Silicon curing catalysts

Reaction of TYZOR DC and 1,3-propanediol gives titanium 1,3-propylenedioxide bis (ethyl acetoacetate) [36497-11-7]y which can be used as a noncorrosive curing catalyst for room-temperature-vulcanizing silicone mbber compositions (99). Similar structures could be made, starting with titanium bis-acetylacetonates, such as that shown in structure (9). 

Model Networks. Construction of model networks allows development of quantitative structure property relationships and provide the ability to test the accuracy of the theories of mbber elasticity (251—254). By definition, model networks have controlled molecular weight between cross-links, controlled cross-link functionality, and controlled molecular weight distribution of cross-linked chains. Silicones cross-linked by either condensation or addition reactions are ideally suited for these studies because all of the above parameters can be controlled. A typical condensation-cure model network consists of an a, CO-polydimethylsiloxanediol, tetraethoxysilane (or alkyltrimethoxysilane), and a tin-cure catalyst (255). A typical addition-cure model is composed of a, co-vinylpolydimethylsiloxane, tetrakis(dimethylsiloxy)silane, and a platinum-cure catalyst (256—258). 

A second class of silicones cures by addition polymerization initiated by a catalyst Polymerization occurs by a free-radical mechanism involving a vinyl, allyl, or other unsaturated group of a silicone monomer (Figure 3.9). Homopolymers can be formed... 

Properties Lt. yel. liq. sol. in benzene, toluene, petroleum ether, aromatic soivs. insol. in water, methanol m.w. 405.11 dens. 1.25 flash pt. > 230 F ref. index 1.4930 Toxicology TLV 0.1 mg(Sn)/m of air toxic irritant Uses Polymerization catalyst for mfg. of PU foam, coatings, adhesives, sealants, elastomers lubricant addition agent stabilizer for transfonner oils curing agent for RTV silicone rubber catalyst for PU resins in food-pkg. adhesives Regulatory FDA 21CFR 175.105... 

Storage Moisture and light-sensitive Uses Electroplating platinizing pumice and the like for catalysts etching zinc for printing platinum mirrors indelible ink ceramics microscopy RTV addition-cured, 2-component silicone rubber catalyst photographic chemicals... 

Uses Polymerization catalyst for mfg. of PU foam, coatings, adhesives, sealants, elastomers lubricant addition agent stabilizer for transformer oils curing agent for R7V silicone rubber catalyst for PU resins in food-pkg. adhesives... 

Weak P-donor interactions could be the reason for the frequently reported high reactivity of hydroxylaminosilanes. These include claims for new cross-linking agents and cold-curing catalysts for silicone polymers [6], and more recently, the catalysis of the alkoholysis of Si-H functions in poly-phenylsilane [7]. 

It is common practice in the silicone rubber industry to prepare specific or custom mixtures of pol5uner, fillers, and cure catalysts for particular applications. The number of potential combinations is enormous. Improved properties of the rubber can be achieved if a premix of some of the inputs is performed. A premixing process for fumed silica, for example, involves the breaking down of gum particles into a fine dispersion in a bed of fumed silica. As the process continues, fumed silica coats the gum surface preventing reagglomeration of these particles (480). 

After the components are mixed and heated, the catalyst initiates the cross-linking reaction by addition of the Si—H group to the double bond (eq. 37). Latent cure catalysts have been developed that allow the formulation of one-component products (499). These systems work by incorporation of platinum ligands that deactivate the platinum hydrosilylation catalysts at room temperature. When heated to temperatures above 100°C, these catalysts become active (see also Silicone Network Formation). 

Silicones are among the least toxic of all polymers. In a few cases they are supplied or applied in common aromatic solvents such as xylene which require normal and appropriate handling precautions. In certain other cases common curing catalysts such as peroxides or organo-metallic salts are used and these additives again call for the usual safe... 

Dibutyltin Di-2-Ethylhexoate n (C4H9)2Sn (OOCCyHis) - A white, waxy solid made by reacting dibutyltin oxide with 2-ethylhexoic acid. Used as a catalyst for silicone curing and in polyether foams. 

Moisture-Curing Silicones. The formulation of moisture-curing sHicones includes a sHicone polymer, filler, a moisture-reactive cross-linker, and sometimes a catalyst. The most common sHicone polymer used in sealant formulations is an alternating sHicon—oxygen backbone with methyl groups attached to the sHicon such as the sHicone polymer (1). 

Silicone reliners are supplied as either a one-component system that cures in the presence of moisture or heat, or a two-component system containing base and catalyst. Both types adhere poody to denture base and carmot be polished satisfactorily. Some silicones support propagation of bacteria such as Candida albicans. Acrylic-based sifloxane monomers and resins have been proposed for overcoming these deficiencies (211). 

Silicon—Ca.rbon Thermoset. The Sycar resins of Hercules are sihcon—carbon thermosets cured through the hydrosilation of sihcon hydride and sihcon vinyl groups with a trace amount of platinum catalyst. The material is a fast-cure system (<15 min at 180°C) and shows low moisture absorption that outperforms conventional thermosets such as polyimides and epoxies. Furthermore, the Sycar material provides excellent mechanical and physical properties used in printed wiring board (PWB) laminates and encapsulants such as flow coatable or glob-top coating of chip-on-board type apphcations. 

Newer silicone adhesives having solids levels up to 97% are also commercially available [109]. Instead of using silanol condensation reactions, they rely on addition chemistry between vinyl functional silicone oligomers and silicon hydride terminated silicones. This addition reaction is typically facilitated with platinum derived catalysts. This hydrosilation process can be run at reduced oven temperatures, but the finished products typically do not yield the same balance of properties as seen for condensation cure materials. 

Hydrosilation silicones or addition cure systems utilize a hydride functional crosslinker with a vinyl functional base polymer and a noble metal catalyst. While the cure can be initiated with UV [48,49], thermal cure versions dominate the commercial market [23,50]. In thermal cure systems, inhibitors are necessary for processing and anchorage additives are common. 

---