In a series of publications we reported on melt rheology, morphology, and mechanical properties of the poly(ethylene terephthalate)/poly(amide‐6,6) blends (PET/PA). The non‐oriented samples had poor interphase bonding resulting in low impact and tensile strengths. To improve these properties the ester‐amide interchange reaction was carried out in solution and in melt. In the latter case a Brabender Plastograph was used in the mixing chamber or twin‐screw extruder configurations with p‐toluenesulfonic acid as a catalyst. The interchange reaction was followed by 400 MHz proton and 13C nuclear magnetic resonance spectroscopy.

Fourier transform infrared (FT-IR) studies of poly-(ethylene terephthalate) (PET)/poly/(amide-6,6) (PA) blends are presented. The blends were prepared in the molten state and in solution with trifluoroacetic acid (TFA) as the solvent. The PET/PA blend is a complex system containing two crystallizable polymers with the ability to interact chemically. Some of the blends were prepared in the molten state in the presence of a catalytic amount of p-toluenesulfonic acid (TsOH) to undergo the ester-amide interchange reaction. Nuclear magnetic resonance (NMR) and FT-IR have proven to be excellent techniques with which to study these blends. 'HNMR was used to follow the ester-amide interchange reaction and FT-IR to detect the presence of hydrogen bonding. FT-IR studies showed the lack of hydrogen bonding in all the blends prepared in the molten state and its presence in the blends prepared in solution.

Following the ester‐amide interchange reaction in the poly(ethylene terephthalate)/poly(amide‐6, 6) (PET/PA) system in the presence of p‐toluenesulfonic acid (TsOH), samples were injection molded and tested in the tensile mode. A brittle fracture was observed for these unoriented specimens. To separate the influence of the crystallinity from that of the interphases, the samples were studied using differential scanning calorimetry (DSC). The DSC results indicated an increase of crystallinity in the blends caused by enhanced nucleation of PA (which crystallizes first) and that of the copolymer resulting from the esteramide interchange reaction. It has been independently verified that neat PET samples of comparable crystallinity to that existing in the PET/PA blends show a similar behavior.

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