The isothermal luminescence decay kinetics in near-surface nanolayers of plasma-activated bulk samples of amorphous polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and their miscible blends with weight ratios PS/PPO of 75/25 and 50/50 has been studied at 77 K. The intensities of isothermal luminescence (I) of homopolymer and blend surfaces have been compared. It has been found that the ratio between the luminescence intensities for PS and PPO (I(PS)/I(PPO)) may be as high as 50, while the luminescence intensities for the PS–PPO blends are close to I(PPO). The results obtained indicate that the PPO concentration in the surface layers of the blends is higher than that in the bulk. 相似文献
The differential orientation of polymer chains has been measured in polystyrene (PS)/poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) compatible blends. Density measurements are reported as a function of binary blend composition at 23°C. Drawing was performed by solid-state coextrusion. PS/PPO blend compositions of 90/10 and 75/25 were drawn within sandwiches of polyethylene at 145°C and isotactic polypropylene at 155°C, i.e. at ca. 25°C above the glass transition temperatures of the two blends. The change in Fourier-transform infrared dichroisms on drawing these blends was measured at 906 and 1190 cm?1, corresponding to predominantly PS and PPO, respectively. The orientation of PS and PPO was observed as a function of draw ratio λ in the range 1–5; orientations increased with λ for both PS and PPO in both blends but to different degrees. Both polymers decreased in orientation with increasing PPO content. Annealing with fixed ends showed that the PPO chains disorient more slowly than those of PS. All binary systems were found to be amorphous and compatible. 相似文献
Photooxidation of blends of polystyrene and poly (vinyl methyl ether) was studied at 30°C. The oxygen uptake by PS was negligible but PVME oxidized readily. The induction period of oxidation of PVME was prolonged by the presence of PS. The steady state rate of oxidation of the blend was strongly influenced by the segmental mobility of the blend which also governed the kinetics and morphology of phase separation. The molecular weight of PVME decreased more slowly in the blend as PS content increased. It was believed that the reaction between PVME radicals and PS resulted in less reactive PS radicals which retarded oxidation. The PS radicals eventually underwent chain scission reactions. 相似文献
The effect of simple shear flow on the phase behavior and morphology was investigated for both polystyrene/poly(vinyl methyl ether) (PS/PVME) and poly(methyl methacrylate)/poly(styrene‐co‐acrylonitrile) (PMMA /SAN‐29.5) blends, which have LCST (lower critical solution temperature)‐type phase diagram. The measurements were carried out using a special shear apparatus of two parallel glass plates type. The PS/PVME blends showed shear‐induced demixing and shear‐induced mixing at low and high shear rate values, respectively. In addition, the rotation speed and the sample thickness were found to have a pronounced effect on the phase behavior under shear flow. On the‐other hand, PMMA/SAN blend showed only shear‐induced mixing and the magnitudes of the elevation of the cloud points were found to be composition and molecular weight dependent. The morphology of the PMMA/SAN=75/25 blend indicated that shear‐induced mixing occurred at a critical shear rate value, below which the two phases were highly oriented and elongated in the flow direction. 相似文献
The dynamic mechanical behavior of 10 and 20% poly(vinyl methyl ether)-polystyrene blends has been studied in the frequency range 10?5 Hz to 5 Hz and temperature range 100–450 K. Isochronal plots of modulus G′ and loss factor, tan ?, show the presence of one relaxation process at temperatures below the transition zone. A second relaxation process at intermediate temperatures but below Tg may be inferred from the breadth of the G″ frequency curves in the transition zone of both blends. This process, at 280 < T < 300 K, is independent of PVME concentration and seems to be associated with the local modes of motions of PS chains. The rheological behavior of the blends shows them to be compatible up to 20% PVME. Their G′ and G″ data cannot be shifted along a frequency axis to produce a satisfactory master curve. The departure from thermorheological simplicity is much more clearly observed in the tan ? than in the modulus-frequency plots. This departure is due to the change in the segmental correlation effects, or length, with temperature near Tg. A molecular model of the growth of microshear domains with hierarchically constrained molecular motions, given elsewhere, quantitatively agrees with the dynamic mechanical behavior. 相似文献
Differential scanning calorimetry (DSC) and laser‐interferometric creep rate spectroscopy (CRS) were used for kinetic and discrete analysis of segmental motion within (and close to) glass transition range in polystyrene ‐ poly(α‐methyl styrene) (PS/PMS) and polystyrene ‐ poly(vinyl methyl ether) (PS/PVME) miscible blends. Two kinds of segmental dynamics heterogeneity were found. Separate ‘unfreezing’ of PS and PMS segmental motions was observed that manifested itself in two Tgs and simultaneous large drop in the Tg s, as well as glass transition activation energy, motional event scale and cooperativity degree values, down to the β‐relaxation parameters. The wide activation energy dispersion within a single broad glass transition in PS/PVME blends was found, and this relaxation region was subdivided, by CRS, into several predicted kinds of segmental motion. Both results are treated in the framework of the concept of common segmental nature of α‐ and β‐relaxations in flexible chain polymers. 相似文献
Phase separation of polystyrene/poly (vinyl methyl ether) (PS/PVME) blends was induced and controlled by irradiation with linearly polarized light. The PS component was made photosensitive by chemically labeled with either anthracene or trans‐stilbene. The former was used to crosslink the PS component whereas the latter induces phase separation by changing polymer segmental volumes. The phase separation and reaction kinetics were observed and discussed in terms of mode‐selection process. 相似文献
We apply broadband dielectric relaxation spectroscopy to probe the dynamics of hydrogen bonded polymer blends. A copolymer consisting of 2,3-dimethylbutadiene (DMB) [86%] and p-(hexafluoro-2-hydroxyl-2-propyl)styrene (HFS) [14%] was synthesized and blended with poly(vinylmethyl ether) (PVME). The copolymer is capable of forming strong intermolecular hydrogen bonds, while minimizing the degree of intramolecular associations, and its blends with PVME are predicted to be miscible over the entire composition range. Two segmental processes, α and α1, are present in blends containing 26, 50, and 76 weight percent copolymer. The slower process (α1) is assigned to the segmental motion of the intermolecularly associated copolymer, and the faster process (α) to segmental motions of PVME modified by the HFS:DMB copolymer. A relaxation associated with residual water is present in the glassy state. A local process due to motions of the PVME ether groups (β) is also present in the glassy state, and does not change with blend composition. 相似文献
The viscoelastic (VE) response of freeze-dried blends of polystyrene (PS) and poly-(2,6-dimethyl phenylene oxide) (PPO) has been studied as a function of composition, frequency, and temperature to examine the degree of rheological compatibility. When blended together, the relaxation processes of both molecular species exhibit the same temperature dependence. However, the temperature dependence of the VE response is a function of composition. It is shown that this behavior can be predicted from the measured glass transition temperatures by assuming the additivity of the free volumes of the components. The properties of the blends are compared at equal free volumes. The effective segmental friction factor is found to be independent of composition while the modulus of the rubbery plateau increases with PPO concentration. This result is interpreted as a change in the entanglement molecular weight Me of the blends. When the changes in Me are considered, the relationship between the zero-shear viscosity η0 and the 3.4 power of the weight-average molecular weight, commonly found for high molecular weight homopolymers, predicts the compositional dependence of η0 for the PPO–PS blends. It is concluded that the PPO–PS system forms a rheologically compatible blend. 相似文献
In recent years, many factors influencing phase behavior of polymer blends have been studied because of their widely technological importance, as a simple method of formulating new materials with tailored properties which make them suitable for a variety of applications. This work has three main goals which were reached by using the Perturbed Chain Statistical Associating Fluid Theory (PC-SAFT) and the Sanchez–Lacombe (SL) non-cubic equations of state (EoS), which in previous works have shown their ability to handle long chain and associating interactions. First, both equations of state were tested with the correlation of the specific volumes of pure blends (PBD/PS, PPO/PS, PVME/PS, PEO/PES) and the prediction of the specific volumes for blends; second, the modeling of blend miscibilities in the liquid–liquid equilibria (LLE) of PBD/PS, PPG/PEGE, PVME/PS, PEO/PES, and PnPMA/PS blends; third, the modeling of the phase behavior of PS/PVME blends at various compositions in the presence of CO2. PC-SAFT and SL pure-component parameters were regressed by fitting pure-component data of real substances (liquid pressure–volume–temperature, PVT, data for polymers and vapor pressure and saturated liquid molar volume for CO2) and the fluid phase behavior of blend systems were simulated fitting one binary interaction parameter (kij) by regression of experimental data using the modified likelihood maximum method. Results were compared with experimental data obtained from literature and an excellent agreement was obtained with both EoS, which were also capable of predicting the fluid phase behavior corresponding to the critical solution temperatures (LCST: lower critical solution temperature, UCST: upper critical solution temperature) of blends. 相似文献
Summary: The toughness of poly(styrene‐block‐butadiene) star block copolymer/polystyrene (PS) blends have been investigated using the essential‐work‐of‐fracture approach. The blends show a co‐continuous or layer‐like structure of polystyrene‐rich and polybutadiene‐rich domains arising from the used extrusion process. A tough‐to‐brittle transition at a critical domain size of polystyrene‐rich domains of about 50 nm and a maximum in the non‐essential work of fracture at 20–30% PS (co‐continuous morphology) have been found.
Non‐essential work of fracture as a function of the mean thickness of polystyrene‐rich domains, demonstrating a tough‐to‐brittle transition at a critical domain thickness about 50 nm. AFM micrograph of a star block copolymer/PS‐blend containing 40% PS. 相似文献
Anisotropic phase separation of polystyrene/poly(vinyl methyl ether) (PS/PVME) blends was induced by photoisomerization of trans-stilbene moieties labeled on the PS chains (abbreviated hereafter as PSS chains) using linearly polarized light. As temperature increases, the anisotropy becomes weaker and eventually disappears at 10°C above the glass transition of the PSS component. It was concluded that the elastic stress associated with the spatial distribution of the reaction is responsible for this morphological anisotropy. 相似文献