Kinetic study on the ring-opening polymerization of octamethylcyclotetrasiloxane (D4) in miniemulsion

Cationic Emulsion Polymerization of Octamethylcyclotetrasiloxane (D4) in Mixtures with Alkoxysilanes

The cationic emulsion polymerization of octamethylcyclotetrasiloxane (D4) in mixtures with methyltriethoxysilane (MTES) and vinyltriethoxysilane (VTES) was studied by FTIR ATR, GC, the development of a toluene insoluble fraction of the polymer and a gravimetric analysis. The polymerization of D4 alone was also conducted for comparison and, additionally, the development of molecular weight of polydimethylsiloxane (PDMS) obtained in that process was studied by GPC. Dodecylbenzenesulphonic acid (DBSA) was used as a surfactant and catalyst. The process was carried out in a “starved feed” mode by adding dropwise the monomer mixture to the aqueous solution of DBSA. FTIR ATR spectra were recorded by the sensor placed in the probe tip of a ReactIR 15^TM apparatus. It was found that the silicone polymer formation proceeded faster when D4 was polymerized in the mixture with alkoxysilanes, especially in the beginning of the process, and that already at the beginning of the process, the partly crosslinked polymer was formed. The induction period of ca. 30 min was observed and the concentration of cyclic siloxanes (D4 and decamethylcyclopentasiloxane—D5) remained at a very low level in the course of the reaction and only traces were detected in the final product. The particle size development in the course of the reaction was also studied and it was found that the particle size distribution was bimodal and was broadening as the reaction proceeded, though this phenomenon was less distinct when D4 was polymerized in the mixtures with alkoxysilanes. The structure of the reaction product was confirmed by ²⁹Si NMR.

Effects of octamethylcyclotetrasiloxane grafting and in situ silica particle generation on the curing and mechanical properties of a styrene butadiene rubber composite

The reinforcement of octamethylcyclotetrasiloxane (D₄) grafted styrene butadiene rubber (SBR-g-D₄) with in situ generated silica was performed using the sol–gel reaction of tetraethoxysilane (TEOS) in latex. The characterization of SBR-g-D₄ and in situ generated silica reinforced SBR-g-D₄ was investigated by Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy. The grafting efficiency of the styrene butadiene rubber (SBR) was determined by a gravimetric method. It was found that the constant silicon content and the grafting efficiency of SBR were 1.72% and 0.13 wt% when the weight ratio of D₄ to SBR was 0.20. The effects of the D₄ and in situ generated silica content on the curing characteristics, mechanical properties and morphology of SBR latex were investigated. The mechanical properties of in situ generated silica reinforced SBR-g-D₄ vulcanizates were improved significantly compared to raw SBR vulcanizate when the in situ generated silica content was 18.05%. Compared with silica reinforced SBR-g-D₄, the tensile strength, wet skid resistance and rolling resistance of the in situ generated silica reinforced SBR-g-D₄ were better. This is because of the higher crosslinking degree in the SBR-g-D₄ matrix and the strong chemical bond between SBR-g-D₄ molecular chains and in situ generated silica. Scanning electron microscopy analysis revealed good silica filler dispersion in all the reinforced SBR-g-D₄ vulcanizates.

The reinforcement of octamethylcyclotetrasiloxane (D₄) grafted styrene butadiene rubber (SBR-g-D₄) with in situ generated silica was performed using the sol–gel reaction of tetraethoxysilane (TEOS) in latex.

Synthesis and characterization of polyvinylmethylsiloxanes by cationic polymerization using a solid green catalyst

The present work is devoted to the synthesis and characterization of vinylsiloxane polymers produced by the use of an activated natural catalyst known as Maghnite-H+. The cationic ring opening polymerization of pentavinylpentamethylcyclopentasiloxane (V5D5) made it possible to obtain the desired polymeric materials. Through this study, we have adapted a new strategy of synthesis of a siloxane polymer with relatively high molecular mass, using a solid initiator activated by sulfuric acid, which has enabled us to combine the ecological aspect of synthesis and the effectiveness of the catalyst in this kind of reaction. Structural [infrared (IR), proton and carbon nuclear magnetic resonance (1H NMR and 13C NMR)], thermal differential scanning (DSC) and chromatographic (GPC) characterization methods have allowed the products obtained to be identified and their various properties to be focused on. The kinetic study was made to determine the order of the reaction. The proposed reaction mechanism shows the advantages of Maghnite-H+.

Biogas upgrading: optimal activated carbon properties for siloxane removal

A total of 12 commercial activated carbons (ACs) have been tested for the removal of octamethylcyclotetrasiloxane (D4) in dynamic adsorption experiments using different carrier gases and D4 concentrations. Characterization of the ACs included several physical and chemical techniques. The D4 adsorption capacities were strongly related with the textural development of the ACs. Results showed that the optimum adsorbent for D4 is a wood-based chemically activated carbon, which rendered an adsorption capacity of 1732 ± 93 mg g(-1) using 1000 ppm (v/v) of D4 with dry N2 as the carrier gas. When the concentration of D4 was lowered to typical values found in biogas, the adsorption capacity was halved. The presence of major biogas compounds (i.e., CH4 and CO2) and humidity further reduced the D4 adsorption capacity. The polymerization of D4 over the surface of all ACs was found to be relevant after prolonged contact times. The extent of this phenomenon, which may negatively affect the thermal regeneration of the AC, correlated reasonably well with the presence of phenolic and carboxylic groups on the carbon surfaces.