Aromatic polymers polyesters

Most polyesters (qv) are based on phthalates. They are referred to as aromatic-aHphatic or aromatic according to the copolymerized diol. Thus poly(ethylene terephthalate) [25038-59-9] (PET), poly(butyelene terephthalate) [24968-12-5] (PBT), and related polymers are termed aromatic-aHphatic polyester resins, whereas poly(bisphenol A phthalate)s are called aromatic polyester resins or polyarylates PET and PBT resins are the largest volume aromatic-aHphatic products. Other aromatic-aHphatic polyesters (65) include Eastman Kodak s Kodar resin, which is a PET resin modified with isophthalate and dimethylolcyclohexane. Polyarylate resins are lower volume specialty resins for high temperature (HDT) end uses (see HeaT-RESISTANT POLYAffiRS). 

PET, PTT, and PBT have similar molecular structure and general properties and find similar applications as engineering thermoplastic polymers in fibers, films, and solid-state molding resins. PEN is significantly superior in terms of thermal and mechanical resistance and barrier properties. The thermal properties of aromatic-aliphatic polyesters are summarized in Table 2.6 and are discussed above (Section 2.2.1.1). 

Hyperbranched aromatic polyesters, synthesis of, 116-118 Hyperbranched aromatic polymers, 286 Hyperbranched polyamine, synthesis of, 519-520... 

Phthalazinone, 355 synthesis of, 356 Phthalic anhydride, 101 Phthalic anhydride-glycerol reaction, 19 Physical properties. See also Barrier properties Dielectric properties Mechanical properties Molecular weight Optical properties Structure-property relationships Thermal properties of aliphatic polyesters, 40-44 of aromatic-aliphatic polyesters, 44-47 of aromatic polyesters, 47-53 of aromatic polymers, 273-274 of epoxy-phenol networks, 413-416 molecular weight and, 3 of PBT, PEN, and PTT, 44-46 of polyester-ether thermoplastic elastomers, 54 of polyesters, 32-60 of polyimides, 273-287 of polymers, 3... 

Additives and copolymers have extended the use of PET fibers into areas where the original commodity products had deficiencies, in, for example, soil-resistance, static protection or poor dyeability. Newer members of the polyester family have found applications in markets where more stretchiness or resiliency were desired (using longer aliphatic chains) or to gain higher modulus, temperature resistance and strength (with fully aromatic polymers). 

Graphite is an excellent but expensive reinforcement for plastics. Aramid (aromatic polyamide), polyester (polyethylene terephthalate PET), and boron filaments are also used as reinforcements for polymers. 

In 2003, the average price of starch blends was around 3.0-5.0 per kg. In 2005, the average price range of starch blends was down to 1.5-3.5 per kg. PLA is now being sold at prices between 1.37-2.75 per kg compared to a price range of 3.0-3.5 per kg three years ago, and is now almost price competitive with PET. The average cost of an aliphatic aromatic co-polyester has fallen from 3.5-4.0 per kg in 2003 to 2.75-3.65 per kg in 2005. Prices are expected to fall further for all biodegradable polymer types over time as production volumes increase and unit costs fall. 

Synthetic biodegradable polymers such as aliphatic-aromatic co-polyesters. 

For conventional technical applications aromatic polyesters such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are widely used. But these polymers are biologically inert and thus not directly applicable as biodegradable plastics. Combining both the excellent material properties of aromatic polyesters and the potential biodegradability of aliphatic polyesters has led to the development of a number of commercially available aliphatic-aromatic co-polyesters over the last decade or so. 

Biodegradable polymers can also be made from mineral oil based resources such as the aliphatic-aromatic co-polyester types. Mixtures of synthetic degradable polyesters and pure plant starch, known as starch blends, are also well-established products on the market. 

In 2005, starch-based materials were the largest class of biodegradable polymer with just over 47% of total market volumes. Loose-fill foam packaging accounts for more than a half of starch biopolymer volumes. Polylactic acid (PLA) is the second largest material class followed by synthetic aliphatic-aromatic co-polyesters. The PHA category is at an embryonic stage of market development with very low market tonnage at the moment. 

Recent developments in the substitution of completely aromatic LC polyesters have produced polymers which show improved solubilities and reduced transition temperatures (29). The presence of these side groups provides a method for producing polymers that are compatible with other similarly modified polymers. In this way, blends of rigid and flexible polymers can be prepared. Substituents have included alkyl, alkoxy (30) and phenyl alkyl groups (21), some of which lead to mesophases that have been reported as being "sanidic" or board-like. This approach has been used with both polyesters and polyamides and has lead to lyotropic and thermotropic polymers depending on the particular composition used. Some compositions even show die ability to form both lyotropic and thermotropic mesophases (22). 

Preparation and characterization of highly branched aromatic polymers, polyphenylenes, polyesters, polyethers, and polyamides, were reviewed. These polymers were prepared from condensation of AB -type monomers, which gave noncrosslinked, highly branched polymers. The polymer properties are vastly different compared to their linear analogs due to their resistance to chain entanglement and crystallization. 

PAr s are aromatic amorphous polyesters, viz. U-polymer , Ardel D-lOO, Durel , Arylon , etc. Their T = 188°C and HOT = 120-175°C. Blends with PPS have been developed to improve the performance of PAr — processability, rigidity and hydrolytic stability. 

The second class contains a fluorescent chromophore, also referred to as a fluorophore, on every repeat unit, either pendent to the chain or in the backbone. Examples of compounds having chromophores pendent to the chain are polystyrene and poly(2-vinylnaphthalene), both of which have been extensively studied as components of polymer blends (7-i3). Compounds having chromophores in the backbone are represented by an aromatic polyamide, polyester (14), or polyurethane (15). 

The polycondensation of difunctional oligomers leads to the preparation of well-defined polymer structures. Monomers in this type of reactions must be soluble in the reaction mixture and stable when the reaction is carried out in the melt, which is the case for some aromatic polymers prepared by polycondensation [22]. As previously described, polycondensation can occur with monomers bearing the same or a different functional group at both ends of the molecule. When one of the reactive functional groups is a hydroxyl moiety, several types of materials can be prepared, such as polyethers, polyesters, and polyurethanes, independently if they are used to form homopolymers, copolymers, or hyperbranched polymers. 

Copolymeric aromatic polyesters, though possessing a somewhat lower level of heat resistance are easier to fabricate than are the wholly aromatic polymers they also possess many properties that make them of interest as high-temperature materials. These materials, called polyarylates, are copolyester of terephthalic acid, and bisphenol A in the ratio of 1 1 2. 

AROMATIC POLYMER A polymer with aromatic ring structure (i.e., polyesters). 

It is far beyond the scope of this chapter to present a comprehensive overview on the different structures of aromatic main chain LCPs and take into account the various property and application aspects. The objective of this chapter is to discuss the impact of structural concepts in modifying the properties of aromatic LCPs, focusing here on aromatic thermotropic LC polyesters. This will be discussed for selected examples. Conclusions from the work on polyesters are transferrable to other classes of thermotropic and lyotropic aromatic polymers. 

As already mentioned, positional isomerism is important for the solubility and fusibility of aromatic LC polyesters. Consequently, polyesters made from symmetrical 2,5-disubstituted or 2,3,4,5-tetrasubstituted monomers should result in polymers that are less soluble and less fusible. This is in general the case with short lateral substituents. Ballauff and others reported that the series of poly( 1,4-phenylene-2,5-dialkoxy tereph-thalate)s with long flexible alkoxy side chains at the terephthalic moiety result in tractable LC polyesters [20] (Fig. 12). These polyesters exhibit a high degree of crystallinity with melting temperatures below 300 °C. Polyesters with short side chains (2350°C for m = 2... 

The same structural modification concepts, which were utilized to modify the properties of para-linked aromatic LC polyesters, have also been applied to aromatic polyamides. Para-linked aromatic polyamides are an important class of LC polymers. In contrast to thermotropic LC polyesters, para-linked aromatic polyamides form lyotropic solutions. Due to the formation of intermolecular hydrogen bridges, these polymers are in most cases unable to melt below their thermal decomposition temperature. Infusibility and limited solubility of unsubstituted para-linked aromatic polyamides are characteristic properties which limit synthesis, characterization, processing, and applications. 

P.Meurisse, C.Noel, L.Monnerie, and B.Fayolle, Polymers with mesogenic elements and flexible spacers in the main chain Aromatic-aliphatic polyesters, Br.Polym.J. 13 55 (1981). 

Other works confirm that the radiation protection is not efficient when aromatic rings are not located into the macromolecular backbone. Babanalbandi and HilP studied immiscible blends of arylpolyesters (bisphenol-A polycarbonate and poly(bisphenol-A-co-phtalate) and poly(3-hydroxybutyrate-co-3-valerate). y-irradiation was performed at 77 K and blends were analyzed by ESR (electron spin resonance). Aromatic polyesters had a greater contribution to the spectrum than the aliphatic one, and this result was explained by the fact that ejected electrons were scavenged more efficiently by the aromatic polymers. Nevertheless, the radiation chemical yields for radical formation in the blends were close to that expected according to the linear additive model. The authors concluded that both polymers are not miscible at the level required for effective radiation protection of poly(3-hydroxybutyrate-co-3-valerate). 

The most frequently apphed technique for the separation of polymers, namely size-exclusion chromatography (SEC), is based on the well-balanced interactions between the column material, the solvent, and the polymer sample. In order to achieve a complete separation according to size, and also to determine reliable polydispersity values, enthalpic interactions between the sample and column material must be excluded, as only entropic interactions lead to SEC separation. This is not always possible in the case of dendritic polymers which, being multifunctional architectures, have interactions with the column material that are effectively predestined. It has been repeatedly observed that this problem is more severe for higher molar mass products. An example of aromatic hb polyesters with different... 

The conformational properties of polymer molecules with mesogenic groups in the main chain were studied in the series of alkylene-aromatic thermotropic polyesters in which the length of flexible methylene parts was varied polydeca-, penta- and tetramethylene-tere-phthaloyl-di-para oxybenzoate (P-IOMTB, P-5MTB, P-4MTB). 

Pam-linked aromatic LC polyesters are semirigid polymers which are typically thermotropic. Although it has only rarely been mentioned in the literature, thermoreversible gelation is a general observation for LC polyesters. An initial study on the thermoreversible gelation has been performed on the polyester shown in Figure 13.6 [48]. 

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