Organosilicone elastomer

Poly(dimethylsiloxane) (PDMS) is the simplest of organosilicone elastomers. PDMS was commercially developed by Dow Coming in the 1960 s. It possesses inertness and usefiil mechanical properties, and can also be readily made into various desired shapes for medical items including prostheses of different bone and soft tissue elements (in surgery), and ancillary components such as tubes, catheters, shunts and dmg carriers. In addition, PDMS has shown good compatibility in clinical research.(7) So it has been a very usefiil synthetic polymer in medicine. In fact, silicone polymers are often employed in checking the biocompatibility of new polymers. Furthermore, organosilicones comprise an important class of compounds used in resins, and room temperature and heat-cured robber industrial and consumer products. 

Hybrid organosilicon-organophosphazene polymers have also been synthesized (15-18) (structure ) (the organosilicon groups were introduced via the chemistry shown in Scheme 11). These are elastomers with surface contact angles in the region of 106°. Although no biocompatibility tests have been conducted on these polymers, the molecular structure and material properties would be expected to be similar to or an improvement over those of polysiloxane (silicone) polymers. 

Pujol, J.-M. Frances, J.-M. Letoffe, M. Condensation Vulcanizing Silicone Elastomers An Overview of Research and Development. In Progress in Organosilicon Chemistry-, Marciniec, B., Ghojnowski, J., Eds. Gordon Breach Basel, 1995 pp 503—521. 

It is necessary that the discussion be confined to those organosilicon products which, on the basis of available information, show the greatest promise of widespread use. This would seem to mean the methyl, ethyl, and various alkyl-aryl silicone resins, methyl silicone oils and elastomers, and the methylchlorosilanes for water-repellent films. 

As outlined in the previous chapters, the preparation of silicone polymers involves first the preparation of organosilicon halides or esters, secondly the hydrolysis of an appropriate mixture of these intermediates, and finally the condensation or rearrangement of the polymers to achieve the desired molecular arrangement. Only in the first step is there a choice of preparative methods the second and third steps are carried out in much the same way, regardless of how the intermediates were made. From the standpoint of synthesis, the problem therefore comes down to the preparation of the methyl-, ethyl-, and phenylchlorosilanes or ethoxysilanes. Of these the methyl compounds are the most important, because they are used directly for the water-repellent treatment and are the only intermediates required for the oils, elastomers, and some types of resin. 

The possible toxicity of methylchlorosilanes and of all the silicone resins, oils, and elastomers is naturally a matter of concern in their manufacture and use. The methylchlorosilanes hydrolyze immediately they are inhaled and so have the odor and effect of hydrogen chloride at all low concentrations they cause no ill effects. Four years experience on the part of a group of laboratory workers has not revealed a single instance of toxic effect, either acute or chronic, from the inhalation of methylchlorosilanes. Fluoroscopic examination has revealed no deposits in the lungs, nor have the individuals in the group suffered any other disorder that could be attributed to silicon or its compounds. It must be concluded that there is no accumulation of organosilicon substances in the body that can be detected over this interval of time. 

Elastomers. The most advanced applications from a commercial viewpoint are found in the use of polyphosphazenes as elastomers that remain flexible at low temperatures, are resistant to hot oil and hydrauhc fluids, and resist combustion. Polymers with both trifluoroethoxy and heptafluorobutoxy side groups were originally developed for aerospace and automotive applications, but other elastomers that bear both trifluoroethoxy and organosilicon side groups are now... 

Well over 100000 organosilicon compounds have been synthesized. Of these, during the past few decades, silicone oils, elastomers and resins have become major industrial products. Many organosilicon compounds have considerable thermal stability and chemical inertness e.g. SiPha can be distilled in air at its bp 428°, as can PhaSiCl (bp 378°) and Ph2SiCl2 (bp 305°). These, and innumerable similar compounds, reflect the considerable strength of the Si-C bond which is, indeed, comparable with that of the C-C bond (p. 338). A further illustration is the compound SiC which closely resembles diamond in its properties (p. 334). Catenation and the formation of multiple bonds are further similarities with carbon chemistry, though these features are less prominent in organosilicon chemistry and much of the work in these areas is of recent... 

The anomalous response of the flame ionisation detector in the analysis of organosilicon compounds has been investigated454,455. The behaviour of the compounds was studied on columns of silicone elastomer on Chromosorb or Celite. Above a critical sample size, the top of the peak became inverted, the maximum height remaining the same, but the depth of the inverted portion increased with increasing sample size. 

The same method was used to prepare thermoplastic siloxane elastomers based on poly(arylenevinylenesiloxanes) compounds [75]. The polyhydrosi-lylation was then performed between an a, (w-dialkenylarylenevinylene and an organosilicon compound containing two Si-H, in the presence of diCpPtCb as shown in Scheme 27. 

Polyaddition of organosilicon dihydrides, mainly dihydro(poly)siloxanes to dialkenyl-substituted organic compounds also known as hydrosilylation copolymerization, leads to polycarbosiloxanes with functionalized organic segments (359). Platinum-catalyzed polymerization hydrosilylation of a,allyl-substituted bisphenols, imides, or amides leads to the synthesis of block copolymers that are useful thermoplastic elastomers (Scheme 40). 

---