The liquid phase ring-opening of octamethylcy-clotetrasiloxane (D 4 ) was investigated over Pt-H 2 SO 4 /Zr-montmorillonite catalyst. Montmorillonite (Mt), Zr-Mt, H 2 SO 4 /Mt, H 2 SO 4 /Zr-Mt and Pt-H 2 SO 4 /Zr-Mt were also detected for evaluation. The catalysts were characterized by X-ray fluorescence, X-ray diffraction, nitrogen adsorption–desorption, NH 3 -TPD and pyridine-FTIR measurements. In comparison to activate clay which is used in the industry of catalyst, Zr-Mt catalyst displayed stronger acidity and more excellent catalytic activity in the polymerization of D 4 , polymethylhydrosiloxane (D 4 H ) and hexamethyldisiloxane (MM) to low-hydro silicone oil. Relative to Zr-Mt, the acidity of H 2 SO 4 /Zr-Mt was noticeably improved and the catalyst exhibited a higher capability of ring-opening of D 4 conversion and yield of low-hydro silicone oil. To enhance the stability of H 2 SO 4 /Zr-Mt catalyst, a small amount of metals (Pt) was doped. The nitrogen adsorption–desorption results indicated that pore textural parameters of the Pt-H 2 SO 4 /Zr-Mt had not changed with larger specific surface area. Compared with H 2 SO 4 /Zr-Mt, the total acidity of Pt-H 2 SO 4 -Zr/Mt catalyst retained, but the content of the Brønsted acid increased and the content of the Lewis acid decreased. The Pt-H 2 SO 4 -Zr/Mt catalyst displayed higher catalyst reproducibility. After 40 h reaction of polymerization, the yield of low-hydro silicone oil decreased from 93% to 42% over H 2 SO 4 /Zr-Mt catalyst, while the yield of low-hydro silicone oil reduced from 93% to 78% over Pt-H 2 SO 4 /Zr-Mt catalyst. A sharp decrease in catalytic activity after 35 h of Pt-H 2 SO 4 /Zr-Mt catalyst was detected. Furthermore, Pt-H 2 SO 4 /Zr-Mt was completely regenerated under appropriate condition and appeared good repeatability in the D 4 , D 4 H and MM to low-hydro silicone oil.
Phenyl-containing polysiloxanes have better thermal stability, low-temperature flexibility, and room-temperature damping performance than polydimethylsiloxanes. Poly [dimethylsiloxane- co -methyl (phenyl)siloxane] and poly (dimethylsiloxane- co -diphenylsiloxane) were synthesized through a bulk copolymerization of octamethylcyclotetrasiloxane and methylphenylcyclosiloxane mixture or octaphenylcyclotetrasiloxane, and the structure and properties of the copolysiloxanes were comparatively studied. The phenyl content in poly [dimethylsiloxane- co -methyl (phenyl)siloxane] can be as high as 50 mol%. With the increment of the phenyl content, the thermal stability of the copolysiloxanes is dramatically improved as evaluated by thermal gravimetric analysis. At a given phenyl content, poly [dimethylsiloxane- co -methyl (phenyl)siloxane] has higher thermal stability than poly (dimethylsiloxane- co -diphenylsiloxane). The former is more difficult to crystalline at low temperatures and has lower room temperature viscosity than the latter as confirmed by differential scanning calorimetry and rotational rheometer. The copolysiloxanes is mixed with hydrogen-containing polysiloxane and silica, and vulcanized at elevated temperature to get copolysiloxane composites with good damping properties, oil resistance, and low-temperature resistance. This study not only enriches the fundamental academic research on functional polysiloxanes, but also provides useful technical references for practical applications of phenyl silicone rubber.
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