Polypropene, atactic physical properties

There are striking differences in physical properties between the atactic and isotactic forms. The atactic material is soft, elastic, somewhat sticky, and rather soluble in solvents such as 1,1,2,2-tetrachloroethane. Isotactic polypropene is a hard, clear, strong crystalline polymer that melts at 175°. It is practically insoluble in all organic solvents at room temperature, but will dissolve to the extent of a few percent in hot 1,1,2,2-tetrachloroethane. That the difference between the atactic and isotactic polymers arises from differences in the configurations of the methyl groups on the chains is shown in a... 

Stereochemical relationships play an especially important role in the properties of polymers. Consider the three polypropylene segments illustrated as Fischer projections in Figure 2.35. In the isotactic polymer, all of the methyl-substituted carbon atoms have the same configuration. In the syndiotactic polymer, the methyl-substituted carbon atoms have alternating configurations. In the atactic polymer there is a random pattern of configurations at the methyl-substituted carbon atoms. As with smaller molecules, the physical properties of diastereomeric polymers differ. Table 2.2 shows file relationship between tacticity and properties of polypropene. ... 

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