Determination of carboxyl endgroups and comonomers in poly(ethylene terephthalate) with hydrazine

On complete hydrazinolysis of poly(ethylene terephthalate), terephthalomonohydrazide is formed from carboxyl‐end terephthaloyl residues in a quantity equivalent to the content of carboxyl endgroups in the polymer. The compound is separated from the reaction mixture by ion exchange and determined photometrically [epsiv; 240 in 0.1 N HCl = 16,700 (1000 cm 2 /mole)]. A COOH determination carried out in this way is endgroup specific and, unlike titration, is not subject to interference by ionogenic fiber additives. Aromatic comonomers with acidic substituents (e.g., 5‐sulfoisophthalic acid) in chemically modified, cationically dyeable poly(ethylene terephthalate) are determined simultaneously with the carboxyl endgroups by the same analytical method. In this case, the terephthalamonohydrazide and 5‐sulfoisophthalodihydrazide are separated by ion exchange, and the difference in their spectral behavior is used for quantitative determination with the aid of a two‐component analysis:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} c_1 {\rm = (6}{\rm .21 }D_{240} {\rm - 1}{\rm .04 }D_{212} ){\rm } \times {\rm 10}^{{\rm - 5}} {\rm mole/l}{\rm .} \\ c_2 {\rm = (2}{\rm .62 }D_{212} {\rm - 0}{\rm .51 }D_{240} ){\rm } \times {\rm 10}^{{\rm - 5}} {\rm mole/l} \\ \end{array} $$\end{document} where c 1 c 2 = concentration of terephthalomonohydrazide and 5‐sulfoisophthalodihydrazide, respectively; and D 240 D 212 = optical density at 240 and 212 nm, respectively. The content of carboxyl endgroups in polyether esters poly( p ‐(2‐ethyleneoxy)‐benzoate), is determined on the basis of the p ‐(β‐hydroxyethoxy)benzoic acid [epsiv; 258 in 0.1 N HCl = 16,100 (1000 cm 2 /mole)] liberated from carboxyl‐end monomer units by hydrazinolysis. For copolyether esters with p ‐(β‐hydroxyethoxy)benzoic acid as a comonomer, the contents of carboxyl‐end terephthalic acid and p‐(β‐hydroxyethoxy)benzoic acid are determined simultaneously with the acid of a spectrophotometric twocomponent analysis:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} c_1 {\rm = (7}{\rm .65 }D_{240} {\rm - 3}{\rm .27 }D_{258} ){\rm } \times {\rm 10}^{{\rm - 5}} {\rm mole/l}{\rm .} \\ c_2 {\rm = (7}{\rm .91 }D_{258} {\rm - 3}{\rm .49 }D_{240} ){\rm } \times {\rm 10}^{{\rm - 5}} {\rm mole/l.} \\ \end{array} $$\end{document} where c 2 , c 2 = concentration of terephthalomonohydrazide and p‐(β‐hydroxyethoxy)‐benzoic acid, respectively; and D 240 , D 258 = optical density at 240 and 258 nm, respectively.