Polycarbonate and process for producing the same

A polycarbonate exhibiting excellent fluidity and moisture resistance and a process for efficiently producing the polycarbonate are provided. The polycarbonate has a main chain comprising a repeating unit represented by general formula (I): ##STR1## wherein R.sup.1 and R.sup.2 each represents hydrogen atom or an alkyl group having 1 to 7 carbon atoms; contains 100 ppm by weight or less of a unit of a phenyl salicylate structure expressed by formula (II): ##STR2## in the main chain; and has a viscosity-average molecular weight of 10,000 or more. The polycarbonate is produced in accordance with a process comprising transesterification in the presence of a catalyst comprising a combination of an organic basic compound containing nitrogen and a quaternary phosphonium salt.

TECHNICAL FIELD 
The present invention relates to a polycarbonate and a process for 
producing the polycarbonate. More particularly, the present invention 
relates to a polycarbonate exhibiting excellent fluidity and moisture 
resistance and a process for efficiently producing the polycarbonate by 
transesterification in the presence of a specific catalyst. 
BACKGROUND ART 
Polycarbonates are engineering plastics having excellent impact resistance, 
heat resistance, and transparency and widely used as various types of 
mechanical parts, optical disks, and automobile parts. Recently, higher 
fluidity is required in the field of optical disks. 
In response to this requirement, a polycarbonate which is obtained by 
interfacial polycondensation using a solvent such as methylene chloride 
and has a chain end structure modified with a group such as cumylphenoxy 
group has been proposed (Japanese Patent Application Laid-Open No. Heisei 
1(1989)-245016). However, complete removal of impurities, such as sodium 
and chlorine, from the polycarbonate obtained by the interfacial 
polycondensation is difficult, and the polycarbonate is not satisfactory 
for optical applications. 
On the other hand, as the process for obtaining a polycarbonate containing 
decreased amounts of impurities without using any solvent, a 
transesterification process (a melt polymerization process) is known. As 
the process for producing a polycarbonate having cumylphenoxy group at the 
chain ends in accordance with this transesterification process, for 
example, a process in which a catalyst comprising a combination of a basic 
compound containing nitrogen, an alkali metal compound or an alkaline 
earth metal compound, and boric acid is used as the polymerization 
catalyst (Japanese Patent Application Laid-Open No. Heisei 2(1990)-175723) 
and a process in which polymerization is conducted in the presence of an 
alkali metal compound or an alkaline earth metal compound used as the 
catalyst, and then an acidic compound is added (Japanese Patent 
Application Laid-Open No. Heisei 5(1993)-9287) have been proposed. 
However, polycarbonates obtained in accordance with these processes have a 
problem in that cracks are formed at high temperatures in high moisture 
and strength is decreased. 
DISCLOSURE OF THE INVENTION 
Under the above circumstances, the present invention has an object to 
provide a polycarbonate exhibiting excellent fluidity and moisture 
resistance (resistance to formation of cracks in steam) and a process for 
producing this polycarbonate efficiently. 
As the result of extensive studies by the present inventors on 
polycarbonates exhibiting excellent fluidity and moisture resistance, it 
was found that the unit of a phenyl salicylate structure contained in the 
main chain in a small amount causes decrease in the moisture resistance 
(resistance to formation of cracks in steam), that a polycarbonate 
exhibiting excellent moisture resistance can be obtained by suppressing 
the content of this unit to a specific value or less, and that a 
polycarbonate satisfying this condition and having p-cumylphenoxy group, 
phenoxy group, and hydroxyl group in specific relative amounts at the 
chain ends exhibits particularly excellent fluidity and moisture 
resistance. It was also found that the above polycarbonates can be 
obtained efficiently by the transesterification process using a specific 
catalyst. The present invention has been completed on the basis of these 
knowledges. 
Accordingly, the present invention provides: 
(1) A polycarbonate which has a main chain comprising a repeating unit 
represented by general formula (I): 
##STR3## 
wherein R.sup.1 and R.sup.2 each represents hydrogen atom or an alkyl 
group having 1 to 7 carbon atoms, may be the same with or different from 
each other, and may be bonded to each other to form a ring structure; 
contains 100 ppm by weight or less of a unit of a phenyl salicylate 
structure expressed by formula (II): 
##STR4## 
in the main chain; and has a viscosity-average molecular weight of 10,000 
or more; and 
(2) A polycarbonate described in (1), which comprises 5 to 98% by mol of 
p-cumylphenoxy group, 1 to 94% by mol of phenoxy group, and 1 to 94% by 
mol of hydroxyl group at the chain ends. 
The present invention also provides: 
(3) A process for producing a polycarbonate described in (1) which 
comprises transesterifying (A) an aromatic dihydroxy compound represented 
by general formula (III): 
##STR5## 
wherein R.sup.1 and R.sup.2 are the same as the above, with (B) a diester 
of carbonic acid in the presence of a polymerization catalyst comprising a 
combination of (a) an organic basic compound containing nitrogen and (b) a 
quaternary phosphonium salt; and 
(4) A process for producing a polycarbonate described in (2) which 
comprises transesterifying (A) an aromatic dihydroxy compound represented 
by general formula (III) and (B') diphenyl carbonate in the presence of 
p-cumylphenol and a polymerization catalyst comprising a combination of 
(a) an organic basic compound containing nitrogen and (b) a quaternary 
phosphonium salt. 
THE MOST PREFERRED EMBODIMENT TO CARRY OUT THE INVENTION 
The polycarbonate of the present invention has a main chain comprising a 
repeating unit represented by general formula (I): 
##STR6## 
and contains 100 ppm by weight or less of a unit of a phenyl salicylate 
structure expressed by formula (II): 
##STR7## 
in the main chain. 
In general formula (I), R.sup.1 and R.sup.2 each represents hydrogen atom 
or an alkyl group having 1 to 7 carbon atoms. The alkyl group may have any 
of a chain structure, a branched chain structure, and a ring structure. 
Examples of the alkyl group include methyl group, ethyl group, n-propyl 
group, isopropyl group, butyl group, pentyl group, hexyl group, heptyl 
group, cyclopentyl group, and cyclohexyl group. R.sup.1 and R.sup.2 may be 
the same with or different from each other and may also be bonded to each 
other to form a ring structure. 
It is necessary that the viscosity-average molecular weight of the 
polycarbonate be 10,000 or more. When the viscosity-average molecular 
weight is less than 10,000, mechanical properties are insufficient for 
practical application. The viscosity-average molecular weight is 
preferably in the range of 10,000 to 100,000, more preferably 14,000 to 
40,000, from the standpoint of the balance between moldability and 
mechanical properties. The viscosity-average molecular weight (Mv) is 
obtained by dissolving a polycarbonate in methylene chloride, measuring 
the intrinsic viscosity .eta.! of the obtained methylene chloride 
solution at 20.degree. C., and then calculating the viscosity-average 
molecular weight from the obtained intrinsic viscosity in accordance with 
the equation: 
EQU .eta.!=1.23.times.10.sup.-5 .times.Mv.sup.0.83 
The unit of the phenyl salicylate structure expressed by formula (II) which 
is comprised in the main chain of the polycarbonate is considered to be 
formed by transfer of the carbon atom in the carbonate group to an 
ortho-position by the effect of heat and a catalyst during polymerization. 
When the content of this unit exceeds 100 ppm by weight, undesirable 
phenomena, such as deterioration in moisture resistance, formation of 
cracks at high temperatures in high moisture, and decrease in impact 
strength, take place. These phenomena take place particularly markedly 
when the viscosity-average molecular weight is approximately in the range 
of 14,000 to 17,000, i.e., when the most advantageous balance between 
fluidity and strength for practical molded articles is exhibited. The 
content of the unit of the phenyl salicylate structure is measured in 
accordance with the following method. 
A polymer in an amount of 500 mg is dissolved in 25 ml of methylene 
chloride, and light absorbance of the obtained solution at 320 nm is 
measured. As the reference solution, a solution is prepared by dissolving 
flakes of a polycarbonate prepared in accordance with the interfacial 
polycondensation (manufactured by IDEMITSU PETROCHEMICAL Co., Ltd.) in 
methylene chloride in the same manner as the above. 
A calibration curve is separately prepared by using phenyl salicylate as 
the reference material. The content (ppm by weight) of the unit of the 
phenyl salicylate structure in the polymer is obtained from the prepared 
calibration curve and the light absorbance obtained above. 
As the process for producing the polycarbonate of the present invention, 
any process can be used as long as the polycarbonate exhibiting the above 
properties can be obtained, and the process is not particularly limited. 
Among such processes, a process for producing the polycarbonate by 
transesterification is advantageous. 
In accordance with the process of the present invention, the desired 
polycarbonate can be efficiently produced by transesterifying (A) an 
aromatic dihydroxy compound represented by general formula (III): 
##STR8## 
wherein R.sup.1 and R.sup.2 are the same as the above, with (B) a diester 
of carbonic acid in the presence of a polymerization catalyst comprising a 
combination of (a) an organic basic compound containing nitrogen and (b) a 
quaternary phosphonium salt. 
Examples of the aromatic dihydroxy compound represented by general formula 
(III) of component (A) described above include 
bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 
1,1-bis(4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)propane 
(so-called bisphenol A), 1,1-bis(4-hydroxyphenyl)butane, 
1,1-bis(4-hydroxyphenyl)isobutane, 2,2-bis(4-hydroxyphenyl)butane, 
1,1-bis(4-hydroxyphenyl)pentane, 2,2-bis(4-hydroxyphenyl)pentane, 
3,3-bis(4-hydroxyphenyl)pentane, 2,2-bis(4-hydroxyphenyl)hexane, 
3,3-bis(4-hydroxyphenyl)hexane, 2,2-bis(4-hydroxyphenyl)heptane, 
3,3-bis(4-hydroxyphenyl)heptane, 4,4-bis(4-hydroxyphenyl)heptane, 
2,2-bis(4-hydroxyphenyl)octane, 3,3-bis(4-hydroxyphenyl)octane, 
4,4-bis(4-hydroxyphenyl)octane, 1,1-bis(4-hydroxyphenyl)cyclopentane, and 
1,1-bis(4-hydroxyphenyl)cyclohexane. 
The aromatic dihydroxy compound of component (A) may be used singly or as a 
combination of two or more types. Among these compounds, bisphenol A is 
particularly preferably used. 
As the diester of carbonic acid used as component (B) in the present 
invention, various compounds can be used. For example, at least one type 
of compound selected from the group consisting of diaryl carbonate 
compounds, dialkyl carbonate compounds, and alkylaryl carbonate compounds 
can be used. 
The diaryl carbonate compound used as component (B) is a compound 
represented by general formula (IV): 
##STR9## 
wherein Ar.sup.1 and Ar.sup.2 each represents an aryl group and may be the 
same with or different from each other, or a compound represented by 
general formula (V) 
##STR10## 
wherein Ar.sup.3 and Ar.sup.4 each represents an aryl group and may be the 
same with or different from each other, and D.sup.1 represents a residue 
group obtained by removing two hydroxyl groups from the above aromatic 
dihydroxy compound. 
The dialkyl carbonate compound is a compound represented by general formula 
(VI): 
##STR11## 
wherein R.sup.3 and R.sup.4 each represents an alkyl group having 1 to 6 
carbon atoms or a cycloalkyl group having 4 to 7 carbon atoms and may be 
the same with or different from each other, or a compound represented by 
general formula (VII): 
##STR12## 
wherein R.sup.5 and R.sup.6 each represents an alkyl group having 1 to 6 
carbon atoms or a cycloalkyl group having 4 to 7 carbon atoms and may be 
the same with or different from each other, and D.sup.2 represents a 
residue group obtained by removing two hydroxyl groups from the above 
aromatic dihydroxy compound. 
The alkylaryl carbonate compound is a compound represented by general 
formula (VIII): 
##STR13## 
wherein Ar.sup.5 represents an aryl group and R.sup.7 represents an alkyl 
group having 1 to 6 carbon atoms or a cycloalkyl group having 4 to 7 
carbon atoms, or a compound represented by general formula (IX): 
##STR14## 
wherein Ar.sup.6 represents an aryl group and R.sup.8 represents an alkyl 
group having 1 to 6 carbon atoms or a cycloalkyl group having 4 to 7 
carbon atoms, and D.sup.3 represents a residue group obtained by removing 
two hydroxyl groups from the above aromatic dihydroxy compound. 
Examples of the diaryl carbonate compound include diphenyl carbonate, 
ditolyl carbonate, bis(chlorophenyl) carbonate, m-cresyl carbonate, 
dinaphthyl carbonate, bis(diphenyl) carbonate, and bisphenol A bisphenyl 
carbonate. 
Examples of the dialkyl carbonate compound include diethyl carbonate, 
dimethyl carbonate, dibutyl carbonate, dicyclohexyl carbonate, and 
bisphenol A bismethyl carbonate. 
Examples of the alkylaryl carbonate compound include methyl phenyl 
carbonate, ethyl phenyl carbonate, butyl phenyl carbonate, cyclohexyl 
phenyl carbonate, and bisphenol A methyl phenyl carbonate. 
In the present invention, one or more types of compound are suitably 
selected from the above compounds and used as the diester of carbonic acid 
of component (B). Among these compounds, diphenyl carbonate is preferably 
used. 
In the process of the present invention, a chain stopper may be used, where 
necessary. Examples of the chain stopper include phenol, o-n-butylphenol, 
m-n- butylphenol, p-n-butylphenol, o-isobutylphenol, m-isobutylphenol, 
p-isobutylphenol, o-t-butylphenol, m-t-butyl phenol, p-t-butylphenol, 
o-n-pentylphenol, m-n-pentylphenol, p-n-pentylphenol, o-n-hexylphenol, 
m-n-hexylphenol, p-n-hexylphenol, o-cyclohexylphenol, m-cyclohexylphenol, 
p-cyclohexylphenol, o-phenylphenol, m-phenylphenol, p-phenylphenol, 
o-n-nonylphenol, m-n-nonylphenol, p-n-nonylphenol, o-cumylphenol, 
m-cumylphenol, p-cumylphenol, o-naphthylphenol, m-naphthylphenol, 
p-naphthylphenol, 2,6-di-t-butylphenol, 2,5-di-tbutylphenol, 
2,4-di-t-butylphenol, 3,5-di-t-butylphenol, 2,5-dicumylphenol, 
3,5-dicumylphenol, compounds expressed by the following formulae: 
##STR15## 
monohydric phenols, such as chroman derivatives expressed by the following 
formulae: 
##STR16## 
compounds represented by the following formulae: 
##STR17## 
wherein n represents an integer of 7 to 30, and compounds represented by 
the following formulae: 
##STR18## 
wherein R.sup.9 represents an alkyl group having 1 to 12 carbon atoms, and 
k represents an integer of 1 to 3. 
Among these compounds, phenol, p-t-butylphenol, p-cumylphenol, and 
p-phenylphenol are preferably used. p-Cumylphenol is more preferable from 
the standpoint of fluidity of the obtained polycarbonate. 
In the present invention, compounds such as phloroglucinol, trimellitic 
acid, 1,1,1-tris(4-hydroxyphenyl)ethane, 
1-.alpha.-methyl-.alpha.-(4'-hydroxyphenyl)ethyl!-4-.alpha.',.alpha.'-bi 
s(4"-hydroxyphenyl)ethyl!benzene, 
.alpha.,.alpha.',.alpha."-tris(4-hydroxyphenyl)-1,3,5-triisopropylbenzene, 
and isatin bis(o-cresol) can be used as the branching agent. 
In the process of the present invention, a combination of (a) an organic 
basic compound containing nitrogen and (b) a quaternary phosphonium salt 
is used as the polymerization catalyst in the transesterification. 
The organic basic compound containing nitrogen of component (a) described 
above is not particularly limited, and various compounds can be used. 
Examples of the organic basic compound containing nitrogen include 
aliphatic tertiary amine compounds, such as trimethylamine, triethylamine, 
tripropylamine, tributylamine, tripentylamine, trihexylamine, and 
dimethylbenzylamine; aromatic tertiary amine compounds, such as 
triphenylamine; and heterocyclic compounds containing nitrogen, such as 
N,N-dimethyl-4-aminopyridine, 4-diethylaminopyridine, 
4-pyrrolidinopyridine, 4-aminopyridine, 2-aminopyridine, 
2-hydroxypyridine, 4-hydroxypyridine, 2-methoxypyridine, 
4-methoxypyridine, imidazole, 2-methylimidazole, 4-methylimidazole, 
2-dimethylaminoimidazole, 2-methoxyimidazole, 2-mercaptoimidazole, 
aminoquinoline, and diazabicylooctane (DABCO). 
Further examples include quaternary ammonium salts represented by general 
formula (X): 
EQU (NR.sup.10.sub.4).sup.+ (X.sup.1).sup.- (X) 
In general formula (X) shown above, R.sup.10 represents an organic group. 
Examples of the organic group include alkyl groups and cycloalkyl groups, 
such as methyl group, ethyl group, propyl group, butyl group, pentyl 
group, hexyl group, octyl group, and cyclohexyl group; aryl groups, such 
as phenyl group, tolyl group, naphthyl group, and biphenyl group; and 
arylalkyl groups, such as benzyl group. The four groups represented by 
R.sup.10 may be the same with or different from each other, and two groups 
represented by R.sup.10 may be bonded to each other to form a ring 
structure. X.sup.1 represents a halogen atom, hydroxyl group, or BR.sub.4, 
wherein R represents hydrogen atom or a hydrocarbon group, such as an 
alkyl group and an aryl group, and the four groups represented by R may be 
the same with or different from each other. 
Examples of the quaternary ammonium salt include ammonium hydroxides having 
alkyl groups, aryl groups, and alkaryl group, such as tetramethylammonium 
hydroxide, tetraethylammonium hydroxide, tetrabutylammonium hydroxide, and 
trimethylbenzylammonium hydroxide; and basic salts, such as 
tetramethylammonium borohydride, tetrabutylammonium borohydride, 
tetrabutylammonium tetraphenylborate, and tetramethylammonium 
tetraphenylborate. 
Among these organic basic compounds containing nitrogen, the quaternary 
ammonium salts represented by general formula (X) shown above, 
specifically, tetramethylammonium hydroxide, tetrabutylammonium hydroxide, 
tetramethylammonium borohydride, and tetrabutylammonium borohydride, are 
preferable because of high catalyst activity and easiness of heat 
decomposition which gives a smaller amount of residues left in the 
polymer. Tetramethylammonium hydroxide is more preferable among these 
compounds. 
The organic basic compound containing nitrogen of component (a) may be used 
singly or as a combination of two or more types. 
The quaternary phosphonium salt of component (b) is not particularly 
limited, and various compounds can be used. For example, compounds 
represented by general formula (XI): 
EQU (PR.sup.11 .sub.4).sup.+ (X.sup.2).sup.- (XI) 
are preferably used. 
In general formula (XI) shown above, R.sup.11 represents an organic group. 
Examples of the organic group include the same groups as those shown above 
as examples of the group represented by R.sup.10 in general formula (X). 
The four groups represented by R.sup.11 may be the same with or different 
from each other, and two groups represented by R.sup.11 may be bonded to 
each other to form a ring structure. X.sup.2 represents a halogen atom, 
hydroxyl group, an alkyloxy group, an aryloxy group, (R'O).sub.2 
P(.dbd.O)O, or BR".sub.4. In these formulae, R' represents a hydrocarbon 
group, such as an alkyl group and an aryl group, and two groups 
represented by R'O may be the same with or different from each other. R" 
represents hydrogen atom or a hydrocarbon group, such as an alkyl group 
and an aryl group, and the four groups represented by R" may be the same 
with or different from each other. 
Examples of the quaternary phosphonium salt include tetra(aryl or 
alkyl)phosphonium hydroxides, such as tetraphenylphosphonium hydroxide, 
tetranaphthylphosphonium hydroxide, tetra(chlorophenyl)phosphonium 
hydroxide, tetra(biphenyl)phosphonium hydroxide, tetratolylphosphonium 
hydroxide, tetramethylphosphonium hydroxide, tetraethylphosphonium 
hydroxide, and tetrabutylphosphonium hydroxide; tetramethylphosphonium 
tetraphenylborate; tetraphenylphosphonium bromide; tetraphenylphosphonium 
tetraphenylborate; methyltriphenylphosphonium tetraphenylborate; 
benzyltriphenylphosphonium tetraphenylborate; tetratolylphosphonium 
tetraphenylborate; tetraphenylphosphonium phenolate; 
tetra(p-t-butylphenyl)phosphonium diphenylphosphate; 
triphenylbutylphosphonium phenolate; and triphenylbutylphosphonium 
tetraphenylborate. 
Examples other than the compounds represented by general formula (XI) shown 
above include bis-tetraphenylphosphonium salt of 2,2-bis(4-hydroxyphenyl 
)propane, ethylenebis(triphenylphosphonium) dibromide, and 
trimethylenebis(triphenylphosphonium) bis(tetraphenylborate). 
Among these quaternary phosphonium salts, tetraphenylphosphonium 
tetraphenylborate, methyltriphenylphosphonium tetraphenylborate, and 
benzyltriphenylphosphonium tetraphenylborate are preferable because of 
high catalyst activity and easiness of heat decomposition which gives a 
smaller amount of residues left in the polymer. 
The quaternary ammonium salt of component (a) may be used singly or as a 
combination of two or more types. 
It is preferable that the organic basic compound containing nitrogen and 
the quaternary ammonium salts contain metal impurities in amounts as small 
as possible. It is particularly preferable that the contents of compounds 
of alkali metals and alkaline earth metals are 50 ppm or less. 
In the process of the present invention, it is preferable that the organic 
basic compound containing nitrogen of component (a) described above is 
used as the catalyst component in an amount of 10.sup.-1 to 10.sup.-6 mol, 
more preferably 10.sup.-2 to 10.sup.-5 mol, and the quaternary phosphonium 
salt of component (b) described above is used as the catalyst component in 
an amount of 10.sup.-3 to 10.sup.-8 mol, preferably 10.sup.-4 to 10.sup.-7 
mol. When the amount of component (a) is less than 10.sup.-6 mol, the 
catalyst activity in the initial period of the reaction is insufficient. 
When the amount of component (a) exceeds 10.sup.-1 mol, the cost of 
production is increased. When the amount of component (b) is less than 
10.sup.-8 mol, the catalyst activity in the later period of the reaction 
is insufficient. When the amount of component (b) exceeds 10.sup.-3 mol, 
the cost of production is increased. Therefore, such amounts are not 
preferable. 
This polymerization catalyst is used in such an amount that the total of 
the amounts of components (a) and (b) is generally 10.sup.-1 to 10.sup.-8 
mol, preferably 10.sup.-2 to 10.sup.-7 mol, per 1 mol of the aromatic 
dihydroxy compound of component (A) used as a raw material. When the 
amount of the catalyst is less than 10.sup.-8 mol, there is the 
possibility that the catalyst activity is not exhibited. When the amount 
of the catalyst exceeds 10.sup.-1 mol, there is the possibility that 
physical properties, particularly heat resistance and hydrolytic 
resistance, of the polycarbonate obtained as the final product are 
decreased, and the cost of production is increased. Therefore, an amount 
exceeding the above range is not preferable. 
As the polycarbonate of the present invention, a polycarbonate containing 
100 ppm or less of the unit of the phenyl salicylate structure expressed 
by formula (II) shown above and comprising 5 to 98% by mol of 
p-cumylphenoxy group, 1 to 94% by mol of phenoxy group, and 1 to 94% by 
mol of hydroxyl group at the chain ends is preferable because excellent 
fluidity and moisture resistance are exhibited. 
The above polycarbonate can be produced efficiently by transesterification 
of (A) the aromatic dihydroxy compound represented by general formula 
(III) shown above with (B') diphenyl carbonate in the presence of 
p-cumylphenol used as the chain stopper and a polymerization catalyst 
comprising a combination of the organic basic compound containing nitrogen 
of component (a) described above and the quaternary phosphonium salt of 
component (b) described above. 
In the present invention, the total amount of the chain stopper may be 
added to the reaction system in advance; alternatively, a portion of the 
chain stopper may be added to the reaction system in advance, and the 
remaining portion may be added in accordance with the progress of the 
reaction; or, where desired, the total amount of the chain stopper may be 
added to the reaction system after transesterification of the aromatic 
dihydroxy compound of component (A) with the diester of carbonic acid of 
component (B) has partially proceeded. When p-cumylphenol is used as the 
chain stopper, p-cumylphenol is used in an amount preferably in the range 
of 0.01 to 0.2 mol, more preferably in the range of 0.02 to 0.15 mol, most 
preferably in the range of 0.02 to 0.1 mol, per 1 mol of the aromatic 
dihydroxy compound. 
When the transesterification is conducted in accordance with the process of 
the present invention, the reaction temperature is not particularly 
limited. The reaction temperature is selected generally in the range of 
100 to 330.degree. C., preferably 180 to 300.degree. C. It is more 
preferable that the reaction temperature is increased gradually from 
180.degree. C. to 300.degree. C. in accordance with the progress of the 
reaction. When the temperature of the transesterification is lower than 
100.degree. C., the rate of the reaction is small. When the temperature 
exceeds 330.degree. C., problems arise in that side reactions take place 
and that the obtained polymer is colored. Therefore, such amounts are not 
preferable. The reaction pressure is set in accordance with the vapor 
pressure of the monomers and the reaction temperature. In other words, the 
pressure can be set at a value suitable for achieving an efficient 
reaction and is not particularly limited. In many cases, the pressure is 
generally set at an atmospheric pressure (an ordinary pressure) or an 
added pressure, i.e., in the range of 1 to 50 atom (760 to 38,000 torr), 
in the initial period of the reaction, and at a reduced pressure in the 
later period of the reaction, preferably in the range of 0.01 to 100 torr 
in the final stage of the reaction. 
As for the reaction time, the reaction can be continued until the object 
molecular weight is achieved. The reaction time is generally about 0.2 to 
10 hours. 
The above transesterification is generally conducted in the absence of an 
inert solvent. The reaction may also be conducted in the presence of an 
inert solvent in an amount of 1 to 150% by weight of the obtained 
polycarbonate, where necessary. Examples of the inert solvent include 
aromatic compounds, such as diphenyl ether, halogenated diphenyl ethers, 
benzophenone, polyphenyl ethers, dichlorobenzene, and methylnaphthalene; 
and cycloalkanes, such as tricyclo(5,2,10)decane, cyclooctane, and 
cyclodecane. The reaction may be conducted in an atmosphere of an inert 
gas, where necessary. Examples of the inert gas include various types of 
gas, such as argon, carbon dioxide, nitrogen monoxide, and nitrogen; 
chlorofluorohydrocarbons; and alkanes, such as ethane and propane. 
In the present invention, an antioxidant may be added to the reaction 
system, where necessary. As the antioxidant, antioxidants containing 
phosphorus are preferable. Examples of such antioxidants include trialkyl 
phosphites, such as trimethyl phosphite, triethyl phosphite, tributyl 
phosphite, trioctyl phosphite, trinonyl phosphite, tridecyl phosphite, 
trioctadecyl phosphite, distearyl pentaerythrityl diphosphite, 
tris(2-chloroethyl) phosphite, and tris(2,3-dichloropropyl) phosphite; 
tricycloalkyl phosphites, such as tricyclohexyl phosphite; triaryl 
phosphites, such as triphenyl phosphite, tricresyl phosphite, 
tris(ethylphenyl) phosphite, tris(butylphenyl) phosphite, 
tris(nonylphenyl) phosphite, and tris(hydroxyphenyl) phosphite; monoalkyl 
diaryl phosphites, such as 2-ethylhexyl diphenyl phosphite; trialkyl 
phosphates, such as trimethyl phosphate, triethyl phosphate, tributyl 
phosphate, trioctyl phosphate, tridecyl phosphate, trioctadecyl phosphate, 
distearyl pentaerythrityl diphosphate, tris(2-chloroethyl) phosphate, and 
tris(2,3-dichloropropyl) phosphate; tricycloalkyl phosphates, such as 
tricyclohexyl phosphate; and triaryl phosphates, such as triphenyl 
phosphate, tricresyl phosphate, tris(nonylphenyl) phosphate, and 
2-ethylphenyl diphenyl phosphate. 
In the present invention, phenols and alcohols which correspond to the used 
diester of carbonic acid, esters of these compounds, and the inert solvent 
leave the reactor as the reaction proceeds. The substances leaving the 
reactor can be recycled after separation and purification. Therefore, it 
is preferable that an apparatus to remove these substances is attached to 
the reactor. 
The reaction can be conducted in accordance with a batch process or a 
continuous process. Any desired apparatus can be used for the reaction. 
When the reaction is conducted in accordance with a continuous process, it 
is preferable that at least two reactors are used and the reaction 
conditions are set as described above. 
The material and the structure of the reactor used in the present invention 
is not particularly limited as long as the reactor has an ordinary ability 
of stirring. It is preferable that the reactor has ability of stirring in 
a high viscosity condition because viscosity of the reaction system is 
increased in the later stage of the reaction. The reactor is not limited 
to a tank reactor, but reactors of other shapes, such as an extruder-type 
reactor, can also be used. 
In the present invention, it is preferable that, after the 
transesterification has been completed, the reaction product is heat 
treated at a temperature above the decomposition temperature of the 
catalyst, preferably at about 300.degree. C., and the catalyst is removed 
by heat decomposition to improve the quality (color) of the obtained 
polycarbonate. 
The thus obtained polycarbonate may be directly formed into granules or 
molded by using an extruder. 
The polycarbonate obtained in accordance with the present invention may be 
used after being mixed with conventional additives, such as plasticizers, 
pigments, lubricants, mold release agents, stabilizers, and inorganic 
fillers. 
It is also possible that the polycarbonate is blended with other polymers, 
such as polyolefins, polystyrenes, polysulfonates, polyamides, and 
polyphenylene ethers. It is particularly effective that the polycarbonate 
is used in combination with polymers, such as polyphenylene ethers, 
polyether nitrites, polysiloxane compounds modified at the chain ends, 
modified polypropylenes, and modified polystyrenes, which have OH group, 
COOH group, NH.sub.2 group, or the like at the chain ends.

EXAMPLES 
The present invention is described in more detail with reference to 
examples and comparative examples in the following. However, the present 
invention is not limited by the examples. 
Example 1 
Into an autoclave having an inner volume of 1.4 liter, made of nickel 
steel, and equipped with a stirrer, 228 g (1.00 mol) of bisphenol A (BPA), 
226.8 g (1.06 g) of diphenyl carbonate, and 6.1 g (0.029 mol) of 
p-cumylphenol were placed, and then a 20% by weight aqueous solution of 
tetramethylammonium hydroxide (TMAH) (Na&lt;1 ppb, Ca&lt;1 ppb, and K&lt;1 ppb) and 
a 40% by weight aqueous solution of tetrabutylphosphonium hydroxide (TBPH) 
(Na&lt;40 ppm and K&lt;5 ppm) were added as the catalyst in such amounts that 
the concentration of TMAH was 2.5.times.10.sup.-4 mol/mol BPA and the 
concentration of TBPH was 1.times.10.sup.-5 mol/mol BPA. The autoclave was 
purged with nitrogen five times. 
After the resultant mixture was heated to 180.degree. C. to melt bisphenol 
A and diphenyl carbonate, the mixture was stirred for 30 minutes. Then, 
the temperature was increased to 210.degree. C., and the pressure was 
reduced to 100 mm Hg. Phenol formed in the mixture was removed by 
distillation. When the rate of distillation of phenol decreased, the 
temperature was increased to 240.degree. C., and distillation of phenol 
was continued. Then, the pressure was further decreased to 10 mm Hg, and 
the reaction was allowed to proceed for 1 hour. Subsequently, the 
temperature was increased to 270.degree. C., and the pressure was 
decreased gradually to 0.4 mm Hg. The reaction was allowed to proceed in 
this condition for 60 minutes. 
A viscous transparent condensate in the autoclave was taken out, and 
properties of the thus obtained polycarbonate were measured in accordance 
with the following methods. The amount of p-cumylphenol and the type and 
the amount of the catalyst are shown in Table 1, and the results are shown 
in Table 2. 
(1) Content of the unit of the phenyl salicylate structure 
The content of the unit of the phenyl salicylate structure in the main 
chain was obtained in accordance with the method described above. 
(2) Mol fractions of chain end structures 
Mole fractions of p-cumylphenoxy group, phenoxy group, and hydroxyl group 
at the chain ends were obtained by .sup.1 H-NMR. 
(3) Viscosity-average molecular weight 
The viscosity-average molecular weight (Mv) was obtained in accordance with 
the method described above. 
(4) Number of formed cracks 
A polycarbonate was molded into a sample of a size of 5.times.5 cm and a 
thickness of 3 mm by pressing at 280.degree. C. After the obtained sample 
was exposed to steam in a sterilizing chamber at 121.degree. C. for 48 
hours, the sample was kept in water. After 24 hours, the number of formed 
cracks per a plate of 5.times.5 cm was measured in accordance with the 
following method. A magnified projection picture (10 times) was taken by a 
universal projector (OLYMPUS UP-350) using a monochromatic filter. The 
obtained picture was analyzed by a scanner set at 25 cm.times.20 cm using 
an image analyzer (IMAGE ANALYSIS SYSTEM V2.0, manufactured by STANLEY 
ELECTRIC Co., Ltd.). The obtained image was converted into binary data in 
accordance with the discrimination analysis. The number of particles 
having 10 or more picture elements (1 picture element=0.3 mm) was counted. 
Five times the value obtained by the measurement was used as the number of 
formed cracks. 
(5) Flowability 
The amount (ml/sec) of a resin flowing out of a nozzle having a diameter of 
1 mm and a length of 10 mm was measured at 280.degree. C. under a pressure 
of 160 kg/cm.sup.2, and the obtained value was used as the flowability. 
(6) Qualitative analysis of the phenyl salicylate structure 
A polymer in an amount of 500 mg was dissolved in methylene chloride and 
hydrolyzed with a 2 N KOH-methanol solution. After the hydrolysis, 
methylene chloride was vaporized. The residual product was neutralized 
with hydrochloric acid and separated into fractions by using a high 
performance liquid chromatography. A fraction having the maximum 
absorption at about 310 nm (the maximum absorption generally shifts from 
320 nm to 308 nm because the phenyl salicylate structure is in the form of 
the methyl ester) is taken, and the mass spectrum of the fraction was 
obtained by a mass spectrometer. The mass spectrum is shown in FIG. 1. 
The reaction taking place in the hydrolysis is shown in the following: 
##STR19## 
Example 2 
The same procedures as those conducted in Example 1 were conducted except 
that methyltriphenylphosphonium tetraphenylborate (MTPTB; Na&lt;7 ppm and 
Mg&lt;5 ppm) in an amount of 1.times.10.sup.-5 mol/mol BPA was used in place 
of TBPH. The amount of p-cumylphenol and the type and the amount of the 
catalyst are shown in Table 1, and the results are shown in Table 2. 
Example 3 
The same procedures as those conducted in Example 1 were conducted except 
that 4.1 g (0.02 mol) of p-cumylphenol was used, and that, as the catalyst 
components, tetrabutylammonium hydroxide (TBAH; Na&lt;5 ppm and K&lt;10 ppm) was 
used in an amount of 2.5.times.10.sup.-4 mol/mol BPA and 
tetraphenylphosphonium tetraphenylborate (TPTB; Na&lt;1 ppm and Mg&lt;1 ppm) was 
used in an amount of 1.times.10.sup.-5 mol/mol BPA. The amount of 
p-cumylphenol and the type and the amount of the catalyst are shown in 
Table 1, and the results are shown in Table 2. 
Example 4 
The same procedures as those conducted in Example 1 were conducted except 
that p-cumylphenol was added after the temperature was increased to 
240.degree. C. The amount of p-cumylphenol and the type and the amount of 
the catalyst are shown in Table 1, and the results are shown in Table 2. 
Example 5 
The same procedures as those conducted in Example 1 were conducted except 
that p-cumylphenol was not used, and that tetraphenylphosphonium 
tetraphenylborate (TPTB; Na&lt;1 ppm and Mg&lt;1 ppm) was used as the catalyst 
component in an amount of 1.times.10.sup.-5 mol/mol BPA in place of the 
aqueous solution of TBPH. 
Comparative Example 1 
The same procedures as those conducted in Example 1 were conducted except 
that compounds shown in Table 1 were used as the catalyst, and that butyl 
p-toluenesulfonate was added in an amount of 1.8 ppm by weight of the 
polymer after the polymerization was completed and a melted product was 
taken out after the resultant mixture was stirred for 30 minutes. The 
results are shown in Table 2. 
Comparative Example 2 
The same procedures as those conducted in Example 1 were conducted except 
that the compounds shown in Table 1 were used as the catalyst, and that 
butyl p-toluenesulfonate was added in an amount of 10 ppm by weight of the 
polymer after the polymerization was completed and a melted product was 
taken out after the resultant mixture was stirred for 30 minutes. The 
results are shown in Table 2. 
Comparative Example 3 
The same procedures as those conducted in Example 3 were conducted except 
that the compounds shown in Table 1 were used as the catalyst. The results 
are shown in Table 2. 
Comparative Example 4 
The same procedures as those conducted in Example 3 were conducted except 
that the compounds shown in Table 1 were used as the catalyst. The results 
are shown in Table 2. 
TABLE 1 
______________________________________ 
amount polymerization catalyst 
of p- compound I compound II 
cumyl- amount amount 
phenol (mol/ (mol/ 
(mol) type mol BPA) type mol BPA) 
______________________________________ 
Example 1 
0.029 TMAH 2.5 .times. 10.sup.-4 
TBPH 1 .times. 10.sup.-5 
Example 2 
0.029 TMAH 2.5 .times. 10.sup.-4 
MTPTB 1 .times. 10.sup.-5 
Example 3 
0.029 TBAH 2.5 .times. 10.sup.-4 
TPTB 1 .times. 10.sup.-5 
Example 4 
0.029 TMAH 2.5 .times. 10.sup.-4 
TBPH 1 .times. 10.sup.-5 
Example 5 
0.000 TMAH 2.5 .times. 10.sup.-4 
TPTB 1 .times. 10.sup.-5 
Comparative 
0.029 TMAH 2.5 .times. 10.sup.-4 
NaOH 1 .times. 10.sup.-6 
Example 1 
Comparative 
0.029 TMAH 2.5 .times. 10.sup.-4 
(CH.sub.3 COO).sub.2 Ca 
2 .times. 10.sup.-6 
Example 2 
Comparative 
0.02 TBAH 2.5 .times. 10.sup.-4 
NaOH 1 .times. 10.sup.-6 
Example 3 
Comparative 
0.02 TMAH 2.5 .times. 10.sup.-4 
-- -- 
Example 4 
______________________________________ 
Notes: 
TMAH: A 20% by weight aqueous solution of tetramethylammonium hydroxide 
(Na &lt; 1 ppb, Ca &lt; 1 ppb, K &lt; 1 ppb) 
TBAH: Tetrabutylammonium hydroxide (Na &lt; 5 ppm, K &lt; 10 ppm) 
TBPH: A 40% by weight aqueous solution of tetrabutylphosphonium hydroxide 
(Na &lt; 40 ppm, K &lt; 5 ppm) 
MTPTB: Methyltriphenylphosphonium tetraphenylborate (Na &lt; 7 ppm, Mg &lt; 5 
ppm) 
TPTB: Tetraphenylphosphonium tetraphenylborate (Na &lt; 1 ppm, Mg &lt; 1 ppm) 
TABLE 2-1 
______________________________________ 
content of 
viscosity- 
unit of phenyl 
average salicylate number of 
molecular structure flowability 
formed 
weight Mv! 
(ppm by wt.) 
(.times. 10.sup.-2 ml/sec) 
cracks 
______________________________________ 
Example 1 
15,500 30 35 0 
Example 2 
15,300 20 26 0 
Example 3 
17,000 20 24 0 
Example 4 
16,100 20 29 0 
Example 5 
15,700 20 26 130 
Comparative 
15,800 150 34 400 
Example 1 
Comparative 
15,100 170 37 600 
Example 2 
Comparative 
16,800 140 34 whitened 
Example 3 
Comparative 
5,600 20 no high molecular 
Example 4 weight polymer formed 
______________________________________ 
TABLE 2-2 
______________________________________ 
mol fractions of chain end structures (% by mol) 
p-cumylphenoxy group 
phenoxy group 
hydroxyl group 
______________________________________ 
Example 1 
60 20 20 
Example 2 
55 25 20 
Example 3 
40 30 30 
Example 4 
70 20 10 
Example 5 
0 60 40 
Comparative 
58 21 21 
Example 1 
Comparative 
55 20 25 
Example 2 
Comparative 
40 25 35 
Example 3 
Comparative 
10 10 80 
Example 4 
______________________________________ 
INDUSTRIAL APPLICABILITY 
The polycarbonate of the present invention contains the unit of the phenyl 
salicylate structure in the main chain only in a small amount, exhibits 
excellent fluidity and moisture resistance, shows suppressed formation of 
cracks at high temperatures in high moisture, and are advantageously used 
in the optical field, the automobile field, and the mechanical field. 
The polycarbonate can be efficiently produced by transesterification in the 
presence of a specific catalyst. 
BRIEF DESCRIPTION OF THE DRAWINGS 
FIG. 1 shows a mass spectrum used in the qualitative analysis of the phenyl 
salicylate structure in the polymer obtained in Example 1.