A study on blends of liquid crystalline copolyesters with polycarbonate. II. Transesterification control

The inhibited and catalyzed ester exchange (transesterification) during melt blending of poly(bisphenol-A carbonate) (PC) and liquid crystalline poly(oxybenzoate-co-ethylene terephthalate) (POB–PET 40/60; P46) was investigated with differential scanning calorimetry. It was found that the ester exchange between P46 and PC was effectively inhibited for a 20% P46 blend at 240°C, as further confirmed by nuclear magnetic spectroscopy. When the blending temperature and P46 concentration increased, only the transesterification between the PET segment in P46 and PC took place under inhibition. The morphology of the blends was analyzed with scanning electron microscopy and displayed a disconnected interface between P46 and PC under inhibition. Conversely, the transesterification took place between the POB segment in P46 and PC when a catalyst was added. © 1996 John Wiley & Sons, Inc.     

A study on blends of liquid crystalline copolyesters with polycarbonate. III. Mechanical properties of compatibilized blends

Blends of liquid crystalline poly(oxybenzoate-co-oxynaphthalate) (Vectra A950) and polycarbonate (PC) were prepared by adding a compatibilizer to the two polymers in a melt-blending process. The compatibilizer was based on controlled transesterification between synthesized poly(oxybenzoate-co-terephthalate) (40/60) and PC. The compatibilizer exhibited birefringence, and its thermal property was analyzed by differential scanning calorimetry. The maximum increase in tensile modulus and tensile strength of these compatibilized Vectra blends were 24% and 54%, respectively, as compared with those of binary Vectra blend without compatibilizer resulting from an injection-molding process. The tensile properties of the compatibilized Vectra blends decreased once the concentration of the compatibilizer exceeded 2 phr. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1527–1533, 1997     

Characterization of liquid crystalline polyester polycarbonate blends

Mechanical and rheological properties of blends of a thermotropic liquid crystalline polyester with a polycarbonate have been investigated. The blends are fibrillar in character and exhibit great hardness and toughness due to high degree of molecular orientation which develops during the melt blending and processing steps. Increases of the Young modulus by 100 percent are observed for blends containing only 10 percent of liquid crystalline polymer, LCP. Time-dependent behavior of the blends was investigated by performing solid state relaxation measurements and the relaxation modulus was also found to increase by the addition of LCP. The effect is relatively small in the glassy zone of viscoelastic response, but increases through the transition and viscous flow regions. The melt viscosity of the polycarbonate is slightly shear thinning whereas that of the unblended LCP increases rapidly with decreasing shear rate at low shear rate. This suggests the presence of yield stresses as confirmed by measurements on the Rheometics RSR in the stress sweep mode. The melt viscosity of the blends was found to be similar to that of the unblended polycarbonate, but more shear-thinning and less viscous. Preliminary results of scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) are also presented.     

Rheology of phase separated blends of two thermotropic liquid crystalline copolyesters

The melt rheology of phase separated blends of two thermotropic liquid crystalline polymers (LCPs) have been studied. The two components are a random copolyesters consisting of 73 mol% 4-hydrobenzoic acid (HBA) and 27 mol% 6-hydroxy-2-napthoic acid (Vectra A900 of Hoechst Celanese Corp.) and a poly(ethylene terephalate-co-4-oxybenzoate) containing 60 mol% HBA units (PET/60HBA of Eastman Kodak Corp.). Most striking is the effect of adding 10% PET/60HBA to Vectra A900: The viscosity at 290°C drops by a factor of 4 and the terminal zone of the relaxation time spectrum is shifted to much shorter times. This is an interesting effect that could be used for LCP processing even if its origin is not yet understood. Differential scanning calorimetry measurements support the hypothesis that the blend is phase separated and that no transestification reaction occurs during the experiments.     

Physical properties of blends of polycarbonate and a liquid crystalline copolyester

Blends of polycarbonate (PC) and poly(ethylene terephthalate-co-p-oxybenzoate) (PET/PHB60) were prepared by melt-blending. Physical and/or chemical interactions between the two phases of the system were studied by thermal analysis and infrared spectroscopy. Rheological measurements in shear flow were carried out both in the low and high shear rate regions in the temperature range of the existence of the mesophase. At low liquid crystalline polymer (LCP) content, the blends showed flow curves similar to those of the unfilled PC, while at higher LCP percentages the rheological behavior of the pure LCP was resembled. Moreover, in the whole shear range, the viscosity values of such blends were in between those of the pure polymers. The influence of the addition of 10% LCP on the mechanical properties of the PC was investigated. Fiber-spinning was performed under different experimental conditions, and it was found that opportune drawing conditions are necessary to improve the modulus of the matrix. Morphological analyses of the pure LCP and of the blends were related to the rheological and mechanical behavior of these systems. While the LCP exhibited an elevated dimensional stability, the inclusion of the LCP in PC matrix did not improve the dimensional stability of the blends.     

Post extrusion hot drawing of polycarbonate/liquid crystalline polymer blends

The post extrusion hot drawing of polycarbonate/liquid crystalline polymer (PC/LCP) blends, over the entire composition range, was studied. The extruded filament morphology and elastic modulus were followed as a function of blends composition, initial phase morphology, and draw ratio (DR). Hot drawing was found to cause further orientation to the already existing partially oriented LCP phase at the die exit, as reflected by the increased blends modulus. The additional orientation depends on the initial filaments structure, the blend composition, and the DR. Moreover, the orientability of the LCP phase is much higher, similar to that of neat LCP, for blends in which the LCP forms the continuous phase. In low LCP content blends, a critical DR was identified, beyond which the LCP fibrils undergo fragmentation and voids at the fibrils/matrix interface are formed, resulting in a decrease in the drawn filament modulus.     

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     

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.     

Compatibility enhancement of ABS/polycarbonate blends

The effects of blend composition, melt viscosity of poly(acrylonitrile-butadiene-styrene) (ABS), and compatibilizing effect of poly(methyl methacrylate) (PMMA) on mechanical properties of ABS/polycarbonate (PC) blends at ABS-rich compositions were studied. As the content of PC was increased, impact strength and Vicat softening temperature (VST) were increased. As the melt viscosity of ABS was increased near to that of PC, finer distribution of dispersed PC phase and consequent enhanced impact strength and VST were observed. The compatibilizing effect of PMMA can be ascer-tained from the enhanced properties of ¼-inch notch impact strength, VST, tensilestrength, and the morphology observed by a scanning electron microscope. The improved adhesion of the ABS/PC interface by PMMA changed the fracture mechanism and reduced the notch sensitivity of blends. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 533–542, 1998     

Rheological properties of liquid crystalline copolyesters

Copolyesters were synthesized by modifying poly(ethylene terephthalate) (PET) with p-acetoxybenzoic acid (PAB) and hydroquinone diacetate/tetrasubstituted (tetramethyl, tetrachloro, and tetabromo) terephthalic acid (HQTS). It was found that the copolyesters containing 33 mol% or higher concentrations of (PAB+HQTS) from mesomorphic liquid crystalline structures. Rheological properties of copolyesters formed of PET, modified with PAB and hydroquinone diacetate/tetramethyl terephthalic acid (HQTM), were measured using a cone-and-plate rheometer. It was found that the copolyesters in the mesomorphic state exhibit yield values at a low shear rate (or at a low shear stress), and negative values of first normal stress difference were observed for certain compositions of (PAB+HQTM), over the range of shear rates (or shear stresses) tested.     

Effects of chemical reactions on the properties of polycarbonate/liquid crystalline polymer blends

Effects of chemical reactions on the properties of the polycarbonate (PC)/liquid crystalline polymer (LCP) blends are considered here. Not only thermal and rheological behaviors, but also morphology and molecular weight change are investigated. Reactive blends were prepared in a cylindrical flask at 300°C with varying processing time in the presence of a catalyst by the melt-phase reactions. For comparison, physical blends, in which chemical reactions were minimized, were also prepared at 300°C in a twin-screw extruder. It seems that transesterification and repolymerization did not occur, but depolymerization reaction took place slightly in PC/LCP physical blends. In reactive blends, however, transesterification and repolymerization as well as depolymerization reaction took place simultaneously. The depolymerization reaction occurred mainly at an early stage of processing; whereas, repolymerization reaction becomes especially dominant after some time (more than 30 min) in the presence of the catalyst, which had a great impact on its molecular weight. Also, chemical reactions changed the glass transition temperature and morphology as well as rheological behavior, which resulted in the enhanced miscibility in reactive blends. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2123–2133, 1999     

Mechanical performance of blends of thermotropic liquid crystalline polymer spheres‐dispersed polycarbonate

Liquid crystalline polymer (LCP) blends with a thermotropic LCP dispersed in the form of microspheres is studied to show the role of LCP spheres. Polycarbonate (PC), p‐hydroxybenzoic acid–poly(ethylene terephthalate) copolyester, and random styrene–maleic anhydride copolymer are used as the matrix, the dispersed phase, and the compatibilizer, respectively. A scanning electron microscopy observation shows the formation of LCP spheres with improved interfacial adhesion in the injection‐molded samples via compatibilization. The mechanical tests show increased modulus, elongation at break, and fracture‐absorbed energy of blends of LCP spheres‐dispersed PC. This shows an optimistic potential for the dispersed LCP phase, in spite of its morphology in the form of fibrils for reinforcing the matrix or in the form of microspheres for toughening the matrix. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 1493–1499, 2003     

Rheological properties of thermotropic liquid crystalline aromatic copolyesters

A series of thermotropic liquid crystalline polyesters based on p-acetoxybenzoic acid, naphthalene dicarboxylic acid, hydroquinone diacetate, and poly(ethylene terephthalate) were prepared via melt polycondensation. The anisotropic melts were studied by means of thermal optical testing, differential scanning calorimetry, scanning electron microscopy. X-ray diffraction, and rheological methods. It was found that the copolyesters in the mesomorphic state exhibit drastic shear-thinning and the experimental results indicate that the non-Newtonian Index n is in the range of 0.17 to 0.50, the flow-activation energies ΔE_η are 297.1 to 182.0 KJ/mol over the shear rate of 10 to 1000 S^?1 at temperature 225 to 270°C; and the mesomorphic copolymers are readily oriented during processing, resulting in highly oriented as-spun fibers.     

Structure and properties of liquid crystalline naphthalenediol copolyesters

Thermotropic liquid crystalline copolyesters with 1.4-, 1.5-, and 2.7-naphthalenediol (NDO) units were prepared by molten-state copolycondensation. It was found that the chain structure of the copolyesters is almost the same as the structure of recurring moieties of five units. The copolyesters have a glass transition temperature above 381 K, decomposition temperature above 703 K, and melting temperature between 513 and 559 K and their melts exhibit nematic texture and stir opalescence. The copolyester melts show a usual rheological behavior depending on the NDO unit content, but much lower extrudate swell. Light-scattering patterns of the copolyester films with low crystallinity are clearly asymmetric and therefore indicate the existence of preferred orientation of the copolyester chains. Scanning electron microscopy observation suggests that the as-spun fibers of 2.7-NDO-containing copolyesters were highly oriented and fibrillated. © 1994 John Wiley & Sons, Inc.     

Thermotropic liquid crystalline block copolyesters with PET as flexible spacers

Summary Propylene oligomers containing isopropenyl end group have been prepared by thermolysis of atactic polypropylene.The chain-end structures and the number-avarage isopropenyl chain end functionality was determined in the product by C-13 NMR spectroscopy. Molecular weight of the oligomers were between 300 and 1000, as characterized by GPC.Conditions leading to the formation of propylene oligomers with number-average isopropenyl chain end functionality of 1.0, have been worked out.     

The mechanism of skin-core morphology formation in extrudates of polycarbonate/liquid crystalline polymer blends

The mechanism of skin/core morphology development and LCP (liquid crystalline polymer) fibril formation in polycarbonate/LCP blends was studied. A certain minimum concentration of the LCP phase must be present for the formation of continuous LCP fibrils in the extrudates. A skin-core morphology characterizes the PC/LCP extrudates. Short LCP fibrils are formed in the capillary converging entrance section, through the elongation of LCP domains and their coalescence. Continuous fibrils were formed in the skin of extrudates emerging from cylindrical capillaries, through the coalescence of the short fibrils, provided the shear stresses are high enough and the LCP viscosity is equal or lower than that of PC. Increasing capillary length enhances the LCP lateral migration and fibrils formation. The high interfacial tension stabilizes the LCP fibrils. In the core region the short fibrils recoil or breakup, resulting in spherical or elongated droplets. Long and continuous fibrils cannot be formed in a zero length capillary, even at high flow rates.     

Studies on the transesterification of polycarbonate/poly(ethylene terephthalate) blends. I: Mechanisms and extent of reaction

Transesterification of polycarbonate/poly(ethylene-terephthalate) (PC/PET) blends and the reaction extent were investigated by DSC, FTIR, ¹H NMR and Soxhlet extraction. A new characteristic peak appeared in the FTIR spectrum of PC/PET blends after heat treatment, which indicates that new copolymers were formed in the transesterification of the PC/PET blends. The reaction extent was characterized by the absorbance ratios of the FTIR characteristic bands. The reaction extent was associated not only with the reaction conditions but also with the composition of the blends. These results were confirmed by chemical analysis of the extracted products in CH₂Cl₂ solvent and FTIR analysis. For all the blends studied, the blend with 50/50 wt% had the highest reaction extent. The reaction mechanisms and extent were also confirmed by ¹H NMR analysis.     

The influence of a copolymer as adhesion promoter for polycarbonate and liquid crystalline polymer blends

The modification of the interface between polycarbonate (PC) and Pet Phb60 was studied. The ester interchange reaction between the components of the 50% w/w mixture, responsible for the formation of molecular segments of intermediate affinity toward the parent polymers, has greatly affected the morphology of extrudate samples. The reacted compound was used in the ratio of 5% as compatibilizer in the formulation of the in situ composite between PC and PetPhb60, containing 10% of the reinforcing thermotropic liquid crystal polymer (TLCP). The effects of the adhesion promoter has been evaluated comparing the morphological features of melt-drawn fibers with the previous result concerning the fibers without the compatibilizer. © 1993 John Wiley & Sons, Inc.     

Compatibility of polymer blends. I. Copolymers with organic solvents

In this work, we present a theoretical discussion regarding the Flory–Huggins χ interaction parameter for 11 random copolymer‐solvent systems along with their corresponding polymer pairs. Copolymers studied are poly(acrylonitrile‐co‐butadiene) in acetonitrile, poly(styrene‐co‐acrylonitrile) in 1,2‐dichloroethane, poly(acrylonitrile‐co‐butadiene) in hexane, and poly(acrylonitrile‐co‐butadiene) in pentane. For ternary systems, the results are expressed in terms of χ_1,23, which is reduced to the classical Flory–Huggins χ₁₂ interaction parameter in case of binary mixtures. The data on χ_1,23 may be used for an approximate estimation of the χ′₂₃ interaction parameter for the limiting case of zero solvent concentration. For this purpose, at the end of each subsection of tables, the limiting value of is given. The limiting values of , , and χ′₂₃ also appear at the end of each table. It should be noted that these values are obtained by the graphical extrapolation of data to zero concentration of solvent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 492–498, 2006     

Thermotropic liquid crystalline copolyesters. I. Synthesis and thermal characterization of the copolyesters of terephthaloyl chloride,hydroquinone, and 1,4-butane diol

A new series of random thermotropic liquid crystalline polyesters (LCPs) was synthesized from terephthaloyl chloride, hydroquinone, and 1,4-butane diol. The copolyester composition was varied by changing the relative mole ratio of hydroquinone and 1, 4-butane diol in the feed. All the copolyesters displayed thermotropic liquid crystallinity at relatively low temperatures. Liquid crystalline behavior of the copolyesters has been characterized by polarizing light microscopy and by differential scanning calorimetry (DSC). The effect of co-polyester composition on the temperature and thermodynamic parameters related to liquid crystalline transition is discussed. © 1993 John Wiley & Sons, Inc.