Polyesters also polymers

LC polyesters belong to the class of thermotropic main-chain LCPs, which also comprises polymers such as polycarbonates, polyethers, polyphenylenes, polyester-imides, polymers containing azo- or azo V-oxide linking groups, some cellulose derivatives, and polypeptides such as po 1 y (y - be n zy 1 -1. - g 1 u tamate). Both from the academic and industrial points of view, polyesters are by far the most important representatives of this class of polymers. 

Polyesters also are used in various polymer blends such as polycarbonate/poly(butylene terephthalate), poly(butylene terephthalate/acrylonitrile-styrene-acrylic) blends, poly(vinyl chloride)/poly(ethylene terephthalate), etc. Pyrolysis results on poly(vinyl chloride)/ poly(ethylene terephthalate) have been reported [64] showing that the two components influence each other, chloroesters of terephthaiic and benzoic acids being found in the pyrolysate. 

Special types of purpose-built polymers can also be made with the intention of enabling more rapid direct microbiological attack and decomposition of these materials. Classes of both condensation and addition polymers among the polyesters, vinylic polymers, and polyhydroxyalkanoates typify current candidate materials being tested in these applications (e.g., Eq. 23.9), but as yet high costs have discouraged large scale exploitation. 

Most plants contain a mixture of the 16- and 18-carbon family of cutln monomers. Even though there appears to be a degree of species specificity In the cutln composition, whether the polymer structure can vary sufficiently to affect major functional properties of the polymer is not known. The polyester also contains covalently attached minor components such as phenolic acids and flavanolds (9,10) which. If released by the attacking pathogen, can play important roles in the Interaction between the pathogens and the host. However, such areas have not been explored adequately to draw firm conclusions. 

Polyesters. Main chain of their macromolecules is characterized by repeated — CO—O— groups. Unsaturated polyester resins are thermosets used mainly for manufacturing glass fibre-reinforced plastics products. The most wide-spread type of thermoplastic polyesters are polymers of an aromatic dicarboxylic acid (mainly terephthalic acid) and an aliphatic diol (e. g. ethyleneglycol or butanediol). The most important representatives of this group are poly(ethylene terephthalate) and poly-(butylene terephthalate). Polyarylate aromatic polyester is a high-temperature thermoplastic of an aromatic dicarboxylic acid (terephthalic acid) and an aromatic diol (bisphenol-A). In the chemical sense, polycarbonate is also a polyester. 

Binders in coatings include polyvinyl acetate and copolymers, polyvinyl butyral, polyesters, acrylic polymers, epoxies and polyurethanes (see Ethylene-vinyl acetate copolymers. Acrylic adhesives, Epoxide adhesives and Polyurethane), polyvinyl chloride, polyvinylidene fluoride and aUcyds (oxygen-convertible media containing polyol esters of long-chain unsaturated acids). All these potential film-formers can adhere through dispersion forces, (which are probably weak). Many binders, however, also contain... 

In some of our recent papers we also made evidence that polyetheric PUs phase separate to a much greater extent than the corresponding polyester-based polymers [135]. This is consistent with previous smdies, that showed polyether macrodiols to give greater phase separation than polyester macrodiols [4, 14]. The reason is believed to be the availability of a >C=0 group on each monomer in a polyester for... 

Transesterification between hydroxyl-esters, carboxy-esters, or two ester groups is one of the most important polyesterification technique used for preparing various aliphatic, aliphatic-aromatic or aromatic polyesters (also known as arylates). Titanium alkoxides are very efficient catalysts for transesterification polymerizations, however in some cases it can cause undesirable discoloration to the resulting polymer [15]. A representative example is the synthesis of a polyester based on dimethyl terephthalate using titanium isopropoxide [16] (Fig. 2.3). 

Polyesters also have a major disadvantage. Most of them degrade by a bulk degradation mechanism," " which leads to the accumulation of acidic prodncts within the polymer bulk that can cause late non-infectious inflammatory responses when released in a sudden burst upon stractuie breakdown." An inflanunatory response to poly(cr-hydroxy acids) was also found to be triggered by the release of small particles during degradation... 

These same considerations apply to other important polymer groups that must be dissolved at elevated temperature. They include polyacetals, polyvinylidene fluoride, polyetherketone (PEK), polyetheretherketone (PEEK), polyether sulfone, polyimide, and imide copolymers. Traditionally polyamides and polyesters also were analyzed at elevated temperature, but HFIP will dissolve them at room temperature (Fig. 17). 

Figure 2 (4,5) summarizes some key points on what was the first reported and wel 1-characterized thermotropic polymer. The Eastman workers melt copolymerized p-acetoxybenzoic acid with poly(ethylene terephthalate) (PET) to form a series of thermotropic aliphatic-aromatic polyesters (X7G polymers). Some of these compositions showed the characteristic melt optical anisotropy typical of nematic small molecules, that is, the melt between crossed polaroids on a hot stage microscope transmits light. This nematic order was persistent. Of course, shear birefringence is also shown by isotropic polymer melts but light transmission decay is quite rapid. 

Polyester also refers to the various polymers in which the backbones are formed by the "esterification condensation of polyfunctional alcohols and acids". Polyester can also be classified as saturated and unsaturated polyesters. Saturated polyesters refer to the family of polyesters in which the polyester backbones are saturated. They are thus not as reactive as unsaturated polyesters. The linear, high molecular weight polymer works as a thermoplastic, such as polyethylene terephthalate (Dacron and Mylar). The common reactants for making saturated polyesters are a glycol and an acid or anhydride. 

As the name indicates, saturated polyesters are polymers with ester linkages in their backbone. They are the condensation products of polyols and polybasic acids. The early development of saturated polyesters traces back to preparation of glyptal resins, formed from glycerol and phthalic anhydride, which are also the foundation for development of alkyd resins, as mentioned earlier. Though in a strictly chemical sense, the term polyester can also be applied to alkyd resins, the essential difference is the presence of oil or fatty... 

The second generation of polymers was introduced during 1950—65 and includes a number of engineering plastics such as high-density polyethylene, isotactic polypropylene, polycarbonates, polyurethanes, epoxy resins, polysulphones and aromatic polyesters, also used for films and fibres. New rubber materials, acrylic fibres made of polyacrylonitrile and latex paint were also introduced. 

DuPont has patented aliphatic/aromatic copolyesters that contain sulfo groups [56-59]. Polyesters that are copolymerised with 5-sulfoisophthalic acid hydrolyse readily. The polyesters are reported to be biodegradable and can be processed at higher temperatures than other biodegradable polymers. These polyesters also offer the cost advantages mentioned earlier for aliphatic/aromatic copolyesters. 

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