The synthesis of poly(methylhydrogeno)siloxane (PMHS) by cationic polymerization of 1,3,5,7-tetramethylcyclotetrasiloxane was studied in aqueous emulsion using dodecylbenzene-(D 4 H) sulphonic acid (DBSA) as emulsiüer/initiator. With pure DBSA, the rates of polymerization are very high and the PMHS formation is not well-controlled (cross-linking reactions, emulsion not very stable). The addition of the sodium salt of DBSA as coemulsiüer does not give satisfactory results. In the presence of a neutral coemulsiüer (Brij35), the process leads to the formation of linear PMHS of controlled molecular weight in the range 7000-70 000 g mol-1 with a yield of 90% . No cross-linking reaction was observed, showing the good stability of the SiwH bond in these experimental conditions.
Preliminary investigations lead to the conclusion that the polymer is probably formed by initiation, propagation and termination reactions taking place simultaneously at the surface of 200 nm diameter monomer particles. Nevertheless, the peculiar mechanism of these reactions seems more complicated than those previously found in the case of anionic polymerization of in aqueous emulsion.