Polyesters early investigations

Thermoset plastics have also been pyrolysed with a view to obtain chemicals for recycling into the petrochemical industry. Pyrolysis of a polyester/styrene copolymer resin composite produced a wax which consisted of 96 wt% of phthalic anhydride and an oil composed of 26 wt% styrene. The phthalic anhydride is used as a modifying agent in polyester resin manufacture and can also be used as a cross-linking agent for epoxy resins. Phthalic anhydride is a characteristic early degradation product of unsaturated thermoset polyesters derived from orf/io-phthalic acid [56, 57]. Kaminsky et al. [9] investigated the pyrolysis of polyester at 768°C in a fiuidized-bed reactor and reported 18.1 wt% conversion to benzene. 

J/n < 6,000). Often, no analytical data or structural characterization was provided. Room-temperature interfacial polycondensation methods were also investigated as a convenient alternative to classical polycondensations. Such methods were first reported for the preparation of polyamides and polyesters from the reaction of l,l -ferrocenyldi-carbonyl chloride with several diamines and diols. The synthesis of polyurethanes using this technique was also reported and involved the condensation of l,T-ferrocenedimethanol and l,T-bis(dihydroxyethyl)ferrocene with diisocyanates. Once again, however, these polymers possessed low molecular weights.The early research in these areas has been summarized and critically reviewed and will not be discussed further here. ... 

A detailed study was devoted to amber forgeries. It was shown by the authors that analytical pyrolysis (Py-GC, PYGC/MS) can provide undeniable proof that materials under investigation are amber forgeries and also quite precisely characterize the nature of these substitutes. Early Bakelites, modem phenolic resins, polystyrene, epoxy resins, and a wide range of unsaturated polyesters were identified as the most often used materials. 

Attempts had been made to synthesise polyesters based on phthalic acid as the diacid component, but these products were amorphous, had low softening points, and were rapidly attacked by organic solvents and acids and bases. Research into polyesters made by the reaction of terephthalic acid (or esters thereof) with aliphatic diols, led to the discovery of polyesters of high commercial value poly(alkylene terephthalate)s [4]. This pairing of diols with terephthalic acid eventually led to the most commercially successful aromatic polyesters, but other synthetic pathways were also investigated towards such products in the early days of polyester development. These included the self-condensation of hydroxy acids of the structure -H0-R-Ph-C02H, where R-OH is para to the acid group and R is -(CH2)- or -(CH2)2- [5], and reactions of aliphatic diacids with 1,4-dihydroxy benzene and similar aromatic diols [6, 7]. Also synthesised about the same time were polyesters based on C2-Cg aliphatic diols and any of the isomeric naphthalene dicarboxylic acids [8]. 

The polymerization of styrene and acrylic acid was observed in 1872 but the polymers of these monomers were not produced commercially until the early part of the twentieth century. Likewise, Gay-Lussac and Pelouze in 1833, Berzelius in 1847, Bemmelen in 1856, Lourenco in 1863 and Watson Smith in 1899 investigated the formation of polyesters but these pol3nners were not commercialized until the early part of the twentieth century. 

Carothers et al. separated and characterized a variety of oligomers by fractional crystallization of aliphatic polyesters of adipic acid. In 1939, the dimeric and trimeric cyclic compounds of e-caprolactam were separated, and linear oligomers from monomer to pentamer (oligomers of nylon-6) were prepared. The linear oligomers were used as model substances for viscosimetric studies. The cyclic urethane oligomers formed from hexamethylene diisocynate with diols were reported in 1941, and systematic investigation on the cyclic and linear oligomers of nylon-6 were performed in the early 1950 s. 

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