Detection of environmental polyorganosiloxanes (silicones) by silicon-29 NMR spectroscopy

The utility of ²⁹Si NMR spectroscopy has been demonstrated on sediment-like materials in the quantitative and qualitative determination of polyorganosiloxanes (silicones) in selected environmental samples. This technique is highly selective for polydimethylsiloxanes (PDMS) and is non-destructive to the sample. Also, specific identification of polyorganosiloxanes in sediment is possible, in contrast to previous methods which provided only quantitative information while consuming the sample. The detection limit for a 9 h experiment is approximately 45 ppm.     

Surface tension of polymer solutions. IV. Three-component mixtures

The lattice-theory equations for the surface tensions of polymer solutions based on the parallel-layer model have been tested for three-component systems. Surface tensions of solutions of some low molecular weight polyisobutylenes and polydimethylsiloxanes in n-heptane–tetralin mixtures and solutions of mixtures of the polymers in these solvents were measured at room temperature. The results are in good agreement with the theoretical calculations.     

Some physical properties of polyorganosiloxanes. II. Nonlinear and irregular polyelementorganosiloxanes

Some physical properties of irregular and nonlinear polydimethylsiloxane elastomers have been studied. The effects of chemical structure, vulcanization, and filler on the glass transition, melting, and crystallization have been investigated. The crystallization kinetics has been studied in detail.     

Synthesis and study of block copolycondensates containing polysiloxane and unsaturated polyester blocks in the chain. II. Poly(unsaturated esters-b-siloxanes) with blocks linked by Si?C bonds and poly(butadienes-b-siloxanes)

Poly(unsaturated esters-b-siloxanes) whose blocks are linked by Si? C bonds and poly(butadienes-b-siloxanes) have been obtained by polycondensation of ω,ω′-diepoxy polydimethylsiloxanes and ω,ω′-dicarboxylic poly(unsaturated esters). The reaction between polysiloxanes with Si? H end groups and allylepoxy has been studied; the resulting ω,ω-diepoxy polysiloxanes have the expected structure. The polycondensation of oligomers with, respectively, epoxy and carboxylic end groups has been studied and the optimal conditions established. The samples with Si? C bonds are not affected by hydrolysis in pure water. The poly(siloxanes-b-unsaturated esters) can be cured by UV light.     

Thermal oxidation of polyorganosiloxanes

The kinetics of noninhibited and inhibited oxidation of poly[(diethyl)siloxane] oligomers (PDES) has been investigated. Phenyl- β -naphthylamine (PNA) and tris(triethylsiloxy)vanadate (TTESV) were used as antioxidants. It is shown that in the presence of PNA the oxidation of PDES proceeds with distinct induction periods. The activation energy of the initiation stage, estimated from temperature dependence of the induction periods, is about 230 kJ/mol. TTESV can act as inhibitor and catalyst in the oxidation of PDES, depending on temperature and content of oxygen in oxidizing mixture.     

Silylation of water glass. I. Solvent extraction and trimethylsilylation of silicic acid

Homogeneous trimethylsilylation of silicic acid in nonaqueous media was studied. The silylation process consisted of three steps: acidification of sodium silicate, solvent extraction. and trimethylation of silicic acid. Sodium silicate was first acidified with dilute sulfuric acid to form silicic acid: extraction followed with hydrophilic organic solvents. The Silicic acid obtained was finally allowed to react with trimethylchlorosilane to give trimethylsilylates with molecular weights of 1000–12,000. Optimum conditions for each step have been intensively sought to achieve trimethylsilylates in high yield. The trimethylsilylates exhibited excellent thermal stability and surface properties, such as water repellency and antifoaming properties, comparable to those of conventional polydimethylsiloxanes.     

Rigid-rod polymers with polysiloxane side chains. I. Synthesis and characterization of rigid-rod polyimides with polysiloxane side chains and their compatibility with linear polysiloxanes

Rigid-rod aromatic polyimdies having polydimethylsiloxane side chains were prepared for the purpose of dispersing rigid-rod molecules in silicone matrices for molecular reinforcement. The polyimides were obtained by imidizing the polyamide-acids bearing the side chains either thermally or chemically, which were synthesized by reacting 4,4′-diaminobiphenyl-terminated polysiloxane macromonomers with pyromellitic dianhydride in THF. The polyamide-acid films obtained by removing the solvent were soluble in THF, but the polyimides were insoluble in any common solvent. The polyimides showed no melting transition below 350°C on DSC analysis, at which temperature the side chain started decomposing. Although all the polyimides were anisotropic as observed by a polarizing microscope, x-ray diffraction analysis suggested the presence of only limited chain organization. Blends with linear polydimethylsiloxanes were prepared by casting the THF solution containing the polyamide-acid and the polydimethylsiloxane, followed by solvent evaporation and thermal imidization. With relatively longer side chains, the polyimides were proved to be compatibilized with polydimethylsiloxanes. © 1994 John Wiley & Sons, Inc.     

SYNTHESIS AND PHOTOCROSSLINKING OF BENZYL (METH)ACRYLATE SUBSTITUTED POLYDIMETHYLSILOXANES: INFLUENCE OF PHOTOINITIATOR NATURE

ABSTRACT

The photoinduced crosslinking of silicones containing benzyl acrylate and benzyl methacrylate groups in the presence of different usual radical photoinitiators (TEPO, Darocur® 1173, Darocur 4265) and azo-containing polydimethylsiloxanes or mono- and bis(phenylmaleimide) functionalized disiloxanes has been investigated by photocalorimetric measurements. The influence of photoinitiator type, temperature and of the exposure time on the photocrosslinking kinetics was followed.     

Preparation et caracterisation de reticulats-modele de polydimethylsiloxanes

Three-dimensional crosslinked gels of polydimethylsiloxanes with well-defined pore-size have been obtained by reaction of the Si-H endgroups with a polyfunctional allyloxy compound. The swelling behaviour of such gels has been investigated. The variation of the swelling degree at equilibrium with the structure of the gel was found in good agreement with the theoretical expectation.     

Block copolymerization of 3,3-dimethyl-2-oxetanone. II. Synthesis of polydimethylsiloxane-containing copolymers

Carboxy-terminated polydimethylsiloxanes (PDMSs) have been prepared by anchoring the functional end group on the main chain via a hydrolytically stable Si? C bond. The neutralized carboxy-terminated PDMSs are effective initiators of the 3,3-dimethyl-2-oxetanone (or pivalolactone) block copolymerization. The yield of block copolymers depends on the initiation efficiency of the carboxylate end groups, but this limit can be overcome by the use of more than one carboxylate group per end chain, and “palm-tree” structures are obtained. The ability to crystallize of poly(3,3-dimethyl-2-oxetanone) is significantly depressed when this polyester is engaged in PDMS-rich block copolymers, but the observed heterophase morphologies (350 Å) are uniformly fine.     

Formation of a physical crosslinked structure in polydimethylsiloxanes modified with long-chain hydrocarbon substituents with polar fragments

The dependence of rheological properties (viscosity and dynamic moduli G′ and G″) and time for formation of a physical network for polydimethylsiloxanes bearing ester and amide groups in aliphatic substituents at silicon atoms on the concentration of modifying units, the heating temperature, and the time of curing at elevated temperatures is studied.     

Thermal analysis of polydimethylsiloxanes. I. Thermal degradation in controlled atmospheres

Thermogravimetric analyses (TGA) of catalyst-free polydimethylsiloxanes (PDMS) have been carried out in controlled atmospheres and a kinetic analysis of the results has enabled the various decomposition processes to be separated and identified. The calculated activation energy for thermal depolymerization is 42 ± 3 kcal/mole, while thermo-oxidation has an apparent activation energy of 30 ± 2 kcal/mole. Quantitative analyses of the major degradation products and molecular weight distribution studies of the residues from degradation studies under isothermal conditions have shown that in vacuo, PDMS fractions depolymerize to cyclic dimethylsiloxanes and low molecular weight linear residues by a randomly initiated mechanism which, it is postulated, involves the formation of an intramolecular, cyclic, four-centered transition state followed by siloxane bond rearrangement. This mechanism is a basic property of linear PDMS fractions and is independent of molecular weight. Molecular weight distribution (MWD) changes observed from further isothermal investigations on hydroxy endblocked PDMS fractions, have shown the presence of a chain-lengthening process in vacuo below the depolymerization temperature. This process, with an apparent activation energy of 8.6 ± 1 kcal/mole, is attributed to the intermolecular condensation of terminal hydroxyl groups.     

Biodegradation of polyorganosiloxanes

Biodegradation of various polyorganosiloxanes (about 30 substances) under the influence of several biotype bacteria strain (16 types) were studied. A special procedure of biodegradation and analytical methods of evaluation the degree of degradation were applied. It was found that nearly all polysiloxanes tested are biodegradable but the degree of degradation depends on their composition and structure, as well as on the type of bacteria strain chosen.     

Structuring of star-like multiarm polydimethylsiloxanes

The in situ structuring of multiarm star-like polydimethylsiloxanes (PDMS) synthesized on the base of the high-generation carbosilane dendrimers was studied. It was shown that, in contrast to the structures with 12, 16, and 48 arms, 128-arm star-like polydimethylsiloxanes form a stable mesophase formed by the PDMS arms. The data from polarized optical microscopy and differential scanning calorimetry revealed for the first time the formation of extended liquid-crystalline domains for the diorganosiloxane chains with the methyl substituents at the silicon atom. This effect can be attributed to the influence of close packing of the PDMS chains at the dendritic branching site in the case of actually multiarm structures.     

Gel-permeation chromatography of polydimethylsiloxanes

The molecular weight distributions of three polydimethylsiloxanes (PDMS) have been determined by gel-permeation chromatography (GPC), by gas–liquid chromatography (GLC), and by precipitation fractionation. The GPC data are greatly improved by correction for band spreading. For a high molecular weight polymer the corrected distribution agrees closely with the theoretical molecular weight distribution calculated from polymerization kinetics.     

Radiation-chemical processes in polyorganosiloxanes

Radiation-induced changes in polymethylphenylsilsesquioxane block copolymers were studied. It was found that a pregel was formed at doses of 30–50 kGy and gel formation mainly occurred in polydimethylsiloxane (PDMS) blocks. The UV spectrophotometry of samples in a cyclohexane solution demonstrated that, at doses of 10–50 kGy, a noticeable broadening of absorption bands due to phenyl groups was observed only in oligophenylsilsesquioxane and not in the block copolymers. Hydrogen atoms formed in the radiolysis of PDMS did not reach polyphenylsilsesquioxane blocks.     

Adsorption of polydimethylsiloxanes from solution on glass

The adsorption of polydimethylsiloxane polymers from solution on glass has been studied. The amount of polymer adsorbed depends markedly on the solvent because of specific solvent—surface interactions. The presence of silanol groups in the polymer, particularly as endgroups, markedly increases the amount of polymer adsorbed. Large differences are shown between the adsorption of the commercially available, and fully trimethylsilylated polydimethylsiloxanes of narrow molecular weight distribut on. Possible adsorption mechanisms are discussed.     

Cationic Photocrosslinkable Polydimethylsiloxane. III. Synthesis and Photocrosslinking of Polydimethylsiloxane Bearing Oxetane Groups

Abstract

From 3-hydroxymethyl-3-methyl oxetane, we synthesized three oxetane monomers with allylic, diethoxysilane or triethoxysilane functions. These monomers allowed us to prepare different polydimethylsiloxanes bearing oxetane groups by two routes. One is hydrosilylation of allylic monomer on hydrogeno polydimethylsiloxane, with different percentages of Si-H bonds. The second route is a condensation of α,ω-dihydroxy polydimethylsiloxane with di and tri ethoxysilane monomers. By using a photocalorimeter, we studied the kinetic of cationic photopolymerization of a polydimethylsiloxane bearing 7.4% oxetane functions. Influence of temperature in the range 35 to 125°C showed a maximum conversion for 80°C due to an increase in transfer and termination reactions.     

Polydimethylsiloxane-based wide-range mass calibration for direct analysis in real-time mass spectrometry

Direct analysis in real-time mass spectrometry (DART-MS) is normally applied for small-molecule analysis up to about m/z 1,000. Here, for the analysis of polydimethylsiloxanes, high-mass capabilities expanding beyond m/z 3,000 are demonstrated. In addition, polydimethylsiloxanes provide an ideal mass calibration standard for positive-ion DART-MS. A mass reference list has been compiled to cover ions from m/z 200 up to m/z 2,600. Species with more than 20 silicon atoms exhibit increasingly broader isotopic patterns with decreasing abundances of the monoisotopic ions. The use of the first isotopic peaks for analyte ions above m/z 2,000 serves as a work-around and ensures easy and reproducible recognition of the reference peaks by the instrument data system. Here, the positive-ion DART mass spectra of polydimethylsiloxanes and the corresponding experimental procedures are described, and the mass reference list is provided.     

Synthesis and Properties of Aryloxy-terminated Polydimethylsiloxanes

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