The Calculated RIS Parameters

The calculations for polystyrene are discussed above, and should be regarded with caution. They do, however, yield sensible RIS parameters, which are like those for polypropylene, except for larger repulsions tetween phenyl and H than between methyl and H. In contrast, poly(vinyl chloride) is intermediate between polystyrene and polypropylene, although in this case a tendency is also evident for neighbouring C-Cl bonds to lie approximately antiparallel, perhaps for dipolar reasons. 

The parameters for polyfmethylacrylonitrile) are less easy to anticipate, because most conformations will involve either steric or dipolar repulsions. The most likely conformations will be r r (m), tt(r) and because these 

Not surprisingly, for the reasons discussed above, the fit for poly(methyl methacrylate) has the biggest error sum of the present series. Nevertheless, the fit is acceptable given the approximations, whidh in this case include ignoring die carboxymethyl orientations. Once again, there is a preference for the four conformers as above, because the carboxymethyl group also has a low steric bulk in some orientations. However, the fit also shows a marginal prrference for the tt state in the m dyad, consistently with the solid-state data noted above [20]. This will no doubt be made possible by a favourable mutual orientation of the carbonyl dipoles. 

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