Study On Synthesis And Application Of Polyoctylmethylsiloxane

Among the universal polymer materials of gas separation membrane,silicone rubber (PDMS)has always been focused just because of its high gas permeability.However,its separation coefficient(α_O2/N2=2.0)and membrane formability are bad,which limited its practical value.Polyoctylmethylsiloxane was synthesized by induct some octyl in side group, The induct of soft octyl can improve the performance of membrane and ensure the separation rate rising and the permeation rate not or a little lowering.In this study,Polyoctylmethylsiloxane was synthesized by two-step method.The first step:2,4,6,8-tetramethyloctylcyclotetrasiloxane was synthesized by hydrosilylation of 2,4,6,8 -tetramethylcyclotetrasiloxan and a-octene in the presence of platinum catalyst.The structure of the sample was characterized with FTIR and ¹H-NMR.And the effects of various reaction conditions,such as the reaction temperature,reaction time,et al,on the conversion of Si-H were investigated by the ¹H-NMR.The conversion of Si-H reached 97.3%at 65℃after 20h with 0.6g catalyst and the molar ratio of D₄^H to a-octene was 1:12.The structure of product was 100%β-adduct in regioselectivity confirmed by ¹H-NMR.The second step:Polyoctylmethylsiloxane was synthesized by ring-opening polymeriza -tion of octamethylcyclotetrasiloxane,2,4,6,8-tetramethyloctylcyclotetrasiloxane and MM^â…µas the blocking agent in the presence of CF₃SO₃H catalyst.The product structure was characterized by FTIR and ¹H-NMR,and the octyl content was the same as expectation.The result showed the best synthetic technics were reaction temperature 60℃,reaction time 120min,mass fraction of CF₃SO₃H 0.02wt%,mass fraction of MM^â…µ1.4-1.9wt%.And at the moment the product has right viscosity and stable performance.The composite membrane was formed by coating the solution which was comprised by 3.0g POMS—10mol%,96.82g petroleum ether,0.06g hydrogenous silicon oil,0.12g chloroplatinic acid catalyst three times on the PEI porous substrate membrane,then vulcanizing 3 hours at 80 temperature.When the pressure was increased,the permeation rate has a rising trend and the separation rate was a little lowering.When the octyl content was 10mol%,the performance of composite membrane was good,the separation rate of oxygen/ nitrogen was about 2.35.At last,analysis of FTIR showed that the cross-linking reactions of POMS was existent and complete.