Fluorosilicone materials

One type of R substituent that features only briefly in these reviews but which is growing in importance is the fluoroalkyl-containing group. There is renewed interest in fluorosilicone materials of all types including silanes. In line with the well-recognized low surface tension of aliphatic fluorocarbon-containing species, the prime interest is in the area of surface energy control. Examples of such silanes of all three types (n = 1, 2 and 3) have been reported and the purpose of this review is to summarize recent (last decade) developments in this topic. 

Fluorosilicone materials have always had the potential of being amongst the lowest known surface energy materials because they combine the low intermolecular forces between aliphatic fluorocarbons with the high flexibility of the siloxane backbone. Historically, commercial emphasis was on minimally fluorinated fluorosilicones such as poly (3,3,3-trifluoropropyl) methylsiloxane (PTFPMS) and it is only recently that more highly fluorinated materials have become available and this potential realized. ... 

Fluorosilicones (FLS) are a class of polymers generally composed of siloxane backbone polymers and fluorocarbon pendant groups. Fluorosilicone materials are familiar because of their excellent properties such as high thermal stability, good chemical and environmental resistance, flame resistance, and surface characteristics. Currently, these materials are extensively used in a wide range of applications such as in the electronic, automotive, dairy, medical, and aerospace industries [1,2]. The primary and most commonly used commercially available fluorosilicone is poly(3,3,3-trifluoropropyl methylsiloxane (PTF-PMS). This polymer was discovered by Dow Coming Company [3] in 1950 and was given the trade name Silastic . It is prepared from l,3,5-trimethyl-l,3,5-tra(3, 3, 3 -trifluoropropyl)cyclotrisiloxane and has the repeat unit sfructure presented in Scheme 6.1. 

Our ongoing strategy to develop new fluorosilicone materials has been to combine the well known preparative chemistry of silicon containing compounds with the relatively new development of perfluorocyclobutane (PFCB) aromatic ether polymers. PFCB materials are prepared by the thermal cyclodimerization of trifluorovinyl ether (TFVE) monomers." " Recently we developed a synthetic... 

Silicone—Fluorosilicone Lenses. Sdicone mbber has long been considered a unique contact lens material (55), and the development of sdicone mbber lenses has been reviewed in earHer editions of the Eniyclopedia. The oxygen permeabdity of sdicone mbber, >300 barrers, is virtually unsurpassed by any other polymeric material considered for contact lens appHcations. 

One of the important breakthroughs in the silicone PSA industry has been the development of new release liners based on fluorosilicones [116]. These new materials significantly improve the release characteristics of the silicone PSAs, something that has been difficult to achieve because of the high adhesion silicone PSAs show to low energy substrates, including silicone rubbers and liners. 

The submitters used a 2.1 m. x 0.64 cm. column with 5% fluorosilicone (FS-1265) supported on Diatoport S as stationary phase. With a column temperature of 170° and a helium flow rate of 60 ml. per minute, 2-ethoxypyrrolin-5-one has a retention time of 2.2 minutes. The analysis was carried out at 160° by the checkers, using a column of 5% diethylene glycol succinate-Bentone supported on Diatoport S. The starting material had a retention time of 3.9 minutes under these conditions. Bentone is available from Applied Sciences Laboratory, Box 440, State College, Pennsylvania 16801. 

The use of silicone elastomers for high-voltage applications (insulators and cable accessories) requires special formulations. Unusually, stringent requirements for these materials must be met.509,510 Fluorosilicone rubbers, which offer some unique combinations of properties (e.g., chemical resistance and higher temperature stability), have attracted considerable attention and have been reviewed in recent publications.511,512 It was noted that a modification of perfluoroether elastomers with silicone elastomer via hydrosilylation reaction opens the possibility of novel applications.5... 

Smith, D. W., Jr. Ji, J. Narayan-Sarathy, S. Neilson, R. H. Babb, D. A. Fluorosilicones Containing the Perfluorocyclobutane Aromatic Ether Linkage. In Silicones and Silicone-Modified Materials-, Clarson, S. J., Fitzgerald, J. J., Owen, M. J., Smith, S. D., Eds. ACS Symposium Series 729 American Chemical Society Washington, DC, 2000 pp 308-321. 

A classification by chemical type is given in Table 1. It does not attempt to be either rigorous or complete. Clearly, some materials could appear in more than one of these classifications, eg, polyethylene waxes [9002-884] can be classified in both synthetic waxes and polyolefins, and fluorosilicones in silicones and fluoropolymers. The broad classes of release materials available are given in the chemical class column, the principal types in the chemical subdivision column, and one or two important selections in the specific examples column. Many commercial products are difficult to place in any classification scheme. Some are of proprietary composition and many are mixtures. For example, metallic soaps are often used in combination with hydrocarbon waxes to produce finely dispersed suspensions. Many products also contain formulating aids such as solvents, emulsifiers, and biocides. 

Fluorosilicones (FVMQ) have excellent low temperature flexibility properties coupled with good oil, fuel, and solvent resistance and excellent aging properties. The materials are compounded and reinforced with fine particle fillers, especially silica. The materials are mixed and processed on especially clean equipment and are peroxide-cured. 

Fluorosilicone elastomers generally respond to ionizing radiation in a fashion similar to fhaf of silicone elastomers (polydimethylsiloxanes). One interesting application is a process of preparing blends of fluoroplastics, such as poly(vinylidene fluoride), with fluorosilicone elastomers to obtain materials having a unique combination of flexibility at low temperatures and high mechanical stiength. ... 

Another class of functional siloxane polymer that has received some attention are the fluorosiloxane materials, especially 3,3,3-trifluoropropylmethylsiloxanes. The use of conventional equilibration catalysts to produce these materials gives products which favour the cyclosiloxane in the bulk. Clarson and coworkers41 report the use of specific condensation catalysts such as stannous octanoate, potassium carbonate and barium hydroxide to prepare hydroxy terminated fluorosilicone polymers. 

Electrical properties — dielectric constant (e), representing polarization dissipation factor (tan 8), representing relaxation phenomena dielectric strength (EB), representing breakdown phenomena and resistivity (pv), an inverse of conductivity — are compared with other polymers in Table 5.14.74 The low dielectric loss and high electrical resistivity coupled with low water absorption and retention of these properties in harsh environments are major advantages of fluorosilicone elastomers over other polymeric materials.74... 

Under normal conditions, PMTFPS is relatively inert. Skin tests performed on albino rabbits have shown no dermal irritation or toxicity. In over 40 years of industrial use of fluorosilicone compounds, no problems have been reported with respect to human dermal contact with these materials, uncured or cured.74... 

There have been many investigations to determine the best chemical structures to provide for resistance to moisture and hydrolysis. Attempts have been made to synthesize epoxy adhesives with improved water resistance by replacing some hydrogen atoms by fluorine.50 However, the cost of processing of such materials has restricted commercial development. For electronic sealants, it is highly desirable to keep moisture from penetrating into critical areas. Hydrophobic polymers have been developed to accomplish this task. They are siloxyimides, fluorosilicones, fluoroacrylics, phenylated silicone, and silastyrene. 

In addition to accumulation of proteinaceous deposits, such as those occurring on soft hydrophilic lenses, the molecular make-up of many RGP lenses also tends to attract lipid deposits, such as cholesterol esters, wax esters, triglycerides, etc. This is especially true of the more hydrophobic materials such as silicone acrylates with high Dk (oxygen permeability) values. Accordingly, more recent developments in material science related to contact lenses have resulted in materials such as fluorosilicone acrylates and fluorocarbons with purportedly less propensity for deposits. 

Silicones and fluorosilicones have traditionally been classified as high performance materials due to their suitability for use under extreme conditions and their processability has been particularly interesting as a result of the very flexible siloxane chain. The present paper discusses selected examples where more recent advances in science and technology have broadened the understanding and uses. Emphasis is given to relating the molecular chemistry and physics to the characteristics of the bulk materials. 

Fluorosilicone, dimethylsilicone homopolymers, as well as their copolymers, are negatively charged and inhibit the blood clotting reaction. There are a number of polyelectrolytes which have negative zeta potentials and are antithrombogenic. The most promising is the ethylene-acrylic acid copolymer, neutralized to the extent of 60% with sodium ions. Another useful and related material is the vinyl acetate-crotonic acid copolymer. 

---