Chemical heterogeneity of poly(ethylene terephthalate) as revealed by temperature rising elution fractionation and its influence on polymer thermal behavior: A comparison with poly(ethylene terephthalate-co-isophthalate)

The chemical heterogeneity of poly(ethylene terephthalate) (PET) and of pol y(ethylene terephthalate-co-isophthalate) (PETI) was investigated using tem perature rising elution fractionation (TREF). NMR and SEC results of the TR EE fractions of the two polymers are compared. Both polymers show the same trend upon fractionation, confirming that diethylene glycol units (DEC;) ca n be considered as a statistical comonomer in PET which influences the crys tallizability of PET. PET and PETI were finally analyzed by the stepwise is othermal segregation technique (SIST). The occurrence of multiple melting p eaks for both polymers, when crystallized isothermally by step from the mel t, is related to the statistical inclusion of the comonomers in the chains.