The invention relates to a heat-activated initiator for polymerising and/or
cross-linking polyorganosiloxane-type monomers, oligomers and/or polymers
with organofunctional groups, comprising a boron derivative of formula
(I): (A).sub.x B(R').sub.y, wherein the symbols R' are the same or
different and represent an alkyl or alkenyl radical in C.sub.1 -C.sub.12,
an alkoxy radical in C.sub.1 -C.sub.12, a phenyl radical substituted by at
least one electroattractor element, an aryl radical containing at least
two aromatic rings such as biphenyl, naphthyl, optionally substituted by
at least one electroattractor element, especially a halogen atom
(particularly fluorine), or an electroattractor group, especially a
CF.sub.3, NO.sub.2, CN group; and a radical --C.sub.2 H.sub.4
--Si(Q).sub.3 with the symbols Q being the same or different and
representing an alkyl or alkoxy group in C.sub.1 to C.sub.10 or a siloxane
oligomer with less than 10 silicon atoms. The invention also relates to a
corresponding cross-linkable composition and to the uses thereof.
