Monomers aluminate

Proposition 2 When the initiator solution is introduced into a monomer solution, the cations react with the double bond to give the active species which is an aluminated carbenium ion containing an Al-C covalent bond, as shown in Equation (iii) ... 

We concluded, therefore, that in sufficiently pure alkyl halide solvents the tert-alkyl tetrahaloaluminates are stable electrolytes and that previous failures to produce them, and the consequent legend of the instability of tcrt-alkyl carbenium ions, arose from the use of inappropriate and insufficiently rigorous experimental techniques. On this basis it seems highly probable that in the polymerised solutions the cations R+ partaking in reaction (viii) were also original ions, i.e., 2 at the end of a live chain and 3 and 4 formed by alumination of a terminal double bond, and not derived ions formed by degradative reactions of monomer or polymer. 

The shortest gel times of all are observed (Figure 3) when the silicate solution is premixed with sufficient alkali to depolymerise it entirely to monomer. Figure 7 shows that increasing the amount of monomer increases the amount of aluminate/silicate association. This species seems to be critical for gel formation, being both the nutrient and the precursor to forming nuclei. When it is present in large quantities, gelation is almost instantaneous. 

Generally the first step is the preparation of the reaction mixture at low temperature (< 60°C). The different ingredients are mixed in this step, which in most cases results in the formation of the so-called synthesis gel. In this gel silicate and aluminate monomers and oligomers in solution are in equilibrium with condensed silicate and aluminate units in the gel phase. In some cases a digestion period is necessary to reach this equilibrium. 

Coordination polymerization of hydroxyl, carboxyl and amino monomers can also be effected by the judicious use of protecting groups. For example, amino and hydroxyl monomers have been protected by silyl ethers and aluminate salts for Ziegler Natta and/or metallocene polynrierization and carboxyl monomers have been protected via aluminate salts. Alternatively, organoborane synthons have been used to carry... 

Alternatively, the acid, amino, or alcohol monomers can be converted to aluminate salts (30) by alkyl aluminum reducing agents. These salts are stable to Z-N catalysts, e.g. vanadium . Specifically, 5-norbomenc-2 carboxylic acid, amine or alcohol is masked by alkyl aluminums, such as (i-Bu)3AL Terpolymerization of the masked monomers with ethylene and propylene and work-up leads to functional (-COOH,-OH,-NHR) EPDM rubbers directly. 

It is assumed that the monomers are present as aluminates. Although separately pretreating the alcoholic monomers with MAO prior to polymerization did not improve comonomer conversion of incorporation (ethylene uptake was improved), the polymerization procedure involves mixing of the polar comonomer with MAO prior to zirconocene addition, and higher total levels of MAO (ca. 10 000 equiv per Zr) were found to have a more favorable effect on conversion. 

Some silicate species are more reactive than others. McCormick et al. [20] have shown that in a silicate solution containing the monomer, dimer and cyclic trimer, the latter was the most reactive towards Al incorporation. Van den Berg et al. [21] have shown that the D4R anion does not react with aluminate anion at room temperature. Al is only incorporated in the D4R at higher (90 C) temperatures, where a crystalline phase is formed. 

VS 7207, 7349] VS 7518. See Cyclomethicone VSA-38P. See Sodium aluminate VT. See Vinyltoluene monomer VT-008 Extract of Burdock. See Burdock (Arctium minus) extract VT-015 Extract of Cornflower. See Cornflower (Centaurea cyanus) extract VT-027 Extract of Kelp. See Kelp (Macrocystis pyrifera) extract... 

The new monomer cation then starts another polymer chain. If, on the other hand, isobutylene (or even norbornadiene) is polymerized with AICI3, saturated end groups and an unsaturated monomer cation are primarily formed. This cation then starts the polymerization of another polymer chain, whereby the unsaturated group formed in this way is aluminated by the initiator. Thus, each polymer molecule contains an aluminum atom, produced as in equation (18-98) or equation (18-101) ... 

Other examples of set retarders are ethylenediamine tetraac-etic acid and nitrilotriacetic acid, or a combination of these compounds (11). StiU another example of a set retarder for Portland cement is a copolymer formed from a monomer of 2-acrylamido-2-methyl-l-propane sulfonic acid. Examples of set retarders for calcium aluminate cements are polymeric phosphate salts such as sodium tripol q3hosphate (12). 

Initiation was shown to proceed mainly by attack of the alkoxide moieties of the aluminate complex, thus yielding poly-(POx) with an alkoxide head group and, after hydrolysis, a hydroxy chain end. The presence of small fractions of poly-(POx) with hydrogen or alkyl head groups indicates the minor contribution of other initiation mechanisms involving ligand reorganization in the initial complex (see Scheme 41), as well as some, but limited, chain transfer to monomer. 

Sol-gel synthesis is the process of formation of porous, three-dimensional, integrated solid network (gel) of either discrete particles or network potymers from the conversion of monomers into stable suspension of colloidal solid particles or pol miers (sol) in a continuous liquid phase. Most popular precursors for the synthesis of colloids are metal alkoxides and alkoxysilanes. Tetramethoxysilane (TMOS) and Tetraethoxysilane (TEOS) are commonly used alkojq silanes, which form silica gel. The remarkable property of these silanes is that they readity react with water in the presence of shorter chain alcohol such as ethanol and ammonia to form monodispersed silica particles [7]. The size of silica particles formed is between 50 and 200 nm and depends on the silica ester used, type of alcohol, and molar ratios of water and alkoxysilane [32]. In this process, alcohol acts as a homogenizing solvent between alkoxides and water as both are immiscible but can be easily dissolved in alcohol. With the presence of this homogenizing agent, hydrolysis can be facilitated [33] due to the complete miscibility. However, aluminates borates and titanates often mixed with TEOS or TMOS are commonly used in sol-gel process. The hydrolysis of alkoxysilane proceeds according to Stober s process (Fig. 18.6). 

At pH > 8, tlie precursor of the hydroxide pha.se is probably the tetrahedral [AI(0H)3(H20) . Indeed, alkaline solutions contain mostly aluminate ions [AI(0H)4j , as confirmed by a1 NMR [56]. This complex ion is. stable as a monomer. Through acidification or reaction with water ... 

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