Preparation And Performance Of Polymethylmethoxysiloxane

Polysiloxanes are semi-inorganic polymers with high thermal stability, good weather resistance, low surface tension, and unusually high permeability. Their unique physical and chemical performances have found applications in industries ranging from aerospace to biomedicine.In this thesis, Polymethylmethoxysiloxane (PMOS) with dense pendant Si-bound methoxy groups was synthesized. The synthesis reactions, crosslinking reactions, performance and usage were studied.1. PMOS with dense pendant silicone-methoxy groups was synthesized from cyclosiloxane monomers by ring-opening polymerization and dehydrocoupling reaction. Synthesis reactions were followed by IR spectroscopy and29Si NMR analyses.2. PMOS was crosslinked at room temperature via hydrolytic condensation to prepare high crosslink density polysiloxane, and the apparent activation energy for crosslink reaction was98.5kJ/mol.3. The residual mass of crosslinked PMOS at760℃was10wt%, E’ at80℃was2.5×108, E" at80℃was3.2x106, tand at-18℃was0.06.4. PMOS was used as thermal resistance resin, and was incorporated with metal powder and CaCO3powder. It was detected that fillers could improve the performance of materials.5. PMOS was used as crosslinking reagent for room temperature vulcanized polydimethylsiloxane (PDMS), and the apparent activation energy for crosslink reaction was3.92kJ/mol. TEM study shows that many dispersed high crosslink density PMOS phases were formed in siloxane elastomer. It was detected that these PMOS phases improved the thermal and mechanical properties of siloxane elastomer significantly because of their in-situ microscale improvement effect. TG analysis demonstrated that the residual mass at500℃was66wt%. The crosslink density went up as the loading of PMOS increased. Tensile stress and elastic module increased twice and three times, respectively, when the PMOS content increased from15.1wt%to41.6wt%.6. Ethanol modified polysiloxane and isopropanol modified polysiloxane were synthesized from polymethylhydrosiloxane (PMHS) by dehydrocoupling reaction. Their apparent activation energies for crosslink reaction were lower than that of PMOS.7. Styrene (St) modified polysiloxane were synthesized from polymethylhydrosiloxane (PMHS) by hydrosilylation reaction. The results showed that the reaction was effected by temperature and catalyst.8. Divinylbenzene (DVB) modified polysiloxane were synthesized from polymethylhydrosiloxane (PMHS) by hydrosilylation reaction. The apparent activation energy for crosslink reaction was53.1kJ/mol. The residual mass at1400℃was74%. The apparent activation energy for degradation reaction was29.6kJ/mol. Divinylbenzene modified polysiloxane could be used to prepare polymer-glass fiber composite.