Saturated cyclic structural units

It is clear that the polymer composition, in terras of the ratio between saturated cyclic structural units and unsaturated linear structural units, is controlled by the competition between intra- and intermolecular propagation reactions. It is clear as well that the change of the monomer concentration does not affect the monomoiecular cyclization, whereas it has an influence on the bimolecular addition of P radical onto a monomer molecule specifically, by decreasing the monomer concentration, the bimolecular addition becomes less favoured in agreement with the experimental findings. 

The cyclohexane ring, either alone or as part of a more complex structural unit, occurs in certain natural products and, accordingly, cyclohexane is the most important saturated cyclic hydrocarbon. Two principal conformational isomers exist. The more stable is called the chair conformation 14, and the less stable the boat conformation (see Section 1.9). In both these conformations the C-C-C bond angles are close to the tetrahedral value of 109°28 consequently, cyclohexane has little angle strain Angle strain becomes significant in saturated hydrocarbons if there are meaningful departures from the above value. 

These results therefore indicate that the soluble, saturated polymers produced by radical initiation of DVF are cyclopolymers containing a three-carbon bridged ferrocene unit (I). However, the Mossbauer spectra obtained for polymers produced by cationic initiation do not show evidence for the three-membered bridge. Certainly PDVF(cationic) contains some acyclic unsaturated units, not necessarily pendant vinyl groups (II), but the low level of unsaturation suggests that cyclic units exist. Thus, for example, a five-carbon bridged bicyclic unit (VI) or a ladder structure (VII) may be found in these polymers, and would be consistent with the Mossbauer parameters obtained. Further polymerisation studies and Mossbauer and other spectroscopic studies of these polymers are in progress. 

The structure of ebonite is basically similar to that of a soft vulcanizate prepared by the use of a low accelerator to sulphur ratio (see Fig. 18.2) although, of course, there are far more sulphur-containing structures per unit volume and the material is essentially saturated. When ebonite is pyrolyzed, various 2-methylthiophens are obtained this suggests that a substantial proportion of the sulphur is present in cyclic monosulphide groups attached to the tertiary carbon atom in the main chain ... 

Polycarbosilanes are polymers in which organosilicon moieties as silanes, disilanes, and trisilanes and carbon as aliphatic or aromatic units lie in the polymer backbone. The general formula for this class of material may be represented by structure 33. Polycarbosilanes may be linear, cyclic, polycyclic, extended networks, or any combination thereof R and R are the usual substituents found in organo-silanes, and (C) represents difimctional aliphatic (saturated or unsaturated) or aromatic groups that can serve as bridges between the silicon moieties. Consequently, a... 

---