Stereoirregular polypropylene

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. 

FIGURE 8.13 Sawhorse representation of two isotactic polypropylene blocks with same (a) or opposite (b) relative configurations separated by a short stereoirregular sequence. 

NMR s ability to characterize the tacticity, or stereoisomerism, of polymers, such as polypropylene, polystyrene, or poly(vinyl chloride), is also significant. The tacticity of these, or of any other stereoirregular polymer, is analyzed as sequences of stereo pairs, or dyads. Each pair is designated as either meso (m) or racemic (r), depending on the stereostructure. In isotactic... 

The poly-thio-A -/ -A -(methyl-aminomethyl)-ethylenes are amorphous and stereoirregular, in contrast to polypropylene sulfide obtained with the same initiator, which is highly crystalline but it should be mentioned that one of the asymmetric centers is in the lateral chain and not in the main chain, as it is in propylene sulfide. Optical rotatory dispersion curves are independent of the polymerization conditions, they are complex for poly-thio-A -sec-butyl-A -methylaminomethyl-ethylene in different solvents and simple for poly-thio-A -methyl-A -(phenyl-l-ethyl)-aminomethyl ethylene. The ORD s of the poly-hydrochlorides of both polymers in water are normal but quite different from those of the polyamines. The OA polybases are soluble, when protonated, in strongly acidic media. By addition of dioxane or, better, acetonitile, the polybases remain soluble even for a degree of deprotonation of 45% [112]. By an irreversible methylation by dimethyl-sulfate (>10%), the polybases become water-soluble. The chiroptical properties permit the following conclusions ... 

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