Use of tin derivatives as latent polycondensation catalysts, and premix containing them

A latent polycondensation catalyst of formula (II):

• R1—(Q)n—R4 (II)
• wherein:
• radicals R1 and R4 identical or different are a hydrogen atom, or a hydrocarbon radical,
• Q is a divalent radical of structure —Z—Y— wherein radicals Y, identical or different, represent a tin-membered chain unit of structure:
• wherein R′ and R″, identical or different are a hydrogen atom or a hydrocarbon radical, and wherein Z represents an oxygen atom or a simple bond with a preceding chain unit Y or with R1, and n is greater than 2, with the proviso that at least two of the groups Z are oxygen.

A reactant useful as a catalyst for the release of masked isocyanate and as a polycondensation catalyst, having:

• at least one tin derivative;
• and
• an oxidation agent bearing oxygen atom selected from the group consisting of halogenates, peroxides, and oxygen-containing gases, wherein said tin derivative is a latent polycondensation catalyst of the formula:
• R1—Yn—R4 (I)
• wherein:
• the radicals Y, identical or different, represent a tin-membered chain unit of structure:
• wherein R′ and R″, identical or different are a hydrogen atom or hydrocarbon radical, and
• R1 and R4 identical or different are a hydrogen atom, a hydrocarbon radical, at least one of the R1 and R4 group being linked to tin of the tin-membered chain Yn through a chalcogen atom, and n is at least equal to 2.