Isotactic polystyrene melt-crystallized

The crystallization of the acetone-insoluble polystyrene is completed by boiling for 2 h in freshly distilled butanone it is then allowed to stand overnight at room temperature and finally filtered and dried in vacuum at 60 °C. Yield of crystalline isotactic polystyrene 95-100% of the acetone insoluble portion.The crystalline melting range and the density see Sect. 2.3.4.1) are determined, as is also the limiting viscosity number in toluene at 20 °C. 

Figure 2.8 Spherulite of isotactic polystyrene crystallized from the melt. (From Ref. 8.)...

PEC, PPO, and PS are amorphous materials as normally melt processed, a fact which prevents the use of melting point depression analyses for experimentally determining AHnix or B for the blends with PS. Isotactic polystyrene, i-PS, is able to crystallize, is miscible with PPO, and has been successfully used to determine the parameters related to AHaix (7,12.18). This study shows that i-PS is also miscible with PEC copolymers which contain up to 20 moleX trimethyl comonomer. This fact permits the use of i-PS melting point depression analysis to determine the effect of comonomer content on AHaix with i-PS. 

The morphology of crystalline isotactic polystyrene, i-PS, has been investigated by others, and they have concluded that i-PS normally crystallizes as stacks of folded chain lamellae which are arranged in volume filling spherulites. The melting point of lamellar polymer crystals depends on the lamella thickness, L, as follows (28 )... 

In 1955, for the first time, G. Natta obtained definite amounts of stereoregular polystyrene by polymerization, in the presence of titanium chloride Cl4Ti. This isotactic polystyrene has a crystallinity ratio which may reach 90 per cent. The melting temperature is 240 °C, The crystals belong to the rhombohedric system. 

Ishihara et al. reported in 1986 that syndiotactic polystyrene can be prepared with the aid of organic or inorganic titanium compounds activated with methylaluminoxane [177]. There is much greater incentive to commercialize syndiotactic polystyrene than the isotactic one. This is because isotactic polystyrene crystallizes at a slow rate. That makes it impractical for many industrial applications. Syndiotactic polystyrene, on the other hand, crystallizes at a fast rate, has a melting point of 275°C, compared to 240°C for the isotactic one, and is suitable for use as a strong structural material. 

M. Al-Hussein and G. Strobl. The melting line, the crystallization line, and the equilibrium melting temperature of isotactic polystyrene. Macromolecules, 35(5) 1672-1676, February 2002. 

Abstract. We performed depolarized light scattering (DPLS) and polarized optical microscope (POM) measurements on the strnctnre formation process or the crystallization process of isotactic polystyrene (iPS) nnder shear flow below and above the nominal melting temperature Tm- It was found in the DPLS measurements that an anisotropic oriented structure on a pm scale was formed even above the nominal melting temperature. This was also confirmed by POM measurements. This oriented structure must be a precursor of primary nucleation, at least, in the early stage of the formation process. The structure and its formation mechanism are discussed based on the analysis of the DPLS data. 

Fig. 12. The beginnings of growth in isotactic polystyrene crystallized from the melt at 220°C for 81 min, then quenched. Replica of an etched cut surface.

Fig. 28. DSC melttQg curves isotactic polystyrene crystallized in the melt at different crystallization tranperanues 7i a 170° C b 215° C c 233° C. Heating rate 8° C/min. [Re (210)]...

Of course, other crystaUizable polymers have been studied (114-119).These include polypropylene (114-117), poly(ethylene oxide) (118), and isotactic polystyrene (119). Wignall et al. (113) have summarized the values of in both the melt and crystalline states (see Table 6.8). Most interestingly, the dimensions in the crystalline state and in the melt state are virtually identical for all these polymers. None of these data show a decrease in Rg on crystallization. That the Rg values in the melt and in the crystallized material are the same all but rules out regular folding. In fact, the data for poly(ethylene oxide) (118) shows a slight increase, if anything. By way of summarizing the above... 

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