Chemistry Reference
In-Depth Information
the presence of Lewis acids and, optionally, Lewis bases in inert solvents. This
process obviates the use of the phosgene monomer. Thus, a mixture of AlCl
3
, di-
methylsulfone, benzoyl chloride, oxalyl chloride, and 4,4
0
-diphenoxybenzophenone
in dichloromethane was subjected to the polymerization conditions, producing a
polymer having a good inherent viscosity.
5.4.3
Polycarbonates
Phosgene is an important raw material for polycarbonate resins, a class of polymers
for which world capacity has reached 1.5 million MT, corresponding to a yearly
phosgene consumption of over 0.6 MT. The production of polycarbonates, pre-
dominately the aromatic carbonates derived from bisphenol A, represents the sec-
ond largest area of phosgene usage and is probably the fastest growing area. The
polycarbonate market is one of the most buoyant sectors in the polymer industry,
at least in volume terms, and over the past decade demand has expanded rapidly at
more than 10% per annum [261]. Growth is likely to continue to be strong, as new
markets and applications (ranging from baby bottles to the digital versatile disc,
DVD) are found for this high-clarity engineering polymer [262].
Research activity in the field of new polymeric materials based on advanced
polycarbonates for optical recording media is very intense, as reflected in the re-
cent patent literature. For example, aromatic polycarbonates based on the 4,4
0
-
dihydroxyphenyl-2,2-propane-phosgene copolymer have been prepared as fire-
resistant thermoplastic resin compositions with good heat and impact resistance
and good moldability [263]. Polycarbonates, as substrates for optical recording me-
dia, have been prepared by reacting phosgene with a diphenol (e.g. bisphenol A)
and a p-C6-30 group substituted phenol blocking agent (e.g. p-tert-octylphenol)
[264]. Digital video disk substrates containing polycarbonate-polyorganosiloxane
materials have also been reported [265]. Polycarbonate-type fire-proofing agents
for thermoplastic resins with low nitrogen content, useful for polycarbonates,
poly(butylene terephthalate), PET, polyarylates, etc., consist of halo-substituted
polycarbonates and, optionally, siloxane copolymers (e.g. 2,2-bis(4-hydroxy-3,5-
dibromophenyl)propane-phosgene copolymer) [266]. 1,1-Bis(4-hydroxyphenyl)-
3,3,5-trimethylcyclohexane was reacted with phosgene, and then with C
20
alkyl-
substituted phenol, to give an aromatic polycarbonate terminated by an
alkylphenol polymer, useful for the manufacture of optical disks [267]. Transparent
polycarbonate-styrene polymer blends are used for optical devices. Injection mold-
ings of a 60:40 blend of bisphenol A-1-phenyl-1,1-bis(4-hydroxyphenyl)ethane-
phosgene copolymer and Styrol HF 10 were found to have a light transmittance of
89% and a low birefringence [268]. High-birefringence polycarbonates are prepared
from dihydric phenols and phosgene. Thus, the addition of mercaptoacetic acid
(10 g) to a solution of o-phenylphenol in acetone at 60
C, followed by passage
of a stream of gaseous hydrogen chloride through the mixture for 36 h gave 2,2-
bis(3-phenyl-4-hydroxyphenyl)propane. Phosgenation in the presence of a mole-
cular weight regulator (e.g. p-t-butylphenol) gave a polycarbonate of high birefring-
ence [269].
