STRUCTURAL-ANALYSIS OF INJECTION-MOLDED SEMICRYSTALLINE POLYMERS BY FOURIER-TRANSFORM INFRARED-SPECTROSCOPY WITH PHOTOACOUSTIC DETECTION AND DIFFERENTIAL SCANNING CALORIMETRY .1. POLY(ETHYLENE-TEREPHTHALATE)

Fourier transform infra-red spectroscopy coupled with photoacoustic de tection (PA FTi.r.) has proved to be a useful tool for finding out abo ut quantitative structural changes in solid materials. Poly(ethylene t erephthalate) (PET) is a well known semicrystalline polymer that shows important changes on annealing. In order to obtain a complete picture of isomer distributions in industrial PET samples, spectroscopic meas urements were correlated with differential scanning calorimetry (d.s.c .). The results obtained indicate that the structural characteristics of the thermally treated samples are related to the fabrication proces s. Two different strata in the plates can be distinguished: a skin lay er and the core. The correlation between the apparent degree of crysta llinity of the surface obtained by d.s.c. and the percentage of trans isomer obtained by PA FTi.r. allows the latter parameter to be separat ed into crystalline and amorphous trans isomer and to follow its evolu tion with the annealing process. Amorphous trans isomer vanishes at th e primary isomerization (approximately 100-degrees-C) while crystallin e trans and gauche conformations show sigmoidal evolution. At higher a nnealing temperatures (> 140-degrees-C) the ordered trans conformation shows an approximately linear increase at the expense of the gauche c onformation. Finally, a direct correlation between the ordered trans i somer and the apparent degree of surface crystallinity can be made.