Viscosity aromatic polyesters

A polyester backbone with two HFIP groups (12F aromatic polyester of 12F-APE) was derived by the polycondensation of the diacid chloride of 6FDCA with bisphenol AF or bisphenol A under phase-transfer conditions (120). These polymers show complete solubkity in THF, chloroform, ben2ene, DMAC, DMF, and NMP, and form clear, colorless, tough films the inherent viscosity in chloroform at 25°C is 0.8 dL/g. A thermal stabkity of 501°C (10% weight loss in N2) was observed. 

Amorphous bisphenol-A polyarylates are soluble in dioxane and in chlorinated solvents such as CH2C12, 1,2-dichlororethane, 1,1,2-trichloroethane, and 1,1,2,2-tetrachloroethane while semicrystalline and liquid crystalline wholly aromatic polyesters are only sparingly soluble in solvents such as tetrachloroethane-phenol mixtures or pentafluorophenol, which is often used for inherent viscosity determinations. 

Not only good solubility but also solution behavior differs for hyperbranched polymers compared to linear polymers. For example, hyperbranched aromatic polyesters, described by Turner et al. [71,72], exhibit a very low a-value in the Mark-Houwink-Sakurada equation and low intrinsic viscosities. This is consist-... 

The general correlations of structure and properties of homopolymers are summarized in Table 2.13. Some experiments which demonstrate the influence of the molecular weight or the structure on selected properties of polymers are described in Examples 3-6 (degree of polymerization of polystyrene and solution viscosity), 3-15, 3-21, 3-31 (stereoregularity of polyisoprene resp. polystyrene), 4-7 and 5-11 (influence of crosslinking) or Sects. 4.1.1 and 4.1.2 (stiffness of the main chain of aliphatic and aromatic polyesters and polyamides). 

It was, however, observed that such systems under appropriate conditions of concentration, solvent, molecular weight, temperature, etc. form a liquid crystalline solution. Perhaps a little digression is in order here to say a few words about liquid crystals. A liquid crystal has a structure intermediate between a three-dimensionally ordered crystal and a disordered isotropic liquid. There are two main classes of liquid crystals lyotropic and thermotropic. Lyotropic liquid crystals are obtained from low viscosity polymer solutions in a critical concentration range while thermotropic liquid crystals are obtained from polymer melts where a low viscosity phase forms over a certain temperature range. Aromatic polyamides and aramid type fibers are lyotropic liquid crystal polymers. These polymers have a melting point that is high and close to their decomposition temperature. One must therefore spin these from a solution in an appropriate solvent such as sulfuric acid. Aromatic polyesters, on the other hand, are thermotropic liquid crystal polymers. These can be injection molded, extruded or melt spun. 

The advantages of these aromatic polyesters are lower cost than conventional polyether polyols, better flame retardance, and high-temperature resistence. However, their disadvantages include compatibility problems with chlorofluorocarbons and quality deviations in viscosity and hydroxyl values. In order to improve the compatibility problems, amine-based polyether polyols have been blended. 

It has been noted (Scheirs, 2000) that this leads to a dramatic decrease in viscosity that renders the polymer unprocessable or, at the best, results in defects such as haze due to crystallites that nucleate more readily from the lower-molar-mass, degraded polymer. The rate of loss of properties due to hydrolysis is orders of magnitude faster than oxidative degradation at the same temperature. To avoid these effects, the moisture level in an aromatic polyester such as PET must be kept below 0.02%. 

Of course the thermal stability and char yield depend on the polyol structure too and the aromatic polyols are superior to aliphatic polyols from this point of view. This is the reason for the extremely rapid growth of aromatic polyester polyols, of low functionality, low viscosity and low cost. 

PET wastes, proved to be an excellent raw material for low cost aromatic polyester polyols. By transesterification with DEG and (or) propylene glycol or dipropyleneglycol (DPG), liquid, low viscosity and low functionality aromatic polyester polyols were obtained. Due to the low cost, DEG is the preferred glycol for transesterification (reaction 16.3) [4, 6-8, 12]. 

Polyester polyols with equivalent weight of 167, functionality of 2 OH groups/mol, hydroxyl number of 310-350 mg KOH/g and viscosity of 1,300-3,000 mPa-s at 25 °C, are used in thermal insulation of appliances. The initial ratio between DEG and PET used in synthesis, followed by the utilisation of one of the previously mentioned procedures avoids solidification (section 16.2, a-e), and means that a large range of aromatic polyester polyols, having various hydroxyl numbers, functionalities and aromaticity can be obtained. 

The first LCP to be launched commercially was Dartco s Xydar, introduced in 1984 [11]. Xydar injectionmolding resins are aromatic polyesters based on terephthalic acid, p-hydroxybenzoic acid, and p,p -dihydroxybiphenyl. Xydar has a high melting point (close to 400°C), which necessitates certain modifications to processing equipment. It also has a high melt viscosity making it difficult to mold in... 

Blends of liquid crystal polymer (LCP) polyester, LCP poly(ester amide) and PAS exhihit a reduced melt viscosity.LCP polyesters are made hy polymerizing aromatic diacids with diols or hy polymerizing aromatic hydroxy acids, e.g. 4-hydroxyhenzoic acid and 6-hydroxy-2-naphthoic acid. In LCP poly(ester amide)s, some of the hydroxyl groups in the monomers are replaced with amino groups. 

The most common form is the nematic, a bimdle of parallel, long, rodlike molecules. Additional cooling to the primary transition temperature, T leads to solidification into a solid crystalline phase (small crystallites). In the region between Tj and T , a liquid of very low viscosity prevails, in contrast to the high melt viscosity. The aromatic polyesters have high heat distortion temperatures (HDT). Vectra, composed of para-hydroxy-benzoic acid (PHBA) and para-hydroxy-naphtoic acid (PHNA), has an HDT of 180 C-240 C. Xy-dar, composed of PHBA, tera-phthalic acid and biphenol, has an even higher HDT of 260 C-350 C. 

Certain aromatic polyesters, containing stiff segments in the chain, exhibit ordered phases which are similar to those seen in small-molecule liquid crystalline, or mesophasic, substances. In particular, the rod-like molecules are oriented in shear to such an extent that interchain entanglement is small, and the melts consequently exhibit a lower than expected viscosity. On cooling of the melt, the molecules remain oriented, effectively self-reinforcing the polymer in the direction of flow. 

Interfacial polymerization was employed to produce aromatic polyesters from 2,5-furan dicarbonyl dichloride with various bis-phenols such as resorcinol, pyrocatechol, hydroquinone, and 2,2-bis(4-hydroxy-phenyl) propane. When 2,5-furan dicarbonyl dichloride was combined with 2,2-bis(4-hydroxyphenyl)propane, workers were able to obtain a maximum yield and maximum logarithmic viscosity number of 80% and 0.17, respectively, when the polymerization solvent was benzene at 25 with two equivalents of sodium hydroxide. In a more in-depth study, this same polyester 14... 

Compositions with terephthalate levels of over 60% would not be as desirable, however, since flow was not measurable above this level (Table 1). The polyesters which were examined all can be prepared with melt flow characteristics similar to those of commercial polysulfone resins as indicated by Figure 2. While the viscosity/temperature relationships for the two types of polymers are different this should not be a serious problem in the utilization of the aromatic polyesters. 

The commercial polymers used in the study are characterized in Table 1. The polypropylenes PP1-PP5 were homopolymers exhibiting different melt viscosities (see Fig. 1) supplied by Neste Chemicals. Liquid-crystalline polymer 1 (LCPl) (Vectra A950 by Hoechst Celanese) is a totally aromatic polyester-type thermotropic main-chain LCP copolymer based on p-hydroxybenzoic acid (HBA) and 6-hydroxy-2-naphthoic acid (HNA). Liquid-crystalline polymer 2 (LCP2) (Rodrun LC-3000 by Unitika Ltd) is a more flexible thermotropic main-chain LCP copolyester consisting of 60%... 

Polyarylates PAR, polyarylester (PAE), aromatic polyester (APE), HTPC. The viscosity of these plastics is even greater than that of PC, and does not diminish as the shear rate rises. The channels should have relatively large cross-sections. The minimum gate diameter... 

The previous paper in this series described the preparation and properties of highly aromatic polyesters that have turbid melts, have melt viscosities highly dependent upon composition and shear rate, and that give unusually anisotropic molded articles. Because these unusual properties are reminiscent of the behavior of nonpolymeric nematic liquid crystalline materials, further work has been done to synthesize and characterize polymers containing other moieties known to lead to liquid crystallinity in nonpolymeric materials. The copolyesters produced were derived by the acidolysis reaction previously described from poly-(ethylene terephthalate) (PET) and a variety of dicarboxylic acids and acetylated difunctional phenols. Some of the copolymer compositions were varied to determine the limits of composition that give the turbid melts characteristic of liquid crystallinity, but which can be melted before decomposition. This paper describes the preparation and the physical and magnetic properties of these polymers. 

Do and his co-workers have developed aromatic polyester dendrimers containing NLO chromophores on the periphery (Figure 19). Dendrimers have a systematic structure with a number of chromophore branches which are controllable by the generation number and exhibit good physical properties with sufficient viscosity for thin film applications. Due to their... 

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