Chemoselective Synthesis Of Catenated Polysiloxanes And Macrocyclic Polysiloxanes

Catenated polysiloxanes and macrocyclic polysiloxanes were found or supposed exist in 1940’s or 1950’s, and they could be used for the development of interpenetrating networks and new materials having excellent thermal stability. However, it is still a challenge to prepare them. In 1953 Martin et al postulated that the polysiloxanes might be presence of large interlocked rings, but until now it is still a postulation, and no feasible methods to synthesize them. On the other hand, three methods were reported to prepare macrocyclic polysiloxanes, including ring-chain equilibration, ring-closure and depolymerization of linear polysiloxanes. The main drawback of these protocols is that mixtures of linear and cyclic polysiloxanes are commonly obtained, and complex and time-consuming separation processes are needed. Moreover, high molecular weight cyclic polysiloxanes were difficult to be obtained via ring-chain equilibration and depolymerization of linear polysiloxanes. Furthermore, in the ring closure process, the reactions must be carried out in highly diluted solution, which is not a feasible procedure for large scale preparation. Hence, the application of catenated and cyclic polysiloxanes were hampered, because there are not efficient preparation methods for them.Here we introduce a new condition to chemoselectively synthesize catenated polysiloxanes and macrocyclic polysiloxanes. We found that high pure catenated polysiloxanes and macrocyclic polysiloxanes were prepared from cyclotetrasiloxanes with water catalyzed by anhydrous iron (III) chloride in concentrated solution in high efficiency.Products were characterized by gas chromatography-mass spectroscopy (GC-MS), gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR),1H and 29Si nuclear magnetic resonance (NMR), and limiting viscosity-molecular weight relationships. Thermodynamic properties of products were studied with thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC). The data demonstrated that the catenated polysiloxanes and macrocyclic polysiloxanes have excellent thermal stability.