The Synthesis And Study Of A Novel Class Of Reactive Alkoxypolysiloxane Polymers

The objective of this work has been the synthesis and study of a novel class of reactive alkoxypolysiloxane polymers. Reviews are presented of the chemistry of organosiloxanes with particular reference to polymerisation reactions, and the preparation and properties of the organoalkoxysilanes. A study has been carried out on the base catalysed alcoholysis of a model polymethylhydrogensiloxane polymer (CH,), Si +0SiMeH?1,4 O0-Si(CH,),: with the following alcohols ROH where R = methyl, ethyl, n-propyl, iso-propyl, n-butyl, iso-butyl, sec-butyl and halo-alcohols X-CH,.CH,OH where X = F, Cl, Br and I. The alcoholysis rates have been quantitatively determined by the use of a modified Van Slyke gas burette technique. Relative rates have been interpreted in terms of the electronic and steric contributions of the R and X groups. The thermal stability of the above polymers has been studied, using thermogravimetric (TGA) techniques, in air and nitrogen, and mechanisms postulated for the degradation processes. Copolymers of methylhydrogensiloxanes and dimethylsiloxanes have been prepared, using acid clay catalyst systems. These have been alkoxylated with the range of alcohols described above, and the thermal stability (by TGA) studied, in air and nitrogen, of the methoxy, ethoxy and halogenated copolymers and appropriate mechanisms postulated. Gellation studies have been carried out on the methoxylated copolymers, using a range of condensation catalysts under various atmospheric humidities. The physical properties, and crosslink densities have been measured on a range of room temperature vulcanising (RTV) elastomers produced from the alkoxylated copolymers.