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Summary: A novel method for the tailoring of unique three‐phase crystalline systems in isotactic poly(propylene) has been proven. It is based on a synergistic application of a specific β‐nucleating agent and high pressure during crystallization. The formation of a γ phase was supported by elevated pressure and high temperature during crystallization; under these conditions the growth of both β and α phases was significantly suppressed. Nevertheless, during the course of crystallization at lower pressure and/or lower temperatures, strong β‐nucleation efficiency favored the formation of a β phase. magnified image

The relation between PVT and rheological measurements of several polymer melts including polyethylenes, polypropylene, polystyrene, poly(methyl methacrylate), and polycarbonate has been taken into investigation. Pressure-temperature dependent viscosities, determined on rotational and backpressure-modified capillary rheometers, were fitted through the Carreau-Yasuda model. PVT data was analyzed by the help of the Simha-Somcynsky equation of state (SS EOS). The thermodynamical parameters of the SS EOS were connected to constant-stress viscosity (experimental) and zero-shear viscosity (extrapolated). The Doolittle relationship was modified into the form of . The relation was employed and tested for the data evaluation. It proved to be a good tool for linearization of PVT and rheological data.

The interrelation between specific β-nucleation, thermal history, and molecular weight of isotactic polypropylene (PP) has been investigated by wide-angle X-ray scattering, differential scanning calorimetry, and scanning electron microscopy. Samples with a broad range of molecular weight (M w ), from 240 000 to 1 300 000, allowed to examine the effect of PP molecular structure on the nucleation sensitivity. N, N 0 -Dicyclohexylnaphthalene-2,6-dicarboxamide (NU 100) was introduced in the concentrations of 0, 0.01, and 0.03 wt % as a β-specific nucleating agent into neat PP. Specimens were then processed via compression molding at various processing temperatures and times. Samples containing 0.01 wt % of NU 100 showed a dramatic decrease of nucleation activity into β-phase with increasing M w , processing time, and temperature. This effect was ascribed to a partial solubility of nucleator in PP melt and a competition between heterogeneous β-nucleation and self R-nucleation.

Structural transformations of semicrystalline polymers form an important field of current scientific research. The preparation of controlled supermolecular structure may lead to significant improvements in mechanical, thermal and optical properties. As for isotactic polypropylene (iPP), its properties essentially depend on its crystalline phase composition, which is due to polymorphism of iPP. Thus, the aim of this work is to analyze the influence of the β-phase content in polypropylene and of its spatial arrangement on mechanical properties, in particular on its impact strength. Commercially available isotactic polypropylene (iPP) was modified by various amounts of a specific β-nucleating agent (N, N'-dicyclohexylnaphtalene-2,6-dicarboxamide). From the prepared mixtures standard impact testing bars were injection molded. The structure of the specimens was studied by X-ray diffractometry, and impact properties were determined using Charpy impact tester. It was found that addition of the nucleator led to β-phase content increase, especially in the core region of the injection molded samples. The skin (surface layer of the samples) contained lower amount of β-phase. Furthermore, notch impact strength dramatically increased with increasing concentrations of the β-nucleating agent. The concentration of 0.03 wt.% of the nucleator can be considered a “boundary value” due to the fact that the maximum notch impact strength value was reached. With further addition of the nucleating agent the impact strength slowly decreased. Therefore it should be noted that the improvement of impact properties is not only due to the presence of β-phase, but also there are some synergy-applied factors – such as the structural heterogeneity and spatial arrangement of the β-phase in injection molded samples.