Determination of Carboxyl End Groups in Polyester, Polyethylene Terephthalate

Abstract

RAPID indicator titration method for the determination of A carboxyl end groups in polyethylene terephthalate has been devised. Previously described methods (1 , 3, f.3, f 4 ) for the titration of polyester acidic end groups or other polymer acidic end groups are inapplicable because of the insolubility a t room temperature of polyethylene terephthalate in any but acidic, phenolic which obscure indicator action. The excellent hot benzyl alcohol titration method for nylon developed by Taylor and Waltz (16) proved inapplicable because of the instability of the polyester in hot basic solutions. It was found, as a result of the present work, that a hot benzyl alcohol solution of polyethylene terephthalate could be poured into chloroform to yield either a cold metastable solution, or a fine suspension which can be satisfactorily titrated with alkali. Nitrobenzene, l-methylnaphthalene, and tetramethylene sulfone, in addition to benzyl alcohol, can act as high temperature solvents for this polymer a t temperatures about 175 to 210' C. Benzyl alcohol was chosen because of its preferred odor, stability with base, and low relative toxicity.