wavelength of 345 nm because the absorbance of a polycarbonate at 345 nm is proportional to the measured b value of the test specimen by injection molding so the absorbance is taken as an index of the b value of a polycarbonate the lower the b value less color the polycarbonate is into a five neck reactor equipped with a nitrogen inlet a stirring rod a sampling opening a condenser and a temperature control device 228 g 1 0 mol of bisphenyl a 220 g 1 025 mol of diphenol carbonate 0 075 g 2 5 u00d7 10 4 mol of ethyltriphenyl phosphonium borohydride catalyst a of the preparative example 1 and 0 114 g 0 05 wt per mol of bisphenol a of irgaphos pepq were charged thereafter the reaction system was evacuated to about 2 mmhg and then purged with nitrogen this purging procedure was repeated three times to insure that all the air in the reactor was expelled under nitrogen atmosphere the temperature was then raised to 140 u00b0 c to dissolve the reactants and then to 180 u00b0 c in order to subject the reactants to transesterification the transesterification was performed for 1 hour and part of the phenol by product was distilled during this period subsequently the reaction temperature was gradually raised from 180 u00b0 c to 210 u00b0 c while the pressure was also gradually reduced to 200 mmhg and stirring was continued under.