Alkoxysilanes monomers

The exact mass determination of emitted secondary ions yields informations about the molecular structure of the thick film. In the low mass area the fragmentation of the quasimolecular cation m/e = 163, i.e. (EtO)3Si+ derived from the alkoxysilane monomer gives rise to the positive ions m/e = 135, 119, 107, 91, 79, 63. The resulting fragmentation pattern can be described as follows ... 

Scheme 3. S M pictures of Tsi/alkoxysilane-modified oligosiloxanes cured in the presence of co-alkoxysilane monomers.

Blocking one substituent of the alkoxysilane monomer, to enable relaxation of the polymer gel. 

Copolymers of a cationic monomer and a vinyl alkoxysilane may be prepared by conventional vinyl polymerization techniques. These techniques include solution polymerization in water and emulsion polymerization with either free radical initiators or redox initiators. 

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. 

All cationically polymerizable monomers can be potentially used in this process however, the main study has been focused so far on the most reactive oxirane and vinyl ethers [4], Alkoxysilane derivatives - the most common acid-sensitive monomers for the synthesis of siloxane materials through the use of sol-gel methods - were not used extensively. Only a few examples of their application in photo-activated cross-linking can be noted, mainly in co-reaction with oxirane sites [5]. Typically, alkoxysilanes are subjected to an acid- or base-catalyzed process involving hydrolysis of an =SiOR group and then condensation of the formed silanol with another molecule bearing an =SiOH or =SiOR function to give a siloxane linkage [6]. It was of interest to combine the properties of cross-linked silicone materials with the ones provided by sterically overloaded... 

Silphenylenes, aromatic-containing silicon monomers, can be produced in 50 88% yields by the reaction of halo- and dihalobenzenes with chloro- and alkoxysilanes under Barbier conditions. Iodine, bromine, and cuprous chloride are used as initiators with THE, TMEDA, toluene, or xylene as solvents. Shavings or powdered magnesium can be used [Eqs. (66) and (67) 134,135]. 

In this paper, physical and gas transport properties of HBPIs synthesized with various dianhydride monomers and their silica hybrid membranes prepared by sol-gel reaction with two kinds of alkoxysilanes, TMOS and methyltrimethoxysilane (MTMS), individually or simultaneously, are discussed. The methyl group of MTMS will prevent the formation of robust three-dimensional Si-O-Si network in the hybrid membranes. It is expected that the loose Si-O-Si network formed from MTMS induces unique physical and gas transport properties of the hybrid membranes. 

TAPOB was synthesized by reduction of l,3,5-tris(4-nitrophenoxy)benzene with palladium carbon and hydrazine in methanol [14], 6FDA was kindly supphed from Daikin Industries, Ltd. Pyromellitic dianhydride (PMDA) and 4,4 -oxidiphthahc anhydride (ODRA) were obtained from Daicel Chemical Industries, Ltd. and Manac Incorporated, respectively. TMOS, MTMS, 3-aminopropyltrimethoxysilane (APTrMOS), and N,N-dimethylacetamide (DMAc) were purchased from Aldrich. Chemical structures of monomers and alkoxysilanes are shown in Figure 8.2. 

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