Polysiloxane crosslinking systems

The observations, coupled with the cured films excellent solvent resistance, indicates a tightly crosslinked structure free from the plasticizing effects of low molecular weight polysiloxanes and in which the colloidal silica particles act as part of the crosslinking system. 

The crosslinking efficiency of the peroxide process can be increased for some systems by incorporating small amounts of a comonomer containing vinyl groups into the polymer. This approach is used for polysiloxanes by copolymerization with small amounts of vinyltrimethylsilanol... 

Itoh et al. [141] patented a blend of polyurethane and silicone gum with vinyl groups. The crosslinking reaction of the silicone component was achieved using a radical generator. Chorvath et al. [142] also patented a system composed of polyamide or polyester as the thermoplastic and vinyl-containing polysiloxane cured by a peroxide or non-peroxidic initiator such as 3,4-dimethyl-3,4-diphenylhexane (HTV). Moreover, they added different compatibilizers such as amino-terminated or amino-grafted polysiloxane, epoxy- or isocyanato-functionalized polysiloxane. 

The so-called RTV-2 method — room temperature vulcanization of a two component system — adds a crosslinking agent such as tri-or tetraalkoxysUane and a metallic salt catalyst to hydroxyl terminated polysiloxane precursors. The hydroxyl end groups react with the silicic ester, e.g., tetraethyl silicate, in a condensation reaction and ethanol is liberated. This condensation reaction is catalyzed by stannous-based catalysts such as dibutyltindilaurate. 

The rate constant kp of the phenol delivery was determined on a system where the crosslinking density is equal to zero, i.e. the 100% BPC modified polysiloxane PSO. It was found to be equal to 4.2 lO" dayl. 

In each series PSO represents the limit system it is the limit of the s-IPNs series with a zero proportion of PC and it is also the limit of the single polysiloxane network series with a zero crosslinking density. 

Figure 10 Formation of linear and crosslinked polydimethylsiloxane networks. Room temperature vulcanization (RTV) is performed by reacting methoxysilyl-terminated polymer 75 and methyltrimethoxysilane 76. Hydrolysis produces transient silanols 77 and 78 whose dehydration yields silicone precursor 79. Two-part systems are based on the platinum-catalyzed addition reaction between vinyl-terminated polysiloxane 80 and polydimethylsiloxane carrying either only terminal 81 or multiple silane (Si-H) pendent groups. Silicone main chains of the resulting polymer 82 are linked through silicon-...

Chem. Descrip. Polysiloxane sol n. in 2,6-dimethyl4-heptanone Uses Defoamer for org. systems incl. chlorinated rubber, epoxy, two-part polyurethane, alkyd, alkyd/melamine, self-crosslinking acrylates, polyesters used in resinous and polymeric coatings in food pkg. 

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