Phase Separation of Ultrahigh Molecular Weight Isotactic Polypropylene Solutions in the Gelation Process Estimated in Relation to the Morphology and Mechanical Properties of the Resultant Dry Gel Films

Abstract

The phase separation of ultrahigh molecular weight isotactic polypropylene (it-UHMWPP) solution in the gelation process was investigated by quenching the solutions to the desired temperature. When an incident beam of an He−Ne gas laser was directed to the gel, the logarithm of scattered intensity increased linearly with time in the initial stage and tend to deviate from this linear relationship in the later stage. The melting endotherm of the differential scanning calorimetry curve showed a clear peak in the later stage, but no peak could be observed in the initial stage, indicating poor ordering of molecules in polymer-rich phase. The scattered intensity of laser beam from the gel showed a peak in the scattering angle direction. The peak became more intense with increasing time, but the peak position did not change. Accordingly, the phase separation of UHMWPP solution in the initial stage was analyzed within the framework of the linear theory of spinodal decomposition. In parallel to this small-angle light-scattering experiment, the time-resolved measurements in the gelation process were carried out for X-ray diffraction and infrared and Raman spectra. These data could be interpreted reasonably in terms of formation of crystallites as cross-linkages of the gels. Under optical microscopy, it was confirmed that the gels prepared by quenching the solution to room temperature compose of periodic honeycomblike structure characterizing the spinodal decomposition of the solution due to thermodynamic instability. The average size of this periodic structure is slightly larger than that estimated from the scattering angle to give the maximum value of growth rate of concentration fluctuation. Periodic honeycomblike structure was also observed for the dry film under a scanning electron microscopy. The hole size of the honeycomblike structure became smaller as the quenching temperature decreased, and the size distribution was narrow. The dried films were stretched up to 60 times, as has been reported already. The possibility of successful elongation up to λ = 60 became higher with decreasing quenching temperature. Young's modulus, crystallinity, and molecular orientational degree of the resultant dry gel films became higher with decreasing hole size of honeycomblike structure. Accordingly, it turns out that the dense network structure created by the spinodal decomposition of the solution plays an important role in ensuring smooth transmission of inner stress in the stretching direction and ultradrawing of UHMWPP film can be achieved.

Changes to the chemical structure of isotactic-polypropylene induced by ion-beam irradiation

“…The spectra of the irradiated samples were obtained near the surface and at a depth near the Bragg peak. The spectra show distinct absorption peaks at 973 and 899 cm À 1 , corresponding to rocking of the CH 3 coupled with stretching of the C-C in the helical sequences of $5 units in length in iPP chain, and rocking of the CH 3 coupled with rocking of the CH 2 in the shorter sequences in iPP chain, respectively (Miyazawa et al, 1963;Bayer et al, 1980;Matsuo et al, 2002;Kang et al, 2010). Both of the peaks significantly decrease in intensity near the surface on irradiation of the samples.…”

Gelation mechanism of ultra-high-molecular-weight polyethylene (UHMWPE) chains in dispersion solutions containing multiwall carbon nanotubes (MWNTs) analyzed in terms of liquid-liquid phase separation

“…Since then, more detailed analysis has been reported for several kinds of polymer. By using successful analysis of the linear theory of spinodal decomposition by Cahn [9,10], Matsuo et al extended to some crystalline polymer solutions such as PVA [11,12], polypropylene [13], agarose [14,15], and polyethylene [16] in order to investigate whether the gelation by the quenching is attributed to the phase separation of solution by the concentration fluctuation.…”

“…Further detailed studies have been carried out by Matsuo et al for UHMWPP [13] based on light-scattering, X-ray, infrared, and Raman measurements. Through a series of experimental results, Matsuo et al provided conclusive evidence that when crystalline polymer solutions are quenched, the liquid-liquid phase separation associated with spinodal decomposition occurs at first and the crystallization occurs subsequently in the polymer-rich phase.…”

“…On the basis of a series of established results [11][12][13][14][15][16], this paper deals with the admixed effect of multiwall carbon nanotubes (MWNTs) on the gelation/crystallization mechanism of UHMWPE solutions. This is very important to make clear the evidence that well-blended UHMWPE-MWNT composites prepared by gelation/crystallization provide characteristics of high modulus and high electric conductivity.…”

Melting Behavior of Bound Solvent in Isotactic Polypropylene/o-Dichlorobenzene Gel

“…Gelation of a crystalline polymer such as isotactic polypropylene (iPP) is closely associated with the formation of crystal as a cross-linking point. [1][2][3][4][5] Okabe et al reported a solgel transition and the morphology of iPP gel by thermal analysis and polarizing microscopy, 6,7 and found that the gel melting temperature is fitted as a function of polymer concentration by a Eldridge-Ferry plot and many spherulites exist in the gel. There exist three types of crystalline modification.…”