Polycondensation reaction polysiloxanes

The polymerization reaction leads to an equilibrium mixture of linear polysiloxanes and cyclic siloxanes, wheras the equilibrium of the polycondensation reaction can be shifted to the polymer side by removing the condensation water. 

Another series of complexes derived from a dihydroxysilylphthalocyanine (Figure 65, M = trans-Si(OH)2), showed hexagonal mesophases from —7 up to 300°C [137]. If such complexes were held at around 180°C for several hours, a polycondensation reaction occurred which eliminated water to form polymeric materials with a polysiloxane spine (Figure 72). These polymers displayed a lamellar periodicity of 31 A from room temperature up to 60°C, where clearing occurred. X-ray diffraction studies in the lamellar phase, showed that the rings were separated by... 

Figure 10. Synthesis of LC polysiloxanes by the polycondensation reaction between a mesogenic monomer containing allylic functions and oligodimethylsiloxanes.

Cuadrado and coworkers have reported the synthesis of polysiloxanes with Fe-Fe bonds using two different methodologies." Polymers with the metal-metal bonds within their backbones (53) were synthesized by polycondensation reactions of disilanols with a dinuclear iron-iron bonded complex, while reaction of a poly-siloxane with Fe(CO)5 resulted in polymer 54. Polymer 54 possessed good thermal stability and poor solubility, which indicates that crosslinking between polymer chains may have occurred. Molecular weight analysis of polymers prepared by polycondensation reactions shows that these polymers have degrees of polymerization between 5 and 10. 

Block copolymers containing polysiloxane segments are of great interest as polymeric surfactants and elastomers. Polycondensation and polyaddition reactions of functionally ended prepolymers are usually employed to prepare well-defined block copolymers. The living polystyrene anion reacts with a,co-dichloropoly(dimethyl-siloxane) to form multiblock copolymers398. ... 

These polysiloxanes were also found to be synthesized by the condensation reaction between organosilanes and organoalkoxysilanes with release of alkane as an inert by-product. For this polycondensation, B(C6F5)3 was used as an effective catalyst [88]. This process involves cleavage of C-0... 

If this complex is sufficiently stable, then no further reaction occurs, and the polycondensation is obviated. However, as mentioned above, by using controlled monomer design, a variety of functionalised polymers (typical by with Mn = 10 000—30 000 and Mw/Mn = 2.0) can be synthesised polyethers [15,48 50], poly(thioether)s [48], polyesters [51,52], polycarbonates [53], polyketones [54], polysiloxanes [55-58], poly(carbosiloxane)s [59], poly(carbosilane)s [60], poly(carbodichlorosilane)s [61] and polymers with a conjugated % system [62]. 

A series of patents were issued to Mammino on various resins like modified polysulfones and polysiloxanes that can be photocrosslinked when Lewis acids are added. In addition, light sensitive polysulfone copolymers can be formed through interfacial polycondensation. " Also, the reactions can be carried out on mixed bisphenols and aromatic disulfonyl chlorides in the presence of Lewis acids. 

Cuadrado et al. prepared a polymer with Fe-Fe bonds (68) by the reaction of a cyclopentadiene-substituted polysiloxane (66) with Fe(CO)5 (Scheme 19)7 The insolubility of the polymer indicated that crosslinking between polysiloxane chains also occurred. Polymers with more controlled structures were prepared by polycondensation of monomers already containing Fe-Fe bonds with disUanols. ... 

Two main types of siUcone elastomer systems are used in biomedical prosthetics polysiloxanes terminated with hydroxyl groups and their subsequent polycondensation is the basis of room-temperature vulcanizing (RTV) systems in which tin compounds are used as catalysts. Another RTV or heat-cured system is based on unsaturated (vinyl) terminated polysiloxanes that undergo polyaddition reactions with the aid of a platinum catalyst. 

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