Atactic polystyrene chemical structure

Figure 12. Half-peak time ti,2 of coherent dynamic structure factor for atactic polystyrene plotted vs. Q. Left, CgD solution right, CS2 solution continuous lines, calculated results at T = 30 °C dashed line, at F = 70 °C. Experimental points from ref. 14. [Model assumptions and parameters same as in Figures 10 and 11, tB = 0.012.] (Reprinted with permission from ref. 14, Copyright 1984, American Chemical Society.)...

However, as we shall see, the results in the asymptotic domain should reveal a different property of polymer chains. Criticism came from Yoon and Flory,10 disturbed by the absence of local chemical structure effects. These authors modelled the atactic polystyrene chain of N beads as realistically as they could (see Chapter 1). Thus, Yoon and Flory accounted for interactions between nearest neighbour monomers in particular, these interactions are responsible for the fact that the three orientations of a bond j, relative to bonds j — 1,/ — 2, are weighted differently in relation to the stereochemical composition. Moreover, we have seen in Chapter 1 that, for atactic polystyrene, pairs of successive benzene rings are slightly more frequent in syndiotactic than in isotactic positions. 

As polymer chains are usually long and flexible, they would be expected to pack randomly in the solid state to give an amorphous material. This is true for many polymers, particularly those with an irregular chemical structure. Examples are the stereoirregular materials atactic polystyrene (1.10) and atactic polypropylene (1.11), in which the Ph and the Me substituents, respectively, are randomly oriented. 

Syndiotactic polystyrene, as generally polymerized with monocyclopentadienyl catalysts, has a high percentage of rrrr pentad structure. The nmr chemical shift for the phenyl-1 carbon and backbone methylene carbon are approximately 145.3 and 44.9 ppm, respectively (1,2). In general these polymers are found to be greater than 99% pnre in syndiotactic structure as defined by nmr. sPS can be further purified of any atactic polystyrene (aPS) developed during the polymerization procednre by extraction with solvents such as methyl ethyl ketone (MEK). 

What are the chemical structures of isotactic, syndiotactic, and atactic polystyrene ... 

Figure 14.1 Comparison of the chemical structures of atactic polystyrene, isotactic...

In contrast to atactic GPPS, the SPS configuration results in a dramatic improvement in the heat and chemical resistance of polystyrene due to the semicrystalhne structure of SPS. With a melting point of 210°C and improvements in the chemical resistance to oils, aliphatic hydrocarbons, esters, and ketones, SPS extends the performance envelope of polystyrene and offers designers another option to capture the inherent benefits of the polystyrene structure. 

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