Liquid crystal polymers. IX. Copolyesters of trans-4,4′-stilbenedicarboxylic acid, 1,4-butanediol,and aromatic dicarboxylic acids

Copolyesters of trans-4,4-stilbenedicarboxylic acid (SDA), terephthalic acid, and 1,4-butanediol exhibit thermotropic liquid crystallinity if at least 40 mol % SDA is present (acids total 100 mol %); SDA/2,6-naphthalenedicarboxylic acid/1,4-butanediol copolyesters are liquid crystalline if at least 30 mol % SDA is present. The effects of SDA content on the thermal, rheological, plastic, and fiber properties of the copolyesters were determined. The SDA component increases the relaxation times of the polymers and enables injection-molded plastics and melt-spun fibers to have significantly increased tensile strength and stiffness.     

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

A series of fully aromatic copolyesters based on p‐acetoxybenzoic acid (p‐ABA), hydroquinone diacetate (HQDA), terephthalic acid (TPA), and m‐acetoxybenzoic acid (m‐ABA) were prepared by a modified melt‐polycondensation reaction. The copolyesters were characterized by DSC, thermogravimetric analysis, ¹H NMR, polarized optical microscopy, X‐ray diffraction, and intrinsic viscosity measurements. The copolyesters exhibited nematic liquid‐crystalline phases in a broad temperature range of about 150 °C, when the content of linear (p‐ABA, HQDA, and TPA) units was over 67 mol %. DSC analysis of the anisotropic copolyesters revealed broad endotherms associated with the nematic phases, and the melting or flow temperatures were found to be in the processable region. The flow temperatures and crystal‐to‐nematic and nematic‐to‐isotropic transitions depend on the type of linear monomer units, and these transitions increased as the content of the p‐ABA units increased, as compared to the HQDA/TPA units. When the content of the p‐ABA units increased, as compared to other linear units (HQDA and TPA), the intrinsic viscosity and degree of crystallinity of the copolyesters also increased, implying a higher reactivity for p‐ABA in the p‐ABA/HQDA/TPA/m‐ABA polymer system. The aromatic region in the ¹H NMR spectra of the copolyesters containing equal molar compositions of p‐ABA, HQDA, and TPA units were sensitive to the sequence distribution of aromatic rings. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3263–3277, 2001     

Wholly aromatic thermotropic liquid crystalline polyesters of 3,3′-bis(phenyl)-4,4′-biphenol with 4,4′-benzophenone dicarboxylic acid

A series of wholly aromatic, thermotropic polyesters, derived from 3,3′-bis(phenyl)-4,4′-biphenol (DPBP), nonlinear 4,4′-benzophenone dicarboxylic acid (4,4′-BDA), and various linear comonomers, were prepared by the melt polycondensation reaction and characterized for their thermotropic properties by a variety of experimental techniques. The homopolymer of DPBP with 4,4′-BDA had a fusion temperature (T_f) at 265°C, exhibited a nematic phase, and had a liquid crystalline range of 105°C. All of the copolyesters of DPBP with 4,4′-BDA and either 30 mol % 4-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA), or 50 mol % terephthalic acid (TA), 2,6-naphthalenedicarboxylic acid (2,6-NDA) had low T_f values in the range of 220–285°C, exhibited a nematic phase, and had accessible isotropization transitions (T_i) in the range of 270–420°C, respectively. Their accessible T_i values would enable one to observe a biphase structure. Each of the copolymers with HBA or HNA had a much broader range of liquid crystalline phase. In contrast, each of the copolymers with TA or 2,6-NDA had a relatively narrow range of liquid crystalline phase. Each of these polyesters had a glassy, nematic morphology that was confirmed with the DSC, PLM, WAXD, and SEM studies. As expected, they had higher glass transition temperatures (T_g) in the range of 161–217°C than those of other liquid crystalline polyesters, and excellent thermal stabilities (T_d) in the range of 494–517°C, respectively. Despite their noncrystallinity, they were not soluble in common organic solvents with the exception that the homopolymer and its copolymer with TA had limited solubility in CHCl₃. However, they were soluble in the usual mixture of p-chlorophenol/1,1,2,2-tetrachloroethane (60/40 by weight) with the exception of the copolymer with 2,6-NDA. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 769–785, 1997     

Fully aromatic thermotropic liquid crystalline polyesters of 3-phenyl-4,4′-biphenol with 4,4′-benzophenone dicarboxylic acid

A series of fully aromatic, thermotropic polyesters, derived from 3-phenyl-4,4′-biphenol (MPBP), nonlinear 4,4′-benzophenone dicarboxylic acid (4,4′-BDA), and various other comonomers was prepared by the melt polycondensation method and characterized for their thermotropic liquid crystalline behavior by a variety of experimental techniques. The homopolymer of MPBP with 4,4′-BDA had a fusion temperature (T_f) at 240°C, exhibited a nematic liquid crystalline phase, and had a narrow liquid crystalline range of 60°C. All of the copolyesters of MPBP with 4,4′-BDA and either 30 mol % 4-hydroxybenzoic acid (HBA), 6-hydroxy-2-naphthoic acid (HNA) or 50 mol % terephthalic acid (TA), 2,6-naphthale-nedicarboxylic acid (2,6-NDA) and low T_f values in the range of 210–230°C, exhibited a nematic phase, and had accessible isotropization transitions (T_i) in the range of 320–420°C, respectively. As expected, each of them had a broader range of liquid crystalline phase than the homopolymer. They had a “frozen” nematic, glassy order as determined with the wide-angle X-ray diffraction (WAXD) studies. The morphology of each of the “as-made” polyesters had a fibrous structure as determined with the scanning electron microscopy (SEM), which arises because of the liquid crystalline domains. Moreover, they had higher glass transition temperatures (T_g) in the range of 167–190°C than those of other liquid crystalline polyesters, and excellent thermal stabilities (T_d) in the range of 500–533°C, respectively. © 1995 John Wiley & Sons, Inc.     

New polymer syntheses. LXVI. Copolyester of 4-hydroxybenzoic acid and 3-(4'-hydroxyphenoxy)benzoic acid or 4-(3'-hydroxyphenoxy)benzoic acid

Copolyesters of 4-hydroxybenzoic acid (HBA) and 3-(4'-hydroxyphenoxy)benzoic acid were prepared by two different procedures. Either the acetyl derivatives were polycondensed in bulk at temperatures up to 300°C or they were polycondensed in an inert reactions medium (Marlotherm-S) at 340°C. Two analogous series of copolyesters were synthesized from 4-acetoxybenzoic acid (4-HBA) and 4-(3'-acetoxyphenoxy)benzoic acid. The copolyesters were characterized by elemental analyses, inherent viscosities, ¹H- and ¹³C-NMR spectroscopy, WAXS and DSC measurements, and by optical microscopy. All copolyesters synthesized in solution were highly crystalline materials which were neither meltable nor soluble. Part of the copolyesters prepared by polycondensation in bulk were semi-crystalline, meltable, and soluble. The copolyester derived from 3-(4'-hydroxyphenoxy)benzoic acid proved to be thermotropic forming a nematic melt, whereas the isomeric copolyesters of 4-(3'-hydroxyphenoxy)benzoic acid only formed isotropic melts. © 1993 John Wiley & Sons, Inc.     

Novel copolyesters containing naphthalene structure. I. From bis(hydroxyalkyl)naphthalate and bis[4-(2-hydroxyethoxy)aryl] compounds

Copolyesters containing naphthalene structure were synthesized from bis(hydroxyethyl)naphthalate (BHEN) or bis(hydroxybutyl)naphthalate (BHBN) and various aralkyloxy diols. The starting bis[4-(2-hydroxyethoxy)aryl] compounds were derived from a nucleophilic substitution of various bisphenols with ethylene carbonate in the presence of KI. Copolyesters having intrinsic viscosities of 0.45–0.60 dL/g were obtained by the melt polycondensation in the presence of metallic catalysts. The effect of reaction temperature and time on the formation of copolyesters were investigated to obtain an optimum condition for copolyesters manufacturing. Most copolyesters have better solubilities than polyethylene naphthalate (PEN) or polybutylene naphthalate (PBN) in aprotic solvents, such as N-methyl-2-pyrrolidone or m-cresol. The thermal properties of the copolyesters were investigated by the differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). Glass transition temperatures (T_g) of copolyesters result from BHEN were in the range of 90–141°C, and 10% weight loss in nitrogen were all above 460°C. Another series of copolyesters result from BHBN have T_g in the range of 75–135°C, and 10% weight loss in nitrogen of over 420°C. © 1996 John Wiley & Sons, Inc.     

Thermotropic copolyesters of 4-hydroxybenzoic acid

Copolyesters of 4-hydroxybenzoic acid were prepared by thermal polycondensation of 4-acetoxybenzoic acid with various acetylated comonomers, such as 4-mercaptobenzoic acid, 3-hydroxybenzoic acid, N-(4-carboxyphenyl)4-hydroxyphthalimide or hydroquinone in combination with 1,12-dodecane bistrimellitimide. The copolyesters were characterized by elemental analyses, inherent viscosities, ¹H- or ¹³C NMR spectroscopy, DSC-measurements, WAXS-measurements at temperatures between 25 and 425°C, microscopic observation, thermomechanical and thermogravimetrical analyses. Copolyesters containing 4-mercaptobenzoic acid or N-(4-carboxyphenyl)4-hydroxyphthalimide possess a reversible first order phase transition which represent a change of modifications and not a melting process. Both classes of copolyesters adopt the same kind of high temperature modification as poly(4-hydroxybenzoate), namely a pseudo-hexagonal chain packing. In contrast, copolyesters of 3-hydroxybenzoic acid or copoly(ester imide)s with aliphatic spacer containing more than 50% 4-hydroxybenzoic acid form a nematic phase over a broad temperature range. However, in the case of copolyesters derived from 3- and 4-hydroxybenzoic acid the homogeneous nematic melt is thermodynamically unstable and gradually turns into a heterogeneous more or less crystalline material with blocks of 4-hydroxybenzoate units.     

Synthesis and mesomorphic behaviour of novel chiral nematic side chain liquid crystalline polysiloxanes

A series of novel thermotropic side chain liquid crystalline polymers was synthesized by grafting copolymerization of a mesogenic monomer, 4-allyloxybenzoyl-4′?-(4-n-alkylbenzoyl)–p-benzenediol bisate and a chiral monomer, menthyl undecylenate. The mesogenic monomers exhibited nematic threadlike textures during heating and cooling. The polymers showed thermotropic liquid crystalline properties with a broad mesomorphic region over a range of 100°C. The polymers exhibited a cholesteric mesophase with a colourful Grand-Jean texture when the content of chiral units was greater than 15?mol?%; the others exhibited nematic threadlike textures. All of the polymers were thermally stable over 300°C, and most were laevorotatory as the chiral monomer.     

Wholly aromatic thermotropic liquid crystalline polyesters of 2-(α-phenylisopropyl)hydroquinone; copolymers with 1,1′-biphenyl-4,4′-diol and 2,6-dihydroxynaphthalene

Two series of new aromatic copolyesters have been synthesized and their properties including liquid crystallinity have been studied. The first series was synthesized by polymerizing mixtures of diacetates of 2-(α-phenylisopropyl)hydroquinone and 1,1′-biphenyl-4,4′-diol with terephthalic acid, and the second by polymerizing mixtures of diacetates of 2-(α-phenylisopropyl)hydroquinone and 2,6-dihydroxynaphthalene with terephthalic acid. These polyesters were characterized by differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray diffractomerty, and optical microscopy. The glass transition temperatures of the first series decrease from 167 to 138°C as one increases the content of the 1,1′-biphenyl-4,4′-diol unit to 50 mol %. The T_g values of the second series are slightly higher than those of the first series, and appear to be less dependent on their composition. The degree of crystallinity of the first series decreases rapidly by copolymerization, much faster than that of the second series. The melting points of the first series copolymers are significantly lower than those of the second series. All of the copolyesters reported in this investigation form nematic melts. The initial decomposition temperatures of the copolymers were higher than 450°C. It was confirmed that thermal stability of the homopolyester, PIBPL-1.00, containing the isopropylidene units is significantly improved when compared with that carrying benzylic hydrogens. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2777–2786, 1997     

Synthesis and characterization of a series of wholly aromatic copolyesters containing 2‐(α‐phenylisopropyl)hydroquinone moiety

Two series of new wholly aromatic thermotropic copolyesters containing the 2‐(α‐phenylisopropyl)hydroquinone (PIHQ) moiety have been synthesized and their basic properties such as glass transition temperature (T_g), melting temperature (T_m), thermal stability, crystallinity, and liquid crystallinity were studied by differential scanning calorimetry (DSC), thermogravimetry (TG), and wide‐angle X‐ray diffractometry (WAXD) and on a polarizing microscope. The first series was prepared from acetylated PIHQ, terephthalic acid (TPA), and 2,6‐naphthalenedicarboxylic acid (NDA), and the second series from acetylated PIHQ, TPA, and 1,1′‐biphenyl‐4,4′‐dicarboxylic acid (BDA). The T_g values (152–168°C) of the two series are not much different, although the values for the first series appear slightly higher. The T_m values (287–378°C) and the degree of crystallinity of the first series are appreciably greater than those of the second series. Such differences can be explained by the geometric structure of NDA and BDA moieties. All of the present polyesters are thermotropic and nematic. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 881–889, 1999     

New polymer syntheses XCIII. Hyperbranched homo- and copolyesters derived from gallic acid and β-(4-hydroxyphenyl)-propionic acid

The hyperbranched homopolyester of gallic acid (GA) was prepared by polycondensation of acetylated gallic acid in bulk. Copolyesters of gallic acid and 3-hydroxybenzoic acid (3-HBA) or β-(4-hydroxyphenyl)propionic acid (HPPA) were prepared via the silylated monomers. The degree of branching was varied in both series via the molar fraction of gallic acid. A model reaction with silylated 4-methoxybenzoic acid suggests that all three acetoxy groups of gallic acid can react by ester interchange reactions under the chosen reaction conditions. Furthermore, highly branched copolyesters derived from equimolar ratios of HPPA and 2-, 3-, or 4-hydroxybenzoic acid, vanillic acid, or 4-hydroxycinnamic acid were synthesized. All these copolyesters were found to be amorphous with glass transition temperatures (T_g's) far below that of the hyperbranched poly(gallic acid). © 1998 John Wiley & Sons, Inc. J. Polym. Sci. A Polym. Chem. 36: 2347–2357, 1998     

Gas transport properties of thermotropic liquid-crystalline copolyesters. I. The effects of orientation and annealing

Gas transport properties are reported for two series of films prepared from copolyesters of 73 mol % hydroxybenzoic acid (HBA) and 27 mol % 2,6-hydroxynaphthoic acid (HNA) which systematically vary the degree of orientation and annealing time. Scanning electron microscopic (SEM) photomicrographs of the liquid-crystalline polymer (LCP) films showed evidence of a skin-core structure and polydomain texture. The degree of orientation in the films was quantified by analyzing the azimuthal intensity of the x-ray reflection associated with the lateral packing of the nematic mesophase. Using heat of fusion data from differential scanning calorimetry (DSC), the films were found to contain low levels of crystallinity estimated to be in the range of 5 to 15 wt %, which increased with annealing time. Permeability measurements were made for He, H₂, O₂, N₂, Ar, and CO₂ at 35°C and the diffusivities were computed from time-lag data. The films exhibited excellent barrier properties resulting largely from very low gas solubility coefficients. A moderate reduction in permeability was observed with increased orientation, which could be attributed directly to a decrease in the effective diffusivity. The effect of increased crystallinity from annealing on the permeability coefficients was smaller than would be expected for similar changes in the crystallinity of conventional polymers. Analysis using a simple two-phase model suggests that a mechanism dominated by transport in a small volume fraction of boundary regions possibly could account for the bulk transport properties of these materials.     

Thermotropic copolyesters having ordered comonomer sequences and flexible spacers

A series of new copolyesters having ordered comonomer sequences were synthesized via multistep routes and their properties such as glass transition (T_g) and melting temperatures (T_m), crystallization tendency, and mesomorphic properties were compared with those of the corresponding random copolyesters. All of the present copolyesters contain 1,8-octamethylene or 1,10-decamethylene spacers and hydroquinone (HQ) and terephthalic acid (TPA) moieties. In general, both melting and clearing temperatures of the ordered sequence copolyesters were much higher than those of the random counterparts. Crystallization tendency, however, was comparable. All of the present copolyesters are thermotropic and form nematic phase in melts. © 1993 John Wiley & Sons, Inc.     

非晶聚对苯二甲酸乙二酯的制备与表征

通过单体酯交换法和聚 2 ,6 萘二甲酸乙二酯 (PEN)与低分子量PET酯交换的方法分别合成了一系列NPA/TPA/EG和IPA/TPA/EG共聚酯 .随着NPA或IPA单元含量的增加 ,等温结晶速度迅速降低 ,共聚物的结晶性降低甚至非晶化 .由NMR分析得知单体酯交换法与聚合物酯交换法得到的共聚酯NPA/TPA/EG序列分布相近 ,链结构都接近完全无规 .由DSC结果分析 ,随共聚单体含量的增加 ,熔点和熔融热降低 ,结晶度也随之降低 .当NPA或IPA含量达到 2 0 %时 ,可以得到非晶的共聚酯 (APET) .本文还对共聚物组成与结晶温度的关系进行了表征     

Synthesis and characterization of potentially biodegradable thermotropic polyesters based on p-hydroxybenzoic acid and glycolic acid

The synthesis of novel thermotropic liquid crystalline copolyesters derived from aliphatic hydroxy acid (glycolic acid, GA) and aromatic hydroxy acid (p-hydroxybenzoic acid, PHBA) via a melt-copolycondensation process in the presence of various catalysts was explored. The following three possible routes were checked: PHBA and GA in different feed ratios with or without a catalyst; PHBA and GA in different feed ratios with or without a catalyst in the presence of acetic anhydride as a condensation agent; and different PHBA derivatives were used to examine the reactivity of aromatic hydroxy acid. The copolycondensability, chemical structure, liquid crystallinity, textures and morphology, phase transition behaviors and thermal stability, and solubility were investigated by FTIR, NMR, DSC, TGA, and polarized-light microscope. It has been found that only the 60–70 mol % PHBA-containing copolyesters could exhibit a nematic liquid crystallinity. The as-prepared polymers were brittle due to relatively lower molecular weights. © 1994 John Wiley & Sons, Inc.     

Synthesis and characterization of wholly aromatic polyesters derived from 1-phenyl-2,6-naphthalene-dicarboxylic acid and aromatic diols

A series of new wholly aromatic polyesters was synthesized by melt polycondensation of 1-phenyl-2,6-naphthalenedicarboxylic acid (PNDA) and diacetates of various aromatic diols. The aromatic diols studied are hydroquinone (HQ), methylhydroquinone (MHQ), phenylhydroquinone (PHQ), (α-phenylisopropyl)hydroquinone (PIHQ), 2,6-naphthalenediol (2,6-ND), 1,4-naphthalenediol (1,4-ND), and 4,4′-biphenol (BP). These polyesters were characterized for their crystallinity, glass transition temperature (T_g), melting temperature (T_m), liquid crystallinity, and thermal stability. In general, crystallinity of the polyesters are very low and the T_g values of the polyesters range from 150 to 172°C depending on the structure of aromatic diols. All of the polymers formed nematic phases above their T_m or T_g. The polyesters derived from PHQ and PIHQ are soluble in chlorinated hydrocarbon solvents. The initial decomposition temperatures of the polyesters are above 400°C under N₂ atmosphere. © 1996 John Wiley & Sons, Inc.     

Design and Synthesis of Aromatic Polyesters Bearing Pendant Clickable Maleimide Groups

A bisphenol bearing pendant maleimide group, namely, N‐maleimidoethyl‐3, 3‐bis(4‐hydroxyphenyl)‐1‐isobenzopyrrolidone (PPH‐MA) was synthesized starting from phenolphthalein. Aromatic (co)polyesters bearing pendant maleimide groups were synthesized from PPH‐MA and aromatic diacid chlorides, namely, isophthaloyl chloride (IPC), terephthaloyl chloride (TPC), and 50:50 mol % mixture of IPC and TPC by low temperature solution polycondensation technique. Copolyesters were also synthesized by polycondensation of different molar proportions of PPH‐MA and bisphenol A with IPC. Inherent viscosities and number‐average molecular weights of aromatic (co)polyesters were in the range of 0.52–0.97 dL/g and 20,200–32,800 g/mol, respectively indicating formation of medium to reasonably high‐molecular‐weight polymers. ¹³C NMR spectral analysis of copolyesters revealed the formation of random copolymers. The 10% weight loss temperature of (co)polyesters was found in the range 470–484 °C, indicating their good thermal stability. A selected aromatic polyester bearing pendant maleimide groups was chemically modified via thiol‐maleimide Michael addition reaction with two representative thiol compounds, namely, 4‐chlorothiophenol and 1‐adamantanethiol to yield post‐modified polymers in a quantitative manner. Additionally, it was demonstrated that polyester containing pendant maleimide groups could be used to form insoluble crosslinked gel in the presence of a multifunctional thiol crosslinker. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 630–640     

Synthesis and characterization of main chain liquid crystalline ionomers containing sulphonate groups

A series of main chain liquid crystalline ionomers containing sulphonate groups pendent to the polymer backbone were synthesized by an interfacial condensation reaction of 4,4′‐bis(1,10‐sebacyloxo)benzoic acid, brilliant yellow (BY), and 4,4′‐biphenyldiol. 4,4′‐Bis(1,10‐sebacyloxo)benzoic acid exhibited nematic schlieren texture during heating and cooling. The ionomers are thermotropic liquid crystalline polymers and thermally stable to about 270°C. They exhibit broad mesophase regions over a range of 220°C and the same nematic mesomogen with a colourful thread texture as B₀‐LCP, which implies that the introduction of an ionic group did not change the texture of the B₀‐LCP. However, the thermotropic liquid crystalline properties were somewhat weakened when the concentration of BY was more than 5%. The inherent viscosity in N,N‐dimethylformamide solution suggested that intermolecular associations of sulphonate groups occurred at low concentration, and intermolecular associations predominated at higher concentration.     

Synthesis and characterization of new unsaturated polyesters and copolyesters containing azo groups in the main chain

A new interesting class of linear unsaturated polyesters based on dibenzylidenecycloalkanones have been synthesized by interfacial polycondensation of 4,4^′-azodibenzoyl chloride or 3,3^′-azodibenzoyl chloride with: 2,5-bis(p-hydroxybenzylidene)cyclopentanone I, 2,6-bis(p-hydroxybenzylidene)cyclohexanone II, 2,6-divanillylidenecyclohexanone III, or 2,7-bis(p-hydroxybenzylidene)cycloheptanone IV at ambient temperature. The copolyesters are also synthesized from the monomers I, II, III or IV with the diacid chlorides. The resulting polyesters and their copolyesters were characterized by elemental analyses, IR spectroscopy and solubility. Additionally, inherent viscosity of the polyesters in the range 0.32-0.86 dL g⁻¹ and the inherent viscosity of the copolyesters in the range 0.28-0.65 dL g⁻¹ were determined. The UV-visible spectra of certain polymers were measured in m-cresol solution and showed a characteristic absorption band at 435-473 nm due to n-π^* transition. The thermal properties of the polymers were evaluated by thermo gravimetric analysis and differential scanning calorimetry measurements and correlated with their structural units. The crystallinity of some polyesters and copolyesters were tested. In addition, the electrical properties of all polyesters and copolyesters were measured.     

Mesogenic random copolymers. II. Copolymers with one flexible and two rigid segments

We have investigated copolyesters based on a single aliphatic dibasic acid flexible segment and two rigid segments arising from 4,4′-dihydroxybiphenyl (PB) and 2,6-dihydroxynaphthalene (PN). Homopolyesters based on the latter rigid segment exhibit no enantiotropic mesophase for 5 ≤ n ≤ 8. The copolymers are designated PBN-n where n is the number of methylene units in the dibasic acid. From the temperature–composition phase diagram, the odd-membered PBN-5 and PBN-7 exhibit only a nematic phase. The temperature range of the nematic phase decreases progressively with increasing mole fraction of naphthalene units. The even-membered PBN-6 and PBN-8 exhibit a smectic S_H mesophase and a newly induced nematic phase. Comparison with a previous study of copolymers involving a single rigid segment and two flexible segments reveals that the smectic S_H phase is more easily disrupted, and converted to a less ordered nematic phase, by different rigid segments than by different flexible segments. The isotropization entropy of a series of nematogenic equimolar copolymers exhibits a marked odd–even effect, with the observed ΔS_NI values being quite large for the even-membered copolymers.