1044
Chemistry Letters 2001
A One-Step Synthesis of Reactive Polycarbonate Precursors by the Coupled Oxidative
Carbonylation of Bisphenol-A and Phenol with Carbon Monoxide
Won Bae Kim and Jae Sung Lee*
Department of Chemical Engineering, School of Environmental Science and Engineering,
Pohang University of Science and Technology (POSTECH), San 31, Hyoja-dong, Pohang 790-784, Korea
(Received July 16, 2001; CL-010660)
The reactive polycarbonate precursors of phenyl carbonate-
one-step from CO.
ended oligomers amenable to polycondensation in the phos-
gene-free polycarbonate process were catalytically synthesized
via a novel one-step reaction of the coupled oxidative carbony-
lation of bisphenol-A and phenol with carbon monoxide.
Polycarbonate (PC) has been produced by the interfacial
polycondensation of bisphenol-A (BPA) and phosgene. The
major drawbacks of the conventional phosgene process are envi-
ronmental and safety problems involved in using highly toxic
phosgene as the reagent and copious amounts of methylenechlo-
ride as the solvent.1 For this reason, phosgene-free processes for
polycarbonate have been proposed, in which melt transesterifica-
tion2,3 or solid state polymerization is employed by using BPA
and diphenyl carbonate (DPC), the latter being synthesized in a
phosgene-free process.4–6 The process consists of prepolymer-
ization of BPA and DPC into reactive polycarbonate precursors
followed by polycondensation of the precursors. However, it is
not easy to obtain DPC efficiently from a phosgene-free process.
In a recently commercialized phosgene-free polycarbonate
process, DPC is produced from transesterification between
dimethyl carbonate (DMC) and phenol, and DMC is, in turn, syn-
thesized via oxidative carbonylation of methanol. The conver-
sion from DMC to DPC proceeds in two steps and both steps are
subject to severe equilibrium constraint. Thus, reactive distilla-
tion is usually employed in order to obtain high yields of DPC.
Because of these difficulties involved in DPC synthesis, there
have been extensive efforts to develop a phosgene-free polycar-
bonate process without employing expensive DPC as an interme-
diate. One such a route is direct oxidative carbonylation of BPA
into polycarbonate oligomers7–11 in a similar manner employed
for an oxidative carbonylation of phenol to DPC.12,13 However,
the oligomers produced from the carbonylation of BPA alone
have dihydroxy-ended (DH) functionality which requires multi-
step processing of pressurized carbonylation9 or subsequent
transesterification of DH with DPC11 in order to high molecular
weight polycarbonate due to its limited reactivity. Furthermore,
the dihydroxy-ended groups weaken the physical and chemical
properties of final polycarbonate.14
In contrast, by obtaining MpC directly from CO–O2, the
proposed new catalytic reaction of coupled carbonylation of
BPA and phenol achieves a one-step synthesis of reactive poly-
carbonate precursors and saves at least two reaction steps from
the commercial process. This reaction, to our best knowledge,
has never been studied before and has a great practical implica-
tion in phosgene-free syntheses of polycarbonate.
For the coupled oxidative carbonylations of BPA and phe-
nol, the reaction system and procedure were employed which
were similar to those generally used for the oxidative carbony-
lation of phenol.13 Thus, Pd(II) acetate (0.06 mmol), Ce(III)
acetate monohydrate (0.30 mmol; inorganic cocatalyst), tetra-
butylammonium bromide (1.50 mmol; base), benzoquinone
(1.50 mmol; organic cocatalyst), tetrahydrofuran (30 mL; sol-
vent), BPA (30 mmol) and the equimolar phenol were charged
in the 100 cm3 autoclave (Parr). All chemicals were purchased
from Aldrich. After purging the reactor three times with O2, 5
MPa of CO and 0.5 MPa of O2 were successively charged and
the reaction temperature was adjusted to 373 K. The reaction
was quenched after a desired reaction time by cooling the reac-
tor with ice water. Identification and quantification of products
were performed by high performance liquid chromatography
(HPLC) and gas chromatography (GC) as well as GC–MS.
A typical reaction profile of the coupled carbonylations of
BPA and phenol with time is shown in Figure 1. The conversions
of reactants and concentrations of products ceased to change with-
in 4 h. This saturation of BPA and phenol conversions after 4-h
reaction was caused by the equilibrium limits, not by deactivation
of catalysts because the conversions were increased to 65% for
BPA and to 25% for phenol, when coproduced water was
removed with 4 g of dehydrated molecular sieve 3 A. The desired
MpC was formed as weight-selectivity of 25.4% and the selectivi-
ties of DH and by-products were respectively 60.5% and 13.2%.
The oligomers up to n = 5 were formed. The by-products were
composed of phenyl salicylate and o-phenylene carbonate-type
bisphenols. The concentration profile of DH(1) shows a sharp
maximum. Hence, although DH(1) has no reactivity in the subse-
quent polycondensation, it is a potential reactant to be converted
into the reactive precursor MpC(n) by further coupled carbonyla-
tion with CO and phenol in the system. The concentraion of
We have studied various probable routes for the phosgene-
free polycarbonate synthesis such as the transesterifications of
BPA with DPC or DMC, and a direct carbonylation of BPA
with CO. Each route produced polycarbonate precursors with
different end groups. In terms of the reactivity in the subse-
quent polycondensation step, monophenyl carbonate-ended
oligomers (MpC(n), n = number of repeating unit) were the
most desired precursors for obtaining high molecular weight
polymers. We found that addition of phenol in the reaction of
BPA carbonylation, resulted in successful synthesis of MpCs in
Copyright © 2001 The Chemical Society of Japan
Kim, Won Bae
