Silastyrene

Interestingly, 56 cannot be obtained photochemically from the benzodisilacyclobutene 57 instead silastyrene 64 is formed as an intermediate46. 64 is produced by homolytic bond scission of the Si—Si bond in 57 followed by intramolecular disproportionation of... 

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. 

The.unusual ability of poly(silanes) to absorb UV light led to the demonstration that Asp5-doped poly(silastyrene) is a semiconductor. The band gap in common silane polymers is about 4eV in contrast to a value of almost 8eV for carbon chains. Conducting and photoconducting properties have been studied. Only holes were found mobile (mobilities of 10 cm V s at 20°C) and it appears hole transport occurs via the a electronic states of the silicon backbone rather than hopping between chain substituents. 

Poly(phenylmethylsilylene) [-SiPhMe-] and Poly(silastyrene) [-SiPhH-SiH2-]... 

MM calculations with full geometry optimization have been carried out to calculate the molecular structure and conformational energies od, ..modeJ -.cpmpounds for poly (phenylmethylsilylene) [-SiPhMe-] and poly(silastyrene) [-SiPhH-SiH2-]. In each case the calculations considered both the isotactic and syndiotactic stereochemical isomeric forms of the model compounds. The structures considered are illustrated in Figures 6 and 7. 

Most of the hydrophobic polymers tested exhibited absorption curves similar to the fluoroacrylic in Pig. 2. The resultant constants and a list of the polymers tested are given in Table 1. It is interesting to note that all materials tested, except the silastyrene, had discernible moisture permeabilities and thus cannot be considered hydrophobic or impermeable by military standards. 

The range of values given for the siloxyimides covers three different materials tested of that type. Fluorosilicone demonstrated various anomalies which did not permit application of the given equation. The silastyrene showed no detectable moisture solubility. This material was selected as potentially hydrophobic due to its apparent low polarity. It contains methyl groups bonded to a silicon backbone. Although silastyrene has potential,... 

The foregoing moisture solubility data shows that the term "hydrophobic polymer" is really not applicable for the materials tested, except possibly the silastyrene. A brief review of some theoretical presentations by L.H. Lee and others (5,6) indicate that the initial objective of finding a hermetic polymer sealant may never be realized. Fig. 3 from a presentation by Lee (5) reveals the reason for this assumption. 

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