End-Group Analysis and Chain Termination
topic
PET chains terminate with hydroxyl (-OH) and carboxyl (-COOH) end groups. COOH end groups are measured by titration (typically 15–35 meq/kg) and catalyse hydrolytic degradation. Monofunctional end-cappers (acetic acid, benzoic acid) control molecular weight ceiling. End-group ratio (COOH/OH) affects thermal stability, hydrolysis resistance, and adhesion to inorganic substrates.
Role
End-group control is critical for PET stability in humid environments (hydrolytic degradation of COOH-terminated chains), for RFL adhesion in tyre cord, and for understanding dyeing kinetics (COOH groups retard disperse dye diffusion).