Polystyrene atactic/isotactic

Polystyrene is unusual among commodity polymers in that we can prepare it in a variety of forms by a diversity of polymerization methods in several types of reaction vessel. j Polystyrene may be atactic, isotactic, or syndiotactic. Polymerization methods include free radical, cationic, anionic, and coordination catalysis. Manufacturing processes include bulk, solution, suspension, and emulsion polymerization. We manufacture random copolymers ... 

Polystyrene (PS) as normally prepared is essentially linear and atactic. Isotactic polymers can be made but this is not of commercial interest because of increased brittleness and more difficult processing than the atactic product. The major application of polystyrene is in packaging. Specific additives are incorporated to achieve product characteristics that depend on the end usage. 

In specifying the tacticity of the polymer, the prefixes it and st are placed before the name or structure to indicate isotactic and syndiotactic structures, respectively. For example, it-polystyrene means that the polystyrene is isotactic. The absence of these terms denotes that the polymer has an atactic structure. 

Fig. 1. a Relation between Ini in toluene and M for fractions of polystyrene (o) isotactic polystyrene ( ) atactic polystyrene. From Ref.2-1, b Relation between [rj] in benzene and M for fractions of polystyrene (o) isotactic polystyrene ( ) atactic polystyrene. From Ref.2)... 

Polystyrene that is manufactured by free-radical polymerization is atactic. Isotactic polystyrene formed with Ziegler-Natta catalysts was introduced commercially in the 1960s, but failed to gain acceptance. Syndiotactic polystyrene is now being produced commercially. 

Atactic polystyrene, as an amorphous material, has been known for centuries. In principle, polystyrene can occur with atactic, isotactic, and syndiotactic configurations. With the extensive studies concerning the stereoselective polymerization of olefins by Ziegler-Natta catalyst systems discovered... 

FIGURE 14.2 NMR spectra (1,2,4-trichlorobenzene, 130 °C, 270.1 MHz) of the methine and methylene protons of polystyrenes (1) isotactic (2) atactic (3) syndiotactic. (Reprinted with permission from Ishihara, N. Seimiya, T. Kuramoto, M. Uoi, M. Macromolecules 1986, 79, 2464—2465. Copyright 1986 American Chemical Society.)... 

Categorize the following polymers with regard to their low-temperature physical structure polyethylene isotactic polypropylene poly (ethylene terephthalate) isotactic polystyrene atactic polystyrene atactic poly(vinyl alcohol) atactic poly(vinyl acetate) poly(ethylene-sfflf-propylene) with 50/50 molar composition, and the same polymer but with molar composition 98/2. 

Figure 9. Aromatic C-1 Carbon Spectra of A-Atactic Polystyrene B-Isotactic Polystyrene Eplmerized a Small Amount C-Isotactic Polystyrene Eplmerized to a Large Extent [78].

FIGURE 3.5 Stereoisomers of polystyrene showing isotactic, syndiotactic, and atactic structures. 

The IR spectra of atactic polystyrene (aPS), isotactic polystyrene (iPS), and syndiotactic polystyrene (sPS) are shown in Figure 8.8. Large differences in both the IR and Raman data, related to the different chain conformations of these isomers, are observed, especially in the regions of 18.51, 10.33, 11.11, 9.34, and 8.33-7.14 pm. 

The regular syndiotactic and isotactic structures are capable of crystallisation whereas the atactic polymer carmot normally do so. In the case of polypropylene the isotactic material is a crystalline fibre-forming material. It is also an important thermoplastic which can withstand boiling water for prolonged periods. Atactic polypropylene is a dead amorphous material. Polystyrene as commonly encountered is atactic and glass-like but the syndiotactic material... 

Polystyrene produced by free-radical polymerisation techniques is part syndio-tactic and part atactic in structure and therefore amorphous. In 1955 Natta and his co-workers reported the preparation of substantially isotactic polystyrene using aluminium alkyl-titanium halide catalyst complexes. Similar systems were also patented by Ziegler at about the same time. The use of n-butyl-lithium as a catalyst has been described. Whereas at room temperature atactic polymers are produced, polymerisation at -30°C leads to isotactic polymer, with a narrow molecular weight distribution. 

Polymers that incorporate steric centers into their backbones can display various types of tacticity. The three principal types of tacticity are isotactic, syndiotactic, and atactic, as illustrated in Fig. 1.8 for polypropylene. Other polymers that display tacticity include polystyrene and poly a-olefins,... 

Fig.l Differential scanning calorimetry (DSC) cooling scans from the melt, at 10°Cmin 1, of the following materials (from top to bottom) Isotactic polypropylene (iPP) iPP after self-nucleation treatment at TS = 162°C 80/20 polystyrene (PS)/iPP melt mixed blend 80/20 PS/iPP melt mixed blend after self nucleation treatment at Ts = 161 °C 80/20 PS/iPP unmixed blend (UB), see text and atactic PS homopolymer. (From [68] with permission)... 

As polystyrene obtained by free radical polymerisation technique is atactic it is therefore non-crystalline. The isotactic polystyrene is obtained by the use of Ziegler-Natta catalysts and n-butyl lithium. Isotactic polystyrene is having a high crystalline Melting point of 250°C. It is transparent. It is more brittle than the atactic polymer. 

Remarkable differences in the G values of F12 were also recorded in atactic and syndiotactic polystyrene. The tacticity itself was also affected by the irradiation. Fligh-temperature irradiation with y-rays caused the reduction of isotacticity of isotactic PMMA... 

In particular, Table 2.1 shows for atactic polystyrenes (in ref. 68 also isotactic polystyrene has been investigated, yielding C = —10300 Br in bromoform) that the influence of molecular weight (measurements in bromo-benzene and on the bulk polymer) is negligible or rather small. 

---