Polyorganosiloxane polymerization

The pioneering work on polyorganosiloxanes dates back to 1863-1871, to the studies of Friedel, Crafts8 "10) and Ladenburg 11 However, it was F. S. Kipping and his coworkers who were first to demonstrate the polymeric siloxane structures in the early 1900 s12). Unfortunately, since their interest was mainly in small molecules, they did not recognize the importance of the polymers and polymerization in this field 13). 

It is impossible to tell at this time whether the spacings and configuration of the polyorganosiloxanes follow those of silicon dioxide or silicon disulfide, or neither of them. Such comparisons must await X-ray analysis of the polymeric structure. Once the interatomic distances and the approximate bond angles are known for several organo-siloxane chains, it tnay become possible to plan stronger and better polymeric structures instead of continuing to seek them on a purely empirical basis. 

In the process of heating, polyorganosiloxane rubbers undergo a series of chemical transformations where, along with destruction and depolymerization reactions, intramolecular conversions, polymerization-type, exchange, and crosslinking reactions proceed. 

Polymer structures are often described by using the capital letters M (mono-), D (di-), T (tri-), and Q (quadruple-) indicating the functionality of the respective monomer units. Thus linear trimethylsilyl terminated silicone fluids are characterized by M(D)xM. Linear polyorganosiloxanes can be produced either from cyclic organosiloxanes by ring-opening polymerization, which is promoted by both anionic or cationic catalysts [3, 4], or from oligomeric hydroxyterminated dimethylsiloxanes by polycondensation in the presence of acid catalysts [5, 6],... 

Another interesting three-component LIPN consists of crosslinked polyorganosiloxane (tet-raethoxysilane as crosslinker) as the first stage, swollen by butyl acrylate monomer (allyl methacrylate as crosslinker) and then polymerized to form the second component, and finally, poly(methyl methacrylate) was grafted onto the IPN core as the shell layer [Isao et al, 1992], Such kind of LIPNs are found to be a good impact modifiers in thermoplastics i.e., they are toughened by the addition of finely divided low phase. 

Synonyms Organosiloxane Organosiloxanes Polymerized siloxane Polyorganosiloxanes Silicone polymer Siloxane Siloxanes... 

Access to the living cationic polymerization technique mentioned earlier has allowed the synthesis of a range of block copolymers, either phosphazene-phosphazene blocks, phosphazene-organic polymer blocks, or phosphazene-polyorganosiloxane blocks.Both di- and triblock copolymers have been produced, and a summary of these structures is shown in Scheme 7.7. 

V.S. Papkov, "Chemical and Physical Aspects of the Behavior of Polyorganosiloxanes as Bases for Thermostable Polymeric Materials, Doctoral Dissertation, Moscow (1979). 

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