ng 1 to 6 carbon atom(s) per radical and R4 is a linear or branched alkylene radical having 1 to 6 carbon atom(s) per radical, R5 is a hydrogen atom, a trimethylsilyl group or a tertiary butyl group,with the proviso that the compounds contain at least one radical B per molecule, with a (meth)acrylic acid in the presence of an acid catalyst (4). 6.