AbstractHeterogeneous linear polysiloxanes containing oxy[chloromethyl (or iodométhyl)méthyl]silanediyle, oxy(diméthyl)silanediyle, and oxy(methylvinyl)silanediyle units were prepared. Heterogeneously chloromethylated polysiloxanes were obtained by rearrangement of siloxane linkages in corresponding mixtures of polysiloxanes and oligocyclosiloxanes. Heterogeneously iodomethylated polysiloxanes were obtained by chlorine displacement in the previously chloromethylated polysiloxanes. The preparation of heterogeneously bromomethylated polysiloxanes is more difficult than that of the chloro and iodo derivatives. Their properties intervene between those of the chloromethylated and the iodomethylated products. Chlorine displacement leading to the bromomethylated derivatives, was studied on the bis(chloromethylated) disiloxa