Isotactic polystyrene chemical structure

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. 

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. 

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

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

Improvements in the performance of homopolymer GPPS through polymerization with traditional Ziegler-Natta catalysts are primarily limited to flow and glass transition temperatures. Polymerization into an isotactic backbone configuration results in a semicrystalUne structure that improves both heat and chemical resistance however, isotactic polystyrene (IPS) is slow to crystallize and therefore of little practical use with modem injection molding production techniques [3]. 

SPS is entirely different from conventional polystyrene (GPPS) in structure, physical properties, and synthetic method. The material is a new crystalline thermoplastic. Its melting point (Tm) is 270 C, the crystallization rate is very fast in comparison with isotactic polystyrene (IPS). And SPS have some superior properties such as heat resistance, chemical resistance, water/steam resistance and so on. A brief summary of these polystyrenes is given in Figure 2. 

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