r1 r2 r3 r4 x1 and y1 in formulae 1 10 11 12 and 13 are as defined in formulae 1 10 11 12 and 13 condensation 1 may be carried out in an organic medium an aqueous medium or an aqueous organic medium and is preferably carried out in the aqueous medium in the presence of an acid binding agent preferred examples of the acid binding agent may include carbonates bicarbonates and hydroxides of alkali metals carbonates bicarbonates and hydroxides of alkaline earth metals alkali metal acetates and mixtures thereof and tertiary amines preferred examples of the alkali metals and alkaline earth metals may include lithium sodium potassium and calcium preferred examples of the tertiary amines may include pyridine triethylamine and quinoline condensation 1 is carried out at a temperature of u2212 10 to 40 u00b0 c and more preferably 0 to 10 u00b0 c and a ph of 1 0 to 9 0 similar to condensation 1 condensation 2 may also be carried out in an organic medium an aqueous medium or an aqueous organic medium and is preferably carried out in the aqueous medium in the presence of an acid binding agent condensation 2 is carried out at a temperature of 10 to 70 u00b0 c and a ph of 2 0 to 9 0 and more preferably.