Monofunctional Oligomers Siloxane Macromonomers

Preparation of Dimethylsiloxane Macromonomers by Living Anionic Polymerization 95 123) 

This area of research is receiving increasing attention due to a better understanding (and recognition) of the properties and potential applications of siloxane containing copolymers. A detailed discussion of this type of graft copolymers and their uses will be given in later sections. 

Although each of these cyclic siloxane monomers can be polymerized separately to synthesize the respective homopolymers, in practice they are primarily used to modify and further improve some specific properties of polydimethylsiloxanes. The properties that can be changed or modified by the variations in the siloxane backbone include the low temperature flexibility (glass transition temperature, crystallization and melting behavior), thermal, oxidation, and radiation stability, solubility characteristics and chemical reactivity. Table 9 summarizes the effect of various substituents on the physical properties of resulting siloxane homopolymers. The 

The most commonly used siloxane modifiers are those having phenyl, trifluoro-propyl and cyanopropyl substituents. Introduction of phenyl units into the polydimethylsiloxane backbone either in the form of methylphenylsiloxane or diphenyl-siloxane increases the thermal and oxidative stability, glass transition temperature and the organic solubility characteristics of the resulting copolymers. At low levels (5-10 percent by weight) of incorporation, bulky phenyl groups also break up the regularity of polydimethylsiloxane chains and inhibit the crystallization (Tc 

Unfortunately, there have been very few studies on the synthesis and characterization of functionally terminated siloxane oligomers with a mixed siloxane backbone. 

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