Isothermal Crystallization Behavior of Isotactic Polypropylene H/D Blends as Viewed from Time-Resolved FTIR and Synchrotron SAXS/WAXD Measurements

Abstract

The melt isothermal crystallization behavior has been investigated for a series of blend samples of deuterated (D) and hydrogenated (H) species of isotactic polypropylene by means of time-resolved Fourier transform infrared (FTIR) spectral measurement and simultaneous small-angle X-ray scattering (SAXS)/wide-angle X-ray diffraction (WAXD) measurements using synchrotron radiation source in SPring-8. The SAXS data collected were analyzed in the three different time regions. The Guinier plot in the early stage of crystallization gave the average size of isolated domains formed in the melt. In the middle stage, the correlation between these domains was analyzed using the Debye−Bueche equation. In the later stage of crystallization, the correlation function was calculated to estimate the degree of crystallinity and the long period of the stacked lamellae. The IR data analysis clarified the formation process of regular helical chains in the isothermal crystallization phenomenon. The combination of FTIR, WAXD, and SAXS data has revealed a concrete structural evolution process as follows: (i) In the early stage, the short helices start to be formed, and they gather together to create an isolated domain of about 330 Å radius of gyration. (ii) The domain size decreases gradually to about 300 Å, and (iii) these domains start to have some weak correlation to each other with ca. 300 Å correlation length. (iv) In these domains, the regular chain segments grow to longer helices, and the correlation distance becomes shorter to ca. 200 Å, and finally, (v) the stacked lamellae with long period of ca. 200 Å are formed and stabilized. The crystallization behavior of the D/H 50/50 blend sample was also investigated, and the origin of cocrystallization phenomenon has been discussed.

Multipurpose soft-material SAXS/WAXS/GISAXS beamline at SPring-8

“…Sector-averaging the data then provided the temperature dependence of the profiles, as presented in the figure. As has been reported previously, 8 the SAXS showed a broad peak of approximately q¼0.2 nm À1 because of the density fluctuation in the molten state at 130 1C. This broad peak then developed into a long-period peak after crystallization and shifted to a higher q, at which point the WAXS pattern then began to display crystalline peaks.…”

Application of the simultaneous measurement system of WAXD, SAXS and transmission FTIR spectra to the study of structural changes in the cold- and melt-crystallization processes of trans-1,4-polyisoprene

“…In the data analysis of the observed SAXS data, we assumed that the crystallization process might be divided into three time regions: (i) the time region immediately after the temperature jump, (ii) the time region before the appearance of lamellae and (iii) the time region of the lamellar structure formation, as seen in several examples of polymers such as nylon and isotactic polypropylene. 41,42 As reported in previous works, region (i) may be analyzed using a Guinier plot [ln(I) vs q 2 ], but the q range observed in the experiment did not always satisfy the effective condition for this approximated equation (qooR g À1 , where R g is a radius of gyration). Hence, the equation of power function of q was used as shown below.…”

“…The band corresponding to the shorter critical sequence length should appear earlier than the band with the longer critical sequence length, which reflects the growth of the regular helix. 41 Thus, the band at 1205 cm À1 corresponds to the shorter helix, and the band at 1050 cm À1 corresponds to the longer one, although the concrete minimal number of monomeric units to make a detectable helical segment must be evaluated experimentally using the isotope dilution method. 39 It must be noted here that the WAXD peak appeared at approximately the same time as the infrared 1050 cm À1 band with the long critical sequence length, which indicates that the crystalline lattice started forming when relatively long helical segments gather together side by side.…”

Understanding the phase behavior from multiple-step isothermally crystallized poly(3-hexylthiophene)s

“…The latter can be representing by a correlation length (x) between the neighboring domains (e -z/x ) separated at distance z [32]. The corresponding scattering intensity at small angle can be analyzed following Debye-Bueche equation (Eq.…”

“…The corresponding scattering intensity at small angle can be analyzed following Debye-Bueche equation (Eq. (1)) [19,32,33]:…”