The crystallization of nylon-6 from the melt was monitored in situ by X-ray diffraction. The nylon-6 was found to crystallize into a high-temperature R′-phase as indicated by the two-peak nature of the diffractogram. On cooling from the crystallization temperature to room temperature, nylon-6 retained the two-peak nature. However, data analysis indicates a change from high-temperature (HT) R′-phase to low-temperature R-phase at ∼180 °C. On heating, the R-phase transformed into the R′-phase at about 190 °C and melted in the R′-phase. The transition took place over a temperature range where both phases coexisted. However, samples crystallized from the melt at temperatures 140 and 180 °C showed the R-phase at room temperature, but on heating the R-phase first transformed into a pseudohexagonal phase and before melting the pseudohexagonal phase further transformed into the R′-phase. The R-phase was transformed into the γ-phase, by potassium iodide-iodine treatment, and the behavior of the γ-phase with temperature had been studied for the first time. The γ-phase was very stable and did not show any crystalline transition below the melting point.

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The empty δ (δ e ) form of uniaxially oriented syndiotactic polystyrene (sPS) was obtained by extracting the solvent molecules from the δ form of the sPS-solvent complex in acetone and methanol. The X-ray fiber diagrams of the δ e form of different solvents like chloroform, toluene, and benzene were found to be appreciably different from each other, probably reflecting the difference in the cavity size after solvent evaporation. Temperature dependence of the X-ray fiber diagram has been measured successfully starting from the uniaxially oriented δ e form at various temperatures for the first time. It has been found that the δ e form transforms to the intermediate form transiently before transforming into the γ form. Temperature-dependent polarized FTIR spectra were measured also for the uniaxially oriented δ e sample derived from the sPS and chloroform complex. The infrared band intensity characteristic of the T 2 G 2 conformation was found to change drastically in the course of transition from the δ e to the intermediate phase and to the γ phase. On the basis of the X-ray diffraction profile and infrared spectra, the intermediate form is speculated to take the structure of disordered chain packing probably due to the empty cavities present in the original δ e form. Thermal data showing an endotherm followed by an exotherm during the transition can be interpreted reasonably using such order-to-disorder-to-order transitions among the δ e , intermediate, and γ forms.

Highly dispersed isotactic polypropylene (iPP) nanocomposites were prepared by incorporating two different sized Mg-Al LDH nanoparticles with different loadings from 1 to 10 wt % using a modified solvent mixing method. Larger sized LDH nanoparticles (∼3-4 μm) were prepared from the gel form of Mg-Al LDH, and the smaller sized nanoparticles (∼50-200 nm) were prepared by sonication of as-synthesized LDH particles. Such obtained LDH nanoparticles were carefully characterized using wide-angle X-ray diffraction (WAXD), transmission electron microscopy, and scanning electron microscopy. WAXD and atomic force microscopy results indicate that the LDH nanoparticles were highly dispersed in the iPP matrix. The influence of LDH nanoparticles size and concentration on the thermal stability, spherulitic morphology, melting behavior, isothermal crystallization kinetics, and lamellar structure of iPP were investigated. Incorporation of low loadings of sonicated LDH particles (e.g., 1-2.5 wt %) show substantial effect on thermal stability, spherulite size, crystallinity, and crystallization half-time and lamellar morphology of iPP compared to the pure iPP and that of nanocomposites with larger LDH particles with same loadings. The better nucleation ability of iPP in the presence of sonicated LDH can be attributed to the high surface area of LDH nanoparticles along with its better dispersibility within the polymer matrix. The incorporation of LDH nanoparticles does not change the crystallization growth mechanism and crystal structure of iPP.