Condensation cure silicones

Two-part room temperature condensation cure. Silicone can be formulated into two-part systems [3,12,14,33] that prevent the reactive groups from coming into contact before they are needed. The reactions in these systems are based on the condensation of a silanol group with an alkoxy silane group, catalyzed by organo-tin compounds (Scheme 9). 

Since the Initial work of White (IQ), the Bell System and other major semiconductor users have extensively used silicones In the protection of numerous thin-film and thlck-fllm devices (24.25). The materials primarily have been condensation-cure silicones In xylene dispersion. The performance of encapsulated semiconductors used within the Bell System Is well documented (26). and studies continually In process support the use of silicones for the prevention of electronic component deterioration under conditions similar to the In-vlvo environment. 

Silicone rubber has a three-dimensional network structure caused by cross-linking of polydimethyl siloxane chains. Three reaction types are predominantly employed for the formation of silicone networks (155) peroxide-induced free-radical processes, hydrosilylation addition cure, and condensation cure. Silicones have also been cross-linked using radiation to produce free radicals or to induce photoinitiated reactions. 

HMIS Health 2, Flammability 2, Reactivity 1 Uses Crosslinking agent for condensation cure silicones raw material for silicone sealants coupling agent release agent lubricant blocking agent chemical intermediate Features Neutral... 

Condensation-cured silicones. Both the heat-cured and RTV silicones are formed by condensation polymerization and are sometimes referred to as alkoxy- or acetoxy-cured systems. The basic hydroxysilane... 

The two-part sihcone adhesive/sealants do not require moisture to cure and produce a superior deep-section cure. Two types are available addition-cure and condensation-cure. Addition of curing produces no by-products, can be heat-accelerated, produces negligible shrinkage, and provides the best high-temperature resistance of all silicone adhesives. Condensation-cure silicones are not easily inhibited and can be used on a greater variety of materials. ... 

Condensation-cured silicones. Both the heat-cured and RTV silicones are formed by condensation polymerization and are sometimes referred to as aUcoxy- or acetoxy-curedsystems. The basic hydroxy silane starting materials are produced by the hydrolysis of mixtures of mono-, di, and trichlorosilanes as depicted inFig. 3.7. Condensation with elimination of water produces hydroxyl-terminated alkylpolysiloxanes. These resins can be further polymerized in the presence of alkoxysilanes such as propylorthosilicates to yield the RTV silicones (Fig. 3.8). Catalysts such as organotitanates or dibutyltindilauratet may accelerate the curing process. 

The following example moves away from condensation-cured silicones to vinyl-addition-cured Pt mediated network elastomers. Given in Figure 13.10 are a series of 1st derivative TGA thermograms of addition-cured model silicone network elastomers with various network architectures. 

Subambient thermal volatilization analysis can also be used to probe the effects of physical fillers in silicone materials. In 2008 Lewicki et al. [51] studied the degradation profiles and product speciation of a series of montmorillonite clay filled silicone elastomers which had been characterized using SATVA. Shown in Figure 13.17 are a series of TVA thermal degradation profiles for the non-oxidative degradation of a bimodal-condensation-cured silicone matrix, filled with 0-8 wt% of organically modified montmorillonite (0-MMT) exfoliated nanoclay platelets. 

Figure 13.18 SATVA differential distillation traces for the products of the thermal degradation of a series of condensation-cured silicone elastomers filled with 0-8 wt% O-MMT nanoclay. A-E correspond to 0,1,2,4 and 8 wt% clay loadings. The left shows the full scale product profile having only 2 peaks (i and ii) making up 95% hy volume of the total distillate. On the right is an expansion of the region from -190 to -40 C and shows the further eight minor products (i-vii) which make up the remainder of the distillate.

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