Effect of ionization of polyamide-66 on its heterogeneous nucleation of poly (ethylene terephthalate) crystallization: An efficient polyamide-66 ionene nucleator promoted by ion-dipole interactions

A polyamide (PA)-66 ionene successfully was prepared by <= 5.0 mol% of ionization of the amide groups of a PA-66 into ammonium cations via facile, room-temperature solution reaction of the PA-66 with a dilute aqueous HCl, which was confirmed by Fourier transform infrared (FTIR) and I H-1 nuclear magnetic resonance (NMR) spectroscopies. A small amount (5.0 wt%) of the PA-66 added was found to effectively nucleate both the meltand solution crystallizations of a poly(ethylene terephthalate) (PET) heterogeneously, as reflected from differential scanning calorimetry (DSC) melt crystallization temperature and -enthalpy increases, a wide-angle X-ray scattering (WAXS) degree of crystallinity (X-c) rise, polarized optical microscopy (POM) schlieren-texture densification and refinement, Mo's method nonisothermal crystallization kinetic a increase and -F(T) decrease of the PET matrix. Compared with the PET/PA-66 (5.0 wt%) system, the same content of the PA-66 ionene incorporated further displayed significantly higher or, say, maximized heterogeneous nucleation efficiency for the PET melt- and solution crystallizations, as verified by similar DSC, WAXS, POM, and Mo's approach observations, to again remarkably expedite the crystallization, enhance the X-c, and refine the crystal size of the PET matrix. Such extraordinarily high efficiency of the PA-66 ionene nucleator arose typically from, at the interphase, the ion-dipole interactions (IDIs) formed between the amide-carbonyl affected ammonium-chloride ion pairs of the PA-66 ionene and the ester groups of the PET, which considerably were stronger in both covalent and ionic components than the hydrogen bonds present between the PA-66 amide groups and the PET ester groups. The IDIs constituted greatly enhanced interfacial adhesion of the PET/PA-66 ionene (5.0 wt%) to presumably improve its interfacial compatibility, hence refine the size and increase the number density of the PA-66 ionene crystal particles, all of which contributed collectively to the efficiency maximization of the PA-66 ionene heterogeneous nucleator for the PET crystallization. It seems that nucleator ionization offers an effective approach to the enhancement of heterogeneous crystalline nucleation of a polymer by another semicrystalline polymer nucleator.