Jt. Gu et al., THE INTERFACIAL POLYCONDENSATION OF TETRABROMOBISPHENOL-A POLYCARBONATE .1. MODEL REACTION AND MECHANISM STUDIES, Die Angewandte makromolekulare Chemie, 208, 1993, pp. 65-77
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.