Sequential reordering in condensation copolymers, 6a average block lengths in Poly(ethylene terephthalate) - Polyamide 6 copolymers as revealed by NMR spectroscopy

Abstract

An equimolar physical blend comprising poly(ethylene terephthalate) (PET), polyamide 6 (PA6) and catalytic amounts of p-toluene sulfonic acid (pTSA) was studied by differential scanning calorimetry (DSC) and 13C NMR spectroscopy before and after reactive blending for various times at 2808C that enables interchange reactions. With the extension of the reaction time, DSC traces showed an abrupt decrease in ability to crystallize, and after two hours of blending the system did not reveal any crystallization or melting behavior. By means of 13C NMR spectroscopy, a clear distinction was made between the PET/PA6 physical blend and the copolymers with different degrees of interchange reactions. The 13C NMR sequence length determination in various PET–PA6 based copolyesteramides showed PET block lengths of 4–10 repeat units which was in good agreement with the crystallizability of these systems. A combination of selective degradation of the PET blocks and 1H NMR allowed, for the first time, the characterization of both PET and PA6 sequence lengths. This method was shown to be more sensitive, as compared to 13C NMR spectroscopy without selective degradation, for sequence analysis in copolymers with close to random distributions of PET and PA6 sequence lengths.