Lead-silicon polymers properties

This chapter first reviews the general structures and properties of silicone polymers. It goes on to describe the crosslinking chemistry and the properties of the crosslinked networks. The promotion of both adhesive and cohesive strength is then discussed. The build up of adhesion and the loss of adhesive strength are explained in the light of the fundamental theories of adhesion. The final section of the chapter illustrates the use of silicones in various adhesion applications and leads to the design of specific adhesive and sealant products. 

The atomic composition of polymers encompasses primarily non-metallic elements such as carbon (C), hydrogen (H) and oxygen (O). In addition, recurrent elements are nitrogen (N), chlorine (Cl), fluoride (F) and sulfur (S). The so-called semi-organic polymers contain other non-metallic elements such as silicon (Si) in silicone or polysiloxane, as well as bor or beryllium (B). Although other elements can sometime be found in polymers, because of their very specific nature, we will not mention them here. The properties of the above elements lead to specific properties that are common of all polymers. These are ... 

Summary During the last few years intense research has been focussed on the elaboration of synthetic materials [1-4] based on modified silicon esters. Products with interesting properties were formed by synthesis of a novel group of derived silicon esters. The condensation of carbonyl- and amino groups leads to organotrialkoxysilanes containing azomethine bonds. From these compounds three-dimensional, cross-linked silicon polymers were synthesized by hydrolysis/condensation. 

Hydrosilylation is also used in the curing of silicone rubber. Such curing leads to cross-linking of the polymer chains and turns a syrupy polymer to a gum rubber or a soft polymer to a hard one. Reactions 5.5.2 and 5.5.3 show the formations of new bonds that can bring about these changes in polymer properties. 

Silicone adhesives are generally applied in a liquid and uncured state. It is therefore the physical and chemical properties of the polymers, or more precisely of the polymer formulation, that guide the various processes leading to the formation of the cured silicone network. The choice of the cure system can be guided by a variety of parameters that includes cure time and temperature, rheological properties in relation with the application process, substrates, the environment the adhesive joints will be subjected to and its subsequent durability, and of course, cost. 

There are several problems encountered with silicon containing polymers that affect their lithographic properties. First, a decrease in Tg often accompanies silicon incorporation into a polymer. This may lead to dimensional instability of features during processing. Also, the hydrophobic nature of most useful silicon substituents may hinder the aqueous development of these resists. Careful selection of the polymer components can alleviate and/or eliminate these problems. 

Research and development in the field are still continuing at a fast pace, particulady in the area of absorption and emission characteristics of the polymers. Several reasons account for this interest. First, the intractable poly dime thylsilane [30107-43-8] was found to be a precursor to the important ceramic, silicon carbide (86—89). Secondly, a number of soluble polysilanes were prepared, which allowed these polymers to be studied in detail (90—93). As a result of studies with soluble polymers it became clear that polysilanes are unusual in their backbone CT-conjugation, which leads to some very interesting electronic properties. 

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