Segmented polyurethanes with 4,4′-bis-(6-hydroxyhexoxy)biphenyl as chain extender. Part 2. Synthesis and properties of MDI-polyurethanes in comparison with 2,4-TDI-polyurethanes

Linear segmented polyurethanes based on poly(butylene adipate)s (PBA) of different molecular weight (M_n 2000, 1000, and 600), 4,4′-diphenylmethane diisocyanate (MDI) and the mesogenic diol 4,4′-bis-(6-hydroxyhexoxy)biphenyl (BHHBP) as well as the unsegmented polyurethane consisting of MDI/BHHBP units have been synthesized and characterized by elemental analysis, ¹³C-NMR and SEC. The thermal behavior and the morphology were studied by DSC, polarizing microscopy, and DMA. The properties of the MDI-polyurethanes were discussed in relation to the BHHBP chain extended 2,4-TDI-polyurethanes and common 1,4-butanediol chain-extended MDI products. MDI polyurethanes based on PBA (M_n 2000) exhibit a glass transition temperature T_g of about −40°C independent of the hard segment content up to ∼50% hard segments. At higher hard segment contents increasing T_gs were observed. Polyurethanes, based on the shorter polyester soft segments PBA (M_n 1000 or 600), reveal an increase in the glass transition temperatures with growing hard segment content. The thermal transitions caused by melting of the MDI/BHHBP hard segment domains are found at 50 K higher temperatures in comparison with the analogous TDI products with mesogenic BHHBP/TDI hard segments. Shortening of the PBA chain length causes a shift of the thermal transitions to lower temperatures. Polarizing microscopy experiments indicate that liquid crystalline behavior is influenced by both the content of mesogenic hard segments and the chain length of the polyester. © 1996 John Wiley & Sons, Inc.     

Calorimetric and Dielectric Study of the Segmented Biodegradable Poly(ester‐urethane)s Based on Bacterial Poly[(R)‐3‐hydroxybutyrate]

Two series of segmented poly(ester‐urethane)s were synthesized from bacterial poly[(R)‐3‐hydroxybutyrate]‐diol (PHB‐diol), as hard segments, and either poly(ε‐caprolactone)‐diol (PCL‐diol) or poly(butylene adipate)‐diol (PBA‐diol), as soft segments, using 1,6‐hexamethylene diisocyanate as a chain extender. The hard‐segment content varied from 0 to 50 wt.‐%. These materials were characterized using ¹H NMR spectroscopy and GPC. The polymers obtained were investigated calorimetrically and dielectrically. DSC showed that the T_g of either the PCL or PBA soft segments are shifted to higher temperatures with increasing PHB hard‐segment content, revealing that either the PCL or PBA are mixed with small amounts of PHB in the amorphous domains. The results also showed that the crystallization of soft or hard segments was physically constrained by the microstructure of the other crystalline phase, which results in a decrease in the degree of crystallinity of either the soft or hard segments upon increase of the other component. The dielectric spectra of poly(ester‐urethane)s, based on PCL and PHB, showed two primary relaxation processes, designated as α_S and α_H, which correspond to glass–rubber transitions of PCL soft and PHB hard segments, respectively. Whereas in the case of other poly(ester‐urethane)s, derived from PBA and PHB, only one relaxation process was observed, which broadens and shifts to higher temperature with increasing PHB hard‐segment content. It was concluded from these results that our investigated materials exhibit micro‐phase separation of the hard and soft segments in the amorphous domains.     

Oxygen permeability in thermoplastic polyurethanes

The thermal and oxygen transport properties of a series of thermoplastic polyurethanes (TPUs) based on 4,4′‐methylene diisocyanate (MDI) and 1,4‐butanediol (BD) as hard segments, and poly(tetramethylene glycol) (PTMG) or poly(butylene adipate) (PA) as soft segments, are studied. Oxygen permeabilities (P) of both polyester‐based and polyether‐based TPUs increase with decreasing hard segment fractions. Oxygen solubility (S) and diffusivity (D) can be derived from permeation curves. S correlates with the amount of excess free volume as determined by the difference between glass‐transition and testing temperatures (i.e., the degree of super cooling) and decreases with the increased T_g in polyester‐based TPUs. The intensity of low temperature gamma transition reflects the activation energy for D; the higher the intensity is, the lower D is annealed TPU samples exhibited higher oxygen permeabilities as well as lower storage moduli at room temperature, despite modest increases in overall crystallinity. Dedensification of the soft segment phase during annealing/crystalline phase growth is the most likely explanation for loss of mechanical and barrier properties after annealing as partially confirmed by Fourier transform infrared spectroscopy. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Effect of thermal-oxidative aging on the microstructure of thermoplastic poly(ether-urethane)

Thermodynamic incompatibility between the hard and soft segments in thermoplastic polyurethanes (TPUs) leads to a two-phase microstructure, which is usually demonstrated by the characterizations of fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The effect of thermal-oxidative aging durations (up to 300 days) and temperatures (40, 50, 55, 70°C) on the microstructure of TPUs were investigated by FTIR, DSC, specific surface energy and dynamic mechanical analysis (DMA) in this work. The TPUs were synthesized by 4,4′-methylenediphenyl diisocyanate and 1,4-butanediol as hard segments and poly(tetramethylene glycol) as soft segments. The result demonstrates that the degree of the phase separation value in virgin TPUs is about 0.332. The specific surface energies of hard and soft segments are 56.9 and 35.7 mJ/cm², respectively. Furthermore, the degree of microphase separation and damping property achieved by the aid of the Gauss method and DMA, respectively, of the TPUs show an obvious decrease during the durations. Moreover, the change of glass transition temperature T _g of the TPUs was also investigated by the DMA. The result indicates that the T _g of the TPUs is almost unchanged with the aging temperatures and durations.     

Quantitative DSC evaluation of phase segregation rate in linear segmented polyurethanes and polyurethaneureas

Linearly segmented polyurethanes and polyurethaneureas are known to be phase separated; one phase is the soft phase, the other, the hard domain. Quantitative evaluation of the degree of phase separation was obtained by DSC. An estimation of the dispersed soft segments outside the soft phase can be made by ΔC_p measurements and the increase in glass transition (T_g) can be attributed to the presence of hard blocks in the soft phase. The segregation rate depends on the nature of the soft segments which decrease from hydrogenated polybutadiene to polybutadiene to polyether. It also depends on the nature of the chain extender from aliphatic to aromatic diol and from aliphatic to aromatic diamine. The presence of soft segments in hard domains can be related to the thermoplastic behavior of the polyurethanes and polyurethaneureas.     

GAS PERMEATION OF SEGMENTED POLYURETHANES AND THEIR BLENDS WITH PVC

Film specimens of four segmented polyurethanes with different soft segments, namely polycaprolactone, polytetramethylene adipate, polytetramethylene oxide and polypropylene oxide, and their blends with PVC of different compositions were obtained by solution cast. The permeability of these films to O_2, N_2 and H_2 and their density were measured by using gas chromatography and technique of density gradient column. The polyether polyurethanes were found to have higher permeability than the polyester ones due to their low glass transition temperature and /or the low density value. The blends of PVC and polyether polyurethanes, especially the PPO-based polyurethane, are incompatible, and their permeability coefficient-composition dependence has the typical S-shaped curves. PVC is well compatible with the soft segments in its blends with polyester polyurethanes. For these blends the composition dependence of permeability is characterized by a negative deviation from the semilogarithmic additivity rule, and it is possible to prepare blends having T_g 20℃lower than that of PVC, but retaining its low permeability almost unchanged, results were discussed in according with the different approaches for the permeation behavior of compatible and incompatible blends.     

Shape memory fiber spun with segmented polyurethane ionomer

The effect of cationic groups within hard segments on shape memory polyurethane (SMPU) fibers was studied and the cyclic tensile testing was conducted to assess the shape memory effect. Mechanical properties, hard segment crystallization, and dynamic mechanical properties of SMPU ionomer fibers composed of 1,4‐butanediol (BDO), N‐methyldiethanolamine (NMDA), 4,4′‐methylenebis(phenyl isocyanate) (MDI), and poly(butylene adipate)diol (PBA) were investigated using a universal tensile tester, differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). The results demonstrate that only 2 wt% NMDA can significantly change the glass transition temperature of the soft segment phase. DSC shows that the ionic group within hard segments can facilitate the crystallization of hard segments in unsteamed SMPU ionomer fibers. But for steamed fiber specimens, this effect is insignificant. Moreover, the ionic groups in hard segments with different hard segment contents (HSC) have different effects. In unsteamed fibers with 64 wt% HSC, 2 wt% NMDA increases the glass transition of soft segments from 63.5 to 70.6°C. However, in fibers with 55 wt% HSC, the glass transition temperature is lowered from 46.7 to 33.5°C. The post‐treatment, high‐pressure steaming is an effective way to remove the internal stress and subsequently improve the dimensional stability of SMPU ionomer fibers. Copyright © 2008 John Wiley & Sons, Ltd.     

Studies on the relationship of structure and properties of the polyesterurethanes adhesives

Three series of linear segment polyurethanes (PHAU, PBAU, PEAU) based on three polyesters (PHA, PBA, PEA), MDI and butanediol were synthesized by solution polymerization. The crystallinity of these polyesters and polyurethanes and the compatibility of Blends of polyurethane (PU) with poly(vinyl chloride) (PVC) were studied by means of X-ray diffraction, DSC, DMA and phase contrast microscopy respectively. The influence of polyester type and molecular weight, the hard-segment content in PU on the crystallinity of PU and the influence of compatibility on adhesion are discussed. The results showed that, on condition that the hard-segment content was not high (< 25%), the crystallinity in PU was mainly caused by the polyester, soft-segment, which was in the order of PHA PBA PEA, and that, PBAU/PVC, PHAU/PVC were compatible systems, but PEAU/PVC was incompatible. The adhesive strength of the three adhesives was quite different from one another, with the order of PBAU PHAU PEAU. An interpretation of adhesion for the PU-PVC system by the diffusion theory is proposed.     

Studies on thermotropic liquid crystalline polyurethanes. II. Synthesis and properties of liquid crystalline polyurethane elastomers

Three series of novel thermotropic liquid crystalline polyurethane elastomers (TLCPUEs) were studied. Hard segments were formed by using hexamethylene diisocyanate (HDI) reacted with a mesogenic unit, benzene-1,4-di(4-iminophenoxy-n-hexanol), which also acted as a chain extender. Three diols: 1,10-decanediol,poly(oxytetramethylene) glycol (PTMEG) M _n = 1000 and PTMEG M _n = 2000 were used as the soft segments. The effects of soft segments of polyurethanes on the liquid crystalline behavior were studied. Higher molecular weight TLCPUEs were obtained by adding 30?50 mol % of mesogenic segments to diisocyanates. In contrast to a conventional chain extender such as 1,2-ethylene glycol or 1,4-butyl glycol, the synthesized polyurethane elastomers exhibited a mesophase transition by using a mesogenic unit as the chain extender. Mesophase was found for all synthesized LC polyurethanes except of polymers H2-A-12 and H2-A-7. The structures and the thermal properties of all synthesized TLCPUEs were studied by using FTIR spectroscopy, wide-angle x-ray diffraction (WAXD) and DSC measurements, a polarizing microscope equipped with a heating stage, dynamic mechanical analysis (DMA), and thermogravimetric analysis (TGA). Mechanical properties were also examined by using a tensilemeter. © 1995 John Wiley & Sons, Inc.     

Morphology of polyurethanes with triol monomer crosslinked on hard segments

Polyester‐based polyurethanes containing ≈60 wt % of polyester were synthesized from low molecular weight polyester (M_n ≈2000) and 4,4′‐methylene bis(phenyl isocyanate) (MDI), with butanediol as a chain extender and glycerol as a crosslinker. The triol crosslinker was used in substitution for the 1,4‐butanediol chain extender; thus, the crosslinker was chemical bonded to the hard segments of polyurethane. The morphologies of these polyurethanes were studied by differential scanning calorimetry (DSC), small‐angle X‐ray scattering (SAXS), TMA (thermal mechanical analysis), and FTIR (Fourier transform infrared spectroscopy). Owing to the highly steric hindrance, the presence of triol crosslinker in the hard segments resulted in a decrease in the aggregation of hard segments through hydrogen bonding. The experimental results revealed that the degree of phase segregation of soft and hard segments decreased with increasing the triol crosslinker content in the hard segments. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2673–2681, 1999     

Polyurethanes containing sulfur. I. New thermoplastic polyurethanes with benzophenone unit in their structure

New thermoplastic nonsegmented thiopolyurethanes were obtained from the low-melting aliphatic–aromatic thiodiols 4,4′-bis(2-hydroxyethylthiomethyl)benzophenone (BHEB), 4,4′-bis(3-hydroxypropylthiomethyl)benzophenone (BHPB), and 4,4′-bis(6-hydroxyhexylthiomethyl)benzenophenone(BHHB) as well as hexamethylene diisocyanate (HDI), both by melt and solution polymerization with dibutyltin dilaurate as the catalyst. The effect of various solvents on molecular-weight values was examined. The polymers with the highest reduced viscosities (0.63–0.88 dL/g) were obtained when the polymerization was carried out in a solution of tetrachloroethane, N,N-dimethylacetamide, and N,N-dimethylacetamide or N,N-dimethylformamide for BHEB-, BHPB-, and BHHB-derived polyurethanes, respectively. These polymers with a partially crystalline structure showed glass-transition temperatures (T_g) in the range of −1 to 39 °C, melting temperatures (T_m) in the range of 107 to 124 °C, and thermal stabilities up to 230 to 240 °C. The BHEB-derived polyurethane is a low-elasticity material with high tensile strength (ca. 50 MPa), whereas the BHPB- and BHHB-derived polyurethanes are more elastic, showing yield stress at approximately 16 MPa. We also obtained segmented polyurethanes by using BHHB, HDI, and 20 to 80 mol % poly(oxytetramethylene) glycol (PTMG) of M̄_n = 1000 as the soft segment. These are high-molecular thermoplastic elastomers that show a partially crystalline structure. Thermal properties were investigated by thermogravimetric analysis and differential scanning calorimetry. The increase in PTMG content decreases the definite T_g and increases the solubility of the polymers. These segmented polyurethanes exhibit the definite T_g (−67 to −62 °C) nearly independent of the hard-segment content up to approximately 50 wt %, indicating the existence of mainly phase-separated soft and hard segments. Shore A/D hardness and tensile properties were also determined. As the PTMG content increases, the hardness, modulus of elasticity, and tensile strength decrease, whereas elongation at break increases. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4140–4150, 1999     

Water effects in polyurethane block copolymers

Equilibrium and dynamic sorption isotherm measurements, differential scanning calorimetry (DSC) measurements, and, mainly, dielectric relaxation spectroscopy (DRS) measurements by means of the thermally stimulated depolarization currents (TSDC) method were used to investigate the hydration properties of linear segmented polyurethane copolymers. Three types of samples were investigated with various fractions of hard and soft block segments. They were based on polyethylene adipate (PEA), 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BDO). At 20°C the water content h of the samples at various values of relative humidity rh increases in proportion to the weight fraction of soft block segments phase. At saturation (rh = 100%) the ratio of sorbed water molecules to polar carbonyl polyester groups is 0.13. At saturation at 20°C there is no fraction of freezable water. The glass transition temperature, T_g, measured by DSC and by TSDC, shifts to lower temperature with increasing h by about 8–10 K at saturation at 20°C. A dielectric relaxation mechanism related to interfacial polarization in the phase-separated morphology is also plasticized by water in a way similar to that observed for the main (α) relaxation. © 1996 John Wiley & Sons, Inc.     

Structure-property relationships in polycaprolactone-polyurethanes

The structure-property relationships of polycaprolactone-based segmented polyurethanes were studied using differential scanning calorimetry (DSC), small-angle x-ray scattering (SAXS), wide-angle x-ray diffraction (WAXD), dynamic mechanical, and stress-strain testing. The materials studied varied in hard-segment type [4,4′-diphenylmethane diisocyanate/butanediol (MDI/BD) or 4,4′-dicyclohexyl methane diisocyanate/butanediol (H₁₂MDI/BD)], soft-segment molecular weight (830 or 2000 MW polycaprolactone), hard-segment content (23–77% by weight), and thermal history. The materials with aromatic (MDI/BD) hard segments had semicrystalline hard-segment domains, while the materials with aliphatic (H₁₂MDI/BD) hard segment had mostly amorphous domains. Materials with the shorter polycaprolactone soft segment (830 MW) exhibited thermal and mechanical behavior which indicated a considerable degree of hard- and soft-segment compatibility. The materials which contained a 2000-MW polycaprolactone soft segment exhibited better-defined microphase separation. SAXS was used to characterize the microphase structure of each system. The effects of hard-segment content and soft-segment molecular weight were similar for the aromatic (MDI) and aliphatic (H₁₂MDI) hard-segment-based block copolymers. Changing the hard segment from aromatic to aliphatic gave materials with larger interfacial area and slightly higher tensile strength. A range of morphologies between isolated hard domains in a rubbery matrix and isolated rubbery domains in a hard matrix was observed.     

Metal‐free synthesis of novel biobased dihydroxyl‐terminated aliphatic polyesters as building blocks for thermoplastic polyurethanes

Using the organic compound 1,5,7‐triazabicyclo[4.4.0]dec‐5‐ene (TBD) as a catalyst for step‐growth polymerization, a series of well‐defined hydroxyl‐telechelic renewable aliphatic polyesters (including poly(1,3‐propylene adipate); poly(1,4‐butylene adipate); poly(1,12‐dodecylene sebacate); and poly(1,2‐dimethylethylene adipate), PDMEA) were synthesized and studied. PDMEA is a novel polyester, which has not been reported before. The results of ¹H NMR and Matrix‐assisted laser desorption ionization time‐of‐flight mass spectrometry indicate that the polymers are fully hydroxyl terminated. From differential scanning calorimetry (DSC) thermograms, we found that the glass transition temperatures (T_g) of these polyesters are below ?20 °C. Only a T_g but no melting peak is observed in the DSC curve of the novel PDMEA. This indicates that PDMEA, contrary to the other renewable polyesters, is totally amorphous. Furthermore, using hexamethylene diisocyanate and hexamethylene diamine, poly(ester urethane urea)s (PEUUs) based on PDMEA were successfully synthesized. The T_g of the prepared PEUUs is below 0 °C, and no melting behavior of the soft‐segment is observed. The PEUU, with a flow temperature of over 200 °C, thus behaves as an elastomer at room temperature. Its mechanical properties, such as a relatively low tensile E‐modulus (≈20 MPa) at room temperature and a sufficiently high strain at break (≈560%), make it suitable for use in, for example, biomedical applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

TEMPERATURE EFFECTED STRUCTURAL TRANSITIONS IN POLYURETHANES SATURATED WITH SOLVENTS STUDIED BY SAXS SYNCHROTRON METHOD

ABSTRACT

A set of segmented polyurethanes (PU) differing in the hard-segment structure was saturated with solvents and after the equilibrium saturation was reached, put to temperature-dependent SAXS investigations. The time-resolved mode of SAXS measurements with a linear increase of temperature from ?70°C to +70°C, i.e., within the temperature range between T_g of soft and hard segments, was applied. The order-order transition leading to a greater degree of order was found at higher temperatures for almost all systems investigated. Some of the PUs exhibit two kinds of microphase separated domains. The results obtained are discussed with respect to the mean-field theory of copolymers and Koberstein and Stein model for hard microdomain structure in PUs, and correlated with temperature dependence of membrane permeability in pervaporation process.     

Studies on thermotropic liquid crystalline elastomers. I. Synthesis and properties of poly (amide-ester) elastomers

Three series of novel poly(amide-ester) (PAE) elastomers were prepared by direct poly-condensation from terephthalic acid (TPA), polyols (M_n = 1000 or 2000), and various diamines. The structures and thermal properties of the synthesized PAEs were examined by FTIR spectroscopy, wide angle X-ray diffraction (WAXD), differential scanning calo-rimetry (DSC), thermal optical polarized microscopy, thermogravimetric analysis (TGA), and dynamic mechanical analysis (DMA). The effects of kinds and amount of diamines and the molecular weight of polyols on the thermal properties of PAEs were studied. By introducing long flexible spacers (PE-1000 or PE-2000) into the polymer main chain, all polymers showed two-phase morphology under the thermal optical microscopic observation. It was interesting that most of the synthesized polymers exhibited only one melting transition corresponding to the soft segments. The melting transition of hard segments could not be detected due to decomposition of the soft segments. However, a thermotropic liquid crystalline PAE (TLCPAE) prepared from methylhydroquinone and 2-chloro-5-methyl-phenylenediamine with PE-1000 could be obtained by lowering the melting transition temperature of the hard segment. © 1995 John Wiley & Sons, Inc.     

Studies on thermotropic liquid crystalline polyurethanes. III. Synthesis and properties of polyurethane elastomers by using various mesogenic units as chain extender

Four series of thermotropic polyurethane elastomers (TPUEs) were synthesized in this study. The hard segments were formed by using 4,4′-methylenedicyclohexyl diisocyanate (H₁₂MDI) reacted with various mesogenic units, such as benzene-1,4-di(4-iminophenoxy-n-hexanol), benzene-1,4-di(4-iminophenol), and 3,3′-(4,4′-biphenylene)dipropanol, which also acted as the chain extender. Poly(oxytetramethylene)glycols (PTMEGs), PTMEG-2000 (M_n 2,000) and PTMEG-1000 (M_n 1,000) were used as a soft segment. The structures of all synthesized thermotropic liquid crystalline polyurethanes (TLCPUs) were characterized by FTIR spectroscopy. The effects of mesogenic units on the LC properties and elastic behaviors of LCPUs were studied. It was difficult to show LC behaviors for the PU elastomers derived from the mesogenic units with a lower aspect ratio, such as 3,3′-(4,4′-biphenylene)dipropanol, or the long soft segments, PTMEG-2000. In addition, these PU elastomers show better elastic properties by using a higher aspect ratio mesogenic unit as the chain extender, such as benzene-1,4-di(4-iminophenoxy-n-hexanol and benzene-1,4-di(4-imino-phenol)). The thermal properties were investigated by DSC measurements, thermal optical polarized microscopy, wide angle X-ray diffraction, dynamic mechanical analysis, and thermogravimetric analysis. The mechanical properties were measured by a tensilemeter. © 1996 John Wiley & Sons, Inc.     

Multiphase structure of segmented polyurethanes: Its relation with spherulite structure

Small-angle light-scattering (SALS), Polarized light microscopy (PLM), differntial scanning calorimetry (DSC), and small-angle x-ray scattering (SAXS) were used to study morphological changes in segmented polyurethanes with 4,4′-diphenylmethane diisocyanate (MDI) and 1,4-butanediol (BD) as the hard segment. It was found. for the first time, that spherulites could form from the melt by quenching the polyurethanes in the melt state to annealing temperatures between 120°C and T_h, the highest annealing temperature for spherulite formation. T_h ranged from 140°C to ca. 170°C and depended upon the hard-and soft-segment compatibility. Within the range 120°C to T_h, the radius of the spherulite increased with increasing hard-segment content at each fixed annealing temperature. Annealing at 135–140°C gave rise to the largest spherulites. SAXS was used to investigate the phase-separated structures corresponding to the spherulite formation. The interdomain spacing increased with increasing hard-segment content and with increasing annealing temperature.The degree of phase separation first increased with increasing annealing temperature from room temperatures (ca. 25°C), reached a maximum at ca. 107°C, and then decreased with further increase in the annealing temperature. On the basis of these observations, the mechanisms of phase separation, crystallization, and spherulite formation are discussed. © 1993 John Wiley & Sons, Inc.     

INTERACTIONS OF ORGANIC SOLVENTS WITH POLYURETHANE

Abstract

Polyurethane elastomers [1] are linear block copolymers of the type in which one of the two blocks is typically a polyether or a polyester diol with a molar mass between 300 to 6000. These blocks comprise the soft segments because at the service temperature they exist in a rubbery or a viscous state and impart elastomeric properties. The other segments are composed of aromatic diisocyanates extended with low diols to produce blocks with molar mass ranging from 500 to 3000. These blocks comprise the hard segments because at the service temperature they exist in the glassy (or semicrystalline) state. Dimensional stability is imparted through microphase separation of the hard segments into domains which act as a reinforcing filler and multifunctional crosslinks. Polyurethanes are mainly thermoplastics because heating above the hard segment glass transition temperature (T_g) will allow the material to flow.     

Model structures of thermoplastic polyesters having regularly alternated aromatic and fluorinated segments

Linear segmented polyesters containing soft perfluoropolyether (PFPE) and hard aromatic segments are obtained by an interfacial polycondensation reaction of an acyl chloride-ended fluorinated prepolymer with various aromatic diphenols in the presence of phase transfer catalysts (PTC) as accelerators. Experimental conditions for reaching high molecular weights are discussed. The calorimetric analysis (DSC) of all the polyesters synthesized shows a typical biphasic morphology, where a very low T_g (< −110°C) corresponding to the segregated PFPE moiety, is always accompanied by another T_g or a higher melting temperature, depending on the nature of the hard phase. Dynamic-mechanical analysis (DMA) has been carried out confirming the DSC results and suggesting diversified mechanical behaviors at the various temperatures in line with the amorphous or semicrystalline nature of the polymer. Chemical resistance was finally tested by dipping in several solvents and chemicals. The new polyesters show high contact angles, a moderate swelling in many organic solvents and excellent stability in aggressive hydrolytic environments. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 939–947, 1998