Kinetics of ring-opening polymerization of octamethylcyclotetrasiloxane in microemulsion

Thermal insulation and stability of polysiloxane foams containing hydroxyl-terminated polydimethylsiloxanes

An effective method was described here to improve the thermal insulation and stability of polysiloxane foam (SIF) by controlling the chain length of hydroxyl-terminated polydimethylsiloxane (OH-PDMS). A series of SIFs were prepared through foaming and cross-linking processes with different cross-linking densities. The morphology of SIF was investigated by environmental scanning electron microscopy. The results demonstrated that increasing the chain length of OH-PDMS reduced the average cell size from 932 μm to 220 μm. Cell density ranged from 4.92 × 10⁶ cells per cm³ to 1.64 × 10⁸ cells per cm³. The thermal insulation capability was significantly enhanced, and the SIF derived from the long-chain OH-PDMSs yielded a minimum thermal conductivity of 0.077 W mK⁻¹. Cell size reduction and an increase in cell density were considered to be the main factors to reduce thermal conductivity. Thermal stability, which was also improved, mainly depended on the free motion rate of the polysiloxane chains and cross-linking density of the polysiloxane networks.

The thermal insulation and stability of polysiloxane foam was improved by an easy operating method.

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+.

Microemulsion systems for catalytic reactions and processes

This mini-review shows the diversity of microemulsion systems for catalytic reactions with the potential for process development.