Polymerization reactions, of unsaturated

Molecular Group 3-5 compounds are currently of considerable interest for two reasons (a) they can serve as volatile low molecular weight single-source precursors for the CVD synthesis of binary and multinary group 3/5 semiconductors with remarkable optoelectronic properties (54), or (b) they are potentially useful cocatalysts for the polymerization reactions of unsaturated organic substrates (55, 56). Various strategies have been employed to synthesize well-defined aggregates. 

On the basis of the nature of the initiation step, polymerization reactions of unsaturated hydrocarbons can be classified as cationic, anionic, and free-radical polymerization. Ziegler-Natta or coordination polymerization, though, which may be considered as an anionic polymerization, usually is treated separately. The further steps of the polymerization process (propagation, chain transfer, termination) similarly are characteristic of each type of polymerization. Since most unsaturated hydrocarbons capable of polymerization are of the structure of CH2=CHR, vinyl polymerization as a general term is often used. 

We have cited several examples which illustrate characteristic ionic polymerization reactions of unsaturated compounds, which may be contrasted with the behavior of alkanes, for which the initial ion-molecule reactions usually lead to stable ion products which do not react further. It was therefore of interest to investigate ionic reactions in cyclobutane, the saturated hydrocarbon isomeric with the unsaturated butenes, to establish whether cyclanes could properly be classified in either of these categories. Additional impetus for such a study was provided by radiolysis data on cyclobutane which suggested that the cyclobutane parent ion rearranges prior to reaction. ... 

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