Synthesis And Properties Of Co-modified Polysiloxane Obtained Via Ring-opening Copolymerization Of Mixed Cyclic Monomers

Polysiloxanes have been widely applied in textile, leather, construction, coating, cosmetic and medicine industries due to their unique properties, such as excellent air permeability, hydrophobicity, electrical insulation, weather tolerance, drug resistance, etc. However, silicones also have a serious drawbacks, for example they are very poor lubricants under conditions of "boundary" lubrication and particularly when the rubbing surfaces are of steel, poor solubleness in organic solvent. This thesis introduce a cost-effective synthesis method to prepare co-modified polysiloxane. They were prepared by ring-opening reaction of mixed cyclic monomers.The first section of this thesis focus on the synthesis of mixed cyclic monomers by dichlorosubstituted silanes. The molecular structure were confirmed by GC/MS and NMR spectra, the results indicate that the cyclic monomers normally contain 3-5 silicone units and the phenyl group could be distributed uniformly among these monomers. A series of samples were synthesized by (a) mixed cyclic monomers and (b) P3 with D4. These products were analyzed by NMR, FTIR, GPC, and TGA. Polyphenylmethylsiloxanes prepared by ring-opening reaction of mixed cyclic monomers (PPMS-M) exhibit good thermal stability while keeping excellent low-temperature flexibility. The results indicated that the synthesized polyphenylmethylsiloxanes by mixed cyclic monomers contain abundant phenyl groups, which are uniformly distributed along the siloxane main chain. Compared with PPMS-PD, the PPMS-M exhibit a decomposition temperature of over 30℃ higher. The influences of molecular weight, microstructure and phenyl group content on the thermal stability were investigated. The thermal decomposition temperature increases intensively with phenyl content when the phenyl content below 10 wt.%; and keep almost unchanged when the phenyl group content being higher than 10 wt.%. And the polymers with high molecular weight exhibit high degradation temperature. However, when the molecular weight is higher than 30000 g/mol, the decomposition temperature almost unchanged.In the second section, cyclosiloxanes with mixed siloxane units (trifluoropropyl, phenyl, dodecyl) were synthesized by dichlorosubstituted silanes, and then produce polysiloxanes through ring-opening reaction with anionic catalyst by bulk polymerization. The molecular structure were confirmed by FTIR, GPC and NMR spectra. The influence of catalyst, reaction time, reaction temperature, reaction medium were investigated. The results indicate that high reaction temperature and long reaction time lead to ideal product. Introduce phenyl content into the system leads to excellent thermal properties, the degradation temperature even higher than 400℃ (Mn=3×104 g/mol, F wt.%=10%, Ph wt.%=5%). The trifluoropropyl group could improve the low-temperature flexibility (low Tg value), surface properties (surface contact angle 112.6°), viscosity-temperature characteristics (the value of VTC lower than 0.60), lubricity (small diameter of wear scar). And dodecyl can improve the compatibility with mineral oil.