Crystallization from the Glassy State

Depending on the cooling conditions from the melt, SPS can be obtained in the amorphous state and successively crystallized at temperatures higher than the glass transition temperature. In this sense, the processing histories of SPS can sensitively influence the microstructure and properties, because, as shown before, from the glassy state the a form is always obtained. 

The thermal crystallization of glassy films was studied using infrared. X-rays, and thermal analysis, in the range 120-220 C [31]. It was found that the growth of the ordered structure occurred in two stages a fast primary stage followed by a slower secondary process. The crystalline and the mesophase are formed in either process. The formation of the mesophase increases in the secondary stage of crystallization. 

To elucidate the nucleation mechanism during the crystallization process from the glassy state, Matsuba et al. [32] performed time-resolved Fourier transform infrared (FTIR) spectroscopy and depolarized light scattering measurements (DPLS) on glassy SPS kept at 120 C. They found an induction 

Wang et al. [33] studied the spherulitic growth rates and the microstructure of SPS cold-crystallized isothermally at various temperatures in the range 115-240 °C, by small-angle light scattering (SALS), optical microscopy, and transmission electron microscopy (TEM Fig. 9.2). 

The derived activation energy for SPS chain mobility at the crystal-growing front is 5.4kJ/mol, which is lower than that of isotactic polystyrene, which is 6.5kJ/mol. Despite a wide range of Tc used, however, the sample crystallinity estimated by Fourier transform infrared spectroscopy remains unchanged. Interconnected domains with a width of approximately 1.8 pm are readily observable in all the crystallized samples under phase contrast microscopy, and the phase-separated structure is conserved within SPS spherulites whose diameters are increased with increasing Tc. 

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Fig. 4 SAXS curves of PET crystallized from the glassy state at 80 °C as a function of annealing time [7]...

Relaxation Dynamics of Amorphous Regions during Isothermal Crystallization from the Glassy State 235... 

The crystallization rate from the glassy state was investigated by Chung and Cebe [59] and they have observed that the crystallization from the glassy state was faster than from melt. The increase in the crystallization rate was ascribed to the formation of short-range ordered noncrystalline structures during quenching. 

Lamellar Morphology of Narrow PEEK Fractions Crystallized from the Glassy State and from the Melt... 

The morphology of semicrystalline PEEK fractions in relation to their molecular weight has been recently investigated 46). The PEEK fractions were crystallized from the glassy state between 250 to 340 °C. The main results of this study will be... 

By strain-induced crystallization, the pure a form is obtained even at temperatures for which thermal crystallization from the glassy state is not observed. De Candia et al. [36] analyzed the drawing behavior of amorphous films of SPS at different temperatures. They found that strain-induced or thermal-induced crystallization was obtained, depending on the drawing temperature. At 110 °C thermal crystallization was not observed, whereas strain-induced crystallization occurred at high draw ratios, resulting in a substantial increase in the elastic modulus of the obtained samples. 

Vittoria, V., Ruvolo Filho, A., de Candia, F. Structure of syndiotactic polystyrene thermally crystallized from the glassy state. J. Macromol. Sci Phys., B29(4), 411 28 (1990). 

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