THE INTERFACIAL POLYCONDENSATION OF TETRABROMOBISPHENOL-A POLYCARBONATE .1. MODEL REACTION AND MECHANISM STUDIES

2,2',6,6'-Tetrabromobisphenol-A (TBBPA), a sterically hindered bisphen ol, is known to give only low-molecular-weight polymers using the inte rfacial phosgenation process. The low reactivity is attributed to the bulkiness and electron-withdrawing character of bromine substituents a t the ortho positions. From the formation of carbamate products in mod el compound (2,4,6-tribromophenyl chloroformate, TBPC) reactions with trialkylamines, the trialkylamine catalyst was found to act as a termi nator by the degradation of the chloroformate-trialkylamine complex. T he generation of carbamate occurs through the decomposition of the acy l ammonium salt proceeding via nucleophilic displacement by Cl- at the carbon attached to the positive nitrogen center. The relative catalyt ic abilities of trialkylamines and pyridine derivatives were determine d in the homogeneous (dichloromethane) and interfacial (dichloromethan e/water) systems. From the results of model reactions with TBPC and so dium tribromophenolate, 4-dimethylaminopyridine (DMAP) was found to be the best catalyst.