Isotactic polystyrene crystallization rate

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. 

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)]...

Fig. 13. A graph showing the variation of growth rate with the inverse of film thickness Ud) for isotactic polystyrene crystals grown at 180 C in nltrathin films. A step in the behavior can be seen at a thickness of 8 nm. At this temperature, this corresponds to the thickness of the single lamella, showing a change in thickness dependence once the film is thinner than the growing crystal. Reprinted from Ref. 98. Copyright (2002), with permission from Marcel Dekker, Inc.

Fig. 2.2 DSC thermogram of pure isotactic polystyrene crystallized at 175 °C for 1 h. An exotherm feature appears between peak II and peak III (Scanning rate 1.25 °C/min). Adapted with permission from figure 3 in Plans J, MacKnight WJ and Karasz FE, Equilibrium Melting Point Depression for Blends of Isotactic Polystyrene with Poly(2,6-dimethylphenylene oxide). Macromolecules 17 810-814. Copyright (1984) American Chemical Society...

Beers KL, Douglas JE, Amis EJ, Kaiim A (2003) Combinatorial measurements of crystallization growth rate and morphology in thin films of isotactic polystyrene. Langmuir 19 3935-3940... 

When SPS is compared with isotactic polystyrene (IPS), a substantial difference is seen in the crystallization. IPS is also crystalline PS, but it has not been commercialized because of its very slow crystallization rate. In contrast, SPS... 

FIGURE 11.1 Radial growth rate r of spherulites of isotactic polystyrene as a function of the crystallization temperature. 

The crystalline content of a polymer has a profotmd effect on its properties, and it is important to know how the rate of crystallization will vary with the temperature, especially drrring the processing and manrrfacturing of polymeric articles. The chemical structure of the polymer is also an important featirre in the crystallization for example, polyethylene crystallizes readily and carmot be quenched rapidly enough to give a largely amorphous sample, whereas this is readily accomplished for isotactic polystyrene. However, this aspect will be discussed more fully later. 

Abstract A number of theories for predicting non-isothermal crystallization of polymers have been proposed (1-5). Some are based on Avrami solution (2,3), others were derived independently (1,4,5). All are based on an "additivity" principle which states that the rate of crystallization at a time, t, depends on the extent of crystallization at time t, but not on the previous history (i.e., it is path independent). In this paper we present experimental results which show that, within a certain regime of cooling rates, the additivity principle applies to isotactic polystyrene. In a previous publication we have shown the same to be true for polyethylene (6). 

Although they have high stereoregularity in the polymer backbone, isotactic polystyrene and syndi-otactic polystyrene are still not perfect from a material applications point of view. The rather slow crystallization rate of iPS prevents its commercial application whereas the high syndiotacticity of... 

SANS) of isotactic polystyrene" indeed stress the complications introduced by morphology and its variation with molecular weight and crystallization rate. 

Beers, K. L., Douglas, J. F., Amis, E. J. and Karim, A., Combinatorial Measurements of Crystallization Growth Rate and Morphology in Thin Films of Isotactic Polystyrene , Langmuir, 19, 2003, p. 3935-3940. 

Polystyrene (PS) now on the market is atactic PS (APS), but there is a problem of low heat resistance. Isotactic PS (IPS) is also known, but there is a problem of low crystallization rate. A homogeneous Ti/metal-locene and MAO system is an effective catalyst for syndiotactic polystyrene (SPS). Advantages of SPS are heat resistance 7 110°C) and chemical resistance like engineering plastics, which are derived from its high crystallinity compared with APS produced by radical polymerization. Furthermore, the crystallization rate of SPS is faster than that of APS or IPS. 

Small amounts of isotactic polystyrene have been synthesized in the laboratory using noncommercial polymerization techniques. These polymers are capable of partially crystallizing, albeit at a very slow rate. Syndiotactic polystyrene was available commercially for several years, but its continued production proved unprofitable. 

The discovery of isotactic polystyrene (IPS) gave a new dimension to this material since it now could crystallize and provide a melting point (Tm) of around 250 °C. Although it still has a Tg of 100 °C, the material will maintain its shape and may be used for many applications above this Tg and below the Tm. IPS has been the subject of several intense efforts for commercialization. Ultimately it has been unsuccessful for one primary reason that being the rate at which the polymer will crystallize is too slow under normal forming... 

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