in coating compositions to improve the weatherability of thermoplastic substrates application_number US 76264496 A description preparation of the novel methylene bridged dibenzoylresorcinol derivatives having a phenol group on the bridging methylene employed in the instant invention is achieved by first making a methylene acetate intermediate having the formula str3 where ar 1 and ar 2 are independently substituted or unsubstituted monocyclic or polycyclic aryl groups and r 1 and r 2 are independently hydrogen an aryl group or a linear or branched alkyl chain having less than about 10 carbons this intermediate is prepared from a dibenzoylresorcinol using a variation of the mannich reaction described by jp 79 19 950 ca 91 20116z it is necessary to reduce the amine catalyst loading from 40 mole percent as taught in the jp reference to about 5 mole percent in order to avoid getting undesirable amounts of a diethylamine substituted derivative when forming the intermediate a small amount of a methylene bridged dimer as shown in formula ii is formed this is easily removed by filtration the isolated intermediate compound as shown in formula i can be heated with an additional dibenzoylresorcinol in acetic acid solution in the presence of an acid catalyst this results in near quantitative formation of a desirable methylene bridged derivative as shown in scheme i str4 alternative reaction conditions for the second step also have been discovered the intermediate acetate i can be heated with a phenol in the absence of any added catalyst to effect coupling the temperature for heating is between about 100 u00b0 150 u00b0 c in an appropriate solvent such as toluene or xylene this procedure is.