Catalytic dehydrocondensation

Comparison of Catalytic Dehydrocondensation/Hydrosilation Reactions of CH2=C(Me)CH2OH in the Presence of Rh and TI-Based Catalysts... 

To increase the level of catalytic dehydrocondensation at the final stage of the reaction, the reaction products were heated up to 80°C during 3-4 hours. General scheme of dehydrocondensation proce-eding is as follows [16, 25] ... 

Since initial dihydride- and dihydroxyorganosiloxanes, used in dehydrocondensation, represent a mixture of cis- and traws-isomers, synthesized copolymers possess atactic structure. As observed from the data, catalytic dehydrocondensation proceeds at a deeper level with formation of higher molecular products, than in the case of homofunctional products. 

Figure 1 show hydrogen conversions for dehydrocondensation at different temperatures of catalysts. It has been found that catalytic dehydrocondensation reaction displays the second order. Dehyd-rocondensation reaction rate constants are determined, and catalytic dehydrocondensation activation energies are calculated /, act = 28.1 -28.5 kJ/Mole. As a consequence, for anhydrous caustic potash and platinum hydrochloric acid application as the catalyst activation energies are almost the same. 

Table 1. Some physical and chemical parameters and the yield of bead-shaped structure polyorganosiloxanes, synthesized in catalytic dehydrocondensation...

Silarylenecyclosiloxanes of structure XIV with higher molecular mass were synthesized by catalytic dehydrocondensation of l,7-dihydride-l,7-dimethyloctaphenylcyclohexasiloxane and l,4-bis(hydro-xydimethylsilyl)benzene [111, 112],... 

During catalytic dehydrocondensation of 1,7-dihydrideorganocyclohexasiloxane with 1,4-bis(hyd-roxydimethylsilyl)benzene in the presence of potassium hydroxide, the reaction order, rate constants and activation energy were determined. Catalytic dehydrocondensation is the second order reaction. Some physical and chemical parameters of low-molecular copolymers are shown in Table 16. 

Synthesis of Organosiloxane Oligomers with Cyclic Fragments in the Side Chain by the Reaction of Catalytic Dehydrocondensation... 

Figure 6.25 Dependence of inverse concentration on the time, in the reaction of catalytic dehydrocondensation of oligoethylhydridesiloxane with hydroxyheptamethylcyclotetrasiloxane at a 1 15 ratio. Where curve 1 is at 40 °C, curve 2 is at 50 °C and curve 3 is at 60 °C.

---