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 1H nuclear magnetic resonance (NMR) spectroscopies. A small amount (5.0 wt%) of the PA-66 added was found to effectively nucleate both the melt- and 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 (Xc) 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 Xc, 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.