A method for preparing polycondensation products of guanidine, aminoguanidine or diaminoguanidine G with one or more benzyl or allyl derivatives BA according to the following reaction scheme is provided: wherein X, R1, Gua, Y and Z are as defined in the specification. In the disclosed method, at least one benzyl or allyl derivative BA is subjected to a polycondensation reaction with excessive guanidine, aminoguanidine or diaminoguanidine G upon elimination of HX.