Polysiloxane synthesis route

Silicon Biotechnology Proteins, Genes and Molecular Mechanisms Controlling Biosilica Nanofabrication Offer New Routes to Polysiloxane Synthesis.5... 

Polysiloxanes gain more and more interest in recent years due to their excellent chemical and physical properties, such as thermal stability, hydrophobicity or electrical resistance (1). One synthesis route towards linear polymers is the ROP of cyclic monomers such as hexamethylcyclotrisiloxane (D3) (2). The functionalization of the substituents on the silicon atom in the polymer is performed via the modification of the cyclic monomers. Especially vinylic side groups are often introduced into the polymer backbone since they are active groups for cross-linking of polysiloxanes to three dimensional networks such as silicone elastomers (3). 

Morse, D.E. (1999b) Sibcon biotechnology Proteins, genes and molecular mechanisms controlling biosilica nanofabrication offer new routes to polysiloxane synthesis, in Organosilicon Chemistry IV From Molecules to Materials (eds N. Auner and J. Weis), Wdey-VCH, Weinheim, pp. 5-16. 

In comparison with the membranes with common aromatic skeletons such as poly-sulfane (PS), poly(ether ether ketone), poly(phthalazinon ether sulfone ketone), poly(etherimide), poly(benzimidazole), poly(phenylene oxide), polysiloxane, poly(oxyethylene) methacrylate, poly(arylene ether sulfone), and polyethersulfone Cardo, which are generally at high price and of complicated synthesis processes, the most important advantages of the aliphatic polymer materials as PEM membranes are their low cost, easy preparation, and simple structure. These aliphatic PEMs are particularly environmentally friendly (e.g., if the quatemization process is proceeded when these aromatic membranes are used for alkaline PEM fuel cells, the synthesis route uses chloromethyl ether for chloromethylation, which is very toxic and carcinogenic). However, the stability of the aliphatic PEMs is not very good. This is probably the biggest challenge when they are used in electrochemical devices. 

Just as the hydrosilylation reaction is important in the synthesis of silanes, so it also serves as a useful route to functional polysiloxanes. The same variety of chemistry as previously described for silanes is available and two further examples are given in equations 82 and 83. One of the main advantages of this route is that the silicon hydride prepolymers are well characterized and readily available materials, which in turn leads to well-defined organofunctional products. A disadvantage is the low efficiency in the use of the precious metal catalyst and the difficulty of its recovery. This is particularly true for systems containing a low level of functionality but this can be partially overcome by using recyclable platinum catalysts on solid supports216,217. 

Acosta S., Corriu RJ.P., Leclercq D., Hubert Mutin P., Vioux A. Monophasic pre-mullite gels prepared by a non-hydrolytic process. Mater. Res. Soc. Symp. Proc. 1994 346 345-350 Alder K.I., Sherrington D.C. Synthesis and characterisation of Ti(IV) and Zr(IV)-containing elastomeric polysiloxane networks a possible route to interesting heterogeneous catalysts. J. Mater. Chem. 2000 10 1103-1111... 

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