Study on poly(oxybenzoate-p-trimethylene terephthalate) copolymer

This study examined copolymers synthesized from poly(trimethylene terephthalate) (PTT) and p-acetoxybenzoic acid using solution proton nuclear magnetic resonance (NMR) spectroscopy. Proton NMR spectra showed that these p-oxybenzoate (POB)/PTT copolyesters were almost random copolymers because the preference factor of POB bonded to another POB unit in these copolyesters is close to 1.0 with a POB content between 20 and 80 mol%.The melting and crystallization behaviors of these copolyesters were studied by differential scanning calorimetry (DSC). In the heating DSC scan of the POB rich composition, the endothermic peak is weaker because the enthalpy of fusion decreased due to a melting transition from a crystalline to anisotropy liquid state. Thermogravimetric analysis results indicated that the decomposition temperature (T_d) increased with POB content. The crystalline morphology of the copolyester was further investigated with a polarized optical microscope, indicating that the POB/PTT copolyesters with 60 mol% POB are highly anisotropic in the liquid state.     

Fiber spinning from the nematic melt. VI. Flow instabilities in the 30:70 copolyester of hydroxybenzoic acid and 2-hydroxy-6-naphthoic acid

The rheological behavior and fiber spinning are investigated for the Celanese liquid crystal copolyester 30 mol% p-hydroxybenzoic acid and 70 mol% 2-hydroxy-6-naphthoic acid (designated as 30HBA/70HNA) with inherent viscosity 7.8 dL/g. Shear thinning viscosity, and yield stress are observed at low shear stress, which probably results from the existence of crystallites in the melt. The crystal-nematic melting point of the copolymer, as measured by differential scanning calorimetry, is around 309°C. Extrudates are collected at four different temperatures ranging from 315 to 345°C. Melt fracture and die swell are observed above 335°C at low shear stress. A wide-angle x-ray diffraction (WAXS) study of an annealed sample indicates that the abnormal phenomenon may be due to crystallites arising from blocky units of HNA. Fiber spinning is performed at high shear rate at 325 and 335°C. Flow is stable under these conditions. The spin draw ratio is the ratio of take-up velocity to the velocity of extrudate existing from the capillary. The initial modulus reaches a maximum at a fairly low spin draw ratio. Instron and wide-angle x-ray (WAXS) studies show that the mechanical properties and orientation are poor for the fiber spun near the crystal-nematic melting point. Also, thermal history is found to affect the rheological behavior. Heat treatment offibers, particularly those which are well oriented, brings an improvement of mechanical properties.     

Chain structure and thermal behavior of reactive blends of PET/LCP with bis(2-oxazoline)

The sequence structure and thermal behavior of reactive blends of poly(ethylene terephthalate) (PET) with the liquid crystalline copolyester 60 PHB/PET containing 60 mol % of p-hydroxybenzoic acid (PHB) with addition of bis(2-oxazoline) (BOZ) were studied in detail. ¹H NMR results indicate that both the number average sequence length of PET and PHB segments (L _PET and L _PHB) decrease with increasing mixing time and temperature via transesterification between PET and LCP. The transesterification is promoted in the presence of BOZ. As a consequence, the sequence structure and in turn the crystallization both from the glassy and the melt state and the melting behavior are markedly affected.     

Melt spinning of thermotropic liquid-crystal polyesters to form ultrahigh-modulus filaments

The properties and structure of ultrahigh-modulus filaments were investigated for wholly aromatic copolyesters (WACPs) containing 60 and 70 mol% p-oxybenzoate, based on p-hydroxybenzoic acid, p,p′-biphenol, terephthalic acid, and isophthalic acid and for poly(ethylene terephthalate co-p-oxybenzoate) containing 60 mol% p-oxybenzoate. As-spun filaments with varying degrees of molecular orientation were spun from melts by taking the spin-extension ratio as a variable at given temperatures. The as-spun filaments were further subjected to thermal annealing. Changes in the structural ordering with the extension ratio were monitored by wide-angle x-ray scattering, scanning electron microscopy, viscoelastic properties, and measurements of the thermal expansion coefficient. The increase in modulus is correlated well with the crystallite orientation at a relatively low extension ratio. However, for extension ratios above 10, the modulus of as-spun filaments is almost independent of the crystallite orientation. Modulus values as high as 100 GPa are obtained for WACP filaments spun at extension ratios above 500. It is suggested that ultrahigh-modulus values can be reached in highly oriented noncrystalline chains. Furthermore, the results for annealed filaments indicated that the relaxation of molecular orientation occurs partially in the oriented noncrystalline regions during the stage of long-time annealing above T_g, leading to depression of the modulus.     

聚芳酯聚碳酸酯液晶共聚物的合成及表征

采用聚合物改性合成方法，以聚碳酸酯和对羟基苯甲酸苯酯（ＰＰＨＢ）为原料，克服了聚碳酸酯高温下易酸解脱羧的现象，合成了链结构为（ＯｐｈＣＯ）ｘ［ＯＰｈＣ（ＣＨ３）２ＰｈＯＣＯ］ｙ的液晶聚酯碳酸酯，并借助于ＤＳＣ，１Ｈ—ＮＭＲ，ＦＴＩＲ，ＴＧＡ，热台偏光显微镜和Ｘ光衍射等手段表征了其性能．结果表明，所合成的液晶聚酯碳酸酯具有较高的对数比浓粘度；当（ＯＰｈＣＯ）结构单元含量大于或等于５５ｍｏｌ％时，聚合物能呈现出向列型液晶行为；聚合物的Ｔｇ随着（ＯＰｈＣＯ）单元的增加而变大，并且聚合物拥有较好的溶解性能和热稳定性能     

Infrared Spectroscopy and X-Ray Diffraction Studies of C?H…O Hydrogen Bonding and Thermal Behavior of Biodegradable Poly(hydroxyalkanoate)

Infrared (IR) spectra and wide-angle X-ray diffraction (WAXD) patterns of poly(3-hydroxybutyrate) (PHB) and its copolyester, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), P(HB-co-HHx) (HHx = 12 mol%) were measured over a temperature range of 20 °C to higher temperatures (PHB, 185 °C, HHx = 12 mol%, 140 °C) to explore their structure change and thermal behavior and molecular interaction. The WAXD measurements revealed that the a lattice parameter increases significantly with temperature, while the b lattice parameter varies a little in the crystalline PHB and P(HB-co-HHx). It seems that the intermolecular interaction between the CO group of one helical structure and the CH₃ group of the other helical structure decreases along the a axis of crystalline PHB and P(HB-co-HHx) with temperature. The temperature-dependent IR spectral variations were analyzed for the CH stretching, CO stretching, CH₃ deformation, and C O C stretching variation regions, and bands characteristic of crystalline and amorphous parts were identified in each region. It was found from the anomalous frequencies of the CH₃ asymmetric stretching and CO stretching bands of PHB and P(HB-co-HHx) and the X-ray crystallographic structure of PHB that there is an intermolecular interaction (C H…OC hydrogen bond) between the CO group and the CH₃ group combining two helical structures in PHB and P(HB-co-HHx). In this review paper we discuss the role of the C H…OC hydrogen bonding and the crystal and lamella structure of PHB and P(HB-co-HHx) (HHx = 12 mol %) in comparison with the structure of Nylon.     

Liquid-crystalline copolyesters based on poly(p-oxybenzoate) and poly(p,p-biphenylene terephthalate)

Two copolymers composed of p-hydroxybenzoate (PHB) and biphenylene terephthalate (BPT) with PHB/BPT ratios of 1/2 and 2/1 were characterized with respect to their tendency to exhibit liquid-crystalline behavior in the melt phase. The BPT -rich copolyester, PHB/BPT = 1/2, displayed a birefringent melt phase of very high viscosity and no tendency to crystallize on cooling. The resulting fused material exhibited what apeared to be a second-order transition at 170°C. The PHB-rich composition, PHB/BPT = 2/1, also exhibited a highly birefringent melt phase of high viscosity which was quite shear sensitive. This polymer melt had little tendency to crystallize on cooling; however, on reheating no apparent second-order transition could be detected. The observed phase changes were characterized by differential scanning calorimetry, hot-stage microscopy, and wide-angle x-ray diffraction techniques. Additional data, pertaining to the compositional nature and apparent sequence distribution, were obtained by ¹³C-NMR spectroscopy of the solid materials through magic-angle spinning, dipolar decoupling, and cross-polarization techniques.     

Thermal properties of random copolyesters of PET and 3- and 3,5-bromo-substituted p-hydroxybenzoic acids. II

Melt-polycondensation of poly(ethylene terephthalate) (PET) and 3-bromo-p-acetoxybenzoic acid or 3,5-dibromo-p-acetoxybenzoic acid in different mole ratios yielded random copolyesters. The copolyesters have higher T_gs than PET because of an increase in mol % of the substituted p-oxy-benzoate units and follow Wood's equation for copolymer T_gs. Using this equation, we calculated the T_gs of the homopolymers of 3-bromo-p-oxybenzoate and 3,5-dibromo-p-oxybenzoate, which are not available experimentally, to be 113 and 123°C, respectively. Up to certain percentages of the comonomer composition the copolyesters exhibited cold crystallization and melt transitions which we attribute to the crystallizable segments of PET. The variation in melting temperatures in the composition of the copolymer was explained by Flory's theory. The differences in the melting behavior of the polymer, annealed at various crystallization temperatures for a constant time interval, throws light on the morphological changes that took place in it. Using the Hoffman and Weeks method, we determined the extrapolated equilibrium melting temperatures of these copolyester which were used to calculate the enthalpy of melting for the crystallizable units.     

Compatibility and fungal degradation of poly[(R)-3-hydroxybutyrate]/aliphatic copolyester blend

Poly[(R)-3-hydroxybutyrate] (PHB) was blended with an aliphatic copolyester, which was synthesized by the esterification of adipic acid, ethylene glycol, and lactic acid. The blend showed a single T_g, which varied systematically but convexly upwards with the composition. The growth rate of PHB spherulites, the crystallization temperature, and the equilibrium melting temperature of the blend were decreased as the amount of the copolyester was increased. Therefore, the blend system was determined to be compatible. However, the degree of crystallinity, and the enthalpies of crystallization and fusion of PHB in the blend remained almost constant, regardless of the compositional change, although the crystallization rate was decreased upon blending. No chemical change such as transesterification was observed as a result of the blending, yet there was a slight change in the crystalline morphology of PHB. The rate of fungal degradation was lowered with an increase in the copolyester content of the blend. © 1996 John Wiley & Sons, Inc.     

Super structure formation in a wholly aromatic copolyester fiber

The structure of a wholly aromatic copolyester fiber containing 60 mol% p‐hydroxybenzoic acid (PHB), 20 mol% 4−4′‐dihydroxydiphenyl, 15 mol% terephthalic acid and 5 mol% isophthalic acid was studied by means of electron microscopy and wide‐angle X‐ray diffraction. The X‐ray diffraction pattern of the wholly aromatic copolyester fibers showed two sets of diffractions: one set was composed of sharp spots which arose from relatively high crystalline phase. The crystal structure analyzed by these spots was orthorhombic and the lattice dimensions were a = 0.869 nm, b = 0.510 nm, c = 1.20 nm and ρ = 1.50 g/cm³. Another set was characteristic of streaks on the meridian extending parallel to the equator. X‐ray scattering intensity distribution on the meridian was calculated as the square of Fourier transform of random chain model. Comparison of this intensity distribution with the observed meridional maxima concluded that the streaks were due to rather disordered chains with a PHB content of less than 50%. Dark field image (DFI) taken from the meridional 002 reflection showed that slender crystallites were distributed over the whole visual field, oriented parallel to the fiber axis. On DFI from the equatorial 200 reflection, some of these crystallites were also observable, forming groups that distributed randomly in the field. All crystallites belonging to the same group co‐oriented in a*‐ and c*‐axis directions, though disordered parts intervened among the crystallites. This is attributed to the fact that, though the content of PHB in the segments of disordered parts was only 50%, these PHB held the co‐orientation among the slender crystallites within one group. Heat treatment induced the development of block segment and subsequent crystallite growth with fiber. This reorganization improved the thermostability and the mechanical properties. Copyright © 2000 John Wiley & Sons, Ltd.     

Fiber spinning from the nematic melt. II. Effect of thermal history on spinning of the copolyester of polyethylene terephthalate and p-oxybenzoate

Fibers were spun from the nematic phase of the copolymer of polyethylene terephthalate having 60 mol % of p-oxybenzoate units. A capillary rheometer was used for spinning with a shear rate at the wall of 6.4 sec^?1, and capillary (length/diameter) ratio of 14.1. The spinning temperature was varied from 250° to 300°C and, at each temperature, the spin-draw ratio was examined as a variable. Spinning was performed under two conditions. When spinning from the melt without preheating, the initial modulus of the fibers increased with spin-draw ratio and increased with increasing spinning temperature for a fixed spin-draw ratio. In the second case, the melt was preheated and then cooled to the desired temperature before spinning the fibers. The preheating temperature was 280°C for spinning at 250°C, and 300°C for spinning at 280°C. Preheating increased the fiber modulus to the value obtained by spinning at the preheating temperature. A reduction of the viscosity due to the melting of poly(p-hydroxybenzoic acid) (PHB) crystallites produces better orientation and higher modulus. However, with increasing spin-draw ratio, the modulus of the preheated fibers decreased to the values expected for the spinning temperature. This decrease in modulus is due to recrystallization of PHB in the threadline.     

Fiber spinning from the nematic melt. IV. Effect of P oxybenzoate crystallinity on the spinning and fiber properties of the copolyester of polyethylene terephthalate and p-oxybenzoate

We have previously reported two studies of the rheology and fiber properties of one sample of the copolymer of polyethylene terephthalate having 60 mol% of p-oxybenzoate (PHB) units. The DSC curve of that sample exhibited crystalline melting transitions, and the sample appeared to contain PHB blocks. Here we compare those results with observations for a second sample that, although nominally the same polymer, appears to be more random because it exhibits little PHB crystallinity. We had previously reported that the flow of the copolymer containing PHB blocks was non-Newtonian at all temperatures, and that it exhibited a thermal history effect. We find the flow of the more random polymer is Newtonian above the melting temperature, and the melt viscosity of the more random copolymer exhibits no thermal history effect. Fibers were spun from the more random copolymer with a capillary rheometer using a capillary having a length/diameter ratio of 14.1 and a shear rate at the wall of 6.4 sec^?1. Spinning temperatures were 250, 260, and 280°C, and the spin draw ratio was examined as a variable. The initial modulus increased with spin draw ratio but exhibited no dependence upon the spinning temperature. For the copolymer containing PHB blocks, the initial modulus increased as the spinning temperature was raised. These differences are due to the larger amount of PHB crystallinity in the more blocky sample. When chips of the more random sample were heated for 1 h at 235°C, the melt viscosity increased and the initial modulus of the fibers decreased. These changes are due to the crystallization of longer PHB blocks produced by melt interchange.     

Phase transitions in mesophase macromolecules. III. The transitions in poly(ethylene terephthalate-co-p-oxybenzoate)

The glass and melting transitions of poly(ethylene terephthalate-co-p-oxybenzoate)s have been studied by differential scanning calorimetry. Despite the higher glass transition expected for polyoxybenzoate, there is almost no change in the glass transition temperature up to 63 mol % oxybenzoate (353 ± 4 K). At high oxybenzoate concentration there seems to be a discontinuous jump to a glass transition of 450 K. This high glass transition has been observed in two-phase materials down to 30 mol % oxybenzoate. The melting transition shows signs of isodimorphism with a minimum in melting temperature at about 60–70 mol % oxybenzoate, 60 K below the melting temperature of poly(ethylene terephthalate). The thermal properties are little affected by the change of the noncrystalline parts of the molecules to a mesophase structure. The transition to the isotropic phase could not be analyzed because of prior decomposition.     

CRYSTALLIZATION AND MULTI-MELTING BEHAVIOR OF POLY (ETHYLENE TEREPHTHALATE) MODIFIED BY SODIUM SALT OF 5-SULPHO-ISOPHTHALIC ACID

The crystallization kinetics of the copolyester, poly(ethylene terephthalate) (PET) modified by sodium salt of 5-sulpho-isophthalic acid(SIPM), was investigated by means of differential scanning calorimeter. The experimental results and polari-microscopy observation all showed that the introduction of SIPM did not affect the nucleation of crystallization. Within the temperature range between their glass transition temperature T_θand melting point T_m, the crystallization rate of the copolyester sample decreased with increasing content of SIPM. The relative crystallization rate constant Z of SIPM/DMT (dimethyl terephthalate) 4mol % sample was about 1% pure PET's Z value. For isothermal crystallized copolyester samples, DSC heating curves displayed multi-melting behavior. This was interpreted by molecular weight fractionation during crystallization and premelting-recrystallization mechanism. This interpretation showed why the second melting point T_(m2) will change according to Hoffman-Weeks(H-W) equation and the first melting point T_(m1) will increase with increasing SIPM. The principal cause of these phenomena is the high temperature crystallization rate decreases rapidly with increasing SIPM.     

Structure and morphology of the 60/40 poly(p-oxybenzoate-co-ethylene terephthalate) copolymer

The copolyester composed of 60 mol% p-hydroxybenzoic acid and 40 mol% ethylene terephthalate has been studied extensively by earlier workers. However, some confusion exists particularly with respect to the nature of the thermal transitions and the possible presence of additional phases. In the present study we have examined this copolyester and found that it is possible to separate the material into soluble and insoluble fractions with significantly different ratios of p-hydroxybenzoic acid to ethylene terephthalate. In fact, the soluble PET-rich fraction is blocky in nature, while the PHBA-rich fraction is more random. The multiple thermal transitions can now be readily interpreted in terms of a heterogeneous composition which tends to segregate and phase separate.     

The thermodynamic properties of polytetrafluoroethylene

Polytetrafluoroethylenes of different crystallinity were analyzed between 220 and 700 K by differential scanning calorimetry. A new computer coupling of the standard DSC is described. The measured heat capacity data were combined with all literature data into a recommended set of thermodynamic properties for the crystalline polymer and a preliminary set for the amorphous polymer (heat capacity, enthalpy, entropy, and Gibbs energy; range 0–700 K). The crystal heat capacities have been linked to the vibrational spectrum with a θ₃ of 54 K, and θ₁ of 250 K, and a full set of group vibrations. C_v to C_p conversion was possible with a Nernst–Lindemann constant of A = 1.6 × 10^?3 mol K/J. The glass transition was identified as a broad transition between 160 and 240 K with a ΔC_p of 9.4 J/K mol. The room-temperature transitions at 292 and 303 K have a combined heat of transition of 850 J/mol and an entropy of transition of 2.90 J/K mol. The equilibrium melting temperature is 605 K with transition enthalpy and entropy of 4.10 kj/mol and 6.78 J/K mol, respectively. The high-temperature crystal from is shown to be a condis crystal (conformationally disordered), and for the samples discussed, the crystallinity model holds.     

Miscibility of a polyarylate with a liquid crystalline copolyester

The miscibility has been investigated for binary blends of a polyarylate (PAr) with a liquid crystalline copolyester of p-hydroxybenzoate and ethylene terephthalate units in a 6/4 molar ratio (PET/PHB). The binary blends were prepared by solution precipitation. The transitions of the PET/PHB have been measured with a rheometrics dynamic spectrometer. The phases in blends have been studied with a differential scanning calorimeter, by ther-mogravimetry and with a polarizing optical microscope. The blends exhibit two glass transitions (T_gs) over the composition range 10–90 wt %. The amorphous PET phase from the PET-PHB is found to be partially miscible with PAr, which leads to a decrease of the PAr T_g. The amount of this partially miscible portion of PET has been estimated by the Couch-man equation. On heat treatment of the blends at 250 to 300°C, transesterficiation takes place, as judged by the shift of the higher of the two T_gs. © 1993 John Wiley & Sons, Inc.     

Attempt to control monomer sequences in copolycondensations of IPA,TPA, BPA,and PHB

Copolycondensations of IPA, TPA, BPA, and PHB were studied to investigate how PHB, which can form mesogenic segments, should be incorporated into the amorphous IPA/TPA–BPA polyester to obtain the thermotropic copolyester, unlike other copolymerizations studied so far by randomly introducing nonmesogenic components into the liquid crystalline polyesters. Random and controlled copolycondensations were attempted to regulate the segment length of mesogenic PHB units by stepwise addition of BPA and PHB through the two- and three-stage reactions using TsCl/DMF/Py as a condensing agent. Thermotropic copolyesters with ca. 40 mol % PHB could be obtained by a three-stage reaction, despite that more than 70 mol % PHB is needed to prepare by usual random copolymerization with PHB. The segment length of the PHB unit was indirectly studied from IPA/TPA–BPA oligomer distribution at initial reaction by means of GPC and from the NMR analysis of the resulting copolymers. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2371–2377, 1999     

Lamellar and whisker single crystals of poly(2,6-oxynaphthoate)

Electron diffraction from single crystal lamellae and whiskers of poly(2,6-oxynaphthoate) reveals the presence of at least 3 unit cells. The equatorial reflections in the patterns from the whiskers correspond to the dominant (phase I) hk0 diffraction pattern from the lamellae; phase I is monoclinic with 2 chemical repeats per physical repeat. The intensity distributions in the hk0 patterns of phase I and II resemble those of the same phases in poly(p-oxybenzoate). The hk0 reflections of phase III suggest a common internapthalene unit spacing, but variable lateral (and possibly axial) shifts; apparently related orthorhombic and monoclinic patterns, with variable γ^*, are observed. At elevated temperature, above the crystalliquid crystal transition (ca. 330°C), quadrant reflections are retained; the change in the hk0 pattern from any given crystal is gradual, extending over some 40°C. Above the liquid crystal-liquid crystal transition (ca. 460°C) the pattern can be interpreted in terms of nematic or possibly smectic A packing. © 1992 John Wiley & Sons, Inc.     

Fluorescence study of thermotropic liquid-crystalline polyesters

Photoluminescence behavior (polarization, lifetime) related to liquid-crystal (LC) formation was examined for the thermotropic liquid-crystalline polyesters poly [(ethylene terephthalate)-co-(p-oxybenzoate)] (PET40/OBA60) (OBA content: 60 mol %) and poly [(ethylene 2,6-naphthalene dicarboxylate)-co-(p-oxybenzoate)] (PEN50/OBA50) (OBA:50 mol %). The Growth of liquid-crystalline (LC) phases of PET40/OBA60 proceeded during annealing. even at low temperature (e.g., 138°C) and were promoted by an increase in annealing temperatures T_a in the experimental temperature range 138–260°C. The concentration dependence of fluorescence spectra of PET40/OBA60 in solution suggested that the fluorescences at 325 and 395 nm can be attributed to monomer and ground-state dimer, respectively. The increase in dimer fluorescence intensity and the decrease in the fluorescence anisotropy ratio r from 0.06 to –0.14 were observed with growth of LC phases. These effects are explained by an increase in the ground-state dimer population and a slight change in the dimer configuration, respectively. PEN50/OBA50 showed monomer fluorescence at 395 nm due to naphthalenedicarboxylate segments and excimer fluorescence at 430 nm. The r value for the excimer fluorescence decreased from zero to about ?0.14 with growth of the LC phase. Such an extraordinary phenomena, in comparison with the usual excimer fluorescences which occurs through energy migration, could be interpreted as the result of formation of high-concentration excimer sites induced by chain orientation in LC domains. © 1993 John Wiley & Sons, Inc.