Silane high polymers

On the basis of the results described, there seem to be at least three processes which are responsible for the molecular weight reduction in substituted silane high polymers upon irradiation in solution (i) Chain abridgement by silylene extrusion which occurs only at short wavelengths (ii) chain scission by silicon-silicon bond homolysis and (iii) chain scission by 1,1-photochemical reductive elimination. 

Table III shows x values for other structurally regular substituted silane high polymers measured both at 1.064 and 1.907 /an. Examination of this data suggests relatively little difference between the polysilanes with nonplanar, yet regular structures and trans planar PDN6S which is included in the table for comparison. This result is a little surprising given that changes in backbone conformation can cause spectral absorption shifts of more than 60 nm.

For a recent review of substituted silane high polymers, see ... 

In summary, substituted silane high polymers are a new class of scientifically interesting radiation sensitive polymers with demonstrated potential as O2-RIE resistant lithographic materials. 

The chemistry of poly silane high polymers is undergoing rapid development because of their scientific interest and technological applications . ... 

Synthesis is typically by alkali metal-mediated coupling of dichlorosilanes or 1,2-dichlorodisilanes, although electrochemical coupling of chlorosilanes and dehydrocoupling of primary and secondary silanes also often lead to oligomeric (as opposed to high polymer) fractions. 

Hydrolysis of a reactive silane derivative under the proper conditions first produces a silanol, but except in the case of a few that are exceptionally stable, this product is not isolated, since the acid or alkaline reagents that are normally present cause most silanols to condense rapidly to form siloxanes. The product generally isolated when a dialkyl-or diaryl-substituted silane is hydrolyzed is, of course, a mixture of cyclic polysiloxanes, (R2SiO)n, from which high polymers (often elastomeric) are obtained by catalytic rearrangement and polymerization reactions. 

The ultimate combination of HPLC and AC is effectuated in High Performance Affinity Chromatography (HPAC).47 The development of this hybrid technique was highly assisted by the use of modified silica. Traditional polysaccharide supports may not be used for HPAC, because they lack mechanical stability to withstand the high pressure drops, inherent to this method. Modified silica beads are well suited. These may be coated with active groups as in normal AC applications. Additionally, if the separation requires the use of an organic stationary phase, the silica beads are modified with a silane or polymer with subsequent deposition of polysaccharides such as dextrans, agarose or cellulose.50... 

Some reactions between alkyl silanes and phosphoric acid, or its alkyl ester salts, can yield complex mixtures of products which include high polymers. Some of the better defined reactions in this category include (9.265) through (9.268)... 

Hyflex silane, Y-5889 OSi product, ethoxylated propylsilane Epoxy polyester, urethane Lower viscosity, higher loading potential, faster dispersion, improved physical properties, high polymer compatibility... 

At present, these silane-terminated polymers have mechanical properties suitable for general use in elastic bonding applications, but usually do not achieve the same high mechanical strengths as pure polyurethane adhesives. 

The high modulus with low hysteresis of the treated clays vs. carbon black, as seen in a natural rubber compoimd in Table 7, suggest that the silane mediated polymer-clay bond is stronger than the polymer-black bonds at the carbon black active sites. Deformation results in loss of fewer polymer-filler bonds with the treated elays, so that energy loss as heat is less compared to the carbon black. This stronger polymer-clay bond is also consistent with the higher modulus and abrasion resistance. 

---