Poly aromatics thermal decomposition

The poly(ester-imides) are produced by the thermal decomposition of the soluble polytamic acids) which are obtained by the condensation of ail aromatic diamine and the bis-fester anhydride) of trimeUitic anhydride as shown in the following equation ... 

Volatile production occurs from polycarbonate by entirely thermal decomposition between 450 and 550°C yielding about 25% solid residue as well. The pyrogram of the most common aromatic polycarbonate, poly(bisphenol A carbonate) is displayed in Figure 12.10. Alkylphenols and phenol are the main constituents of the boiling range 180-250°C and... 

The presence of the double bonds in the polymer backbone and its further thermal decomposition may explain the formation of certain aromatic compounds in poly(acrylic acid) pyrolysate. 

As seen from Table 6.7.18, the thermal decomposition of poly(methacrylic acid) generates at lower temperature the anhydride, and at higher temperatures undergoes decarboxylation. It can be assumed that the process leads to the formation of unsaturated chains that further decompose to form small hydrocarbon molecules and some aromatic compounds. Residual carboxyl groups may be retained on some of these molecules. 

Among the polymers containing aromatic rings and unsaturated hydrocarbon groups in the backbone are poly(phenylene-ethynylenes) (PPE). This type of polymer has been synthesized by alkyne metathesis of 1,4-dipropynylated benzenes [11] and has applications in optical and electronic industry. A comprehensive study on thermal decomposition of several poly(substituted p-phenylene-ethynylenes) is available [12], The general formula for this group of polymers is the following ... 

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. 

Poly(ether sulfones) containing aromatic rings in the backbone have much better thermal stability compared to poly(sulfur dioxide-co-alkenes). For example, PSF degrades very slowly in vacuum above 400° C, and only above 460° a more rapid decomposition begins [4], Other poly(ether sulfones) behave similarly [5]. Several reports on the thermal decomposition for poly(ether sulfones) are available in literature. A summary of such reports are given in Table 12.2.3. 

Numerous studies have been performed on thermal stability and on pyrolysis of aliphatic poly(amides) [1-12], etc.. Similarly to other classes of polymers, there is a considerable difference in the thermal stability of the polymers with aliphatic segments in their backbone and those with aromatic groups. The compounds containing aliphatic segments decompose at lower temperatures, and it is not uncommon that in addition to the cleavage of other bonds, the C- bonds also are split. On the other hand, the aromatic rings are very resistant to thermal decomposition. The thermal decomposition of aliphatic poly(amides) was studied in connection to various practical purposes, such as the resistance of fibers to fire. Some information on thermal decomposition of aliphatic poly(amides) is summarized in Table 13.3.1 [13]. 

The aromatic heterocyclic rodlike polymers poly(p-phenylenebenzobisoxazole) (PBO) and poly(p-phenylene-benzobisthiazole) (PBZT or PBT) [14—20] possess rigid rodlike structures which provide superior tensile properties and excellent thermal stability. Thermal analysis of PBO and PBT reveals minimal weight loss in air at 316 °C. Thermal decomposition of both polymers begins at 600 °C and reaches a maximum between 660 and 700 °C. The total weight loss for both PBO and PBT is about 28% at 1,000 °C [16]. 

Other nitrogen containing polymers which have been subjected to thermal decomposition studies include aromatic polyester imides containing 2,7-bis(4-aminobenzoyloxy) naphthalene groups [16], poly-4-vinylpyridine [17], poljmrethanes [18], polybutyl cyanoacrylate [19], and polypropyl acrylate [20]. 

Degradation of polymers at higher temperatures results in a variety of different products poly(oxy-l,4-phenyleneoxy-l,4-phelylenecarbonyl-l,4-phenylene) or poly ether ether ketone (PEEK) is an aromatic polyketone with low flammability and excellent mechanical properties [19]. Although a wealth of literature is available on the thermal decomposition products of PEEK and relevant kinetic parameters, there have not been many investigations about the mechanistic aspects of PEEK degradation. Patel et al. [20] propose decomposition mechanisms based on prior literature. Table 6.3 summarizes Patel s reports of volatile products identified at different temperatures. 

Some information regarding thermal stability of this type of polymer is available in literature. These polymers typically generate CO2, some maleic anhydride, and fragments related to the olefin. For example, poly(maleic anhydride-co-frans-stilbene) (alternating), when heated from ambient to 500° C, generates CO2, styrene, maleic anhydride small amounts of benzene, cyclohexadiene, dimethylbutene, ethylcyclobutanol, and 4-methoxystyrene. Major decomposition products for this polymer are chain fragments (79%), including aromatic, ketonic and unsaturated structures [5],... 

A number of polyamide copolymers are known to have practical uses. The copolymers include those with different amides such as poly(caprolactam-co-laurolactam), poly(2,2,4-trimethyl-1,6-hexandiamine-co-2,4,4-trimethyl-1,6-hexandiamnie-co-1,4-benzendicarboxylic acid), poly(s-caprolactam-co-hexamethylene diamine-co-terephthalic acid), poly(hexamethylenediamine-co-terephthalic acid-co-isophthalic acid), etc. The addition of longer alkyl chains in an aromatic polymeric amide may improve some mechanical properties, but thermal resilience is in general reduced. For example, poly(hexamethylenediamine-co-m-xylylenediamine-co-isophthalic acid-co-terephthalic acid) starts decomposing at about 310° C, significantly lower than Nomex , for example. The same decrease in the decomposition temperature is seen for other mixed copolymers such as nylon 12 copolymers that include cycloaliphatic and aromatic segments. 

Later, the same methodology was applied by Wallow and Novak for the synthesis of water-soluble poly(p-phenylene) derivatives via the poly-Suzuki reaction of 4,4 -biphenylylene bis(boronic acid) with 4,4 -dibromodiphenic acid in aqueous di-methylformamide [26]. These aromatic, rigid-chain polymers exhibit outstanding thermal stability (decomposition above 500 °C) and play an important role in high-performance engineering materials [27] conducting polymers [28] and nonlinear optical materials [29]. 

---