A noncrystallizable semiaromatic polyamide copolymer(NSAP) was dissolved in molten caprolactam, and PA6/NSAP blends were produced in-situ via the anionic ring-opening polymerization of caprolactam. The presence of a single loss tangent(tanδ) peak measured by means of dynamic mechanical analysis(DMA) proves the miscibility between PA6 and NSAP in the blends. It was found that there existed drastic changes in the crystallographic form and crystallization kinetics for the in-situ blends, e.g., when 20% NSAP was added, nearly all crystallites existed in the γ form and the crystallization could hardly occur upon cooling even at a rate of 2.5 ℃/min. Moreover, cold crystallization appears during the subsequent heating, and its melting point is 40 ℃ lower than that of the virgin system. On the other hand, the size of the spherulites only decreases modestly. It is suggested that the introduction of irregular stiff segments originated from NSAP into PA6 macromolecule chain, which resulted from transamidation during the polymerization play a dominant role in the drastic change of crystallization kinetics and the resultant morphology of the in-situ blends.
The effects of ethylene vinyl acetate copolymer(EVA) as a compatibilizer on the dispersion of organically modified montmorillonite(org-MMT) into low-density polyethylene(LDPE) during melt extrusion compounding were studied. The X-ray diffraction patterns reveal that as compared with LDPE, EVA can intercalate more easily into the interlay gallery of org-MMT when the composites contain a low org-MMT content. Exfoliated LDPE/org-MMT nanocomposites in the presence of an EVA compatibilizer could be prepared by using a two-step melt compounding technique with a twin-screw extruder.
20 wt% polyamide 12(PA1212)pellets were dissolved in molten caprolactam.The caprolactam was then catalyzed at 180℃and polymerized by means of anionic ring-opening polymerization to produce in situ blends of the resultant polyamide 6(PA6)and PA1212.Mechanical blends with same ingredient were prepared through melt blending on a twin-screw extruder.Scanning electron microscopy(SEM)observation revealed that contrary to the mechanical blends with small spherulites embedded in the matrix,no phase-separation existed in the in situ blends.The results of thermal analysis by differential scanning calorimetry(DSC)showed that single melting peak and crystallization peak existed for the in situ blends,while two melting and crystallization peaks appeared for the mechanical blends.The in situ blend film and the mixed blend film,both cast from a dilute formic acid solution with a concentration of 0.5 g/L,remained similar crystallization and melting behavior as above.It is proved by solution ^(13)C-NMR analysis that transamidation took place during the in situ blending,and it is suggested that the combination of temperature increasing and the basic surrounding derived from NaOH during polymerization resulted in the occurrence of transamidation.Furthermore,it is proposed that the interchange reaction between PA1212 and PA6 also resulted from the degradative reaction during the anionic polymerization.
