Polyesters structure-aromatic type

Unusual properties of fully aromatic polyesters are observed if they have at least partially a rigid planar chain structure. In particular, they can form thermotropic liquid crystalline states (see Example 4-5). As already discussed in Sect. 1.2.4 an important structural prerequisit for LCPs of Type A in order to attain the liquid crystalline state of aromatic polyesters (and aromatic polyamides, see Example 4-14), is a rigid main chain according to the following construction principle ... 

Over the past decade, literally dozens of new AB2-type monomers have been reported leading to an enormously diverse array of hyperbranched structures. Some general types include poly(phenylenes) obtained by Suzuki-coupling [54, 55], poly(phenylacetylenes prepared by Heck-reaction [58], polycarbosilanes, polycarbosiloxanes [59], and polysiloxysilanes by hydrosilylation [60], poly(ether ketones) by nucleophilic aromatic substitution [61] and polyesters [62] or polyethers by polycondensations [63] or by ring opening [64]. 

Solid-state 13C NMR was employed to characterize intact samples of cutin and suberin biopolyesters. Although a considerable degree of structural heterogeneity was observed for both materials, it was possible nonetheless to resolve and assign many NMR peaks, even when the polyesters were accompanied by waxes or cell walls. Quantitative estimates for the various aliphatic, aromatic, and carbonyl carbon types indicated that cutin was primarily aliphatic in composition, whereas suberin had more aromatic and olefinic moieties. Additional analysis should be facilitated by the biosynthetic incorporation of selectively 13C-enriched precursors (26,27). 

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 reaction of trimellitic anhydride (7) with ethanolamine (9) giving the hydroxy acid (10) and with 4,4 -diaminodiphenylmethane (8) giving the diacid (11) has been published in the first poly(ester-imide) patent [l].The second one is nowadays the predominant reaction for making poly(ester-imide)s. Trimellitic anhydride is the basic dianhydride for introducing the imide structure into the polyesters. Nearly every example in patents is based on trimellitic anhydride alone or mixtures with other anhydrides, e.g., tetrahydrophthalic anhydride [59]. The imides made from aromatic anhydrides are thermally more stable than the ones resulting from aliphatic structures (Fig. 4). Both types have been protected by patents, and products made from them are on the market. 

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. 

In selecting a solvent for a certain binder, one of the oldest rules still holds alike dissolves alike . Thus a solvent with a similar basic structure as the solute and a volatility adapted to the application technique was chosen as the first approach. For instance, for a long oil alkyd a low aromatic hydrocarbon solvent and for a short oil alkyd, containing relatively more aromatic entities, a high aromatic spirit or a pure aromatic solvent were suitable starting points. For polyesters, ester type solvents came under consideration. Brush... 

Eisai [89] and Ciba-Geigy [90] claim thermal stabilisers for aromatic polyesters of the dioxasilepin and dioxasilocin type. These are similar in structure to the Ciba-Geigy biphenyl phosphites, with silicon replacing phosphorus. 

Another newer version of HALS is exemplified by hydroxy-substituted N-alkoxy hindered amines, i.e., molecules with at least one active moiety of the structure >N-OR-(OH). A very wide range of such additives has been covered in a family of patents assigned to Ciba Speciality Chemicals [193-198], and claims for applications include aromatic polyesters. These additives are said to have as good as or better UV stabilising ability and antioxidant properties as the earlier HALS. The hydroxyl group(s) is said to impart additional advantages not possible with the NOR types, e.g., antistatic attributes, and better pigment dispersion in polar polymers. 

The Structure of the Fibertect fabric allows different types of fibers such as polyester, raw cotton, bleached cotton, among others, to be used for different applications such as industrial cleaning and oil absorption. Raw cotton-based Fibertect wipes can be used to absorb oil and adsorb volatile vapors that emanate from polycyclic aromatic hydrocarbotts. ... 

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