TMO polymerization

Tetramethylolacetylenediurea cotton cross-linking agent, 8 26 Tetramethylolmethane, 2 47 Tetramethylorthosilicate (TMOS), polymerization of, 23 62 Tetramethylphosphonosuccinate (TMPS), 19 29... 

On the basis of our prior work on PO polymerization, with this same chelate catalyst CD, TMO polymerizes about 10 times more slowly than PO does under the same conditions. Also, the TMO homopolymer is much less soluble than poly(propylene oxide), since the latter polymer is soluble in heptane and methanol, both nonsolvents for poly(trimethylene oxide). The TMO homopolymer is, of course, crystalline because of its very regular structure. On the other hand, the poly(propylene oxide) prepared with the chelate catalyst is largely amorphous because of tacticity and head-to-tail variations in structure which are not possible in poly(tri-methylene oxide). 

This TMO polymerization with the chelate catalyst no doubt involves coordinate propagation and is the first such case of coordinate propagation of an oxetane. Heretofore, oxetanes have been cationically polymerized. There are several reasons for concluding that this chelate catalyst system is a coordination polymerization. First, the very high molecular weight obtained at elevated temperature with a low rate is characteristic of coordination polymerization rather than of cationic polymerization. Also, Vandenberg s work on the cis- and trans-2,3-epoxy-... 

For silica, much of the work in this area was carried out in the 1980s and the reader is referred to the series of proceedings volumes from the Materials Research Society entitled Better Ceramics through Chemistry. 63 To illustrate typical precursor structures, and the role of reaction chemistry on precursor structure, Fig. 2.3 presents capillary gas chromatography results for the hydrolysis of tetramethoxysilane [TMOS Si(OCH3)4].72 Typical polymeric species formed (Fig. 2.3a) include linear and cyclic structures. 

The preferentially employed approach for the fabrication of inorganic (silica) monolithic materials is acid-catalyzed sol-gel process, which comprises hydrolysis of alkoxysilanes as well as silanol condensation under release of alcohol or water [84-86], whereas the most commonly used alkoxy-silane precursors are TMOS and tetraethoxysilane (TEOS). Beside these classical silanes, mixtures of polyethoxysiloxane, methyltriethoxysilane, aminopropyltriehtoxysilane, A-octyltriethoxysilane with TMOS and TEOS have been employed for monolith fabrication in various ratios [87]. Comparable to free radical polymerization of vinyl compounds (see Section 1.2.1.5), polycondensation reactions of silanes are exothermic, and the growing polymer species becomes insoluble and precipitates... 

Silica precursors, tetraethoxysilane and tetramethoxysilane (TEOS and TMOS) are able to solvate some organic polymers. This enables the silica precursor to polymerize in the environment of an organic polymer solution. The number of polymers that form solutions with sol-gel formulations is, however, limited. Some initially soluble polymers tend to precipitate during gelation when a change in solvent composition leads to phase separation. 

A second, equally powerful means to prepare such materials relies on traditional inorganic polymerization tools, most notably sol-gel polymerization.24 25 A number of excellent reviews have appeared on this subject as well.5,12,17 In sol-gel processing, the functional monomer [i.e., an organoalkoxysilane such as 3-aminopropyltrimethox-ysilane (APTMS)] is combined with the cross-linking agent [i.e., a tetrafunctional alkoxysilane such as tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS)], a catalyst (such as hydrochloric acid or ammonia), and the template molecule. The resultant sol can be left to gel to form a monolith, which can then be dried, sieved, and extensively washed to remove the template. Alternatively, the sol can be spin coated, dip coated, or electrodeposited on a surface to yield a thin film, which can be subsequently washed with a solvent to remove the template and yield the imprinted cavities. 

Small molecule imprinting in sol-gel matrices has received considerable interest in recent years, undoubtedly due to the flexibility offered by the sol-gel process.5 Two different approaches have been utilized covalent assembly and noncovalent self-assembly.9 In the covalent assembly approach, the polymerizable functional group (i.e., the silicon alkoxide group) is covalently attached to the imprint molecule. The functionalized imprint molecule is then mixed with appropriate monomers (i.e., TMOS) to form the imprinted materials. After polymerization, the covalent bonds are cleaved to release the template and leave the molecular recognition pocket. Figure 20.4 shows a diagram of this process. 

For the xerogel of 54 these peaks are always present, and their position is unchanged regardless of the texture of the solid or of the kinetic parameters (solvent, catalyst, concentration) used in the hydrolysis/polycondensation step. However, co-polymerization with various amounts of TMOS was found useful for the investigation of the structure of these materials. 

The (n.BuO).Al-O-Zn compound, with a mean degree of association n = b In non polar solvents is particularly efficient the half-polymerization time of methyloxi-rane (MO) in h tane at 50 C amounts to 5 minutes (with Tmo] = IM, andjzn1= 10. M) the reaction follows a simple... 

Despite the fact that gelation can be conducted under either acidic or basic conditions, sihca aerogels are most often formed from base-catalyzed reactions. This is because the polymeric fi amework of the acid-catalyzed gel contains a larger portion of smaller pores than the base-catalyzed colloidal analog. Removal of solvent from these smaller pores without gel compaction is difricult, even under supercritical conditions. One successful approach to access ultra-low-density aerogels with polymeric frameworks is to use a two-step acid/base gelation process such as that used by TUlotson and Hrubesh (14). The first step is to perform acid catalysis of tetramethox-ysilane (TMOS) with hydrochloric acid to produce a sol from which the alcohol... 

The preparation of a material from a nanoobject can be performed by the sol-gel route, by which it is included it as a host compound in a polymerizing mixture of water, solvent and a silica source (TMOS (tetramethoxysilane), TEOS (tetraethoxysilane)) (Fig. 6). The resulting solid is a biphasic system at the molecular scale but also sometimes at the macrometer scale. As a consequence the two components can be separated by physical means. 

X-ray analysis of materials prepared by co-polymerization of a rigid precursor with various amounts of TMOS also agrees with the short-range order organization. In this case the fluctuations in the position and intensity of the peaks observed in X-ray patterns indicate the formation of a lamellar structure partially swelled one-dimensionally by the silica phase that results from the hydrolysis of the TMOS (Fig. 17) [106]. 

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