Phase separation in semicrystalline polymer blends and copolymers studied via thermal segregation and crystallization kinetics

The miscibility versus immiscibility in a crystalline two component system is discussed, based on phase separation and crystallization kinetics considerations. The thermal segregation was used to create or enhance the phase separation in crystalline two component systems. By comparing the crystallization kinetics before and after thermal segregation, one can distinguish two types of phase separation: (1) intrinsic phase separation in the melt for an immiscible system, or (2) phase separation induced via crystallization for a miscible system. Metallocene short‐chain branching polyethylene (SCBPE) and nylon 6/polyimide triblock copolymer systems were taken as examples, and the phase behaviour determined via this thermal segregation and crystallization kinetics method. It is evident that the crystallization kinetics after thermal segregation are substantially faster than that before thermal segregation, and become much faster after keeping the sample in the melt for some time for the SCBPE system. Our results suggest that the molecules with different SCB contents in the SCBPE system may exhibit liquid–liquid phase separation in the melt. In contrast, studies on the crystallization kinetics of the nylon 6/polyimide system showed that nylon 6/polyimide triblock copolymer exhibits lower phase separation compared with in situ or solution blends. Thermal segregation and crystallization kinetics may serve as a very useful method to study the phase behaviour in semicrystalline blends and copolymers. © 2000 Society of Chemical Industry     

Thermally induced phase separation in liquid crystalline polymer/polycarbonate blends

Thermally induced phase separation in liquid crystalline polymer (LCP)/polycarbonate (PC) blends was investigated in this study. The LCP used is a main‐chain type copolyester comprised of p‐hydroxybenoic acid and 6‐hydroxy‐2‐naphthoic acid. Specimens for microscopic observation were prepared by melt blending. The specimens were heated to a preselected temperature, at which they were held for isothermal phase separation. The preselected temperatures used in this study were 265, 290, and 300°C. The LCP contents used were 10, 20, and 50 wt %. These parameters corresponded to different positions on the phase diagram of the blends. The development of the phase‐separated morphology in the blends was monitored in real time and space. It was observed that an initial rapid phase separation was followed by the coarsening of the dispersed domains. The blends developed into various types of phase‐separated morphology, depending on the concentration and temperature at which phase separation occurred. The following coarsening mechanisms of the phase‐separated domains were observed in the late stages of the phase separation in these blends: (i) diffusion and coalescence of the LCP‐rich droplets; (ii) vanishing of the PC‐rich domains following the evaporation‐condensation mechanism; and (iii) breakage and shrinkage of the LCP‐rich domains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

The effect of end groups of PEG on the crystallization behaviors of binary crystalline polymer blends PEG/PLLA

The effect of end groups (2OH, 1OH, 1CH₃ and 2CH₃) of poly(ethylene glycol) (PEG) on the miscibility and crystallization behaviors of binary crystalline blends of PEG/poly(l-lactic acid) (PLLA) were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM). A single glass-transition temperature was observed in the DSC scanning trace of the blend with a weight ratio of 10/90. Besides, the equilibrium melting point of PLLA decreased with the increasing PEG. A negative Flory interaction parameter, χ₁₂, indicated that the PEG/PLLA blends were thermodynamically miscible. The spherulitic growth rate and isothermal crystallization rate of PEG or PLLA were influenced when the other component was added. This could cause by the change of glass transition temperature, T_g and equilibrium melting point, T⁰_m. The end groups of PEG influenced the miscibility and crystallization behaviors of PEG/PLLA blends. PLLA blended with PEG whose two end groups were CH₃ exhibited the greatest melting point depression, the most negative Flory interaction parameter, the least fold surface free energy, the lowest isothermal crystallization rate and spherulitic growth rate, which meant better miscibility. On the other hand, PLLA blended with PEG whose two end groups were OH exhibited the least melting point depression, the least negative Flory interaction parameter, the greatest fold surface free energy, the greatest isothermal crystallization rate and spherulitic growth rate.     

Phase behavior of thermotropic liquid crystalline/conducting polymer blends

Summary Liquid crystalline/conducting polymer blends have been prepared. The conductingpolymer [poly(2,5-dimethoxyphenylene vinylene)] retards the liquid crystallinity of the liquid crystalline polymer (hydroxypropyl cellulose), while the liquid crystalline polymer reduces the conductivity of the conducting polymer. However, blends with 17% conducting polymer were both liquid crystalline and conductive. Dedicated to Prof. Dragutin Fleš on the occasion of his 70th birthday     

In situ FTIR microscope study on crystallization of crystalline/crystalline polymer blends of bacterial copolyesters

This study describes in situ observation of crystallization in a spherulite of blends of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) [PHBV] and poly(3-hydroxybutyrate-co-3-hydroxypropionate) [PHBP] by FTIR microscopy. In order to trace the crystallization processes of blend components separately, PHBV was deuterated. The C-D and CO stretching bands in the IR spectra, respectively, show the crystallization behavior of PHBV and the whole blend. D-PHBV containing 6 and 8% HV [D-PHBV6 and D-PHBV8] are blended with PHBP containing 11% HP [PHBP11]. The crystallization rates of D-PHBV6, D-PHBV8 and PHBP11 decrease in this order. In case of the blend of D-PHBV8 and PHBP11 the crystalline peaks of C-D and CO bands grows simultaneously during crystallization, and the growth rates are rather close to that of D-PHBV8. The results indicate that D-PHBV8, which is the component that shows higher crystallization rate in the pure state, leads the cocrystallization of the blend. For D-PHBV6/PHBP11, on the other hand, the crystalline peak of C-D band grows faster than that of CO band, indicating that the crystallization of D-PHBV6 proceeds before the crystallization of PHBP11. During the crystallization of D-PHBV6, PHBP11 molecules get away from the growing front of the spherulite, i.e. the phase segregation precedes the crystallization. These results demonstrate that FTIR microscopy is a powerful tool to trace the formation of different crystalline phases, such as cocrystallization and phase segregation.     

Phase separation,crystallization, and structure formation in immiscible polymer solutions

Morphological and calorimetric studies of phase separation have been carried out in solutions of a crystallizable polymer in poor solvents. Hydrogenated polybutadiene with low branch content was investigated in solutions with diphenyl ether and diphenyl methane, in which the equilibrium phase diagram exhibits both liquid–liquid phase separation and crystallization of the polymer. Emphasis is placed on sample preparation protocols using thermal treatments at low concentrations where it is anticipated that both phase separation mechanisms may influence the resulting morphology. Samples prepared using either ramp cooling or isothermal crystallization exhibit porous structures such as those seen in membrane materials, that predominantly reflect liquid phase separation. However, the interplay between the different kinetics of liquid demixing and crystallization provides a mechanism to control, for instance, pore size. DSC studies during ramp cooling showed evidence of two discrete crystallization processes associated with the two liquid phases expected to be present under these circumstances. Finally, high concentration samples showed morphological evidence of liquid phase separation induced at the growth front of spherulites in otherwise single-phase polymer solutions. © 1995 John Wiley & Sons, Inc.     

Phase separation and gelation of epoxy resin/hyperbranched polymer blends

The structural buildup during reticulation of thermoset systems containing reactive modifiers can strongly influence the final properties of such blends. This was studied by considering the rheological behavior during cure of an epoxy/amine thermoset system blended with reactive dendritic hyperbranched polymers (HBPs). Depending on the chemical structure of the HBP used in the blend, a phase separation could be observed. The onset and offset of the phase separation process could be detected by observing the evolution of the viscoelastic properties. The phase separation onsets obtained by rheological measurements were compared with the values obtained by traditional cloud point observations. Good agreement between the two techniques was observed. Hyperbranched polymers that did not phase separate during the curing process were used to study gelation phenomena and its dependence on the reactivity and functionality of the HBP. The gelation of the homogeneous blend system using the Flory‐Stockmayer theory was also modeled. This highlighted the influence of both functionality and reactivity of the components, and the appearance of co‐operative polymerization mechanisms in homogeneous blends.     

Phase separation in epoxy resin‐reactive dendritic hyperbranched polymer blends

Equilibrium phase diagrams in composition‐conversion space have been calculated for stoichiometric blends of an epoxy resin with a diamine hardener and dendritic hyperbranched polymers, to which various numbers of epoxy groups have been grafted. An attempt has been made to incorporate both the effects of the polydispersity of the resin and the reactivity of the functionalized hyperbranched polymers for any given value of the interaction parameter. However, if the reactivities of all the epoxy groups are comparable, the presence of a highly functionalized modifier is expected to lead to a reduction of the gel point conversion and a narrowing of the composition‐conversion window available for cure induced phase separation. The experimental cloud point data are consistent with the model, although they sugget that the functionalized hyperbranched polymers may be significantly less reactive than the resin. Moreover, in the present system, the influence of functionalization on the phase behavior is also strongly linked to the accompanying changes in the interaction parameter.     

Phase separation and crystallization behavior in extruded polypropylene/ethylene–propylene rubber blends

Liquid–liquid (L–L) phase separation and its effects on crystallization in polypropylene (PP)/ethylene–propylene rubber (EPR) blends obtained by melt extrusion were investigated by time‐resolved light scattering (TRLS) and optical microscopy. L–L phase separation via spinodal decomposition (SD) was confirmed by TRLS data. After L–L phase separation at 250°C for various durations, blend samples were subjected to a temperature drop to 130°C for isothermal crystallization, and the effects of L–L phase separation on crystallization were investigated. Memory of the L–L phase separation via SD remained for crystallization. The crystallization rate decreased with increasing L–L phase‐separated time at 250°C. Slow crystallization for the long L–L phase‐separated time could be ascribed to decreasing chain mobility of PP with a decrease in the EPR component in the PP‐rich region. The propylene‐rich EPR exhibited good affinity with PP, leading to a slow growth of a concentration fluctuation during annealing. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 695–700, 2001     

Co-phase continuity in immiscible binary polymer blends

Methods of microscopic observation and macroscopic characterization have been developed for determining the co-phase continuity in immiscible binary blends. After selective dissolution of the component polymers, the morphologies of microscopic observation are consistent with the results of macroscopic observation and weight percentage determination. By using these methods, the relationship between co-phase continuity, composition and blending time has been explored for two immiscible binary polyblends with different viscosity ratios (λ), polyamide 6/polyethersulfone (PA/PES, λ = 0.03) and poly(butylene terephthalate)/polystyrene (PBT/PS, λ = 1). Both blend systems show a similar dependence of co-phase continuity on the composition and mixing time. That is at short mixing time (for example, 2 minutes), the co-phase continuity takes place in a wide composition range. With increasing blending time, the composition range of co-phase continuity becomes narrow, and finally shrinks to one point. After a long enough mixing time the co-phase continuity region will occur only at a volume fraction of

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, no matter what the viscosity ratio of the blend is. © 1997 Elsevier Science Ltd.     

Thermomechanical analysis of binary polymer blends

Thermomechanical analysis by penetration and extension modes, was performed on polyolefin/polystyrene blends (high density polyethylene, low density polyethylene or isotactic polypropylene with atactic polystyrene) and polyolefin/polyolefin mixtures (high density polyethylene or low density polyethylene with isotactic polypropylene). All the measurements were performed on cylindrical specimens obtained directly by extrusion on which extensive mechanical and morphological studies were previously made. It was found that the addition of small quantities of a polymer to a different polymeric matrix tend to modify the thermomechanical behaviour of the whole system. Furthermore the results showed that such an analysis seems to be a suitable tool to get useful information on the thermal and morphological transitions as well as on the interactions between the components in the blends.     

Crystallization of double crystalline symmetric diblock copolymers

We report dynamic Monte Carlo simulation results on the crystallization of double crystalline symmetric A-B diblock copolymer, wherein the melting temperature of A-block is higher than B-block. Crystallization of A-block precedes the crystallization of B-block upon cooling from a homogeneous melt. The morphological development is controlled by the interplay between crystallization and microphase separation. With increasing segregation strength, we observe a gradual decrease in crystallinity accompanying with smaller and thinner crystals. During crystallization, A-block crystallizes first and creates confinement for the crystallization of B-block. Thus, crystallization of B-block slows down influencing the overall crystal morphology. At higher segregation strength, due to the repulsive interaction between blocks, block junction is stretched out, which is reflected in the increased value of mean square radius of gyration. As a result, a large number of smaller size crystals form with less crystallinity. The onset of microphase separation shifts towards higher temperature with increasing segregation strength. Isothermal crystallization reveals that the transition pathways strongly depend on segregation strength. The value of Avrami index shows the formation of two dimensional lamellar crystals of both the blocks. Two-step (sequential), compared to one-step (coincident) isothermal crystallization, produces higher crystallinity in A-block, however, the crystallinity of B-block is almost identical in both the cases.     

Liquid crystalline polymer blends with stabilized viscosity

The rheology of blends of thermotropic liquid crystalline copolyester co(hydroxybenzoate-isophthalate-hydroquinone) (HIQ) and polyetherimide were studied at different temperatures. As a result of the anisotropic-to-isotropic transition, the viscosity of the biphasic HIQ was found to be able to compensate that of the host polyetherimide at proper composition when the temperature increased or decreased in the capillary rheometer study. The 33% HIQ blend had almost stabilized viscosity between 350 and 370°C, whereas the 15% HIQ blend did not have stabilized viscosity. For the nonisothermal spiral molding trial, the 33% HIQ blend stabilized at a mean length of 21 inches (53 cm) with a standard deviation of 2.1 inch (5.3 cm) when the melt temperature increased by 30 Celsius degrees from 340 to 370°C.     

Influence of composition,crystallization conditions and melt phase structure on solid morphology,kinetics of crystallization and thermal behavior of binary polymer/polymer blends

Results of an investigation on the morphology, the crystallization and the thermal behavior of several binary crystallizable blends are reported. The composition, molecular mass and crystallization conditions strongly influence the crystallization and the thermal behavior as well as the overall morphology of crystallizable binary blends. Quantities such as nucleation density (N), radial growth rate (G) of spherulites, overall rate of crystallization (K), and equilibrium melting temperature (T_m) are strongly dependent upon composition, crystallization conditions, and molecular mass of components. The type of dependence is to be related to the physical state of the melt, which, at the crystallization temperature, is in equilibrium with or coexists with the developing solid phase. In the ease of compatible blends such as poly(ethylene oxide)/poly(methyl methacrylate) the depression observed for G and T_m is mainly to be attributed to the diluent effect of the non-crystallizable component. For such a blend it is found that, after crystallization, the non-crystallizable component is trapped in intralamellar regions increasing the distance between adjacent lamellae. Depression of G, in the case of incompatible blends such as isotactic polypropylene/rubbers is mainly accounted for by rejection and deformation of rubber drops. The coexistence during crystallization of different processes such as molecular fractionation and segregation, preferential inclusion or dissolution of molecules with lower molecular mass and/or high degree of steric disorder of the crystallizable component in the phase rich in non-crystallizable component and vice versa may explain some minima observed in the plots of T and T^m, vs. composition in the case of blends semicompatible in the melt. It was found that the addition of a second non-crystallizable component causes drastic variations on some morphological and structural quantities of the semicrystalline matrix (isotactic polypropylene or nylon 6) such as the shape, dimensions, and regularity of spherulites and interspherulite boundary regions and lamella and interlamella thickness. In some cases the formation of new boundary lines connecting occluded particles are also observed. Such phenomena may have great importance on crack propagation and on impact behavior as well as on the tensile mechanical properties of binary blends characterized by a semicrystalline polymer component with a relatively high T^g and a rubber-like component with a lower T^g.     

Morphology control in symmetric polymer blends using spinodal decomposition

This paper studied, through modeling and computer simulation, the thermal-induced phase separation phenomenon in a symmetric polymer blend via spinodal decomposition. The one-dimensional model consisted of the Cahn–Hilliard theory for spinodal decomposition, and incorporated the Flory–Huggins–deGennes free energy equation, the slow mode mobility theory and reptation model for polymer diffusion. The numerical results replicated frequently reported experimental observations published in the literature for the early and intermediate stages of spinodal decomposition for symmetric polymer blends. Furthermore, the numerical results indicate that a dimensionless diffusion coefficient may be used as a parameter to control the formation and evolution of the phase-separated regions during spinodal decomposition as a means to customize functional polymeric materials with predefined material properties.     

Phase separation in polypropylene and metallocene polyethylene blends

Blends of a metallocene linear low density polyethylene (m‐LLDPE) and polypropylene random copolymer (PP) have been prepared using a twin screw extruder and characterized by thermal analysis, mechanical properties, and wide angle X‐ray scattering to determine their degree of compatibility. The blends were either directly quenched in water from the melt‐ or slow‐cooled to room temperature. In both cases, the two components formed separate phases and crystallized independently. The slow‐cooled specimens had higher yield stress, tensile modulus, and lower elongation at break consistent with higher degree of crystallinity. The elongation to break also varied with composition reaching a minimum at 50% consistent with the incompatible nature of the blends. Crystallization kinetics and melting studies confirm that the two components formed separate phases and crystallized independently. POLYM. ENG. SCI., 46:889–895, 2006. © 2006 Society of Plastics Engineers     

Phase behavior of semicrystalline polymer blends

The phase behavior of the semicrystalline polymer blend composed of isotactic polypropylene (iPP) and linear low density polyethylene (PE) was studied using small angle X-ray scattering (SAXS) and optical microscopy (OM). Based on the random phase approximation, the iPP/PE interaction parameter, χ, was obtained, and used to construct the iPP/PE phase diagram. The χ values reported in this study are lower than the χ values for deuterium-labeled moieties, measured by small angle neutron scattering (SANS). The predicted phase diagram has upper critical solution temperature (UCST) behavior with a critical temperature of 143 °C for the molecular weights used in this study. OM was used to locate cloud points and the results are consistent with the predicted phase diagram. Since iPP melts above the critical point, care was taken to distinguish phase separation from iPP crystallization by studying the kinetics of iPP crystallization, and the iPP crystallization was discerned from dewetting. In PE-rich blends, the iPP crystallization was suppressed and no dewetting was observed.     

Study on compatibilization of polypropylene-liquid crystalline polymer blends

The mechanical properties, melt rheology, and morphology of binary blends comprised of two polypropylene (PP) grades and two liquid crystalline polymers (LCP) have been studied. Compatibilization with polypropylene grafted with maleic anhydride (PP-g-MAH) has been attempted. A moderate increase in the tensile moduli and no enhancements in tensile strength have been revealed. Those findings have been attributed to the morphology of the blends, which is predominantly of the disperse mode. LCP fibers responsible for mechanical reinforcement were only exceptionally evidenced. Discussion of PP-LCP interfacial characteristics with respect to mechanical properties-morphology interrelations allowed evaluation of the compatibilizing efficiency of PP-g-MAH. Factors important for successful reinforcement of PP with LCP have been specified. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 969–980, 1997     

Electrical conductivity of polymer blends containing liquid crystalline polymer and carbon black

This paper presents results of a study of melt‐processed immiscible polymer blends of high impact polystyrene (HIPS), liquid crystalline polymer (LCP) and carbon black (CB). Relationships between composition, electrical resistivity and morphology of the blends produced by Brabender mixing followed by compression molding, extrusion through a capillary rheometer, extrusion through a single‐screw extruder and injection molding were investigated. The LCP phase morphology in the blends was found sensitive to the processing conditions. A blend composition of at least 20 wt% LCP and 2 phr CB is necessary to preserve the conductivity of filaments produced over a wide range of shear rates. Enhancement of conductivity of blends containing CB and 30 wt% or more LCP was observed, under processing at 270°C and increasing levels of shear rate. An important role of the skin region in determining the resisitivy of injection molded samples was found. A good agreement between resistivity values of extruded or injection molded blends with resistivity values of filaments produced at similar conditions by a capillary rheometer was shown. Hence, the study of shear rate effect on resistivity of capillary rheometer filaments may serve as a predictor of resistivity behavior in real processing procedures. Polym. Eng. Sci. 44:528–540, 2004. © 2004 Society of Plastics Engineers.     

Phase separation in polymer blends comprising copolymers: 4. Polycarbonate/polystyrene ABCP system

An AB-crosslinked copolymer (ABCP) with polycarbonate as A-chain and polystyrene as B-chain was prepared and characterized. A series of blends of the ABCP and homopolystyrene fractions with different molecular weights were prepared and examined by electron microscopy. The results show that the miscibility between the homopolymer and the like chains in the copolymer is limited even if the molecular weight of the former is much less than that of the latter. Considering the relatively large miscibility in diblock copolymer/homopolymer blends and the limited miscibility in ABCP/homopolymer-A blends reported in literature, this study leads to an argument that the molecular architecture of a copolymer is an important factor governing its miscibility with homopolymer. The relatively complicated architecture of ABCPs causing more restriction to the chain conformation might be one of the main reasons for its low miscibility with homopolymers.