Aromatic polyesters thermal resistance

In die presence of oxygen, more complex thermo-oxidative processes occur in polyesters containing aliphatic moieties. They result in crosslinked products and in the formation of compounds such as aldehydes, carboxylic acids and vinyl esters, as reported in the case of PET.93,94 On the other hand, the presence of oxygen has little effect on the thermal resistance of wholly aromatic polyesters below 550°C. Above this temperature a char combustion process takes place.85... 

Aromatic polyesters formed from 4,4 -isopropylidenebis(2,6-dibromophenol), from various analogous bisphenols differing in the character of the bridge [94] or from 2,2 -bis[3,5-dibromo-4-(2-hydroxyethoxy)phenyl]propane and terephthalic or isophthalic acids possess [194] good thermal resistance and flame retardance. 

A number of studies were done to assess thermal stability of aromatic polyesters. Some of these studies describe flash pyrolysis [27-32]. Some studies are dedicated to slow thermal degradation in an inert atmosphere, and others describe the decomposition in specific conditions such as in the presence of humidity or in the presence of catalysts [33]. For example, thermal decomposition of poly(butylene terephthalate) was significantly influenced by the presence of water vapor, and the amount of the residues decrease with increasing the partial pressure of water in the atmosphere [34]. In another study, thermal stability of some small molecule phthalate esters was studied [35]. The results can be used for inferring information on the thermal stability of related polymers. The influence of substitution on the p-carbon atom was evaluated on compounds such as bis(2-aminobutyl) phthalate, bis(2-nitrobutyl) phthalate, bis(2,4-diphenylbutyl) phthalate, and dineopentyl phthalate. Only the phenyl groups were found to improve the heat resistance by the obstruction of the planar configuration necessary for the c/s-elimination and the hindrance of the formation of a six-membered cyclic transition state. 

Work on improving the thermal resistance and particularly the resistance to carbonization (short circuiting of layers of enameled wires under the influence of temperature) via special glycols led to diphenols [29,30]. Diphenols are not reactive under the conditions of a normal poly(ester-imide) synthesis. In synthesis the lower aliphatic diesters of diphenols were used [29-32]. The use of acid chlorides in the polyester reaction with aromatic OH-groups was also protected by patents [33-35] but it seems unlikely that this reaction was performed on the production scale. 

Due to the low cost, the excellent physico-mechanical properties of the resulting urethane - isocyanuric foams, thermal and fire resistance and low level of smoke generation, the most important applications of aromatic polyester polyols are for rigid PU/PIR foams in the boardstock market (continuous rigid foam lamination) and for building insulation. 

Liquid crystal polymers (LCP) are highly ordered crystalline aromatic polyesters with high mechanical strength. They are exceptionally inert, having very high thermal and chemical stability, are highly resistant to UV radiation and are inherently flame retardant and antistatic. 

The need for moldable grades of polyester prompted a major research effort in the area of copolymers (the chemistry of the materials described here was developed by Dr. Steve Gottis). To retain the excellent thermal resistance of the p-oxybenzoyl homopolymer (continuous use ten era-ture of 550-600°F, short exposure temperatures of 750-800°F), only completely aromatic systems were investigated. Para- -hydroxybenzoic acid was formulated with several co-monomers. These included the meta and para diaclds (isophthalic and terephthalic acid), and various dlhydroxy aromatic compounds, such as hydroqulnone and resorcinol. 

The -hydroxybenzoic ( -oxybenzoic) acid has been extensively used at polymeric synthesis for the improvement of thermal stability of polymers for the last years [18, 19]. The aromatic polyester ECONOL, homopolymer of poly -oxybenzoic acid, possesses the highest thermal resistant among the all homopolymeric polyethers [20] and attracts attention for the industry. 

Further incorporation of metal ions and aromatic structure in the main chain of these polyester enhances the thermal stability as well as resistance towards solvents. Owing to these properties, these metal-containing polyesters may be used for hard surface coatings where thermal resistance is required. 

Because thermotropic wholly aromatic LC polyesters have characteristics such as high strength, low melt viscosity, low shrinkage, ease of processibility, excellent thermal resistance, low water, and gas absorption. They have wide applications in following areas fibers, rods, sheets, composites used in mechanical and chemical industries chip carriers, connectors, switches used in electronics connectors, couplers, buffers used in fiber optics interior components, brackets in aerospace and so on. 

A methyl or chloro substituent attached to a hydroquinone moiety in a liquid crystalline aromatic polyester decreases the thermal-oxidative stability of the polyester, but the substituent does permit greater chemical resistance of a shaped object to be obtained by heat treatment in air at 300°C. The stability of substituted hydroquinone polyesters in air at 150 C decreases with various substituents in the order of phenyl, tert-butyl, chloro, methyl. 

Polycarbonates are polyesters of carbonic acid formed by reaction of diols (aromatic, aliphatic or a mixture of both) with a derivative of carbonic acid. The first preparations of polycarbonates were reported by Einhorn in 1898 [155], by reaction of phosgene with resorcinol or hydroquinone in a pyridine solution. Bischoff and van Hedenstrom in 1902 [156] obtained the same aromatic polycarbonates via transesterification with diphenyl carbonate (DPC). Thus the main routes to polycarbonates were established early, but the properties of the products seemed uninteresting. Around 1930 aliphatic polycarbonates were studied by Carothers and van Natta [157]. These carbonates have low melting points and thermal resistance and are not commercially interesting as stand-alone thermoplastics. Low molecular... 

These copolyesters combine the biodegradability of aliphatic polyesters with the excellent properties imparted by aromatic polyesters. While aliphatic polyesters are easily biodegradable, they lack thermal stability and mechanical properties needed for many applications. Aromatic polyesters, on the other hand, provide excellent use properties but are resistant to mierobial attack under environmental conditions.Both BASF and Eastman Chemicals produce aliphatic-aromatic copolyesters from terephthaUc acid, adipic acid, and 1,4 butane diol. Witt et al. reported on a new group of copolyesters, which combine both biodegradability and excellent properties." These copolyesters are synthesized by conventional bulk condensation techniques from various ahphatic diols with a defined mixture of different aliphatic dicarboxyhc acids and terephthaUc acid. The key to biodegradability is the blocklength of the aromatic unit, which should preferably be no more than a trimer. 

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). 

The sensitivity to hydrolysis is a key issue in many applications. The ester bond in 4GT-PTMO copolymers is sensitive to hydrolysis however, it is fairly protected since most of the ester is contained in a crystalline structure. The addition of a small amount (1-2%) of a hindered aromatic polycarbodiimide substantially increases the lifetime of this material in the presence of hot water or steam (Brown et al., 1974). Polyurethanes are susceptible to hydrolytic attack, especially those with polyester soft segments. However, polyester soft segment polyurethanes are generally more resistant to oils, organic solvents, and thermal degradation. lonomers will swell when exposed to water in fact, a commercial hydrated perfluorosulfonic ionomer (Nation) is used as a membrane separator in chlor-alkali cells. Styrene-diene copolymers and polyolefin TPEs are insensitive to water. 

Standard bisphenol-A fumarate resins are derived from the propylene glycol or oxide diether of bisphenol-A and fumaric acid. The aromatic structure provided by the bisphenol-A provides several benefits. Thermal stability is improved, and the heat distortion point of the resin is mainly raised from the more rigid nature of the aromatic structure. The number of interior chain ester groups is reduced so the resistance to hydrolysis and saponification is increased. Bisphenol A fumarate polyesters have the best hydrolysis resistance of any commercial unsaturated polyester. 

Chem. Descrip. Etherified acrylated melamine/formaldehyde resin (62-68%) in tripropylene glycol diacrylate Uses Crosslinking agent in radiation-cure applies, such as polyester and epoxy acrylates, unsat. polyesters, aliphatic and aromatic urethane acrylates, and most acrylate monomer diluents imparts hardness and gloss, stain and chem. resist, to coatings, paper coatings Features Cured by free radical polymerization initiated by U V or thermal processing... 

It is well known that conventional polyester-based urethane elastomers extended with butanediol can withstand continuous use temperatures of about 80 °C. At higher temperatures, a reduction in the physical and mechanical properties is seen due to degradation of the material. The thermal stability of the polyurethanes is related to the nature of the starting materials such as the aromatic diisocyanate and diol chain extender. The hard segment of the urethane elastomer is primarily responsible for temperature resistance, and the soft segment determines the material s performance at low temperature. 

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