Preparation and characterizations of thermotropic copolyesters of p-hydroxybenzoic acid,sebacic acid,and hydroquinone

A series of copolyesters of p-hydroxybenzoic acid (HBA), sebacic acid and hydroquinone were prepared by melt polycondensation of p-acetoxybenzoic acid, sebacic acid and p-phenylene diacetate. The copolyesters were characterized by IR, NMR, DSC, polarized microscopy, and X-ray diffraction. It was found that the copolyesters exhibited liquid crystallinity when the HBA content was 25–67 mol %. The copolyesters with an HBA content of 25–43 mol % showed a nematic phase and a biphasic range, and the isotropization temperature increased as the HBA content increased. The copolyesters with an HBA content of 54–67 mol % showed a nematic phase up to above 400°C. The liquid crystalline order increased as the HBA content increased due to the increased of the average length of the rigid moieties. © 1995 John Wiley & Sons, Inc.     

Studies on co[poly(ethylene terephthalate-p-oxybenzoate)] thermotropic copolyester (I): Synthesis and thermogravimetric behavior

A series of co[poly(ethylene terephthalate-p-oxybenzoate)] thermotropic copolyester was synthesized from various ratios of two different moieties of either poly(ethylene terephthalate) (PET) or its oligomer as moiety ( II ) with p-acetoxybenzoic acid as moiety ( I ) through the polycondensation process. The polymeric products obtained were then ground and subjected to solid-state polymerization under vacuum for various polymerization times. Thermogravimetric analysis (TGA) and the derivative thermogravimetric analysis (DTG) were performed with these samples obtained. Also, a commercial product, Eastman 10109, was analyzed in comparison with these samples. It was found that the copolyesters made of PET and of its oligomer in a p-oxybenzoate (POB):PET = 80 : 20 composition ratio and subjected to 8 and 4 h solid-state polymerization times, respectively, showed the most similar thermogravimetric behavior with Eastman 10109. © 1993 John Wiley & Sons, Inc.     

Synthesis and properties of copolyesters of p,p′‐bibenzoic acid,dimer acid,and alkylene glycol

Copolyesters of p,p′‐bibenzoic acid, dimer acid, and an alkylene glycol are prepared by melt polycondensation of of dimethyl p,p′‐bibenzoate, dimer acid, and an alkylene glycol. The copolyesters are characterized by the inherent viscosity, FTIR, proton NMR, DSC, polarized microscopy, and X‐ray diffraction. The polymer composition and sequence distribution of the copolyesters can be seen from the NMR spectra. The copolyesters exhibit a degree of randomness of about 1, indicating that they are random copolymers. The glass‐transition temperature (T_g) and the melting point (T_m) of the copolyesters are found from the DSC heating curves. When the content of the flexible dimer acid unit increases, the T_g of the copolyesters decreases significantly. The copolymerization effect decreases the crystallinity and the T_m of the copolyesters. It can be seen from the DSC, polarized microscopy, and X‐ray diffraction data that some copolyesters derived from 1,6‐hexanediol and 1,5‐pentanediol exhibit a monotropic smectic phase. As the molar content of the dimer acid unit increases, the isotropic–mectic transition temperature and the smectic order decreases significantly. The liquid crystallinity is completely destroyed at certain molar contents of the dimer acid unit. The smectic order of the copolyesters derived from 1,6‐hexanediol is significantly higher than that of the copolyesters derived from 1,5‐pentanediol, and it is described as an odd–even effect. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 750–758, 2003     

Studies on co[poly(ethylene terephthalate-p-oxybenzoate)] thermotropic copolyester: Thermomechanical and thermodynamic properties

A series of co[poly(ethylene terephthalate-p-oxybenzoate)] thermotropic copolyesters were prepared by the copolymerization of poly(ethylene terephthalate) (PET) as moiety (II) and p-acetoxybenzoic acid (POB) as moiety (I). The polymeric products obtained were subjected to solid-state polymerization. Characterization of the copolyesters by thermomechanical analysis shows that properties such as the coefficient of thermal expansion, transition temperature, and maximum softening rate temperature varied directly as a function of composition as well as did solid-state polymerization time. All thermomechanical data were found to increase with the solid-state polymerization time due to the increase in the degree of polymerization and the effect of annealing. The coefficient of thermal expansion behaves in a manner that is interpretable by the crystalline state of the copolyester. The relationship between the free-volume fraction and thermodynamic properties is further correlated for a more comprehensive discussion on its molecular arrangements. © 1995 John Wiley & Sons, Inc.     

Synthesis and properties of poly(alkylene p,p′-bibenzoate-co-adipate)s

Various poly(alkylene p,p′-bibenzoate-co-adipate)s were prepared by melt polycondensation of dimethyl-p,p′-bibenzoate, adipic acid, and an alkylene glycol. The copolyesters were characterized by inherent viscosity, FTIR, proton NMR, DSC, polarized microscopy, and X-ray diffraction. The polymer composition and sequence distribution of the copolyesters can be seen from NMR spectra. The copolyesters exhibit a degree of randomness of about 1, indicating that they are random copolymers. From the DSC data, the glass transition temperature (T_g) and melting point (T_m) of the copolyesters can be detected. When the content of the flexible adipate unit increases, the T_g of copolyesters decreases significantly. The type of alkylene glycol used also affects the T_g to some extent. The copolymerization effect decreases crystallinity and the T_m of the copolyesters. The DSC, polarized microscopy, and X-ray diffraction data show that some copolyesters derived from 1,6-hexanediol exhibit a monotropic smectic phase. As the molar fraction of adipate unit in diacid units, x, is more than 0.4, the liquid crystallinity is completely destroyed. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:893–900, 1997     

Co[poly(ethylene terephthalate-p-oxybenzoate)] thermotropic copolyester. II. X-ray diffraction analysis

A series of co[poly(ethylene terephthalate-p-oxybenzoate)] thermotropic copolyester with different compositions were prepared by the copolymerization of either poly(ethylene terephthalate) (PET) polymer or its oligomer with p-acetoxy-benzoic acid. The polymeric products were subjected to solid-state polymerization for various time intervals. Effects of composition ratio and solid-state polymerization time on X-ray diffraction behavior were investigated. It is found that the effect of transesterification induced by solid-state polymerization causes an increase in crystallinity with the copolyesters having high mol % of p-oxybenzoic acid (POB) moiety and causes a decrease in crystallinity with the copolyesters having high mol % of PET moiety. In general, the crystallinity of copolyesters is first increased and then decreased as solid-state polymerization time proceeds. However, the crystallinity of copolyester having POB/PET = 80/20 composition is increased generally at 4-h solid-state polymerization. It is also found that the crystallinity of copolyesters is decreased by quenching. The copolyester based upon either PET oligomer with 4-h solid-state polymerization or PET polymer with 8-h solid-state polymerization shows the most similar X-ray diffraction pattern with that of Eastman 10109. © 1993 John Wiley & Sons, Inc.     

Study on co[poly(butylene terephthalate‐p‐oxybenzoate)] thermotropic copolyester. I. Composition analysis and sequence distribution

Copolyesters made from Poly(butylene terephthalate) (PBT) and p‐acetoxybenzoic acid (PAB) have been examined in solution by proton nuclear magnetic resonance (NMR) spectroscopy. Proton NMR spectra of solutions have shown that the sequence distribution for POB/PBT copolyesters can be described in terms of a probability model in which POB (p‐oxybenzoate) has a chance that is almost random of being bonded to another POB in the copolyesters, with POB content ranging from 20 to 40 mol %. From the experimental data, we can predict that the higher the content of POB in copolyester is, the larger the deviation from randomness of sequence distribution is. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 949–954, 2000     

Effect of monomer composition on the rheological properties of poly(p-oxybenzoate-co-ethylene terephthalate)s

Summary Effect of monomer composition on the dynamic viscoelastic properties and the steady flow properties of thermotropic liquid crystalline poly (p-oxybenzoate-co-ethylene terephthalate)s in the fluid state have been investigated as compared with the isotropic melt of the copolyester including 28 mol% p-oxybenzoate unit (POB). The liquid crystalline copolyesters show the rheological transition temperature, which increases with increasing the content of POB unit. Above the transition temperature, all the thermotropic copolyesters exhibit much higher compliance and much more shear-thinning behavior of the apparent viscosity than the isotropic melt of the non-liquid crystalline copolyester.     

Composition,thermal properties,and biodegradability of a new biodegradable aliphatic/aromatic copolyester

A series of new aliphatic/aromatic copolyesters [poly(hexylene terephthalate‐co‐hexylene adipate) (PHTA)] were synthesized on the bases of 1,6‐hexanediol, adipic acid, and dimethyl terephthalate and characterized by gel permeation chromatography, ¹H‐NMR, wide‐angle X‐ray diffraction (WAXD), differential scanning calorimetry (DSC), and compost testing. ¹H‐NMR results show that the compositions of the copolyesters were in accordance with the feed molar ratios. The WAXD patterns indicated that the crystal structures of the PHTA copolyesters were determined by the dominant crystal units, and the copolyesters became less crystallizable, even amorphous, with increasing comonomer content. The DSC curves showed that the glass‐transition temperatures (T_g′s) of the PHTA copolyesters decreased linearly, and both the melting temperature (T_m) and heat of fusion decreased first and then increased with increasing hexylene adipate unit content. Under compost conditions, PHTA copolyesters with less than 60 mol % aromatic units were biodegradable. Particularly, compared with the copolyester poly(butylene terephthalate‐co‐butylene adipate), the PHTA copolyester with the same aliphatic/aromatic composition possessed a lower T_g and T_m and better biodegradability. Additionally, the biodegradability of the copolyesters could be predicted by the number‐average sequence length of aromatic units, T_g, and the temperature difference between T_m and the temperature at which biodegradation took place. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Synthesis and melt spinning of fully aromatic thermotropic liquid crystalline copolyesters containing m‐hydroxybenzoic acid units

Fibers of fully aromatic thermotropic copolyesters based on p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA), and m‐acetoxybenzoic acid (m‐ABA) were prepared by a high‐temperature melt‐spinning technique. Two types of the copolyesters were prepared by a high‐temperature melt polycondensation reaction using 33 mol % of kink (m‐ABA) and 67 mol % linear monomer units (p‐ABA, TPA, HQDA), and characterized by differential scanning calorimetry (DSC), polarized optical microscopy, wide‐angle X‐ray diffraction (WAXD), and intrinsic viscosity measurements. The mechanical properties and the morphology of the fibers were also determined by tensile tester, WAXD, and scanning electron microscopy (SEM). The copolyesters exhibited phase‐separated nematic liquid crystalline morphology within a broad temperature range in an isotropic matrix. DSC analysis of the copolyesters revealed broad endotherms associated with the nematic phases. The melting and spinning temperatures were in a processable region. Fibers exhibit well‐developed fibrillar structure parallel to the fiber axis. The highly oriented morphology of the fibrils is slightly dependent on the type of the linear monomer. The strength and modulus values determined for the fibers that contain equal molar composition of the linear p‐ABA, HQDA/TPA units are comparable to other reported rigid systems containing fully aromatic species. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2580–2587, 2002     

High-resolution thermogravimetry of liquid crystalline copoly(p-oxybenzoate–ethylene terephthalate–m-oxybenzoate)

Thermotropic liquid crystalline terpolymers consisting of three units of p-oxybenzoate (B), ethylene terephthalate (E), and m-oxybenzoate (M), were investigated through high-resolution thermogravimetry to evaluate their stability and kinetic parameters of thermal degradation in nitrogen and air. Overall activation energy data of the first major decomposition was calculated through three calculating methods. Thermal degradation occurs in three major steps in both nitrogen and air. Three kinds of degradation temperatures (T_d, T_m1, T_m2) are slightly higher and the first maximum weight-loss rates are slightly lower in nitrogen than in air, suggesting a higher thermostability in nitrogen. The thermal degradation temperatures range from 450 to 457°C in nitrogen and 441 to 447°C in air and increase with increasing B-unit content at a fixed M-unit content of 5 mol %. The temperatures at the first maximum weight loss rate range from 452 to 466°C in nitrogen and 444 to 449°C in air and increase slightly with an increase in B-unit content. The first and second maximum weight-loss rates are maintained at almost 9.2–10.8 and 4.0–6.1%/min in nitrogen (11.2–12.0 and 3.9–4.2%/min in air) and vary slightly with copolymer composition. The residues after the first major step of degradation are predicted on the basis of the complete exclusion of ester and ethylene groups and hydrogen atoms and compared with those observed experimentally. The char yields at 500°C in both nitrogen and air are larger than 42.6 wt % and increase with increasing B-unit content. However, the char yields at 800°C in nitrogen and air are different. The activation energy and ln(pre-exponential factor) for the first major decomposition are slightly higher in nitrogen than in air and increase with an increase in B-unit content at a given M-unit content of 5 mol %. There is no regular variation in the decomposition order with the variation of copolymer composition and testing atmosphere. The activation energy, decomposition order, and ln(pre-exponential factor) of the thermal degradation for the terpolymers are located in the ranges of 212–263 kJ mol⁻¹, 2.4–3.5, 33–41 min⁻¹, respectively. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2911–2919, 1999     

Thermogravimetric kinetics of thermotropic copolyesters containing p‐oxybenzoate unit by multiple heating‐rate methods

Two series of thermotropic liquid crystalline copolyesters containing mainly the p‐oxybenzoate unit were studied by thermogravimetry to ascertain the kinetic parameters of their thermal degradation by six multiple heating‐rate techniques for the first time. The two copolyesters are (1) poly(p‐oxybenzoate‐co‐ethylene terephthalate‐co‐vanillate) and (2) poly(p‐oxybenzoate‐co‐2,6‐oxynaphthoate). The effect of copolymer composition, degradation stage, and test atmosphere on the three kinetic parameters of the thermal degradation in the weight loss range from 5 to 70% is discussed. Comparison of the multiple heating‐rate techniques with single heating‐rate techniques for calculating the kinetic parameters of thermal degradation was made. The respective activation energy, order, and natural logarithm of the frequency factor of the thermal degradation in nitrogen for the poly(p‐oxybenzoate‐co‐ethylene terephthalate‐co‐vanillate)s are between 180 and 230 kJ/mol, between 2.0 and 5.0, and between 28 and 38 min⁻¹ for the first degradation step and between 250 and 390 kJ/mol, between 6.4 and 7.6, and between 38 and 64 min⁻¹ for the second degradation step of the poly(p‐oxybenzoate‐co‐ethylene terephthalate‐co‐vanillate)s with the unit‐B content in the range of 70–75 mol %. The respective activation energy, order, and natural logarithm of frequency factor of the first degradation stage for the poly(p‐oxybenzoate‐co‐2,6‐oxynaphthoate) (Vectra) are between 380 and 570 kJ/mol, between 2.0 and 3.1, and between 55 and 68 min⁻¹ in nitrogen and between 160 and 210 kJ/mol, between 0.8 and 1.8, and between 25 and 32 min⁻¹ in air. The best methods of calculating the kinetic parameters of the thermal degradation for the copolymers are suggested. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2016–2028, 1999     

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.     

Characterization and biodegradability of poly(butylene adipate‐co‐succinate)/poly(butylene terephthalate) copolyester

Characterization of poly(butylene adipate‐co‐succinate) (PBAS)/poly(butylene terephthalate) (PBT) copolyesters resulting from the intermolecular ester‐exchange reaction between molten PBAS and PBT have been analyzed using ¹H‐NMR spectroscopy, differential scanning calorimetry, wide‐angle X‐ray diffraction, and total organic carbon lab analyzer. Using the assignment of proton resonance due to homogeneous and heterogeneous dyads, the average block lengths were investigated over the entire range of copolymer composition. A decrease in melting temperature was observed with the increase of a terephthalate unit in the composition. The result of X‐ray diffraction curve matches well with that of average block length and thermal property. When a rich component is crystallized, the poor component is excluded completely in a crystal formation. The biodegradability in copolyesters also depended on the terephthalate unit in the composition and average block length of the aromatic unit. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 593–608, 1999     

Syntheses and characterization of poly(ethylene terephthalate) modified with p-acetoxybenzoic acid

Though the structure and properties of a copolyester of 40 mole % of polyethylene terephthalate (PET) and 60 mole % p-hydroxybenzoic acid (PHB) (PET/60PHB) and their blends have been well documented, no work has been reported in an open literature on the systematic investigation of the PET copolymers modified with broad range of p-acetoxybenzoic acid (PABA) composition as yet. In this study, several PETA-x copolyesters having various PABA compositions from 10 to 70 mole % were prepared by the melt reaction of PABA and PET without a catalyst, where x denotes the mole % of PABA. And the modified polyesters obtained were characterized by ¹H-NMR spectrophotometry, X-ray diffraction pattern, polarizing microscopy, thermal analysis, and rheometry. The anisotropic phase appeared when x is above 50 mole % of PABA, and especially for the x's of 60 and 70 mole %, the nematic liquid crystalline texture appeared clearly on the whole matrix. As the mole % of PABA increased, melting temperature, heat of fusion, crystalline temperature, degree of crystallinity, and the glass transition temperature of the modified PET were decreased, but the thermal stabilities of those copolyesters were increased. The dependence of melt viscosity on the shear rate for PETA-50 ∼ 70 followed the typical rheological behavior of liquid crystalline polymers. Finally, it was concluded that the PETA-x copolyesters having compositions of higher than 50 mole % of PABA exhibit the behavior of thermotropic liquid crystalline polymers. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 1707–1719, 1999     

Synthesis and characterization of poly(L‐lactic acid)‐b‐poly(ethylene terephthalate‐co‐sebacate)‐b‐poly(L‐lactic acid) copolyesters

Random copolyester namely, poly(ethylene terephthalate‐co‐sebacate) (PETS), with relatively lower molecular weight was first synthesized, and then it was used as a macromonomer to initiate ring‐opening polymerization of l ‐lactide. ¹H NMR quantified composition and structure of triblock copolyesters [poly(l ‐lactic acid)‐b‐poly(ethylene terephthalate‐co‐sebacate)‐b‐poly(l ‐lactic acid)] (PLLA‐PETS‐PLLA). Molecular weights of copolyesters were also estimated from NMR spectra, and confirmed by GPC. Copolyesters exhibited different solubilities according to the actual content of PLLA units in the main chain. Copolymerization effected melting behaviors significantly because of the incorporation of PETS and PLLA blocks. Crystalline morphology showed a special pattern for specimen with certain composition. It was obvious that copolyesters with more content of aromatic units of PET exhibited increased values in both of stress and modulus in tensile test. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Main‐chain liquid‐crystalline polymers containing azobenzene mesogen having long lateral aliphatic side chain: effect of copolymerization on thermal and phase behaviors

Homo‐ and copolyesters of derivatives of hydroxyazobenzenecarboxylic acid with various percentage compositions of m‐hydroxy benzoic acid (m‐HBA)/p‐hydroxy benzoic acid (p‐HBA) were synthesized and characterized. The properties of the copolyesters were compared with their corresponding homopolyesters. The solubility of the copolyesters with m‐HBA increased because of the decrease in the rigidity of the polymer chain attributed to the introduction of nonlinear molecules, whereas the solubilities of the copolyesters with p‐HBA changed only slightly compared to their corresponding homopolyesters. Thermal and phase behaviors of the polymers were characterized by TGA, DSC, and polarizing light microscopy (PLM) methods. Above 30% composition of m‐HBA, the thermal stability of the copolyesters with m‐HBA decreased compared to that of the homopolyester P1, whereas the copolyesters of p‐HBA possessed greater thermal stability than that of their homopolyesters at all compositions. The introduction of the long, flexible alkyl side chain laterally to the backbone of the azobenzene moiety drastically reduced the transition temperature of the homopolyester, but without destroying the mesophase. The effect of copolymerization on liquid‐crystalline behavior and transition temperature of the copolymers was discussed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 1976‐1982, 2004     

Co[poly(ethylene terephthalate-p-oxybenzoate)] and its blends with poly(ethylene terephthalate): Transesterification reaction and fractured surface morphology

A series of co[poly(ethylene terephthalate-p-oxybenzoate)] copolyesters, viz., P28, P46, P64, and P82, were synthesized. These copolyesters were blended with poly(ethylene terephthalate) (PET) at the level of 10 wt % at 293°C for different times. The results from proton NMR analysis reveal that a significant amount of the transesterification has been detected in the cases of PET/P28, PET/P46, and PET/P64 blends. The blending time necessary before any transesterification reaction could be detected depends on the composition of copolyester, e.g., a time less than 3 min is needed for both PET/P28 and PET/P46 blends, while a longer time of 8–20 min is needed for the PET/P64 blend. It is concluded that the higher the mol ratio of the POB moiety in the copolyester is the longer the blending time needed to initiate the transesterification. The degree of transesterification is also increased as the duration of melt blending is prolonged. Two-phase morphology was observed by scanning electron microscopy (SEM) micrographs in all the blends. It was observed that the more similar the composition between the copolyester and PET in the blends is the better the miscibility or interfacial adhesion between the two phases. Moreover, the miscibility can be markedly improved by the duration of melt blending. © 1996 John Wiley & Sons, Inc.     

Studies on co[poly(ethylene terephthalate-p-oxybenzoate)] thermotropic copolyester (IV) thermal history by differential scanning calorimetry

A series of co[poly(ethylene terephthalate-p-oxybenzoate)] thermotropic copolyesters with various compositions were prepared by the copolymerization of either poly(ethylene terephthalate) polymer (PET) or its oligomer (OET) as moiety (II) and p-acetoxy-benzoic acid (POB) as moiety (I). The polymeric products obtained were then subjected to solid-state polymerization. The glass and melting transitions of the copolyesters obtained have been studied by differential scanning calorimetry (DSC). Effects of composition and solid-state polymerization on DSC are discussed. The melting point of copolyesters possesses a higher value if the PET polymer is used as PET moiety in the copolyesters. In the DSC scan of the POB rich composition, the endothermic peak shows obscurely and enthalpy of fusion becomes small due to the change in the crystalline morphology from isotropic to anisotropic. In general, the melting point of copolyesters is increased by the solid-state polymerization reaction. It is also found that both the melting temperature and enthalpy of fusion of the copolyesters can be increased simultaneously by the solid-state polymerization reaction only when the composition of POB/PET is 80/20. This phenomenum at this composition may be attributed to the annealing effect caused by the randomness of two moiety units on the backbone chain of copolyesters and the increased molecular weight as well. © 1994 John Wiley & Sons, Inc.