The present invention relates to a process for preparing
multifunctionalized polyorganosiloxanes (POSs) comprising alkoxyl
functional siloxyl units and siloxyl units each having an SH functional
group, which consists in introducing the SH functional group by the
reaction of H.sub.2 S on a precursor POS of formula: A--(RXSiO).sub.a
--(RYSiO).sub.b --B where R is especially a C.sub.1 -C.sub.6 alkyl
radical, X is a C.sub.1 -C.sub.15 alkoxyl radical, Y is a C.sub.2
-C.sub.30 hydrocarbon group which includes an ethylenically unsaturated
group from which the SH functionality derives, a is a number ranging from
1 to 150, b is a number ranging from 1 to 150, the number a+b ranging from
2 to 300 and A and B are terminal groups which are selected respectively,
from, in particular, on the one hand (R).sub.3 SiO-- radicals taken alone
or as mixtures with (R).sub.2 XSiO-- and/or R(X).sub.2 SiO-- and/or
(X).sub.3 SiO-- radicals and on the other hand --Si(R).sub.3 radicals
taken alone or as mixtures with --SiX(R).sub.2 and/or --Si(X).sub.2 R
and/or --Si(X).sub.3 radicals.