Sulfone-Containing polymers as high barrier materials

Three types of sulfone-containing polymers, poly(carbonate-sulfone)s, poly(ester-sulfone)s, and poly(urethane-sulfone)s, were characterized as high barrier materials. They were made by condensing sulfone-containing diol, 1,3-bis(3-hydroxypropylsulfonyl)propane (Diol-333), or 1,4-bis(3-hydroxypropylsulfonyl)butane (Diol-343), with diphenyl carbonate, diphenyl esters, and diisocyanates, respectively. The incorporation of polar sulfone groups into polymer backbones increases the glass transition temperature of polymers in all cases; however, the increment is different with different functional linkages. The increments in polycarbonates and polyesters are higher than that in polyurethanes. This is because the interactions between carbonate or ester groups are much weaker than the interactions between sulfone groups, whereas the hydrogen bonding between urethane groups is comparable with the polar interaction between sulfone groups. The polymers were coated on 50-μm-thick Kapton films by solution casting and their permeabilities toward carbon dioxide were measured at 25°C using the ASTM D1434 volumetric method. The sulfone-containing polymers have carbon dioxide permeability coefficients at least 50 times smaller than the corresponding polymers without sulfone groups. The carbon dioxide barrier properties of sulfone-containing polymers are comparable with ethylene/vinyl alcohol copolymers (EVAL), which are commercial high barrier polymers. An isomer effect on polymer permeability was observed in the aromatic-aliphatic poly(ester-sulfone) series. The permeability coefficients of the aromatic-aliphatic poly(ester-sulfone)s decrease from terephthalate to isophthalate to phthalate, corresponding to the increase of chain flexibility above the T_g. These results support the hypothesis that high chain flexibility in the rubbery state and a glass transition temperature above room temperature are two key factors that promote low permeability. © 1994 John Wiley & Sons, Inc.     

Synthesis and characterization of poly(urethane-sulfone)s

Eight poly(urethane-sulfone)s were synthesized from two sulfone-containing diols, 1,3-bis(3-hydroxypropylsulfonyl)propane (Diol-333) and 1,4-bis(3-hydroxypropylsulfonyl)butane (Diol-343), and three diisocyanates, 1,6-hexamethylene diisocyanate (HMDI), 4,4′-diphenylmethane diisocyanate (MDI), and tolylene diisocyanate (TDI, 2,4- 80%; 2,6-20%). As a comparison, eight polyurethanes were also synthesized from two alkanediols, 1,9-nonanediol and 1,10-decanediol, and three diisocyanates. Diol-333 and Diol-343 were prepared by the addition of 1,3-propanedithiol or 1,4-butanedithiol to allyl alcohol and subsequent oxidation of the resulting sulfide-containing diols. The homopoly(urethanesulfone)s from HMDI and MDI are semicrystalline, and are soluble in m-cresol and hot DMF, DMAC, and DMSO. The copoly(urethane-sulfone)s from a 1/1 molar ratio mixture of Diol-333 and Diol-343 with HMDI or MDI have lower crystallinity and better solubility than the corresponding homopoly(urethane-sulfone)s. The poly(urethane-sulfone)s from TDI are amorphous, and are readily soluble in m-cresol, DMF, DMAC, and DMSO at room temperature. Differential scanning calorimetry data showed that poly(urethane-sulfone)s have higher glass transition temperatures and melting points than the corresponding polyurethanes without sulfone groups. The rise in glass transition temperature is 20–25°C while the rise in melting temperature is 46–71°C. © 1994 John Wiley & Sons, Inc.     

Dipole–dipole interaction directed liquid crystalline polymers. I. Aliphatic poly(carbonate-sulfone)s based on 1,3-bis(3-hydroxypropylsulfonyl)propane

Aliphatic poly(carbonate-sulfone) homo- and copolymers were prepared from 1,3-bis(3-hydroxypropylsulfonyl)propane (Diol-333) and various alkanediols. The copolymers are random in nature since they were prepared by melt copolymerization. Both the homopolymer and the copolymers exhibited multiple reproducible first-order transitions during differential scanning calorimetry (DSC) heating scans, but most of them exhibited only single exotherm during cooling scans. Typical schlieren textures were observed when these polymers were cooled from their isotropic melts. The copolymers have wide-angle x-ray diffraction (WAXD) patterns almost identical to that of the homopolymer except in the low-angle spacing, indicating their packing in the crystalline domain in similar. DSC, cross-polarized optical microscopy, and WAXD revealed that these polymers were smectic liquid crystalline at room temperature. Since aliphatic poly(carbonate-sulfone)s are flexible linear polymers with no rigid rod components, the liquid crystalline phase formation is probably directed by the dipole–dipole interactions between sulfone groups in adjacent chains. © 1994 John Wiley & Sons, Inc.     

Synthesis and dielectric analysis of aliphatic poly(carbonate-sulfone)s based on 1,4-bis(3-hydroxypropylsulfonyl) butane

High molecular weight aliphatic poly(carbonate-sulfone) homopolymer (PC-343) and random copolymer (PC-343-10) were synthesized from 1,4-bis(3-hydroxypropylsulfonyl)butane (Diol-343) and a 1/1 molar mixture of Diol-343 and 1,10-decanediol, respectively. As a comparison, an aliphatic polycarbonate homopolymer (PC-10) was prepared from 1,10-decanediol. While PC-10 exhibited a single melting peak during its DSC heating scan, both PC-343 and PC-343-10 exhibited multiple reproducible first-order transitions during DSC heating scans. Both PC-343 and PC-343-10 showed broad reflections in their WAXD diagrams; the crystalline order of PC-343 is higher than that of PC-343-10. Based on the DSC and WAXD results and our discovery on the liquid crystalline behavior of aliphatic poly(carbonate-sulfone)s from 1,3-bis(hydroxypropylsulfonyl)propane, we suggest PC-343 and PC-343-10 are liquid crystalline and the liquid crystalline phase formation is directed by the dipole–dipole interactions between sulfone groups. Films were obtained from these polymers by compression molding and dielectric analyses were conducted on them. One glass transition related dielectric relaxation was observed in PC-343-10. One glass transition related dielectric relaxation and one sub-glass transition related dielectric relaxation were observed in PC-343. The glass transition temperature increases with the increase of sulfone content in the polymers. A dramatic rise in dielectric constant with temperature was observed in PC-343 and PC-343-10 at low frequencies, which is probably due to the sulfone dipole interaction with the electrical field. © 1994 John Wiley & Sons, Inc.     

Synthesis and properties of phosphorus polyesters with systematically altered phosphorus environment

Monomers with phosphorus-containing substituents were incorporated into aromatic-aliphatic polyesters to develop polymeric halogen-free flame retardants as additives for poly(butylene terephthalate) (PBT). They were built into the polyester backbone of PBT substituting 1,4-butane diol as monomer by phosphorus-containing aromatic-aliphatic diols. Starting from 10-(2,5-bis(2-hydroxyethoxy)phenyl)-9,10-dihydro-9-oxa-10-phospha-phenanthrene-10-oxide (DOPO-HQ-GE), the chemical structure of the phosphorus monomers was systematically varied resulting in new polymers with diphenyl phosphine oxide substituents and bridged phosphine oxide units. The polymers were prepared by transesterification polycondensation in the melt in lab-scale as well as in a 2.4 l-autoclave. The properties of the polyesters were determined and compared to the DOPO-based polyester with respect to the achieved molar mass and polydispersity, solid state structure, glass transition temperature, thermal stability and combustion behavior.It was found that the different phosphorus substituents lead to different glass transition temperatures. The polymers containing bridged phosphorus structural units showed higher glass transition temperatures T_g and resulted in higher char yields after thermal decomposition. Both phosphine oxide structures showed only one-step decomposition with a shoulder at the end of the step. In contrast, two separate steps were observed in the polyesters with DOPO-substituents. The results indicated that the phosphorus polyesters under discussion are suitable to adjust the flame retarding mechanism.     

Complete miscibility of ternary aryl polyesters demonstrating a new criterion and horizon for miscibility characterization

A ternary miscible blend system comprising only crystallizable aryl polyesters [poly(ethylene terephthalate), poly(trimethylene terephthalate), and poly(butylene terephthalate)] was characterized with the criteria of thermal analyses, microscopy, and X‐ray characterizations. The reported ternary miscibility (in the quenched amorphous state of blends of the three aryl polyesters) was truly physical and under the condition of no chemical transesterifications; this justified that transesterification was not a necessary condition for miscibility in polyester blends in this case. This study further proposed and tested a novel concept of a new criterion for miscibility characterization for polymer blends of only crystallizable polymers. A single composition‐dependent cold‐crystallization‐temperature (T_cc) peak in blends of only semicrystalline polymers was taken as an indication of an intimate mixing state of miscibility. The theoretical background for establishing the single composition‐dependent T_cc peak as a valid miscibility criterion for crystallizable polymer blends was examined. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2394–2404, 2003     

Hydrolytic degradation of carbohydrate-based aromatic homo- and co-polyesters analogous to PET and PEI

The hydrolytic degradation of a series of homo- and co-polyesters analogous to poly(ethylene terephthalate) (PET) and poly(ethylene isophthalate) (PEI), prepared from carbohydrate-based monomers, was studied. The degradation process was carried out at temperatures of approximately 10 °C above the T_g of the polymers. All the studied polyesters were found to degrade at significant rates, and degradability showed a clear dependence on the configuration of the sugar units present in the polymer chain. No weight loss was detected upon degradation, apparently due to the non-solubility of the degraded products in the aqueous incubation medium. Hydrolysis of co-polyesters took place preferentially by cleavage of the ester groups of the sugar units.     

Conformational characteristics of poly(ethylene phthalate)s

The conformational characteristics, as embodied in the unperturbed mean‐square end‐to‐end distances (〈r²〉_o) and the characteristic ratios of the dimensions [C_n = 〈r²〉_o/(n〈l²〉] are calculated for the para, meta, and ortho isomers of poly(ethylene phthalate)s: poly(ethylene terephthalate) (PET), poly(ethylene isophthalate) (PEI), and poly(ethylene phthalate) (PEP), respectively. Although each of these isomeric and partially aromatic polyesters has identical permissible conformations available to their ethylene glycol fragments, their connections through the ester bonds to the phenyl rings are quite distinct. In addition, for the ortho isomer (PEP), the close spatial proximity of the ester groups bonded to the same phenyl ring results in an interdependence of their orientations with respect to each other and the phenyl ring to which they are attached, unlike the independent orientations of ester groups in the para and meta isomers (PET and PEI). Conformational energy calculations, dependent on the orientation of the ester groups in PEP, are used to characterize their rotational interdependence to modify the rotational isomeric state (RIS) conformational models for PET and PEI and thereby obtain an RIS model appropriate for PEP. This leads to calculated relative dimensions (〈r²〉_o) of 1.0:0.70:0.37 PET:PEI:PEP and characteristic ratios [C_n = 〈r²〉_o/(n〈l²〉)] of 4.13:4.67:2.49 PET:PEI:PEP. These results are discussed in an effort to obtain some understanding of the inherent static (or equilibrium) and dynamic flexibilities of the isomeric poly(ethylene phthalate)s. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 40: 1254–1260, 2002     

Broad-line NMR and dynamic mechanical behavior of some aromatic polyesters

The dynamic mechanical properties of four aromatic polyesters were measured at temperatures in the 78–540°K region at 10³–10⁴ cps. The polymers studied were: poly(1,3 phenylene isophthalate), poly(1,4 phenylene terephthalate), poly(4,4′ diphenylene isophthalate), and poly(4,4′ diphenylene terephthalate). All four polymers had β loss peaks at about 280°K. Distinct β^* mechanical processes were found for the two terephthalate esters. Broad-line nuclear magnetic resonance measurements were carried out in the 150–440°K temperature range on the four polyesters mentioned above in addition to poly(4,4′ diphenylene 4,4′ biphenyl dicarboxylate). A change in NMR second moment takes place in the 190–330°K region, the magnitude of which is dependent on the polymer structure. The results are compared with those found for a series of aromatic polyamides and are discussed in terms of possible motional processes.     

Thermal stability of some aromatic polyesters and poly(ester carbonates)

The thermal stability of some hydroxyl-terminated poly(bisphenol A tere- or isophthalates) and their corresponding poly(ester carbonates) made by subsequent coupling with phosgene has been investigated by thermogravimetry. Samples have been studied in nitrogen or air using constant rates of temperature rise or isothermal conditions.The isophthalate-containing polyesters are more thermo-oxidatively stable than their terephthalate analogues and molecular weight has a significant effect on stability. In contrast, there is little difference in the thermal stability of the poly (isophthalate carbonates) and the poly(terephthalate carbonates) and the stability of the latter is relatively independent of the ratio of the diester to carbonate group content. The stability of the poly(terephthalate carbonates) is also relatively insensitive to end-group modifications.     

Poly(ethylene terephthalate) terpolyesters containing isophthalic and 5‐tert‐butylisophthalic units

Poly(ethylene terephthalate‐co‐isophthalate‐co‐5‐tert‐butylisophthalate) (PETI^tBI) terpolymers were investigated with reference to poly(ethylene terephthalate) (PET) homopolymer and poly(ethylene terephthalate‐co‐isophthalate) (PETI) copolymers. Three series of PETI^tBI terpolyesters, characterized by terephthalate contents of 90, 80, and 60 mol %, respectively, with different isophthalate/5‐tert‐butylisophthalate molar ratios, were prepared from ethylene glycol and mixtures of dimethyl terephthalate, dimethyl isophthalate, and 5‐tert‐butylisophthalic acid. The composition of the terpolymers and the composition of the feed agreed. All terpolymers had a random microstructure and number‐average molecular weights ranging from 10,000 to 20,000. The PETI^tBI terpolyesters displayed a higher glass‐transition temperature and a lower melting temperature than the PETI copolymers having the same content of terephthalic units. Thermal stability appeared essentially unchanged upon the incorporation of the 5‐tert‐butylisophthalic units. The PETI^tBIs were crystalline for terephthalate contents higher than 80 mol %, and they crystallized at lower rates than PETI. The crystal structure of the crystalline terpolymers was the same as that of PET with the 1,3‐phenylene units being excluded from the crystalline phase. Incorporation of isophthalate comonomers barely affected the tensile modulus and strength of PET, but the brittleness of the terpolymers decreased for higher contents in 5‐tert‐butylisophthalic units. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 124–134, 2003     

Synthesis of novel poly(ethylene glycol) based amphiphilic polymers

The synthesis of new amphiphilic polyesters based on poly(ethylene glycol) (PEGs) and studies on their solution properties are reported. Two novel monomers, dimethyl 5-n-butoxy isophthalate (2) and dimethyl 5-n-octoxy isophthalate (3) were synthesized. Three series of novel amphiphilic polyesters, i.e. poly(ethyleneoxy isophthalate)s (10-15), poly(ethyleneoxy n-butoxy isophthalate)s (16-21) and poly(ethyleneoxy n-octoxy isophthalate)s (22-27) have been synthesized from PEGs of different sizes and dimethyl isophthalates 1-3 via the transesterification-polycondensation using dibutyltin diacetate as a catalyst. The structures of the polyesters were established from a detailed analysis of their spectra, i.e. FTIR, ¹H-NMR (one- and two-dimensional) and ¹³C-NMR. By adjusting the ratio of hydrophobic (diesters) and hydrophilic (PEGs) segments in polymers, their main chain structures and solution properties could be changed. The viscosity molecular weights (M_v) of polymers, obtained from Mark-Houwink-Sakurada relationship having poly(ethylene terephthalate) as a model, were in the range of 4500-32,000 g/mol. Intrinsic viscosities were studied based on polymer backbone length (PEGs effect) and pendant group (diesters effect) and these were found to be dependent on molecular weights of the PEGs used.     

The Effect of Trifluoroacetic Acid on Molecular Weight Determination of Polyesters:An in Situ NMR Investigation

Due to the poor solubility of aromatic polyesters in common organic solvents,trifluoroacetic acid is usually used as a co-solvent to increase their solubility for characterizations.However,only few studies have reported the side reactions induced by it.We present here the application of in situ 1H-NMR techniques to explore its effect on the hydroxyl end-groups,which are usually used for the molecular weight determination of polyesters by end-group estimation method.Using bis(2-hydroxyethyl) terephthalate (BHET) as model compound,1H quantitative NMR results show the peak integration of hydroxyethyl end-groups decreased with time via a pseudo-first-order kinetics in d-trifluoroacetic acid/d-chloroform mixture solvent (1∶10,V∶V).This is due to the esterification of hydroxyethyl groups with trifluoroacetic acid,revealed by the 1H-13C gradient-enhanced heteronuclear multiple bond correlation (gHMBC) spectrum.The mixtures of dimethyl terephthalate and BHET with different molar ratios were used to represent poly(ethylene terephthalate) (PET) with different degrees of polymerization,and the effect of trifluoroacetic acid on the estimation of hydroxyethyl groups and subsequent molecular weight determination of polyesters was studied.Our results show that if a relative error of 5％ is allowed,the NMR measurements must be finished within 1.3 h of solution preparation at 25 ℃ in the mixture solvent.The results were confirmed in PET sample,while in poly(ethylene adipate),the obtained esterifaction constant is faster that those in aromatic system.The results can be applied to other polymer systems with alcohol functionalized groups,and used as a guideline for the characterization of polyesters and polyethers by end-group estimation method.     

Effect of crystallization on oxygen‐barrier properties of copolyesters based on ethylene terephthalate

The effect of crystallization from the glassy state (cold crystallization) on the oxygen‐barrier properties of copolyesters based on ethylene terephthalate with up to 10 mol % isophthalate, phthalate, or naphthalate was examined. Generally, crystallization affected diffusivity D more than solubility S; thus, the reduction in permeability P reflected primarily a reduction in D. Systematic changes in crystallinity made it possible to test free‐volume concepts in which permeation of a small gas molecule through a semicrystalline polymer is viewed as proceeding through the amorphous regions with an increased pathway (tortuosity) imposed by plateletlike crystallites. Of the copolymers studied, those with the highest isophthalate or phthalate content (10 mol %) conformed to the simple two‐phase model with constant densities of an impermeable crystalline phase and a permeable amorphous phase. Within the two‐phase model, solubility S correlated linearly with the volume fraction of the amorphous phase, and diffusivity D depended on crystallinity in accordance with the Nielsen model for randomly dispersed platelets with an aspect ratio of 4. The reduction in permeability of the other examined copolyesters could not be described only by the filler effect of crystallites. Data on solubility demonstrated a decrease in amorphous‐phase density upon cold crystallization (de‐densification) like that previously reported for polyethylene terephthalate. Increasing the isophthalate or phthalate content reduced the de‐densification effect, and 10 mol % of these comonomers was sufficient to eliminate the effect altogether. In contrast, 10 mol % naphthalate did not prevent de‐densification. This was attributed to different effects of kinked and linear comonomers on chain packing in the amorphous phase. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1911–1919, 2001     

THERMAL PROPERTY, MISCIBILITY AND CRYSTALLIZATION BEHAVIOR OF POLY（3-HYDROXYBUTYRATE-co- 3-YDROXYHEXANOATE） AND POLY（BUTYLENE SUCCINATE-ADIPATE） （PHBHHX/PBSA） BLENDS

Blends of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) and poly(butylene succinate-adipate) (PBSA), both biodegradable semicrystalline polyesters, were prepared with the ratio of PHBHHx/PBSA ranging from 80/20 to 20/80 by melt mixing method. Differential scanning calorimetry (DSC), thermogravimetry analysis (TGA), dynamic mechanical thermal analysis (DMA), polarizing optical microscopy (POM) and wide angle X-ray diffractometer (WAXD) were used to study the miscibility and crystallization behavior of PHBHHx/PBSA blends. Experimental results indicate that PHBHHx is immiscible with PBSA as shown by the almost unchanged glass transition temperature and the biphasic melt.     

Neopenthyl glycol containing poly(propylene terephthalate)s: structure–properties relationships

Poly(propylene/neopenthyl terephthalate) random copolymers (PPT‐PNT) and poly(neopenthyl terephthalate) (PNT) were synthesized and subjected to molecular characterization. Afterwards, the polyesters were examined by TGA, DSC, andX‐ray. The copolymers, which displayed a good thermal stability, at room temperature appeared as semicrystalline materials: the main effect of copolymerization was a lowering in the amount of crystallinity and a decrease of the melting temperature with respect to homopolymer PPT. XRD measurements allowed the identification of the PPT crystalline structure in all cases. Amorphous samples were obtained after melt quenching, with the exception of PPT‐PNT5, and an increment of T_g as the content of NT units is increased was observed due to the effect of the side methylene groups in the polymeric chain. The Wood equation described well T_g‐composition data. Lastly, the presence of a rigid‐amorphous phase was evidenced in the copolymers, whose amount depended on composition and on thermal treatment. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 170–181, 2008     

THERMAL PROPERTY, MISCIBILITY AND CRYSTALLIZATION BEHAVIOR OF POLY(3-HYDROXYBUTYRATE-co-3-YDROXYHEXANOATE) AND POLY(BUTYLENE SUCCINATE-ADIPATE) (PHBHHX/PBSA) BLENDS

1. INTRODUCTION Biodegradable polymers have received considerable attention in the last two decades due to their potential applications in the fields related to human life such as environmental protection and ecology. According to the difference in the preparation methods, biodegradable polymers can be classified into two types. One is the biosynthetic polymers, such as bacterialpolyhydroxyalkanoates (PHAs). Among them, the most extensively studied biodegradable thermoplastic polymers ar…     

Sulphur-containing polymers: Synthesis and thermal properties of novel polyesters based on dithiotriethylene glycol

Poly(dithiotriethylene terephthalate) (PSSTET), poly(dithiotriethylene adipate) (PSSTEA), poly(triethylene terephthalate) (PTET) and poly(triethylene adipate) (PTEA), these two last for comparison, were synthesized and characterized in terms of chemical structure and molecular weight. The thermal behaviour was examined by thermogravimetric analysis and differential scanning calorimetry. All the polymers showed a good thermal stability, even though lower for the sulphur-containing polyesters. At room temperature they appeared as semicrystalline materials, except PTEA, which was an oil; the effect of substitution of ether oxygen atoms with sulphur ones was found to be a lowering in the T_g value, an increment of the melting temperature and an increase of the crystallization rate. The results were explained as due to the presence of flexible C-S-C bonds in the polymeric chain. Lastly, the absence of a rigid-amorphous phase was evidenced in PSSTET and PTET.     

Poly(ethylene terephthalate) copolymers containing 5‐nitroisophthalic units. II. Crystallization studies

The microstructure and crystallization behavior of a set of poly(ethylene terephthalate‐co‐5‐nitroisophthalate) copolymers (PETNI) containing 5‐nitroisophthalic units in the 10–50 mol % range were examined and compared to those of poly(ethylene terephthalate) (PET) and poly(ethylene terephthalate‐co‐isophthalate) (PETI) copolymers. A ¹³C NMR analysis of PETNI copolymers in a trifluoroacetic acid solution indicates that they are random copolymers with average sequence lengths in accordance with ideal polycondensation statistics. Differential scanning calorimetry (DSC) studies show that PETNI containing 5‐nitroisophthalic units up to 20 mol % are able to crystallize and that crystallization takes place in these copolymers at much slower rates than in PET. Wide‐angle X‐ray diffraction from powder and fibers reveals that crystallizable PETNI adopts the same triclinic crystal structure as PET, with the nitroisophthalate units being excluded from crystallites. Fourier transform infrared in combination with cross‐polarization/magic‐angle spinning ¹³C NMR spectroscopy demonstrates the occurrence of a gauche–trans conversion encompassing the crystallization process. A correlation between DSC and spectroscopic data leads us to conclude that the content of trans conformer in the noncrystallized phase of PETNI is higher than in both PET and PETI copolymers and suggests that secondary crystallization in the homopolymer must proceed by a mechanism different than that in copolymers. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1553–1564, 2001     

Poly(ethylene terephthalate) reinforced by N,N′‐diphenyl biphenyl‐3,3′,4,4′‐tetracarboxydiimide moieties

Starting with 3,3′,4,4′‐biphenyltetracarboxylic dianhydride and methyl aminobenzoate, we synthesized a novel rodlike imide‐containing monomer, N,N′‐bis[p‐(methoxy carbonyl) phenyl]‐biphenyl‐3,3′,4,4′‐tetracarboxydiimide (BMBI). The polycondensation of BMBI with dimethyl terephthalate and ethylene glycol yielded a series of copoly(ester imide)s based on the BMBI‐modified poly(ethylene terephthalate) (PET) backbone. Compared with PET, these BMBI‐modified polyesters had higher glass‐transition temperatures and higher stiffness and strength. In particular, the poly(ethylene terephthalate imide) PETI‐5, which contained 5 mol % of the imide moieties, had a glass‐transition temperature of 89.9 °C (11 °C higher than the glass‐transition temperature of PET), a tensile modulus of 869.4 MPa (20.2 % higher than that of PET), and a tensile strength of 80.8 MPa (38.8 % higher than that of PET). Therefore, a significant reinforcing effect was observed in these imide‐modified polyesters, and a new approach to higher property polyesters was suggested. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 852–863, 2002; DOI 10.1002/pola.10169