Properties of Polysiloxanes

Dvornic, P. R. Thermal Properties of Polysiloxanes. In Silicon-Containing Polymers. The Science and Technology of Their Synthesis and Applications, Jones, R. G., Ando, W., Chojnowski, J., Eds. Kluwer Dordrecht, 2000 pp 185-212. 

Permethylated /1-cyclodextrin has also been used as a solution in moderately polar polysiloxanes (e.g., OV-1701)161 165. By diluting the chiral selector, the inherent enantioselec-tivity of cyclodextrins is combined with the unique chromatographic properties of polysiloxanes. Even unfunctionalized saturated hydrocarbons, e.g., l-ethyl-2-methylcyclohexane and l-methyl-2-propylcyclohexane, can be resolved (Figure 15). 

A very versatile and important methodology for controlling the properties of polysiloxanes involves hydrosilylation [eqn (10.33)]. Reaction of poly(methyl-hydrosiloxane) or poly(methylhydrosiloxane)-poly(dimethylsiloxane) copolymers with vinyl-capped species allows the introduction of side groups which give rise to a variety of interesting properties. 

Synthesis and Antibacterial Properties of Polysiloxanes-bearing Quaternary Ammonium Salt Groups... 

SURFACE ACTIVE PROPERTY OF POLYSILOXANE GRAFT COPOLYMERS... 

One of the most characteristic properties of polysiloxane graft copolymers is their surface activity. Since PDMS has a very low surface energy, it accumulates at the... 

Hu, Y. Zhuo, R., The S)uithesis and Drug Release Property of Polysiloxane Bearing Pendant Long Alkyl Ether Group. Acta Polym. Sinica 1997,1,62-67. 

Viers, B. D. Mark, J. E., Elastomeric Properties of Polysiloxane Networks. Bimodal Elastomers That Are Spatially Inhomogeneous and Others That Are Very Broadly Multimodal. J. Macro. Sci., PureAppl. Chem. 2007,44,131-138. 

These characteristics of polysiloxanes are also reflected in their many other properties such as their high water repellency (hydrophobicity), low surface tension etc. Among the other desirable properties of polysiloxanes are their high gas permeability, thermal stability, oxidative stability and low volatility. In addition, their fire points are quite high and so they do not present a fire hazard [1, 5, 7]. Also, polysiloxanes have high biocompatibility and very low toxicity. These properties of polysiloxanes have helped them to carve out a niche for themselves in the area of polymers and have helped their ever expanding utility some of which are outlined in the following section. 

The physical properties of polysiloxanes are relatively unaffected by temperature owing to their exceptionally weak inter-molecular forces. High-molecular chain-like compounds of this series are always liquids, and their glass transition temperatures may be as low as 150 K. They fail to meet the requirement of sufficient mechanical strength at room temperature. This weakness can be overcome by crosslinking the chains by "hot vulcanization." Peroxides of the usual type are added to the polydimethyl siloxanes followed by curing at 70 to 120 C (343 to 393 K) see Fig. 12. 

The unique properties of polysiloxanes are associated with the presence of both polar inorganic backbone and organic nonpolar functional groups, e.g methyl as in the case of PDMS (Figure 13.4) [16],... 

Unusual properties of polysiloxanes that were covered at the symposium are solubility parameters (Rigby), photoluminescence (Pemisz), formation of mesophases (51-53) (Godovsky), films (Takahara, Inagaki), and surfaces (Wynne, Owen, Kowalewski, Jukarainen) (26). 

Poly(carbosiloxane)s having carbosilane and silyloxy linkages in the backbone are attractive materials since they combine useful properties of polysiloxanes and poly(carbosilane)s. A convenient route to poly(carbosiloxane)s is an AROP of l-oxa-2,5-disilacydopentanes (see stmcture 5). 

S. D. Burnside, E. P. Giannelis (2000) Nanostructure and properties of polysiloxane-layered silicate nanocomposites, J. Polym. Sci. Part B Polym. Phys. 38, 1595. 

Burnside S D, Giannelis E P, Nanostructure and properties of polysiloxane-layered silicate nanocomposites , J. Polym. Sci. Part B Polymer Physics, 2000 38 1595-604. Bohning M, Goering H, Hao N, Mach R, Oleszak F, Schonhals A, Molecular mobihty and gas transport properties of polycarbonate-based nanocomposites . Rev. Adv. Mater. Sci., 2003 5 155-9. 

Burnside, S.D. and E.P. GianneUs, Nanostructure and properties of polysiloxane-layered siUcate nanocomposites. Journal of Polymer Science, Part B Polymer Physics, 2000. 38(12) 1595-1604. 

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