Dimethyl silane determination

CMCs of these polyfluorinated surfactants are of the order of 10 5 m.47 Plots of the observed H chemical shifts versus surfactant concentration of cetyl trimethyl ammonium chloride, cetyl pyridinium chloride, cetyl dimethyl phenyl ammonium chloride, cetyl dimethyl benzyl ammonium chloride, cetyl dimethy 1-2-phenyl ethyl ammonium chloride, and cetyl dimethyl-3-phenyl propyl ammonium chloride, are sigmoidal and were fitted to a model based on the mass action. The H chemical shift-based CMC values are in excellent agreement with those determined by the surface tension method.48 The micellization processes of dodecyl trimethyl ammonium halides (chloride and bromide) studied by calorimetric titration show different behaviors at 298 K. However, these disappear at 313 K, while the results measured by the chemical shift versus surfactant concentration do not show this difference.49 The CMC of 3-aminopropyl triethoxy silane in toluene is ca. 0.47m, measured by H and l3C chemical shifts.50 The CMC of optically active potassium A -n-dodecanoyl alaminate measured by H and l3C chemical shifts is lower (11-15 him) in D20 than that in a mixed solvent of 1,4-dioxane and D20 (19mM).-51 The H chemical shift shows that the CMC of resorcinol-type calix[4] phosphoric esters having four alkyl side-chains, [4]Ar 5P-R-n, is insensitive to the length of the side-chains, n.52 The CMC values of a family of surfactants, the sodium cyclohexyl alkanoates, with different lengths of the alkanoate side-chains, were obtained from 13C chemical-shift measurements. The results show that these amphiphiles have high CMCs (0.12-1.02 m).-53... 

Mark and Semiyen, in a series of papers, have studied the mechanism and the effect of trapping cyclics in end-linked elatomeric networks [100-103], Sharp fractions of cyclics of polyfdimethylsiloxane) (PDMS), varying in size from 31 to 517 skeletal atoms, were mixed with linear chains for different periods of time and the linear chains were then end-linked using a tetrafunctional silane. The untrapped cyclics were extracted to determine the amount trapped. It was found that while cyclics with less than 38 skeletal atoms were not at all trapped, for n>38, the percentage of cycUcs trapped increased with size, with 94% trapped in the case of the cychc with 517 skeletal atoms. In effect, the system of trapped cycUcs in the end linked PDMS network is a polymeric catenane. It is thus possible to control the elastomeric properties of the network by incorporating the appropriate sized cyclics. This study has been extended to cyclic PDMS in poly(2,6-dimethyl-l,4-phenylene oxide) [104,105] and cyclic polyesters in PDMS [106]. 

Adsorption Isotherm Experiment. Crystalline quartz (SlOj) in the form of Berkeley HIN-U-SIL 5 and MIN-U-SIL 30 were supplied by Pennsylvania Glass Sand Corp., whose metal oxide analysis yields 99.72 SiOj. This nonporous powdered solid was acid cleaned with repeated washes of concentrated HCl. Reaction with dlchloro-dimethylsllane converted the very hydrophilic surface of clean SiO to a hydrophobic methylated surface. Covalent bonds are formed with the SiOj surface through elimination of HCl. The Si-OH groups on the quartz surface and the -SiCl groups of the dichlorodlmethylsilane react to produce Si-O-Sl bonds, with the dimethyls of the silane at the newly modified Interface. Surface areas were determined on these powdered solids using the BET (Brunauer, Emmett, Teller) Nj adsorption isotherms measured on a Quantasorb Jr. (Quantachrome). The hydrophilic NIN-U-SIL 5 has a specific surface area of 5.06 m /g. Acid-cleaned HIN-U-SIL 30 has a surface area of 2.16 m /g which decreases to 1.81 m /g upon methylation. 

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