Crystallization behavior and toughening of syndiotactic polystyrene/ poly(2,6-dimethyl-1,4-phenylene oxide) blends

Abstract

Crystallization behavior, crystal growth and toughening of syndiotactic polystyrene (SPS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) blends were investigated. Isothermal and non-isothermal crystallization experiment on the blend sample revealed that (1) melt crystallization temperature ($T_c$) decreased from 239℃ to 212℃, (2) half-time of crystallization($τ_(1/2)$) increased from 20sec to 90sec, (3) Avrami index increased from 1.7 to 3.1, (4) melting temperature($T_m$) decreased from 272℃ to 270℃, and (5) nucleation density are decreased. As the crystallization temperature increases, $T_m$ increased from 270.5℃ to 272℃ while Avrami index decreased from 2.9 to 1.7. Multiple melting behaviors were notable in melting of SPS and SPS/PPO blend system. Different multiple melting behaviors were observed for different compositions, showing optimum annealing temperature. The optimum annealing temperature for the pure SPS was found to be 265℃. The optimum annealing temperature for the 70/30, 80/20, and 90/10 blends of SPS/PPO were found to be 258.5, 261.0, and 263.5℃, respectively. When annealed below the optimum annealing temperature, the ordering took place, the crystallinity increased and lamellae were thickened. Lower temperature peak in DSC thermograms shifted to higher temperature region by annealing by the result of growth of large crystals. On the other hand, annealing at the higher temperature did not promote the crystal growth. In order to analyze such multiple melting phenomena in relation to crystal structure, the combined morphology was observed using polarizing optical microscopy (POM), wide angle x-ray diffraction (WAXD), small angle x-ray scattering (SAXS). The analysis lead to conclusion that in low temperature (at 220℃) crystallization PPO prohibited crystallization of SPS while it was promoted in high temperature crystallization (at 240℃). The thermal behavior of the pure SPS and SPSIPPO (70/30) blend taken from the isothermally crystallized spec...