Nonlinear phase‐separation behavior of poly(methyl methacrylate)/poly(styrene‐co‐maleic anhydride) blends

The nonlinear phase‐separation behavior of poly(methyl methacrylate)/poly(styrene‐co‐maleic anhydride) (PMMA/SMA) blends over wide appropriate temperature and heating rate ranges was studied using time‐resolved small‐angle laser light scattering. During the non‐isothermal process, a quantitative logarithm function was established to describe the relationship between cloud point (T_c) and heating rate (k) as given by T_c = Alnk + T₀, in which the parameter A, reflecting the heating rate dependence, is much different for different compositions due to phase‐separation rate and activation energy difference. For the isothermal phase‐separation process, an Arrhenius‐like equation was successfully applied to describe the temperature dependence of the apparent diffusion coefficient (D_app) and the relaxation time (τ) of the early stage as well as the late stage of spinodal decomposition (SD) of PMMA/SMA blends. Based on the successful application of the Arrhenius‐like equation, the related activation energies could be obtained from D_app and τ of the early and late stages of SD, respectively. In addition, these results indicate that it is possible to predict the temperature dependence of the phase‐separation behavior of binary polymer mixtures during isothermal annealing over a range of 100 °C above the glass transition temperature using the Arrhenius‐like equation. © 2012 Society of Chemical Industry     

Effect of poly(styrene‐co‐maleic anhydride) imidization on the miscibility and phase‐separation temperatures of poly(styrene‐co‐maleic anhydride)/poly(vinyl methyl ether) and poly(styrene‐co‐maleic anhydride)/ poly(methyl methacrylate) blends

The objective of this work was to study the miscibility and phase‐separation temperatures of poly(styrene‐co‐maleic anhydride) (SMA)/poly(vinyl methyl ether) (PVME) and SMA/poly(methyl methacrylate) (PMMA) blends with differential scanning calorimetry and small‐angle light scattering techniques. We focused on the effect of SMA partial imidization with aniline on the miscibility and phase‐separation temperatures of these blends. The SMA imidization reaction led to a partially imidized styrene N‐phenyl succinimide copolymer (SMI) with a degree of conversion of 49% and a decomposition temperature higher than that of SMA by about 20°C. We observed that both SMI/PVME and SMI/PMMA blends had lower critical solution temperature behavior. The imidization of SMA increased the phase‐separation temperature of the SMA/PVME blend and decreased that of the SMA/PMMA blend. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Phase separation in polymer blend thin films studied by differential AC chip calorimetry

AC chip calorimetry is used to study the phase separation behavior of 100 nm thin poly(vinyl methyl ether)/poly(styrene) (PVME/PS) blend films. Using the on-chip heaters, very short (10 ms-10 s) temperature jumps into the temperature window of phase separation are applied, simulating laser heating induced patterning. These temperature pulses produce a measurable shift in the glass transition temperature, evidencing phase separation. The effect of pulse length and height on phase separation can be studied. The thus phase separated PVME/PS thin films remix rapidly, in contrast with measurements in bulk. AC chip calorimetry seems to be a more sensitive technique than atomic force microscopy to detect the early stages of phase separation in polymer blend thin films.     

Determination of the phase diagram of HBA‐HNA liquid crystalline polymer/polycarbonate blends

The phase diagram of blends of liquid crystalline polymer (LCP) and polycarbonate (PC) was constructed. The effect of temperature on morphological development in melt‐blended samples was examined with a polarized light microscope, in conjunction with a heating stage. Phase separation in the blend was observed as the temperature was increased. For a particular LCP/PC blend composition, two‐phase separation temperatures (T_sp1 and T_sp2) were determined. Consequently, the corresponding phase diagram relating to phase separation was constructed. It was divided into three regions. No phase separation occurred when the blend was below T_sp1. However, a slight phase separation was detected when the temperature was between T_sp1 and T_sp2. Moreover, pronounced phase separation was observed when the blend was at a temperature above T_sp2. The phase‐separated structure varied according to the initial composition of the blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of selective localization of cellulose nanowhiskers on viscoelastic phase separation

Viscoelastic phase separation (VPS) is a fundamental physical phenomenon that creates percolated network structure in dynamically asymmetric mixtures. The object of this study was to investigate the effect of rod shape nanoparticles with different surface chemistries on VPS in the polystyrene/poly(vinyl methyl ether), PS/PVME, blend. For this purpose, hydrophilic (CNWs) and hydrophobic (M‐CNWs) cellulose nanowhiskers (CNWs) were prepared to be used as nanorods. Rheological measurments were employed to investigate the effect of nanowhiskers on phase separation temperature, kinetics of phase separation, and dynamic asymmetry. The evolution of morphology during the phase separation at a fixed quench depth was assessed using polarized optical microscopy. The nanowhiskers were effective in decreasing the correlation length, which slowed down the phase separation. CNWs self‐assembled into the PVME‐rich phase during the phase separation, which led to a decrease in the dynamic asymmetry and beyond a critical volume fraction of CNWs, the VPS mechanism changed to spinodal decomposition (SD). However, in the presence of M‐CNW, the localization of M‐CNWs into the PS‐rich phase enhanced the dynamic asymmetry and at 2 vol% M‐CNWs, the induced PS‐rich network by VPS was arrested. The linear and non‐linear viscoelastic behavior of the samples were studied as well. POLYM. ENG. SCI., 58:928–942, 2018. © 2017 Society of Plastics Engineers     

Phase diagrams of thermally stable,polymer‐dispersed liquid crystals: Exploring the impact of chain length and chemical structure

Polymer‐dispersed liquid crystals (PDLCs) have garnered significant interest and motivated the investigation of the phase behavior of thermally stable smectic liquid crystals (LCs) via thermally induced phase separation (TIPS). In this study, we examined a series of two, biphenyl‐based smectic LCs suitable for high temperature polymer blend processing. Phase diagrams for LC/polystyrene (PS) blends at various compositions (0–60 wt%) were constructed. Less than 15 wt% of 8B8 (1,1′‐biphenyl‐4,4′‐diyl dioctanoate) LC in PS led to good polymer miscibility, while phase separation was induced at concentrations higher than 15 wt%. The LC concentration at saturation decreased with increasing aliphatic chain length. We also investigated the chain length (C6‐C16) effect on the PS glass transition temperature (T_g) at the LC saturation point. The T_g increased with increasing chain length due to reduced plasticization. We further examined the role of chemical structure (relatively less polar ether vs. more polar ester) on the phase diagram regions and the T_g of the nonpolar PS matrix, respectively. It is anticipated that these LC/PS phase diagrams will benefit elevated temperature processing for TIPS by highlighting the role of LC chemical structure and chain length on blend morphology. POLYM. ENG. SCI., 56:388–393, 2016. © 2016 Society of Plastics Engineers     

The effect of addition of poly(propylene‐g‐acrylic acid) on the morphology of poly(vinyl methylether) and isotactic polypropylene blend

The interfacial adhesion of blend of isotactic polypropylene/poly(vinyl methylether) (i‐PP/PVME) has been improved by the addition of poly(propylene‐g‐acrylic acid) (PP‐g‐AA) as a compatibilizing agent. The phase morphologies of the blends are investigated by optical microscopy (OM) and lateral force microscopy (LFM). The i‐PP/PVME (80/20) blend with no addition of PP‐g‐AA from extrusion process shows a coarse morphology with the dispersed domain size as large as several micrometers; After the addition of 2.5% PP‐g‐AA in the blends, the dispersed PVME domain size decreases greatly. The addition of 5% PP‐g‐AA results in a homogeneous morphology. The blending of PP‐g‐AA with PVME reduces the crystallization temperature of PP‐g‐AA, which is different from that of blending i‐PP with PVME. The increase of the interfacial adhesion is attributed to the specific intermolecular interaction between the acrylic acid group of PP‐g‐AA and the ether group of PVME. The specific interaction is studied by Fourier transform infrared spectroscopy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 4098–4103, 2006     

A modified rheological model of viscosities for BR–SBS blends

Blends of polybutadiene (BR) and styrene–butadiene–styrene triblock copolymer (SBS) have been prepared by a two‐roll mill. The morphologies of extruded samples from a capillary rheometer were observed by scanning electron microscopy (SEM). It is found that PS phase is dispersed in the BR phase. The glass transition temperature (T_g) of the blend has been examined by using differential scanning calorimetry (DSC). From the T_g behavior and the electron microscopy study, it is found that certain degree of miscibility between the polystyrene phase and the BR phase is observed. The rheological behavior of the blend has been investigated by a capillary rheometer. It is found that the viscosity of the blend increases with increased content of PS phase. The behavior is in accord with the expected behavior of filler effect. To predict the filler effect of PS phase on the BR–SBS blend, a modified model of Chen and Cheng is proposed to elucidate the rheological properties of the BR–SBS blends with different compositions. Chen and Cheng's micromechanical model derived in Part I of this series, which relates the macroscopic shear stress to the macroscopic shear rate of a rigid non‐Newtonian suspension when the direct contribution of Brownian force is completely neglected. The agreement between the theoretical predictions and the experimental results is satisfactory. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 39–46, 1999     

Crystallization behavior of dry‐brush PEO‐PS block copolymer and PEO homopolymer blend

The crystallization behavior of semicrystalline PEO homopolymer/triblock PS‐PEO‐PS copolymer blend system, which exhibited “Dry‐Brush” in the melt. A symmetric polystyrene–poly(ethylene oxide)–polystyrene triblock copolymer was blended with PEO homopolymer (h‐PEO) having the same molecular weight as that of the PEO block in the copolymer. Considering the composition of the blend (W_ps ≥ 0.8), PEO spheres were formed in the blend. Because of the dry‐brush phase behavior of this blend, h‐PEO added was localized in the PEO microdomains, which increases the domain size without changing the microdomain morphology. The crystallization of PEO block was confined within the microdomains and the crystallization temperature was about 60°C lower than normal. Self‐seeding tests were performed to clarify the nucleation mechanism of the blend. Because the droplets size varies greatly, multicrystallization peaks were witnessed in the self‐seeding process. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Dynamic mechanical properties of polystyrene‐block‐poly[ethylene‐co‐(ethylene‐propylene)]‐block‐polystyrene triblock copolymer/hydrocarbon oil blends

Blend systems of polystyrene‐block‐poly(ethylene‐co‐(ethylene‐propylene))‐block‐polystyrene (SEEPS) triblock copolymer with three types of hydrocarbon oil of different molecular weight were prepared. The E″ curves as a function of temperature exhibited two peaks; one peak at low temperature (? ?50°C), arising from the glass transition of the poly[ethylene‐co‐(ethylene‐propylene)] (PEEP) phase and a high temperature peak (? 100°C), arising from the glass transition of the polystyrene (PS) phase. The glass transition temperature (T_g) of the PEEP phase shifted to lower temperature with increasing oil content. The shifted T_g depended on the types of oil and was lower for the low molecular weight oil. The T_g of PS phase of the present blend system, were found to be constant and independent of the oil content, when molecular weight of the oil is high. However, for the lower molecular weight oil, the T_g of the PS phase also shifted to lower temperatures. This fact indicates that the oil of high molecular weight is merely dissolved in the PS phase. The E′ at (75°C, at which temperature both of PEEP and PS phases are in glassy state, was found to be independent of oil content. In contrast, at 25°C, at which temperature the PEEP phase is in rubbery state, the E′ decreased sharply with increasing oil content. This result indicates that the hydrocarbon oil was a selective solvent in the PEEP phase. It mainly dissolved in the PEEP phase, although slightly dissolved into the PS phase as well, when molecular weight of oil is low. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Studies on phase separation rate in porous polyimide membrane formation by immersion precipitation

Phase separation rate during porous membrane formation by immersion precipitation was investigated by light scattering in a polyimide/N‐Methylpyrrolidone (NMP)/water system. In the light scattering measurement, plots of scattered intensity against scattered angle showed maxima in all cases, which indicated that phase separation occurred by a spinodal decomposition (SD). Characteristic properties of the early stage of SD, such as an apparent diffusion coefficient D_app and an interphase periodic distance Λ, were obtained. The growth process of Λ was also followed by light scattering. The growth rate had the same tendency as D_app when water content in the nonsolvent bath and the polymer concentration in the cast solution were changed. The pore size of the final membrane increased with decreasing water content, which was opposite to the tendency of Λ growth rate. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 292–296, 2003     

Compatibilization of poly(vinyl chloride) and polystyrene blends with poly(styrene‐co‐n‐methylolacrylamide)

In this work, the compatibilization of blends of plasticized polyvinyl chloride (PVC) and polystyrene (PS) with poly(styrene‐co‐n‐methylolacrylamide) (PSnMA) was investigated. The PSnMA was synthesized by emulsion polymerization with different amounts of n‐methylolacrylamide (nMA). Particle size and phase behavior was determined by scanning electron microscopy, and mechanical properties were determined in an Universal Testing Machine. Micrographs revealed that an appreciable size reduction of the dispersed phase was achieved when small amounts of PSnMA were added to the blend, and as the amount of nMA was increased, particle size decreased. When the (PVC/PS/PSnMA) blend was subjected to solvent extraction to remove PS and unreacted PVC, the residue showed a single T_g. Tensile modulus and the ultimate strength of the blends increased with PSnMA content. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Physical aging in the mechanical properties of miscible polymer blends

Changes in mechanical properties during isothermal physical aging were investigated for three miscible blends: polystyrene (PS)/poly(2,6-dimethyl 1,4-phenylene oxide) (PPO), PS/poly(vinylmethylether) (PVME), and poly(methylmethacrylate) (PMMA)/poly(ethyleneoxide) (PEO). The kinetics of stress relaxation was investigated for the blend, dilute in one component, and compared with that of the neat major component at equal temperature distances, Tg-T, from the midpoint glass transition temperature. It is demonstrated that for all three blends, the mean stress relaxation time (τ) does not scale with Tg-T. For PS/PPO and PS/PVME blends, the stress relaxation rates are faster compared to neat PS; for PMMA/PEO, they are slower than for neat PMMA. Two effects appear to be important in contributing to this discrepancy. First, addition of the second component produces a change in the packing density of the blend: less dense for PS/PPO and PS/PVME; more dense for PMMA/PEO. Comparison of average free volume hole sizes and fractional free volumes measured via orthopositronium annihilation lifetime measurements for all three blends versus the pure constituents are qualitatively consistent with this interpretation. Second, because of the presence of concentration fluctuations in the blend, it is expected that the initial stress decay is dominated by regions enriched in the more mobile component. From observations of the change in width of the stress relaxation time distribution, this effect appears to be particularly significant in the PS/PVME blend. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 483–496, 1997     

Construction of the state diagram of polymer blend thin films using differential AC chip calorimetry

The phase separation behavior of polymer blend thin films of 100-150 nm was studied using differential AC Chip calorimetry. By taking advantage of the low sensor and sample mass inherent to chip calorimetry, a new methodology based on temperature jumps was developed. This methodology allowed the construction of the state diagram of polymer blend thin films as evidenced for two model systems (PVME/PS and PVME/Phenoxy) displaying a lower critical solution temperature behavior.The state diagram in thin films was compared to the one obtained in bulk using Modulated Temperature DSC. In comparison with bulk, a lower phase separation temperature and a broadening of the homogeneous glass transition temperatures is observed for both model systems. This might be an indication of a surface induced ‘destabilization’ by composition gradients which are not present in bulk.     

Kinetics of phase separation of poly(styrene‐co‐methyl methacrylate) and poly(styrene‐co‐acrylonitrile) blends

The phase behavior and kinetics of phase separation for blends of the random copolymer poly(styrene‐co‐methyl methacrylate) (SMMA) and poly(styrene‐co‐acrylonitrile) (SAN) were studied by using small‐angle laser light scattering. The partially miscible SMMA/SAN blends undergo spinodal decomposition (SD) and subsequent domain coarsening when quenched inside the unstable region. For blends of SMMA and SAN, the early stages of the phase separation process could be observed, unlike a number of other blends where the earliest stages are not visible by light scattering. The process was described in terms of the Cahn–Hilliard linear theory. Subsequently, a coarsening process was detected and the time evolution of q_m at the beginning of the late stages of phase separation followed the relationship q_m∝t^?1/3, corresponding to an evaporation–condensation mechanism. Self‐similar growth of the phase‐separated structures at different timescales was observed for the late stage. Copyright © 2004 Society of Chemical Industry     

Orientation of miscible and immiscible polymer blends

Polystyrene (PS) and poly(vinylmethylether) (PVME) were used to study the orientation of miscible and immiscible polymer blends. A miscible blend containing 60 wt% PS was prepared by casting the sample from a benzene solution. The immiscible blend was made by annealing the initially miscible mixture above its lower critical solution temperature for different times and temperatures. Fourier transform infrared spectroscopy and birefringence were used to measure the orientation of PS and PVME, before and after phase separation. Stress-strain curves were also measured for the two types of systems. It was found that the two polymers orient differently and that phase separation induces an increase in the overall orientation of the mixture, in the modulus and in PS orientation. The differences observed between pure PS and PS in the blend were attributed to changes in specific interactions and density of entanglements. The variations with phase separation were attributed to a change in the morphology of the system.     

Stereocomplex formation between poly(L‐lactic acid) and poly(D‐lactic acid) with disproportionately low and high molecular weights from the melt

Poly(L ‐lactic acid) (PLLA) and poly(D ‐lactic acid) (PDLA) with very different weight‐average molecular weights (M_w) of 4.0 × 10³ and 7.0 × 10⁵ g mol^?1 (M_w(PDLA)/M_w(PLLA) = 175) were blended at different PDLA weight ratios (X_D = PDLA weight/blend weight) and their crystallization from the melt was investigated. The presence of low molecular weight PLLA facilitated the stereocomplexation and thereby lowered the cold crystallization temperature (T_cc) for non‐isothermal crystallization during heating and elevated the radial growth rate of spherulites (G) for isothermal crystallization, irrespective of X_D. The orientation of lamellae in the spherulites was higher for the neat PLLA, PDLA and an equimolar blend than for the non‐equimolar blends. It was found that the orientation of lamellae in the blends was maintained by the stereocomplex (SC) crystallites. Although the G values are expected to decrease with an increase in X_D or the content of high‐molecular‐weight PDLA with lower chain mobility compared with that of low‐molecular‐weight PLLA, G was highest at X_D = 0.5 where the maximum amount of SC crystallites was formed and the G values were very similar for X_D = 0.4 and X_D = 0.6 with the same enantiomeric excess. This means that the effect of SC crystallites overwhelmed that of chain mobility. The nucleating mechanisms of SC crystallites were identical for X_D = 0.1–0.5 in the T_c range 130–180 °C. Copyright © 2011 Society of Chemical Industry     

Stress‐relaxation behavior of natural rubber/polystyrene and natural rubber/polystyrene/natural rubber‐graft‐polystyrene blends

We studied the stress‐relaxation behavior of natural rubber (NR)/polystyrene (PS) blends in tension. The effects of strain level, composition, compatibilizer loading, and aging on the stress‐relaxation behavior were investigated in detail. The dispersed/matrix phase morphology always showed a two‐stage mechanism. On the other hand, the cocontinuos morphology showed a single‐stage mechanism. The addition of a compatibilizer (NR‐g‐PS) into 50/50 blends changed the blend morphology to a matrix/dispersed phase structure. As a result, a two‐step relaxation mechanism was found in the compatibilized blends. A three‐stage mechanism was observed at very high loadings of the compatibilizer (above the critical micelle concentration), where the compatibilizer formed micelles in the continuous phase. The aged samples showed a two‐stage relaxation mechanism. The rate of relaxation increased with strain levels. The aging produced interesting effects on the relaxation pattern. The rate of relaxation increased with temperature due to the degradation of the samples. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Compatibility study in poly(tetramethyleneadipate‐co‐terephthalate)/polystyrene bioblends

Bioblends of the biodegradable copolyester poly(tetramethyleneadipate‐co‐terephthalate) (EBU) and polystyrene (PS) were prepared in different weight compositions on a twin‐screw extruder at 160–200°C. The various bioblend compositions were then investigated using thermogravimetric analysis (TGA), modulated differential scanning calorimetry (MDSC), and Fourier transform infrared photoacoustic spectroscopy (FTIR‐PAS). TGA studies showed that 25/75 and 50/50 EBU/PS blends had higher thermal stability than the more thermally stable blend component, PS. The MDSC studies showed a single T_g and single T_m for the blends, that were concentration independent. The FTIR‐PAS studies indicated a small shift (4–8 cm^?1) in the carbonyl absorption peaks of EBU to lower wavenumbers in 50/50 EBU/PS blend relative to that of neat EBU. It is concluded that, while the MDSC results were inconclusive, the TGA and FTIR‐PAS results support the existence of some degree of intermolecular interaction between EBU and PS components and, hence, partial compatibility in EBU/PS blends. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Properties and pervaporation characteristics of chitosan–poly(N‐vinyl‐2‐pyrrolidone) blend membranes for MeOH–MTBE

Clear blends of chitosan with poly(N‐vinyl‐2‐pyrrolidone) (PVP) made from aqueous solutions appear to be miscible from visual appearance. Infrared (IR) spectra used to investigate the carbonyl—hydroxyl hydrogen bonding in the blends indicated compatibility of two polymers on a molecular level. The IR spectra were also used to determine the interaction change accessing with increasing temperature and indicated that a significant conformational change occurred. On the other hand, the blend membranes were evaluated for separation of methanol from methyl tert‐butyl ether. The influences of the membrane and the feed compositions were investigated. Methanol preferentially permeates through all the tested membranes, and the partial flux of methanol significantly increase with the poly(N‐vinyl‐2‐pyrrolidone) content increasing. The temperature dependence of pervaporation performance indicated that a significant conformational change occurred with increasing temperature. Combined with the IR results, the pervaporation properties are in agreement with characteristics of interaction between chain–chain within the blend membranes. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1452–1458, 1999