Development of the crystallinity and rigid amorphous fraction in cold‐crystallized isotactic polystyrene

Abstract

The phase structure of crystalline isotactic polystyrene (iPS) has been investigated with temperature-modulated differential scanning calorimetry (TMDSC), wide-angle X-ray scattering (WAXS), and Fourier transform infrared (FTIR) spectroscopy. Quenched amorphous samples have been cold-crystallized at 140 or 170°C for various crystallization times. The degree of crystallinity obtained from WAXS, with the ratio of the crystal peak intensity to the total peak intensity, shows excellent agreement with the crystallinity determined from TMDSC total heat flow endotherms. For the first time, FTIR results show that the absorbance peak ratio (I 981cm Ϫ1/I 1026cm Ϫ1) has a linear correlation with the crystalline mass fraction ( c ) for cold-crystallized iPS according to the following relation: I 981cm Ϫ1/I 1026cm Ϫ1 ϭ 0.54 c ϩ 0.16. This relationship allows the crystallinity of iPS to be determined from infrared spectroscopy analyses in cases in which it is difficult to perform thermal or X-ray measurements. On the basis of the measurements of the heat capacity increment at the glass transition, we find that a significant amount of the rigid amorphous fraction (RAF) coexists with the crystalline and mobile amorphous phases in cold-crystallized iPS. The RAF increases systematically with the crystallization time, and a greater amount is formed at a lower crystallization temperature. A three-phase model (crystalline phase, mobile amorphous phase, and rigid amorphous phase) is, therefore, appropriate for the interpretation of the structure of cold-crystallized iPS. The origin of the low-temperature endothermic peak (annealing peak) has been investigated with TMDSC and FTIR spectroscopy and has been shown to be due to irreversible relaxation of the RAF.

Characterization of the Physical State of Spray-Dried Inulin

“…In some systems, the origin of the double endothermic peak is attributed to a melting- recrystallization-melting phenomena, in which Tm1 is attributed to the melting of original crystals, and Tm2 is due to the melting of recrystallized material during heating after these crystals have initially melted. 13,22 However, it was not the case in our study. Indeed, a semicrystalline sample (the starting material) was scanned at various heating rates (1, 2.5, 5, 10, 15, and 20°C min −1 ), and the dual endotherm observed at these different experimental conditions was observed for all heating rates (data not shown).…”

“…13 Each individual diffraction peak was fitted with a Lorentz wave function; whereas a Gaussian function was used for the amorphous halo. For this purpose, the PeakFit™ software was used (PeakFit™ v4.06, AISN Software Inc.).…”

“…23,24 Another hypothesis is the existence of dual lamella stacks containing different crystal populations with different melting points. 13 Hébette et al 25 pointed out two types of crystals during dynamic crystallization from inulin solutions: one resulting from the primary nucleation and thus crystallizing at high temperature and a second one formed by crystallization at lower temperature. Moreover, Hébette 26 presented in his thesis, crystallization of inulin observed by transmission electronic microscopy, confirming a two-phase model consisting of stacks of lamellar crystals separated by amorphous regions.…”

Preparation and Characterization of Anisotropic Submicron Particles From Semicrystalline Polymers

“…Both cold crystallization and double-melting behavior are well-known phenomena. [43][44][45][46] However, the observation of a single melting peak for the macroemulsion prepared from iPS is somewhat unexpected. As we did not fi nd any tabulated values for the enthalpy of cold crystallization for iPS, the degree of cold crystallization was not calculated.…”

A thermodynamic approach to model the caloric properties of semicrystalline polymers

“…The rigid amorphous phase forms an interphase of immobilised macromolecules or parts of them which are located between the crystalline regions and the mobile amorphous phase (cf. [4,[8][9][10][11] or [12]). Wunderlich [4] mentioned that the evolution of the rigid amorphous phase is in parallel with that of the crystalline phase: during Communicated by Andreas Öchsner.…”