|
Phase Behavior
|
The phase behavior of polystyrene and poly(n-pentyl methacrylate) (PS/PnPMA) blend with small amounts of PS-block-PnPMA copolymer (PS-PnPMA) was studied by turbidity measurement, light scattering method (LS), and and small angle neutron scattering method (SANS). PS/PnPMA with lower molecular weights were synthesized by anionic polymerization, thus the molecular weight distributions of all polymers are less than 1.03. This blend exhibited both the upper critical solution transition (UCST) at lower temperature and the lower critical solution transition (LCST) at higher temperature behavior, and for the higher However, when molecular weights of PS,is just increased to 5 2 %, this blend showed an hour-glass type of phase behavior was observed. When a very small amount (~ 0.5 wt %) of symmetric PS-PnPMA is added to the blend, LCST increases but UCST decreases. This indicates that the miscibility window is expanded and the PS-PnPMA plays an effective compatibilizer on PS/PnPMA blend. However, when the amount of PS-PnPMA is larger than ~ 1 wt %, the turbidity temperatures for the LCST are essentially the same regardless of blend composition; thus at asymmetric blend compositions (for instance, 20/80 PS/PnPMA and 80/20 PS/PnPMA), the turbidity temperature for the LCST is smaller than that for blend without the block copolymer. Thus, incompatibilization effect of the block copolymer was observed for asymmetric blend composition. This interesting phase behavior was discussed by using SANS and compared with predictions by the incompressible mean field theory and the lattice cluster theory
|
|
|
|
|
Related Journals
|
|
