Crystallization of Isotactic Polypropylene from Prequenched Mesomorphic Phase

Abstract

The crystallization process of isotactic polypropylene (iPP) by heating from the prequenched mesomorphic phase has been studied using wide-angle X-ray diffraction, small-angle X-ray scattering, and optical microscopy. Mesomorphic iPP as quenched shows the well-known nodular structure of ca. 100 Å. In heating process the nodules grew larger keeping self-similarity, with the mesomorphic phase partially transforming into the crystalline phase inside the nodules. After reaching the isothermal process, the nodules stopped to grow at a certain quasi-equilibrium size depending on the annealing temperature. During the long annealing, the interface among the nodules became obscure, and the nodules in nanometer scale merge into larger structure of pure R-phase in micrometer scale. The relation between the quasi-equilibrium nodule size and the annealing temperature leads an extrapolated melting temperature of the mesomorphic phase, which is located above the equilibrium melting temperature of the R-crystal.

Crystallization of isotactic polypropylene from mesomorphic phase: a constant heating rate study

“…In order to discuss the crystallization behaviour quantitatively, component analysis for WAXD profiles was carried out assuming each profile consists of three components such as alpha-crystal, mesomorphic, and amorphous, according to the previously reported method [1]. Dividing the integrated intensity of each component by the integrated intensity of observed (total) intensity for each profile, fractions of alpha-crystal Φ cryst , mesomorphic Φ meso and amorphous Φ amorph as a function of temperature during heating process were obtained, as shown in figure 3.…”

“…The absence of the spherulites and the transparency not necessarily imply that the pre-quenched iPP does not crystallize. The pre-quenched iPP indeed crystallizes in the heating process [1], but the higher order structure is quite different from one that is crystallized from molten state [2]. The specific behaviour of the crystallization of iPP from the pre-quenched state is considered to be due to the presence of mesomorphic phase.…”

Lamellae evolution of poly(butylene succinate-co-terephthalate) copolymer induced by uniaxial stretching and subsequent heating

“…A wealth of researches have been conducted on lamellar structure developments during stretching, as well as heating using a host of experimental techniques such as small-angle X-ray scattering (SAXS), [12][13][14][15][16][17][18][19] wide-angle X-ray diffraction, [20][21][22][23][24][25][26] transmission electron microscopy, 27,28 Fourier transform infrared microscopy, 29,30 and atomic force microscopy. 31,32 stretching can transform the original spherulite morphology into a highly oriented brillar one, in which polymeric chains are preferentially aligned along the stretching direction.…”

“…14,18,33 Moreover, a set of uniaxial stretching experiments were carried out at different temperatures to explore the inuence of temperature on polymeric structure development during stretching. 12,13,21,23,24,38,39 Actually, the molecular mobility mechanism during heating is dependent on crystallization conditions, thermal history and other treatments to which it is subjected. Only taking the temperature without deformation into consideration, the structural evolution of semi-crystalline polymers has also been extensively investigated during heating and annealing processes.…”

Tailoring Mechanical Properties of Isotactic Polypropylene Via Crystallization of the Mesophase and Control of Stereodefects Concentration

“…In the case of isotactic polypropylene (iPP), a mesomorphic form is generally obtained by rapid quenching the melt at low temperatures,3, 4, 7–24 or, more precisely, by cooling the melt at temperature below 0 °C at cooling rates higher than 100 °C s −1 14. The formation of the mesophase in iPP is of great technological importance because the crystallization of the mesophase may offer various options to tailor properties of polypropylene.…”