The porous, disordered, and fibrous silica derived from serpentine slag containing chrysotile asbestos by selective acid-leaching was converted to a silicone polymer through the silylation reaction of the silanol residue with chlorodimethylvinylsilane (DMVSCl). The polymer silylated with 1.2 equiv. of DMVSCl to the silica showed a 93% degree of silylation, which was fully soluble in various organic solvents. The 29Si-NMR measurement indicated that the obtained polymers have Q
 4-, Q
 3-, and M-type siloxane units.

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Synthesis and Property of Silicone Polymer from Chrysotile Asbestos by Acid-Leaching and Silylation

Polymerizable methacryloyl- or epoxy-end silicone oligomers were prepared from water glass by two methods, i) Silicic acid, which was prepared by acidification of aqueous water glass, was end-capped with methyldichloro(3-methacryloyloxypropyl)silane and trimethylchlorosilane. ii) Silicic acid was allowed to react with dimethylchlorosilane and trimethylchlorosilane and then subjected to hydrosilylation with allyl methacrylate or allyl glycidyl ether. The methacryloyl-end silicone oligomers were copolymerized with methyl methacrylate to produce soluble and film-forming copolymers. Addition of only 1 wt% of the copolymers to PMMA showed high water-repellency on the air side of the film. The methacryloyl-end silicone oligomers were also subjected to coating on various test panels followed by curing with UV or electron beam irradiation.

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Synthesis and Application of Polymerizable Silicone Oligomers from Water Glass

Chrysotile asbestos was transformed into polysiloxanes through processes involving selective acid leaching and the reaction with various silylation reagents. The silylation with trialkoxy(vinyl)silanes followed by adding chlorotrialkylsilane effectively proceeded to afford a polymer with a low-silanol residue. The obtained polymers were radically crosslinked producing a polymer with a good thermal stability. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Polysiloxanes Derived from Chrysotile Asbestos via Acid-Leaching and Silylation Processes

Polymeric tributylstannyl ester of silicic acid (PTBS) was demonstrated to be an effective material for the preparation of functionalized polysiloxane derivatives (2). The reaction of PTBS and monochlorosilane (1), which possessed an organofunctional group such as the acetoxy or methylmethacrylate group, proceeded readily at room temperature under neutral conditions to give 2 with the elimination of the tributyltin group. The molecular weight of 2 estimated by GPC measurement was almost the same as that of starting PTBS. Such metal-exchange reaction was applicable for the incorporation of two kinds of silyl units into polysiloxane 2 by employing these monochlorosilanes 1 at the same time in the reaction.

Synthesis of organofunctionalized polysiloxane from polymeric tributylstannyl ester of silicic acid and chlorosilanes

Silicone polymers containing the silanol residue were prepared from a silica gel and were successively used for the synthesis of interpenetrating polymer networks (IPNs) with acrylamides, such as N-isopropylacrylamide (NIPAM) and N,N-dimethylacrylamide. During gelation, the condensation of silanols to form a siloxane linkage and the radical polymerization of acrylamides with a cross-linker simultaneously proceeded to afford IPNs composed of both the silicone polymer and polyacrylamide gels. The swelling properties of the obtained IPNs were then investigated. For example, the IPNs synthesized with NIPAM showed a much lower percentage of equilibrium mass swelling (PES) values at 3 °C in water, 378–545%, than the NIPAM polymer gel (>1500%), and in addition, these IPNs barely showed an apparent volume phase transition temperature (VPTT) in contrast to the NIPAM polymer gel.

Synthesis of interpenetrating polymer networks using silicone polymer with silanol residue

Homogeneous trimethylsilylation of silicic acid in nonaqueous media was studied. The silylation process consisted of three steps: acidification of sodium silicate, solvent extraction. and trimethylation of silicic acid. Sodium silicate was first acidified with dilute sulfuric acid to form silicic acid: extraction followed with hydrophilic organic solvents. The Silicic acid obtained was finally allowed to react with trimethylchlorosilane to give trimethylsilylates with molecular weights of 1000–12,000. Optimum conditions for each step have been intensively sought to achieve trimethylsilylates in high yield. The trimethylsilylates exhibited excellent thermal stability and surface properties, such as water repellency and antifoaming properties, comparable to those of conventional polydimethylsiloxanes.

Takahisa Yasuda

Papers

Silylation of water glass. I. Solvent extraction and trimethylsilylation of silicic acid