Polymethylsiloxanes constitute a class of organosilicon polymers of primary importance. They include linear oils and rubbors and the three dimensional resins. With the exception of the rubbers, the preparation of the oils and resins are done by hydrolyzing a mixture of methylchlorosilanes of different functionalities. By varying the proportion of the monomers, it is possible to obtain polymers of different molecular weights with different degreo of branching and cross-linking.