Hardenable compositions

A composition comprising:

• (A) a compound of formula I ##STR9## wherein R.sub.1, R.sub.2, R.sub.3 and R.sub.4 are identical or different and each is hydrogen or methyl, and X is a divalent organic radical comprising 2 to 60 carbon atoms,
• (B) a compound of formula II ##STR10## wherein R.sub.5 and R.sub.6 are identical or different and each, independently of the other, is C.sub.1 -C.sub.8 alkyl, and Y is hydrogen or an allyl radical, and
• (C) an alkenylphenol of formula IV, V or VI ##STR11## wherein each of R.sub.11, R.sub.12 and R.sub.13, independently of the others, is a hydrogen atom or a C.sub.3 -C.sub.10 alkenyl group, at least one of the radicals R.sub.11 to R.sub.13 being an alkenyl group, and Z is hydrogen, C.sub.1 -C.sub.10 alkyl, C.sub.6 -C.sub.10 aryl or C.sub.3 -C.sub.10 alkenyl, ##STR12## wherein Q is a direct bond, methylene, 2,2-propylidene, --CO--, --O--, --S--, --SO-- or --SO.sub.2 --, and each of R.sub.14, R.sub.15, R.sub.16 and R.sub.17, independently of the others, is a hydrogen atom or a C.sub.3 -C.sub.10 alkenyl group, at least one of the radicals R.sub.14 to R.sub.17 being an alkenyl group, and Z is hydrogen, C.sub.1 -C.sub.10 alkyl, C.sub.6 -C.sub.10 aryl or C.sub.3 -C.sub.10 alkenyl, ##STR13## wherein each of R.sub.18, R.sub.19, R.sub.20, R.sub.21, R.sub.22 and R.sub.23, independently of the others, is a hydrogen atom, C.sub.1 -C.sub.4 alkyl or C.sub.3 -C.sub.10 alkenyl, at least one of the radicals R.sub.18 to R.sub.23 being an alkenyl group, and a is a number from 0 to 10, and Z is hydrogen, C.sub.1 -C.sub.10 alkyl, C.sub.6 -C.sub.10 aryl or C.sub.3 -C.sub.10 alkenyl.