Sequential reordering in condensation copolymers, 4. Crystallization-induced sequential reordering in poly(ethylene terephthalate)/polycarbonate copolymers as revealed by the behavior of the amorphous phases

An equimolar blend of poly(ethylene terephthalate) (PET) 3

1 Systematic IUPAC name: poly(oxyethyleneoxyterephthaloyl).

and bisphenol-A-polycarbonate (PC) 4

2 Systematic structure-based IUPAC nomenclature: poly(oxycarbonyloxy-1,4-phenylene-1-methylethylidene-1,4-phenylene).

is studied by dynamic-mechanical thermal analysis (DMTA) and X-ray scattering after thermal treatment that enables transesterification. As demonstrated by wide-angle X-ray scattering (WAXS) measurements, prolonged thermal treatment at 280°C gives rise to a copolymer that no longer reveals melting or crystallization. In accordance with previous reports, this effect is attributed to the formation of a random copolymer. Additional annealing of such samples below the melting temperature of PET results in restoration of the crystallization ability. This effect is explained by crystallization-induced sequential reordering from random to block copolymer by means of transreactions which closes the cycle of transformations from two homopolymers via block- and random copolymer back to a block copolymer. The behavior of the amorphous phases is studied by means of DMTA demonstrating that their glass transition temperatures T_g's vary in accordance with the crystallinity changes. The random copolymer is characterized by a more or less homogeneous amorphous phase. In contrast to this, the mechanical mixture and the two block copolymers (the initial and that with the restored blocky structure) show DMTA peaks of two amorphous phases, clearly separated and with distinct individual T_g's. Viscosity measurements also demonstrate that the random copolymer significantly differs in its viscosity as compared to all other samples. These results represent a further evidence for the effect of block restoration via crystallization-induced sequential reordering.     

Sequential reordering in condensation copolymers, 1. Melting- and crystallization-induced sequential reordering in immiscible blends of poly(ethylene terephthalate) with polycarbonate or polyarylate

Unlike previous attempts, the entire cycle of melting- and crystallization-induced reordering is realized in binary polymer blends in the following order: two homopolymers → block copolymer → random copolymer → block copolymer. Blends of poly(ethylene terephthalate)

1 Systematic IUPAC name: poly(oxyethyleneoxyterephthaloyl).

(PET) and bisphenol-A/polycarbonate (PC) as well as PET/polyarylate (PAr) blends, are annealed directly in a differential scanning calorimeter at 280°C for various times. Scanning the samples in the heating mode reveals the complete disappearance of crystallization or melting in the blends where the ratio of PET/PC repeating units is less than 5.7/1.0. Such an amorphization is attributed to the formation of random copolymers. This statement is confirmed by NMR measurements, by the observation of one glass transition temperature T_g in the range between the initial two T_gs, and by solubility tests. Once randomized, annealing the samples at 235°C and 245°C, i. e., below melting of PET, results in a T_g shift toward the T_g of PET as well as in reappearance of melting. This effect is accompanied by an eight-fold crystallinity increase in the equimolar blend, as compared to the randomized sample. The regenerated crystallization ability is explained by restoration of the blocks. According to previous findings, it is concluded that the considerable enthropy increase is the main driving force of randomization. The rival trend to the formation of a block copolymer by sequential reordering is driven by the crystallization of PET blocks formed. The conclusion that the observed changes in the crystallization ability and T_g-values are based on sequential reordering is supported by experiments with samples containing increased amounts of transesterification catalyst leading to a much faster appearance of these changes. No randomization is observed with the blend composition ratio of repeating units PET/PC > 5.7/1.0. When the annealing is performed for 300 min at 165°C, where no significant exchange reactions are expected to occur, no restoration of the crystallization ability is observed.     

Crystallization behaviour of poly(ethylene terephthalate) and poly(tetramethylene terephthalate) blends

The isothermal and non-isothermal crystallization behaviour of blends of poly(ethylene terephthalate) (PET) and poly(tetramethylene terephthalate) (PBT) is investigated at low percentage of the second component. The melting behaviour of the isothermally crystallized sample shows that the crystallization behaviour in the blend is governed by the mobility of PBT. Below 200°C the crystallization process is hindered, whereas above 200°C the PET crystals are larger in case of added PBT. The non-isothermal crystallization behaviour shows that the crystallization process is hindered when the PBT content in the blend is less or higher than 6 wt.-%.     

Pivalolactone, 3. Reactive blending of polypivalolactone with polycarbonate

The occurrence of interchange reactions during heating of polypivalolactone (PPVL) with three polymers and their influence on the blend properties were studied. Physical blends of PPVL and bisphenol-A polycarbonate (PC) were found to be immiscible. By heating of PPVL/PC blends in the melt at 280°C, in diphenyl ether at 260°C and in a twin-screw extruder (TSE) at 280°C partial formation of copolymers was observed, provided that tetrabutyl orthotitanate (TnBT) was added. After heating of equimolar PPVL/PC blends in a TSE for 15 min, a PPVL-PC block copolymer could be isolated containing 25 mol-% pivalolactone (PVL) units. The results from thermal analyses indicated that PPVL/PC blends had become more miscible, due to the presence of copolymers formed by interchange reactions. After heating of equimolar mixtures of PPVL and a polyarylate (PAr) in a TSE for 15 min, PPVL-PAr copolymers with 5 mol-% PVL units could be isolated. Probably due to this low degree of interchange, no effect on the miscibility of the initially immiscible PPVL/PAr blends could be observed. PPVL/poly(butylene terephthalate) (PBT) blends, obtained after heating in a TSE, decomposed at a temperature between the melting temperatures of PPVL and PBT, indicating that interchange reactions may have occurred.     

Morphology and Growth Kinetics in Crystalline/Crystalline Polymer Blends of Poly(butylene terephthalate)/Polyarylates Based on Bisphenol A Isophthalate

The spherulitic morphology and growth kinetics of a crystalline/crystalline blend comprising poly(butylene terephthalate) and a homopolymer of Bisphenol A isophthalate (PBT/PAr(I‐100)) were investigated using wide‐angle X‐ray diffraction and polarized‐light optical microscopy. Neat PAr(I‐100) exhibits an unusual sheaf‐like pattern and switches to a spherulitic morphology in PAr(I‐100)‐rich blends, in which PBT cannot crystallize. Furthermore, the non‐crystallizable PBT is expelled out of the PAr(I‐100) spherulites. In PBT‐rich blends, the PAr(I‐100) does not crystallize, and it was found that the spherulitic morphology exhibits a traditional Maltese cross pattern and then became coarser and more open with increasing amount of PAr(I‐100). The non‐crystallizable PAR(I‐100) was trapped inside the spherulites. For medium composition blends, PBT and PAr(I‐100) spherulites co‐exist separately. In PBT‐rich blends, the spherulitic growth rate of PBT is reduced by the addition of PAr(I‐100) and remains constant with time. In PAr(I‐100)‐rich blends, the growth rate of PAr(I‐100) increases with increasing PBT and decreases upon further addition of PBT. Furthermore, the growth rate of PAr(I‐100) decreases slightly with time. For medium composition blends, the spherulitic growth rate of PBT increases with time while PAr(I‐100) is crystallizing, but it remains constant if the PAr(I‐100) was preformed.     

Compatibilizing Effect of Transesterification Copolymers on Bisphenol‐A Polycarbonate/Poly(ethylene terephthalate) Blends

After considerably long time of transesterification reactions between poly(ethylene terephthalate) (PET) and bisphenol‐A polycarbonate (PC) in the molten state, random copolymers, referred to be TCET's, can be obtained, which have fairly good compatibilizing effect on the immiscible PC/PET blend. The compatibilizing effect of these transesterification random copolymers is proved to be closely related to their compatibility with PET and PC. Being completely compatible both with PET and PC, the TCET50 copolymer with 50 wt.‐% ethylene terephthalate content is an efficient compatibilizer, it can greatly improve the compatibility between PET and PC. With increasing content of the TCET50 copolymer in the PC/PET/TCET50 ternary blend, the two glass transition temperatures, which belong to the PET‐rich and PC‐rich phase respectively, approach each other gradually. When the content of the TCET50 copolymer in the blend reaches 60 wt.‐%, only one glass transition temperature can be detected by differential scanning calorimetry (DSC). The TCET30 and TCET70 copolymer, which have 30 and 70 wt.‐% ethylene terephthalate content respectively, are less efficient in compatibilizing the PC/PET blend, since the TCET30 copolymer and PET, as well as the TCET70 copolymer and PC, are compatible to a certain degree instead of being completely compatible.     

Blends of poly(tetramethylene terephthalate) with a liquid-crystalline polyester,poly(decamethylene 4,4′-terephthaloyldioxydibenzoate), 2. Crystallization kinetics and melting behaviour

The isothermal crystallization kinetics, the morphology and melting behaviour of blends of poly(tetramethylene terephthalate) {poly(butylene terephthalate), (PBT)} with a thermotropic liquid-crystalline polyester, poly(decamethylene 4,4′-terephthaloyldioxydibenzoate) (HTH10), were studied in the composition range 0—50 wt.-% of HTH10 by optical microscopy and differential scanning calorimetry. The spherulite growth rate and the overall crystallization rate of PBT from melt blends are markedly depressed by the presence of the mesomorphic component. Changes of superstructure and of primary nucleation density of PBT spherulites in the blends were observed. The analysis of the melting behaviour of these samples indicates that the stability of PBT crystals and their reorganization processes on heating are dependent on the blend composition. A decrease of the equilibrium melting temperature of PBT is found with increasing the amount of HTH10. According to previously reported investigations on the same system, the results are discussed in respect of the onset of interactions between the two polymers in the liquid state.     

Crystallization and Melting Behavior of Liquid Crystalline Copolyesters Based on Modified Poly‐ [(p‐hydroxybenzoic acid)‐co‐(ethylene terephthalate)]

A series of copolyesters were prepared from p‐hydroxybenzoic acid (HBA), hydroquinone (HQ), terephthalic acid (TPA) and poly(ethylene terephthalate) (PET) by an acidolysis reaction and subsequent polycondensation. On the basis of viscosity measurements, these copolyesters have the same level of intrinsic viscosity as the original PET, and ¹H‐NMR analyses indicated the total insertion of comonomers. They exhibit a nematic phase above melting temperature, as observed by polarized light microscopy. Their crystallization and melting behavior were studied with differential scanning calorimetry and wide angle X‐ray diffraction. It was found that these copolyesters are more crystalline than poly[(p‐hydroxybenzoic acid)‐co‐(ethylene terephthalate)] (PET/HBA). Introduction of HQ/TPA disrupts longer rigid‐rod sequences formed by HBA, and thus enhances molecular motion and increases crystallization rate and crystallinity. Isothermal crystallization under solid phase polymerization conditions (up to 24 hours at 200°C) resulted in increased randomness of the copolymer (by ¹H‐NMR) and increased melting point and crystallinity, the latter attributed to structural annealing.     

Evolution of the Morphology and Characterization of Compatibilized PBT/EVA Blends Prepared by Reactive Extrusion

Summary: In this work, the possibility of preparing compatibilized blends of poly(butylene terephthalate) (PBT) and an ethylene vinyl acetate (EVA) copolymer by reactive extrusion in the presence of an ethylene acrylic acid copolymer (EAA) and a bisoxazoline compound (PBO) as compatibilization promoters has been studied. In addition, the evolution of the morphology of the blends under different annealing conditions in the presence and absence of the compatibilizing promoters has been studied. Binary blends of PBT and EVA showed behavior typical of incompatible blends with a gross morphology and bad mechanical performance. The situation was however different for ternary PBT/EVA/EAA and especially for quaternary PBT/EVA/EAA/PBO blends. In the latter case, the morphology was finer, the adhesion improved and the mechanical properties were enhanced, with values almost doubled with respect to those of uncompatibilized blends. These results can be explained by the formation of in situ EAA‐g‐(PBO)PBT copolymers which act as compatibilizers for the blends. While the binary and, to some extent, the ternary blend display coalescence under annealing with rapid coarsening of the morphology, the quaternary compatibilized blends showed the best morphological stability as the particle dimensions remained practically unchanged. This phenomenon was interpreted considering the role of kinetic hindrance played by the compatibilizer formed in situ.

SEM micrograph of PBT/EVA/EAA/PBO blend at 5 000×.     

Sequential Reordering in Condensation Copolymers, 6. Average Block Lengths in Poly(ethylene terephthalate) – Polyamide 6 Copolymers As Revealed by NMR Spectroscopy

An equimolar physical blend comprising poly(ethylene terephthalate) (PET), polyamide 6 (PA6) and catalytic amounts of p‐toluene sulfonic acid (pTSA) was studied by differential scanning calorimetry (DSC) and ¹³C NMR spectroscopy before and after reactive blending for various times at 280°C that enables interchange reactions. With the extension of the reaction time, DSC traces showed an abrupt decrease in ability to crystallize, and after two hours of blending the system did not reveal any crystallization or melting behavior. By means of ¹³C NMR spectroscopy, a clear distinction was made between the PET/PA6 physical blend and the copolymers with different degrees of interchange reactions. The ¹³C NMR sequence length determination in various PET–PA6 based copolyesteramides showed PET block lengths of 4–10 repeat units which was in good agreement with the crystallizability of these systems. A combination of selective degradation of the PET blocks and ¹H NMR allowed, for the first time, the characterization of both PET and PA6 sequence lengths. This method was shown to be more sensitive, as compared to ¹³C NMR spectroscopy without selective degradation, for sequence analysis in copolymers with close to random distributions of PET and PA6 sequence lengths.     

Bilayered biodegradable poly(ethylene glycol)/poly(butylene terephthalate) copolymer (Polyactive) as substrate for human fibroblasts and keratinocytes.

The purpose of this study was to find an optimal polymer matrix and to optimize the culture conditions for human keratinocytes and fibroblasts for the development of a human skin substitute. For this purpose porous, dense bilayers made of a block copolymer of poly(ethylene glycol terephthalate) (PEGT) and poly(butylene terephthalate) (PBT; Polyactivetrade mark) with a PEGT/PBT weight ratio of 55/45 and a PEG molecular weight (MW) of 300, 600, 1000, or 4000 Da were used. The best performance was achieved with PEGT/PBT copolymer with MW of PEG 300 D (300PEG55PBT45). When fibroblasts were seeded into the porous underlayer and cultured for 3 weeks in medium supplemented with 100 microg/mL ascorbic acid, all pores were filled with fibroblasts and with extracellular matrix, which was judged from the presence of collagen types I, III, and IV, and laminin. When seeded onto the dense top layer of the bilayered (cell free or fibroblast populated) copolymer matrix, human keratinocytes grew out into confluent sheets. After subsequent lifting to the air-liquid interface, a multilayered epithelium with a morphology corresponding to that of the native epidermis was formed. Some differences could still be observed: the expression and localization of some differentiation specific proteins was different and close to that seen in hyperproliferative epidermis; a basal lamina and anchoring zone were absent.     

Ester Exchange Reactions in Equimolar Poly(ethylene terephthalate)/Poly(phenylene sebacate) Blends

The morphology, thermal behavior and microstructure of novel polymer materials, prepared either by reactive blending of equimolar amounts of poly(ethylene terephthalate) (PET) and poly(phenylene sebacate) (PQS), or by polycondensation of the PQS monomers in the presence of PET, have been studied by DSC, optical and electron microscopy and WAXS. Both the reactive blending and the polycondensation have been performed at temperatures higher than the fusion temperatures of the two crystalline polymers. The characterization of the products has shown that reactive blending causes a gradual transformation of the starting homopolymers into block copolymers and, finally, into a macroscopically homogeneous copolyester with a randomized structure. In fact, the calorimetric and microscopic analyses of the blend prepared with a fairly long mixing time (180 min) and of the copolyester synthesized by polycondensation indicate that these products are homogeneous and mesomorphic. However, a deeper insight into the structure of these materials, obtained by X‐ray diffractometry, indicates the initial formation of a crystalline phase probably arising from the organization of chain segments rich of aromatic units (T and Q). This seems to indicate that partial reordering of the microstructure of the copolyester with formation of blocks rich of aromatic and, respectively, aliphatic units, favored energetically by the crystallization of the former, has taken place in systems where the transesterification reactions were allowed to run further towards the thermodynamic equilibrium.     

Dynamic mechanical relaxations in a copolyterephthalate based on ethylene glycol and 1,4-cyclohexanedimethanol

The dynamic mechanical relaxations of poly(ethylene terephthalate) (PET), poly(1,4-cyclo-hexylenedimethylene terephthalate) (PCHDMT), and a copolymer of them (COP) were measured in the temperature range from ?150 to 150°C by use of a dynamic viscoelastometer. The viscoelastic relaxations of COP are studied and compared with those of PET and PCHDMT. The anisotropy of the viscoelastic properties of stretched COP samples was also studied in order to distinguish between main and secondary relaxations.     

Biocompatibility and degradation of poly(ether-ester) microspheres: in vitro and in vivo evaluation

Microspheres of a hydrophobic and a hydrophilic poly(ether–ester) copolymer were evaluated for their in vitro and in vivo biocompatibility and degradation. The microspheres prior to and after sterilization were tested for in vitro cytotoxicity. The in vivo biocompatibility of the poly(ethylene glycol) terephthalate and poly(butylene terephthalate) (PEGT/PBT) microspheres was evaluated subcutaneously and intramuscularly for 24 weeks in rabbits. The in vivo degradation of the microspheres was studied microscopically and compared to the in vitro degradation. The in vitro and in vivo studies showed the biocompatibility of the microspheres of both the hydrophobic and the hydrophilic PEGT/PBT copolymer. Extracts of these microspheres showed no cytotoxic reactivity in the in vitro cytotoxicity test. Sterilization of the microspheres by gamma irradiation did not affect the cytotoxicity. PEGT/PBT microspheres injected subcutaneously and intramuscularly in rabbits showed a mild tissue response in vivo, in terms of the inflammatory response, the foreign body reaction and the granulation tissue response. Although an in vitro degradation experiment showed a decrease in molecular weight due to hydrolysis, the in vivo degradation of the microspheres was slower than previously published.     

Relaxation Behavior of Poly(ester carbonate) Block Copolymer Across the Melting Region

The dielectric behavior of a family of block copolymers based on poly(butylene terephthalate) (PBT) and aliphatic polycarbonate (PC), with the composition of PBT varying from 100 wt.‐% to 40 wt.‐%, has been investigated by broad‐band dielectric spectroscopy in the frequency range from 10^–1 to 10⁹ Hz. At temperatures above the glass transition, the merging of local γ process and the cooperative β process was studied for PBT and 40/60 and 60/40 PBT‐PC copolymers. The experimental data can be satisfactorily analyzed considering a sum of two Havriliak‐Negami functions indicating that both β and γ relaxations can be treated as independent processes. Dielectric measurements for the 40/60 copolymer were extended over and above the melting region to characterize the influence of crystal melting on the dynamic behavior. It is shown that the progressive loss of the crystalline lamellar stack microstructure, as characterized by differential scanning calorimetry and small‐ and wide‐angle X‐ray scattering, provokes a dramatic change in the dynamic behavior of both the β and γ process.     

Tissue/biomaterial interface characteristics of four elastomers. A transmission electron microscopical study

The tissue/biomaterial interface reactions of four elastomers--selected as candidates for scaffolding for tympanic membrane tissue in a total alloplastic middle ear prosthesis--were studied at the electron microscopical level after implantation in the rat middle ear. Time-dependent changes in the phagocyte/polymer interface suggested degradation of porous implants made of Estane polyether urethane, polypropylene oxide, and a poly(ethylene oxide hydantoin) and poly(tetramethylene terephthalate) segmented polyether polyester copolymer (HPOE/PBT copolymer), but not of dense Silastic silicone rubber implants. Silastic was always encapsulated in fibrous tissue. Contact between fibrous tissue and HPOE/PBT copolymer or Estane was established in the third month, but fibrous tissue was never seen close to polypropylene oxide. Bone made contact only with Estane and HPOE/PBT copolymer implants. The bone/copolymer interface showed an electron-dense layer morphologically similar to that seen between bone and hydroxyapatite ceramic, suggesting that with respect to bone HPOE/PBT copolymer behaves like a bioactive implant material. The electron-dense layer was absnet at the bone/Estane interface. Estane and especially HPOE/PBT copolymer seem to be suitable as alloplastic tympanic membrane because of their interface behavior with respect to fibrous tissue and bone.     

Three-dimensional fiber-deposited PEOT/PBT copolymer scaffolds for tissue engineering: influence of porosity, molecular network mesh size, and swelling in aqueous media on dynamic mechanical properties

Among novel scaffold fabrication techniques, 3D fiber deposition (3DF) has recently emerged as a means to fabricate well-defined and custom-made scaffolds for tissue regeneration, with 100% interconnected pores. The mechanical behavior of these constructs is dependent not only on different three-dimensional architectural and geometric features, but also on the intrinsic chemical properties of the material used. These affect the mechanics of the solid material and eventually of 3D porous constructs derived from them. For instance, poly(ethylene oxide terephthalate)-poly(butylene terephthalate) (PEOT/PBT) block copolymers are known to have mechanical properties, depending on the PEOT/PBT weight ratio in block form and on the molecular weight of the initial poly(ethylene glycol) (PEG) blocks. These differences are enhanced even more by their different swelling properties in aqueous media. Therefore, this article examines the influence of copolymer compositions in terms of their swelling on dynamic mechanical properties of solid material and porous 3DF scaffolds. The molecular weight of the starting PEG blocks used in the copolymer synthesis varied from 300 to 1000 g/mol. The PEOT/PBT weight ratio in the blocks used varied from 55/45 to 80/20. This corresponded to an increase of the swelling ratio Q from 1.06 to 2.46, and of the mesh size xi from approximately 9 Angstrom to approximately 47 Angstrom. With increased swelling, dynamic mechanical analysis (DMA) revealed a decrease in elastic response and an increase of viscoelasticity. Thus, by coupling structural and chemical characteristics, the viscoelastic properties of PEOT/PBT 3DF scaffolds may be fine tuned to achieve mechanical requirements for a variety of engineered tissues. Ultimately, the combination of 3DF and DMA may be useful to validate the hypothesis that mimicking the biomechanical behavior of a specific tissue for its optimal replacement is an important issue for at least some tissue-engineering applications.     

Effect of the temperature on the chemical healing of poly(ethylene terephthalate)

The effect of temperature on the chemical healing of poly(ethylene terephthalate) (PET) – healing as a result of chemical reactions between neighboring macromolecules located in the interface surface — was studied. The healing process was carried out in vacuum on pressed partially overlapped strips of commercial PET, previously annealed at 258°C, at temperatures between 140 and 250°C for 24 h. It is demonstrated that the fracture behavior of the welded samples depends strongly on the healing temperature T_h. At T_h > 200°C the strips break beyond the contact area, at 160 < T_h < 200°C debonding occurs, and at T_h < 160°C no bonding is observed. It is assumed that the bonding effect is mainly a result of chemical reactions (solid state postcondensation and transreactions) taking place during the healing procedure.     

Structure and properties of segmented poly(ether esters), 4. Compatibility of oligo(tetramethylene terephthalate)s with oligoethers and block copoly(ether ester)s

The mutual compatibility of oligo(tetramethylene terephthalate)s 1a—d and their compatibility with oligoethers 2, 3 , and 4 and block copoly(ether ester)s 5a—c based on poly(tetramethylene terephthalate) and poly(oxytetramethylene) is reported. From the binary phase diagrams of the oligoesters it is concluded that the oligoesters do not cocrystallize and the melt of the lower melting compound is not a good solvent for the higher melting homologue. For the trimer/pentamer ( 1b/1c )-blend the eutectic composition contains 3 mole-% of the pentamer 1c . Oligo(oxytetramethylene) ( 3 ) is a better solvent for the oligoesters than oligo(oxyethylene) ( 2 ). The addition of an oligoester to the block copoly(ether ester) induces a change in the phase behaviour of the polymer, resulting in a melting point of the blend higher than for the pure polymer or oligomer.     

Block copolymers with poly(oxy-1,4-phenylene) and liquidcrystalline polyester segments

Block copolymers were synthesized composed of an isotropic, crystallizable poly(oxy-1,4-phenylene) block and a thermotropic liquid-crystalline (LC) polyester block. Crystalline as well as amorphous LC polyesters were used, derived from substituted poly(1,4-phenylene terephthalate). The block of poly(oxy-1,4-phenylene) was introduced via telechelic 1 . 1 was prepared with a functionality of 2 in a Cu-catalyzed reaction of 4-bromophenolate 4 with 4,4′-isopropylidenediphenol (bisphenol A). The molecular weight of the telechelic is given by the ratio 4 /bisphenol A. The increase in molecular weight during formation of the block copolymer is shown by viscosity and gel-permeation chromatography measurements. The maximum weight loss of the block copolymer as obtained by thermogravimetry is in the range of 450–500°C. Both segments in the block copolymers have a strong influence on their mutual crystallization behaviour. Short segments of poly(oxy-1,4-phenylene) suppress the crystallization of both blocks. When using longer segments of poly(oxy-1,4-phenylene) the melting endotherms of both blocks are observed, but the degree of crystallinity is lower than that of the homopolymers. The fracture behaviour of the liquid-crystalline polyester 2a is changed by modification with 20 wt.-% of poly(oxy-1,4-phenylene) and the shear-banded texture is lost.