Carboxylic endgroups

Due to the high reaction temperatures required during the last stages of these syntheses, side reactions cannot be avoided. Acetaldehyde, carboxyl endgroups, and vinyl endgroups are formed during PET and PEN synthesis. The formation of 2,2/-oxydiethylene moieties in polymer chains by etherification of hydroxyl endgroups is also a well-known side reaction of EG polyester syntheses.264 These reactions should be carefully controlled since they can exert an important influence on polymer properties such as Ts, mechanical properties, hydrolytic stability, and discoloration. 

Similarly, triphenylphosphine dichloride (TPPCI2) can activate aromatic carboxylic acids in pyridine through the formation of acyloxyphosphonium salts (Scheme 2.30).313 A side reaction between tire intermediate acyloxyphosphonium species and a second carboxyl endgroup leading to the formation of anhydrides has been reported.313 This chain-limiting reaction decreases tire molar mass, while the presence of anhydride linkages in tire chains adversely affects the thermal and hydrolytic stability of the final polyester. 

Carboxy-hydroxy reactions, 63 Carboxyl endgroup chemical titration, 94 Carboxylic acid-aryl acetate interchange reactions, 62, 63... 

Polymers having one or two carboxyl endgroups are prepared by anionic polymerisation and subsequent chain termination with C02+ and further reaction with mineral acids. 

W 4 Ward, I. M. Measurement of hydroxyl and carboxyl endgroups in polyethylene terephthalate. Trans. Faraday Soc. 53, 1406 (1957). 

Neale endeavoured to explain the swelling of cellulose in sodium hydroxide solutions (which shows a marked maximum at a concentration of about 2 mole/liter) on the basis of the Donnan theory, thereby considering cellulose as a weak acid capable of splitting off hydrogen ions. Though the results were consistent with the experimental data, the behaviour of this system seems to require another explanation, since Hess and coworkers have shown that the results of experiments on the distribution of added neutral salts lead to the conclusion that the theory does not hold. Moreover, the assumption that cellulose acts as a weak acid seems not to be sufficiently justified. It is true that carboxylic endgroups frequently occur in cellulose, but these cannot be held responsible for the acid character postulated by Neale, since they have a much larger dissociation constant than the one required by Neale s theory. 

Palit S R and Ghosh P, Quantitative determination of carboxyl endgroups in vinyl polymers by the dye-interaction method, a theoretical investigation of molecular core binding and relaxation , J. Polym. Sci., 1962, 58, 1225. 

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