Fischer projections vinyl polymers

Figure 4.9 Stereoregular vinyl polymers in (a) the ideal zig-zag conformation, and (b) in the Fischer projection. If the termini of the chain are chemically different, all tertiary C atoms assume the same configuration and each isotactic chain becomes chiral. When the two chain termini are identical, each chain is superimposable with its mirror image. When R = methyl, we have polypropylene.

FIGURE 1.13 Diagrams of (a) isotactic, (b) syndiotactic, and (c) atactic configuration in a vinyl polymer. The corresponding Fischer projections are shown on the right. 

H-NMR and C-NMR are very useful for characterizing sequences of m or r placements in polymers. Thus, the resonances of methylene protons or carbons can be used to characterize dyad (m,r), and tetrad (mmm, rmm, mrm, etc) stereosequence distributions, whereas the resonances associated with the other atoms can be used to characterize triad (mm, mr + rm, rr) pentad (mmmm, rmmm + rommr, rmrm + mrmr, rmmr, etc) or higher distributions. Shown below is a representative segment of a vinyl polymer chain (Fischer projection), along with listings of the various dyads, triads, tetrads and pentads present. 

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