A method for producing a reaction product (A) comprising the following step (i): (iv) a reaction mixture comprising at least one radically reactable monomer (a) is reacted in radical conditions in the presence of at least one radical initiator and a compound of formula (I), wherein R1-R4 represent independently from each other hydrogen, a respectively unsubstituted or substituted alkyl radical, a cycloalkyl radical, an aralkyl radical, an unsubstituted or substituted aromatic hydrocarbon radical, under the proviso that at least two from R1-R4 represent an unsubstituted or substituted aromatic hydrocarbon radical.