Phase separation of off‐critical polymer blends of poly(styrene‐co‐maleic anhydride) and poly(methyl methacrylate). II. Morphology and mechanical properties

The effects of the phase‐separation temperature and time on the mechanical properties and morphology of poly(methyl methacrylate)/poly(styrene‐co‐maleic anhydride with 10 wt% ethyl acrylate) (SMA) blends were studied. Two compositions (20/80 and 40/60 w/w SMA/PMMAe) were prepared with a miniature twin‐screw extruder. Compared with those of the miscible blends, the Young's modulus values of the blends increased after the phase separation of the 40/60 SMA/PMMAe blend and within the early stage of spinodal decomposition of the 20/80 SMA/PMMAe blend. The mechanical properties, in terms of the tensile strength at break and the elongation, were better for the miscible blends than for the phase‐separation blends. This was believed to be the result of changes in the composition and molecular reorganization. The changes in the phase‐separating domains of both compositions, as observed by transmission electron microscopy, had no significant influence on the tensile moduli. Detailed studies of the morphology revealed a cocontinuous structure, indicating that the blends underwent spinodal decomposition. A morphological comparison of the two compositions illustrated the validity of the level rule. The growth rate of the droplet size was determined by approximation from the light scattering data and by direct measurements with transmission electron microscopy. The discrepancies observed in the droplet size growth rate were attributed to heat variations induced by the different sample thicknesses and heat transfer during the investigation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 886–897, 2004     

Rheology and interdiffusion in miscible blends of a low molar mass liquid crystal and bisphenol A–polycarbonate

The melt rheology of blends of a low molar mass liquid crystal (LC) blended with bisphenol A–polycarbonate (PC), and the self‐diffusion of the polycarbonate in the blends are reported. Results of small angle light scattering indicate that the LC is miscible in the mixture for weight fraction of LC less than 6%. The rheological properties of the blended sample within the miscible regime of the blends vary significantly with LC content. Although at low shear rates, the viscosity is similar to that of the pure polycarbonate, at high shear rates the curves show three regions of behavior, as has been described previously for pure LCs. The diffusion coefficient was obtained from interdiffusion studies using nuclear reaction analysis of bilayer films. An addition of only 1 wt % LC to the polycarbonate significantly increased the diffusion coefficient, but at higher concentration the converse was found. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2187–2195, 2007     

The crystallinity and miscibility of syndiotactic polystyrene blends after mixing with low molar mass liquid crystal or commercial lubricant

The quantities of the crystallinity of syndiotactic polystyrene (SPS) blended with another polymer in the group of poly(α-methyl styrene), poly(n-butyl methacrylate) or poly(cyclohexyl acrylate) with or without the additives were measured by X-ray diffraction and calculated by Ruland’s method. The SPS was synthesized by using metallocene catalyst and modified-methylaluminoxane as cocatalyst. The additive of low molar mass liquid crystal chemical (cyclohexyl-biphenyl-cyclohexane (CBC33)) or lubricant (glycerol monostearate (GMS)) was individually added to the blends of SPS in order to investigate the effects on the crystallinity of the blended SPS. From the experimental results, it was found that the percent crystallinities of the blends decreased with decreasing the percent of SPS in the blend because of the dilution of SPS. The depression of the percent crystallinity was in the order of PaMS > PCHA > PBMA according to the compatibility with SPS. The addition of GMS or CBC33 slightly decreased the percent crystallinity of the pure SPS. The addition of GMS impeded the depression of the SPS crystallinity in the blends, because their percent depression from pure SPS is similar (at around 25%) regardless to the components of the blends. The blends with added CBC33 have the similar depression of crystallinity as the pure blends because of the low concentration of CBC33 and the good compatibility of CBC33 with the SPS.     

Phase separation of off‐critical polymer blends of poly(styrene‐co‐maleic anhydride) and poly(methyl methacrylate). I. Kinetics of spinodal decomposition

The kinetics of phase separation via the spinodal decomposition of poly(styrene‐co‐maleic anhydride)/poly(methyl methacrylate) from a delay time period to late stages were investigated with a light scattering technique. The standard procedure for identifying four stages of spinodal decomposition, based on the characteristics of concentration fluctuations, was clearly introduced with the light scattering method. The spinodal limits were divided into four stages: the delay time, the early stage, the intermediate stage, and the late stage. The validity of the linearized theory was reviewed because it was used as an indicator of the limit of the early stage of spinodal decomposition, which divided the delay time period from the early stage and the early stage from the intermediate stage. The linearized theory fit the experimental results very well after the delay time. The scaled structure function of the melt‐mixed blend was analyzed. The universality of the scale structure function, F(x) = S(q,t)q_m³(t) (where S is the structure function, x is equal to q/q_m, q is the scattering wave vector, q_m is the maximum wave vector, and t is the time in seconds), indicated the late stage of phase separation and divided the late stage from the intermediate stage. The simple normalized scaling function profile for the cluster region proposed by Furukawa described the experimental data very well, whereas the profile for deep quenching, which was recently suggested, showed some discrepancies. As a result of the phase separation, the processing of this blend may be able to be developed to provide the most suitable morphology. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 871–885, 2004