DETERMINATION OF THE END-GROUP CONCENTRATION AND MOLECULAR-WEIGHT OF POLY(ETHYLENE NAPHTHALENE-2,6-DICARBOXYLATE) USING INFRARED-SPECTROSCOPY

Infra-red (i.r.) end-group analysis is used to determine the hydroxyl and carboxyl end-group concentrations and therefore the number-average molecular weight of poly(ethylene naphthalene-2,6-dicarboxylate)(PEN) film samples in the solid state. The end-group i.r. spectrum of a sam ple is obtained by subtracting the i.r. spectrum of a deuterated contr ol sample from the experimental sample i.r. spectrum. We have used int egral absorbances obtained from fitted absorption bands in the i.r. sp ectra of PEN for the calculation of end-group concentrations. Using th is method, the limitations of chemical methods of determination of end -group concentrations caused by the poor solubility of PEN are avoided . In addition, corrections can readily be made to allow for difference in crystallinity between the control and the experimental samples. Th e extinction coefficients for the OH stretching vibration in the hydro xyl and for the carboxyl end-groups have been determined for PEN as we ll as for poly(ethylene terephthalate). Both the hydroxyl and the carb oxyl end-group concentrations, and the number-average molecular weight of the samples, can then be easily determined from the i.r. absorbanc es.