and calculated thicknesses using Tg‐depression in thin films was found. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013