The degree of crystallinity of monoclinic isotactic poly(propylene)

Abstract

The degree of crystallinity of a set of monoclinic (alpha) isotactic poly(propylenes), prepared by a metallocene‐type catalyst, were determined at room temperature. Three different methods were used: density, enthalpy of fusion, and wide‐angle X‐ray scattering, and the results compared. The relation between the heat of fusion and the specific volume of these poly(propylenes) was found to be nonlinear, thus precluding any linear extrapolation to obtain the heat of fusion of the pure crystal (ΔHu). The value of ΔHu obtained from depression of the melting temperature by diluents is used. Based on the unit cell density of monoclinic crystals formed from a low defected fraction, the density obtained crystallinity levels were found to be between 0.l5–0.25 higher than those calculated from the heat of fusion. This relatively large difference holds for the isothermally crystallized and quenched isotactic poly(propylenes), and reflects the contribution of the interphase to the density determined crystallinity, which does not contribute to the heat of fusion. Paralleling results found in other systems, the crystallinity levels obtained from wide‐angle X‐ray scattering agree with those obtained from density, indicating a significant contribution of the partially ordered phase to the total diffraction. Emphasis is given on the need to account for the large differences in the crystallinities of poly(propylene) measured by different techniques when evaluating the dependence of properties on this quantity. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 323–334, 1999

Competition between α, β, and γ Polymorphs in a β-Nucleated Metallocenic Isotactic Polypropylene

“…The corresponding values are plotted in Figure , compared with the WAXS crystallinities. It can be observed that in all the cases the DSC values are around 0.16 units lower than the WAXS crystallinities, in good agreement with the previous results 10 WAXS-determined and DSC-determined degrees of crystallinity as a function of the cooling rate for the different samples. …”

Interfacial agent effect on rheological response and crystallite characteristics in germicidal polypropylene/titanium dioxide nanocomposites

“…Consequently, the values obtained using WAXS are usually higher than those obtained using DSC. 48 Figure 12 shows the crystallization process for the various samples obtained from the cooling DSC thermograms. Incorporation of TiO 2 clearly has a nucleant effect on the iPP matrix.…”

Thermal analysis and X‐ray scattering study of metallocene isotactic polypropylene prepared by partial melting

“…Previous studies have shown that the α modification is favored by rapid cooling and low crystallization temperatures, whereas γ is favored by higher crystallization temperatures 31–36. This is confirmed in our self‐nucleation experiment.…”

“…Previous studies have shown that the ␣ modification is favored by rapid cooling and low crystallization temperatures, whereas ␥ is favored by higher crystallization temperatures. [31][32][33][34][35][36] This is confirmed in our self-nucleation experiment. At the start of the heating tests, X-ray results show that the standard-state sample contains about the same amount of ␣and ␥-phase crystals.…”