Process for producing polycarbonate having terminal hydroxyl groups

A process for producing a polycarbonate having terminal hydroxyl groups obtained by reacting an aliphatic polyol with a carbonate monomer, characterized by comprising the first step of producing a low molecular weight polycarbonate while removing the alcohols produced as by-products from the reaction mixture containing the aliphatic polyol and the carbonate monomer and the second step of adding to the reaction mixture the carbonate monomer in portions or continuously under the conditions that the concentration of the aliphatic polyol in the reaction mixture in the first step is 5% by weight or less and effecting the reaction while removing the alcohols produced as by-products, whereby connecting the low molecular weight polycarbonates to one another through the carbonate monomer to heighten the molecular weight.

TECHNICAL FIELD! 
This invention relates to a process for producing a polycarbonate having 
terminal hydroxyl groups useful as a starting material for polyurethane in 
an emulsion, a coating, a thermoplastic elastomer, a paint, an adhesive or 
the like. 
BACKGROUND ART! 
As the process for producing a polycarbonate having terminal hydroxyl 
groups, there is a process which comprises subjecting a carbonate monomer 
along with a divalent alcohol monomer to interesterification to obtain a 
low molecular weight polycarbonate and then self-condensing this to obtain 
a high molecular weight polycarbonate as disclosed in JP-B-63-12,896 
(corresponding to U.S. Pat. No. 4,131,731). In this process, 
self-condensation is effected in the latter half of the process, so that 
the amount of the divalent alcohol monomer distilled out becomes large, 
and therefore, the yield of polycarbonate is low and it is necessary to 
apply severe conditions of high temperature and high vacuum over a long 
period of time. When a product is exposed to a high temperature for a long 
period of time, the coloration of the product is feared, and decomposition 
of product becomes easy to cause. Therefore, in order to keep a high 
vacuum under such conditions, a cooling trap having a higher performance 
and a vacuum pump of a larger size become necessary. Under such 
circumstances, there has been desired a development of a process for 
producing a polycarbonate more economically without applying severe 
conditions of high temperature and high vacuum over a long period of time. 
In particular, when a butanediol type polycarbonate is produced using 
1,4-butanediol as the divalent alcohol monomer according to the 
above-mentioned prior art, there have been such problems that 
tetrahydrofuran is easily produced as a by-product by reaction of the 
carbonate monomer with the butanediol and/or decomposition of the 
1,4-butanediol residue terminals of the polycarbonate produced and that in 
the step of self-condensation requiring the application of severe 
conditions of high temperature and high vacuum, the reaction under reduced 
pressure becomes difficult because of the large amount of hydrofuran 
produced as a by-product and the molecular weight does not become high. 
Moreover, since it is difficult to completely trap the tetrahydrofuran in 
the vacuum system using a cooling trap, an equipment such as an absorption 
tower or the like becomes necessary for lowering the concentration of the 
tetrahydrofuran discharged into the atmosphere through the vacuum pump and 
the commercial scale production of a high molecular weight butanediol type 
polycarbonate has been difficult. 
However, 1,4-butanediol is very inexpensive and hence a butanediol type 
polycarbonate produced using the same can become very inexpensive. In 
addition, it is clear that a polyurethane obtained using a low molecular 
weight butanediol type polycarbonate is superior in chemical resistance to 
other polyurethanes obtained using other polyols; however, even when the 
low molecular weight butanediol type polycarbonate is used, for example, 
as the soft segment of a polyurethane, the proportion of the hard segment 
becomes high and no urethane having soft and good feeling is obtained. 
Therefore, the low molecular weight butanediol type polycarbonate has not 
been so often used as the starting material for polyurethane. 
Under such circumstances, a development of a process for producing a high 
molecular weight butanediol type polycarbonate has been desired. 
In JP-A-4-153,218, a process is proposed which comprises subjecting a 
carbonate monomer and a divalent alcohol monomer to interesterification, 
to obtain a low molecular weight polycarbonate, then adding thereto a 
carbonate monomer and further subjecting the resulting mixture to 
interesterification reaction to heighten the molecular weight. This 
process is effective for heightening the conversion of the dihydric 
alcohol monomer to increase the one batch yield; however, the reaction for 
heightening the molecular weight is not fast, and the production of 
polycarbonate per unit volume per unit time is small. In addition, the 
polycarbonate monomer is added in one portion and hence the rake of 
increasing the molecular weight is lowered as the reaction proceeds and 
the molecular weight increases. Therefore, the self-condensation reaction 
must be carried out when it is intended to produce the high molecular 
weight polycarbonate more economically. In this case, the same problem has 
occurred as stated about the self-condensation reaction in JP-B-63-12,896 
(corresponding to U.S. Pat. No. 4,131,731). Under such circumstances, a 
development of a process for more economically producing a high molecular 
weight polycarbonate has been desired. 
DISCLOSURE OF THE INVENTION! 
This invention solves the problems of the above-mentioned prior art and 
aims at providing a process for more economically producing a 
polycarbonate in an increased production per unit volume per unit time 
without applying severe conditions of high temperature and high vacuum 
over a long period of time and also a process for commercially 
advantageously producing a high molecular weight butanediol type 
polycarbonate useful as a starting material for polyurethane. 
The present inventors have made extensive study in view of such 
circumstances and have consequently found that by adding continuously or 
in portions a carbonate monomer in the stage in which a low molecular 
weight polycarbonate has been produced and under the conditions that the 
concentration of an aliphatic polyol in the reaction system is 5% by 
weight or less and under reduced pressure, the molecular weight of a 
polycarbonate having terminal hydroxyl groups can be heightened in a 
surprisingly short time without using such high temperature conditions as 
in the self-condensation of the above-mentioned prior art; the production 
per unit volume per unit time is increased; and the production process can 
be made excellent industrially and economically. The present inventors 
have completed this invention based on the above knowledge. 
Furthermore, by using the production process of this invention, the 
commercial scale production of a high molecular weight butanediol type 
polycarbonate having excellent physical properties at a very low cost with 
a good efficiency is easily made possible, and this invention has a very 
great economical effect. 
BEST MODE FOR CARRYING OUT THE INVENTION! 
That is to say, this invention is a process for producing a polycarbonate 
having terminal hydroxyl groups obtained by reacting an aliphatic polyol 
with a carbonate monomer selected from the group consisting of a dialkyl 
carbonate, a diaryl carbonate and an alkylene carbonate, characterized by 
comprising the first step in which a low molecular weight polycarbonate is 
produced while removing the alcohols produced as by-products from a 
reaction mixture containing the aliphatic polyol and the carbonate monomer 
and the second step in which the carbonate monomer is added in portions or 
continuously to the reaction mixture of the first step under the 
conditions that the concentration of the aliphatic polyol in the reaction 
mixture of the first step is 5% by weight or less to effect the reaction 
while removing the alcohols produced as by-products, thereby connecting 
the low molecular weight polycarbonates to one another through the 
carbonate monomer to heighten the molecular weight. 
This invention is explained in detail below. 
The polycarbonate monomer used in this invention is selected from the group 
consisting of a dialkyl carbonate, a diaryl carbonate and an alkylene 
carbonate. As the dialkyl carbonate, there are mentioned those whose alkyl 
group has 1 to 12 carbon atoms, and specifically mentioned are dimethyl 
carbonate, diethyl carbonate, dibutyl carbonate and the like. As the 
diaryl carbonate, there are mentioned those whose aryl group has 6 to 20 
carbon atoms, and specifically mentioned are diphenyl carbonate, 
dinaphthyl carbonate and the like. The alkylene carbonate comprises a 
5-membered to 7-membered ring, and specifically includes ethylene 
carbonate, propylene carbonate and the like. These carbonate monomers are 
used alone or in combination of two or more. 
The aliphatic polyol used in this invention (referred to hereinafter as the 
polyol monomer) is preferably a dihydric alcohol (diol), and in many 
cases, it is selected from an alkylene glycol and a polyoxyalkylene 
glycol. However, particularly preferable are alkylene glycols whose main 
chain has 3 to 20 carbon atoms and polyoxyalkylene glycols in which the 
number of carbon atoms between oxygen atoms is 2 to 12. The alkylene 
referred to herein may contain a group derived from an alicyclic compound. 
These dihydric alcohol monomers are used alone or in combination of two or 
more. 
Examples of the dihydric alcohol monomers include ethylene glycol, 
1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 
3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,5-hexanediol, 1,7-heptanediol, 
1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 
1,12-dodecanediol, neopentyl glycol, 2-ethyl-1,6-hexanediol, 
2-methyl-1,3-propanediol, 1,3-cyclohexanediol, 1,4-cyclohexanediol, 
2,2'-bis(4-hydroxycyclohexyl)propane, 1,4-dimethylolcyclohexane 
bishydroxytetrahydrofuran, di(2-hydroxyethyl)dimethylhydantoin, diethylene 
glycol, triethylene glycol, polypropylene glycol, polytetramethylene 
glycol, 6-hydroxyethylhexanol, 5-hydroxyethylpentanol and the like. 
These dihydric alcohol monomers may be used in admixture with a 
trifunctional or more functional hydroxyl compound (trihydric alcohol). 
Examples of this trihydric alcohol include trimethylolethane, 
trimethylolpropane, hexanetriol, pentaerythritol and the like. It may also 
be used in admixture with such a polyol as a polyesterpolyol or the like. 
The main reaction in the first step in this invention is an 
interesterification reaction between the polyol monomer and the carbonate 
monomer and, for example, when a dihydric alcohol monomer is used as the 
polyol monomer, the above reaction is shown by the following scheme (1) or 
(2): 
##STR1## 
wherein R.sup.1 represents an alkylene glycol residue having 3 to 20 
carbon atoms or a polyoxyalkylene glycol residue in which the number of 
carbon atoms between oxygen atoms is 2 to 12; 
R.sup.2 and R.sup.3 represent alkyl groups having 1 to 12 carbon atoms or 
aryl groups having 6 to 20 carbon atoms; and 
a, b, c, d and e are constants determined stoichiometrically; 
m is a natural number of 2 to 4; and 
n is a natural number of 2 or more. 
Since said reaction is an equilibrium reaction, it is necessary to remove 
the alcohol produced as a by-product from the reaction system in order to 
allow the reaction to proceed with a good efficiency. In order to 
selectively remove only the alcohol produced as a by-product, it is 
desirable that the reaction is effected in a reactor equipped with a 
distillation tower. 
The reaction temperature in the first step is 80.degree. to 200.degree. C. 
At a temperature of not less than 200.degree. C., the decomposition 
reaction of a polycarbonate having terminal hydroxyl groups is easily 
caused and at a temperature of not more than 80.degree. C., the 
interesterification reaction is slow. The pressure is gradually reduced 
between atmospheric pressure and 6.7.times.10.sup.2 Pa (5 mmHg) for 
securing the amount of the distillate. 
The first step is completed when the conversion of the polyol monomer 
reaches 40 to 90 mole %; however, the conversion is preferably determined 
taking economization into consideration. For example, when the production 
is effected continuously, it is preferable to complete the first step when 
the conversion at which the production per unit volume per unit time in 
the overall process becomes the maximum is reached. The polycarbonate 
having terminal hydroxyl groups obtained at the time of completion of the 
first step is a low molecular weight polymer having a degree of 
polymerization of about 2 to 10. The degree of polymerization referred to 
herein is n stated in the above schemes (1) and (2). The molecular weight 
of the low molecular weight polycarbonate obtained in the first step can 
be adjusted by the amount of the by-product alcohol removed from the 
reaction system, and it is also possible to adjust the same by the feed 
ratio of the carbonate monomer and the polyol monomer. Usually, the 
carbonate monomer:polyol monomer feed ratio is selected from the range of 
from 1:10 to 10:1, preferably from the range of from 1:2 to 2:1. When the 
ratio is outside the range of from 1:10 to 10:1, the yield is extremely 
lowered and economically disadvantageous. In many cases, the economically 
excellent reaction conditions are obtained in the range of from 1:2 to 
2:1. 
In the second step, first, in order to adjust the polyol monomer 
concentration in the reaction mixture obtained in the first step to 5% by 
weight or less, preferably 1% by weight or less, the polyol monomer is, if 
necessary, removed from the reaction system. When the polyol monomer 
concentration exceeds 5% by weight, no quick increase of the molecular 
weight of the low molecular weight polycarbonate is recognized at the time 
of addition of the polycarbonate monomer, and only under the conditions 
that the concentration is 5% by weight or less, the molecular weight is 
quickly increased. In particular, under the conditions that the 
concentration is 1% by weight or less, the rate of increase of the 
molecular weight is remarkably heightened. 
As the method of removing the polyol monomer, a method by which the 
pressure is lowered to a reduced pressure of 13 Pa to 2.7.times.10.sup.4 
Pa (0.1 mmHg to 200 mmHg), preferably 13 Pa to 2.7.times.10.sup.3 Pa (0.1 
mmHg to 20 mmHg), a method by which the temperature is elevated to 
100.degree. to 200.degree. C., a method by which an inert gas such as 
nitrogen gas or the like is blown, and other methods, which are generally 
employed, are used alone or in combination of plural methods. 
Subsequently, the polycarbonate monomer is added to this reaction system to 
connect the low molecular weight polycarbonates produced in the first step 
to one another through the carbonate monomer, whereby the molecular weight 
is efficiently heightened. In this step, the main reaction is shown by the 
following schemes (3) and (4): 
##STR2## 
wherein R.sup.1 represents an alkylene glycol residue having 3 to 20 
carbon atoms or a polyoxyalkylene glycol residue in which the number of 
carbon atoms between oxygen atoms is 2 to 12; 
R.sup.2 and R.sup.3 represent alkyl groups having 1 to 12 carbon atoms or 
aryl groups having 6 to 20 carbon atoms; 
m is a natural number of 2 to 4; and 
n and n' are natural numbers of 2 or more. 
Incidentally, for comparison, the main reaction in the step of heightening 
the molecular weight in JP-B-63-12,896 (corresponding to U.S. Pat. No. 
4,131,731) is shown by the scheme (5). That is, the technique of the above 
JP-B-63-12,896 is to obtain a high molecular weight carbonate by 
self-condensation reaction of low molecular weight polycarbonates with one 
another, while in the process of this invention, the molecular weight is 
heightened by connecting the low molecular weight polycarbonates to one 
another by interesterification reaction through the carbonate monomer, and 
in this respect, the process of this invention and the technique of 
JP-B-63-12,896 are essentially different from each other. 
EQU H(OROCO).sub.(n-1) OROH+H(OROCO).sub.(n'-1) 
OROH.revreaction.H(OROCO).sub.(n+n'-2) OROH+HOROH (5) 
wherein 
R represents an alkylene glycol residue having 3 to 20 carbon atoms or a 
polyoxyalkylene glycol residue in which the number of carbon atoms between 
oxygen atoms is 2 to 12 and 
n and n' are natural numbers of 2 or more. 
When an alkylene carbonate is used as the carbonate monomer in the method 
of JP-A-4-153,218, the main reaction in the step of heightening the 
molecular weight is shown by the scheme (6) and the scheme (7). However, 
since the carbonate monomer is added without controlling the polyol 
monomer concentration, the interesterification reaction with the polyol 
monomer represented by the scheme (6) is mainly caused, the yield is 
higher than that in the process of this invention, but a longer time is 
required for heightening the molecular weight of the polycarbonate and the 
production per unit volume per unit time is inferior to that in the 
process of this invention. That is to say, since in the process of this 
invention, the concentration of the polyol monomer is controlled in the 
step of heightening the molecular weight, the ratio of the reaction of the 
scheme (7) to the reaction of the scheme (6) is much larger than that in 
the process of JP-A-4-153,218 and the scheme (7) is the main reaction. 
Thus, the process of this invention is greatly different from the process 
of JP-A-4-153,218. 
##STR3## 
wherein R represents an alkylene glycol residue having 3 to 20 carbon 
atoms or a polyoxyalkylene glycol residue in which the number of carbon 
atoms between oxygen atoms is 2 to 12; 
a, b and c are constants which are stoichiometrically determined; 
m is a natural number of 2 to 4; and 
n and n' are natural numbers of 2 or more. 
The temperature for effecting the interesterification reaction in the 
second step is 100.degree. to 200.degree. C., and the pressure is 13 Pa to 
2.7.times.10.sup.4 Pa (0.1 mmHg to 200 mm Hg), preferably 13 Pa to 
2.7.times.10.sup.3 Pa (0.1 mmHg to 20 mm Hg). In order to allow these 
reactions to proceed quickly, the alcohols produced as by-products are 
required to be taken out of the reaction system. Therefore, in this step, 
it is preferable to directly evacuate vapor without through a distillation 
tower for taking out the alcohol produced as a by-product of the reaction 
system with a good efficiency. For this purpose, the use of a thin film 
evaporator is also effective. In addition, in order to take out the 
alcohol produced as a by-product of the reaction system with a good 
efficiency, it is effective that such methods as elevating the 
temperature, lowering the pressure and blowing an inert gas such as 
nitrogen gas or the like are carried out alone or in combination of plural 
methods in association with the heightening of the molecular weight of the 
polycarbonate. It is advantageous in process that the unreacted monomer 
distilled out in this step is recovered and then re-used. 
Under said conditions, the unreacted carbonate monomer is distilled out in 
a large amount and the concentration of the carbonate monomer in the 
reaction system at this time becomes a value as low as 0.1% by weight to 
5% by weight; however, surprisingly, it has become clear that the 
heightening of the molecular weight of the polycarbonate proceeds in a 
relatively short time in spite of the fact that the concentration of the 
carbonate monomer is thus low. This is considered to be because the 
proceeding of the reactions of the formula (3) and the formula (4) depends 
more greatly on the concentration of the alcohol produced as a by-product 
rather than on the concentration of the carbonate monomer though this has 
not been expected at the beginning. 
That is to say, the technical point of the second step is to add the 
carbonate monomer under such conditions that the polyol monomer 
concentration is 5% by weight or less and that the concentration of the 
alcohol produced as a by-product can be controlled to a low value. The 
concentration of the alcohol produced as a by-product in this reaction 
system is required to be made lower when the molecular weight of the 
polycarbonate is higher. Also, slightly depending upon the kind of the 
carbonate monomer, the concentration of the alcohol produced as a 
by-product in the reaction system need be made lower when a carbonate 
monomer whose equilibrium constants of the reactions shown in the above 
formulas (3) and (4) are small is used. 
The addition of the carbonate monomer is effected in portions or 
continuously; however, the continuous addition is preferred in that the 
heightening of the molecular weight can be achieved in a relatively small 
addition amount. When the carbonate monomer is added in one portion as in 
the method of JP-A-4-153,218, it is difficult to quickly heighten the 
molecular weight. In the process of this invention, when the addition in 
portions is effected, it is preferable to add a uniform amount of the 
polycarbonate monomer at a uniform interval from the start of addition to 
obtaining a polycarbonate having the desired molecular weight; however, 
the amount of the carbonate monomer added in the former half or latter 
half of or during the above period may be increased or the carbonate 
monomer may be added at uneven intervals. Also, when the continuous 
addition is effected, it is also preferable to add the carbonate monomer 
at a constant flow rate from the start of addition to obtaining a 
polycarbonate having the desired molecular weight; however, the flow rate 
of the carbonate monomer added in the former half or latter half of or 
during the above period may be increased. 
Moreover, the total amount of the carbonate monomer added is controlled so 
that the amount of the carbonate monomer recovered in all the steps 
becomes not more than the amount of the carbonate monomer converted in one 
batch, and it is advantageous in process that the carbonate monomer 
recovered is recycled to be used as the feed in the subsequent reaction. 
In addition, the carbonate monomer added may be the same as or different 
from that charged in the initial stage of the reaction. Further, the said 
carbonate monomers may be added alone or in combination of plural kinds. 
In this invention, the reaction proceeds in the absence of a catalyst; 
however, it is possible to use a catalyst. As the catalyst, a known 
interesterification catalyst is added in an amount of 0.0001% by weight to 
3% by weight based on the starting material fed. Examples of the known 
interesterification catalyst include titanium alkoxides such as titanium 
tetrapropoxide, titanium tetrabutoxide and the like; metals such as 
sodium, potassium, lithium, rubidium, cesium, magnesium, calcium, 
strontium, barium, aluminum, cobalt, germanium, cerium, manganese, lead, 
antimony, tin, zinc and the like; salts thereof; oxides thereof; complexes 
thereof; alkoxides thereof; inorganic acids, organic acids; inorganic 
alkalis; organic alkalis and the like. 
At the time of completion of the second step, it is possible to stop the 
addition of the carbonate monomer and continue the reaction under 
conditions as they are to allow all the remaining carbonate monomer to 
react. It is also possible to carry out such methods as elevating the 
temperature, lowering the pressure, blowing a nitrogen gas or the like, 
etc. alone or in combination of plural methods to remove the remaining 
carbonate monomer with a good efficiency, thereby shortening the reaction 
time. 
Japanese Patent Application No. 6-071,045 upon which the present 
application relies for Convention Priority is wholly incorporated into the 
present specification by reference. 
Examples are shown below to explain this invention in detail; however, 
these do not restrict the scope of this invention at all.

EXAMPLE 1 
In a 3-liter reactor equipped with a stirrer, a thermometer and a 
fractionating column were placed 1,584 g (18 moles) of ethylene carbonate, 
1,440 g (16 moles) of 1,4-butanediol and 30 mg of lead acetate and they 
were subjected to reaction at a temperature of 130.degree. C. at a 
pressure of 2.3.times.10.sup.3 Pa to 4.7.times.10.sup.3 Pa (17 mmHg to 35 
mmHg) for 10 hours. In this case, the ethylene glycol produced as a 
by-product and unreacted ethylene carbonate were distilled out of the top 
of the fractionating column, and in the cold trap, it was found that 2.5 
mole % based on the 1,4-butanediol fed of tetrahydrofuran (referred to 
hereinafter as THF) was produced. The number average molecular weight of 
the product in the reactor at this time was measured by GPC to find it to 
be about 400. Subsequently, the pressure was returned to normal pressure, 
the fractionating column was removed to make direct evacuation possible, 
and thereafter, the temperature was adjusted to 140.degree. C., at which 
unreacted diol was taken out at a pressure of 5.3.times.10.sup.2 Pa to 
8.0.times.10.sup.2 Pa (4 mmHg to 6 mmHg) for one hour until the diol 
concentration in the reaction system became 3% by weight. Subsequently, 
the temperature was adjusted to 140.degree. C. to 150.degree. C., at which 
ethylene carbonate was continuously added to the reaction system at a rate 
of 100 g per hour at a pressure of 5.3.times.10.sup.2 Pa to 
1.3.times.10.sup.3 Pa (4 mmHg to 10 mmHg) for 4 hours and subjected to 
reaction. In this case, the ethylene glycol produced as a by-product was 
distilled out together with unreacted ethylene carbonate. The 
concentration of the ethylene glycol produced as a by-product in the 
reaction system during the reaction was 0.05% by weight or less and the 
concentration of the ethylene carbonate was 1% by weight to 0.6% by 
weight. In the cold trap, THF was produced in an amount of 1.5 mole % 
based on the 1,4-butanediol fed. At this time, in the reactor, 1,302 g of 
polytetramethylene carbonate diol was produced, and the number average 
molecular weight thereof was 2,020 (hydroxyl value=55.5 
mg.multidot.KOH/g). As a result of analysis, the ether linkage unit 
component resulting from the decomposition of the ethylene carbonate 
(referred to hereinafter as the ether unit) was contained in a proportion 
of 0.8 mole % in the polytetramethylene carbonate diol produced. The total 
amount of THF produced as a by-product from the initial stage of the 
reaction was 4 mole % based on the 1,4-butanediol fed. The reaction time 
required from the start of reaction to the completion of this step was 15 
hours. Subsequently, 200 g of the polytetramethylene carbonate diol 
obtained was placed in a 500-ml egg plant type flask and the residual 
monomer was removed in a film evaporator at a temperature of 140.degree. 
C. at a pressure of 267 Pa (2 mmHg) for one hour to obtain 195 g of 
polytetramethylene carbonate diol having a number average molecular weight 
of 2,035 (hydroxyl value=55.1 mg.multidot.KOH/g). 
EXAMPLE 2 
In a 3-liter reactor equipped with a stirrer, a thermometer and a 
fractionating column were placed 1,397 g (15.9 moles) of ethylene 
carbonate, 751 g (7.2 moles) of 1,5-pentanediol, 852 g (7.2 moles) of 
1,6-hexanediol and 30 mg of lead acetate and they were subjected to 
reaction at a temperature of 150.degree. C. at a pressure of 
2.7.times.10.sup.3 Pa to 6.0.times.10.sup.3 Pa (20 mmHg to 45 mmHg) for 7 
hours. In this case, the ethylene glycol produced as a by-product and 
unreacted ethylene carbonate were distilled out of the top of the 
fractionating column. The number average molecular weight of the product 
in the reactor at this time was measured by GPC to find it to be about 
450. Subsequently, the pressure was returned to normal pressure, the 
fractionating column was removed to make direct evacuation possible, and 
thereafter, the temperature was adjusted to 150.degree. C., at which 
unreacted diol was taken out at a pressure of 5.3.times.10.sup.2 Pa to 
1.3.times.10.sup.3 Pa (4 mmHg to 10 mmHg) for one hour until the diol 
concentration in the reaction system became 1.6% by weight. Subsequently, 
at a temperature of 150.degree. C. at a pressure of 5.3.times.10.sup.2 Pa 
to 1.6.times.10.sup.3 Pa (4 mmHg to 12 mmHg), 300 g of ethylene carbonate 
was added in portions in a proportion of 300 g per one portion at the same 
intervals over 3 hours to the reaction system and subjected to reaction. 
In this case, the ethylene glycol produced as a by-product was distilled 
out together with unreacted ethylene carbonate. At this time, in the 
reactor, 1,386 g of copolymeric polycarbonate diol was produced, and the 
number average molecular weight thereof was 1,560 (hydroxyl value=71.9 
mg.multidot.KOH/g). As a result of analysis, the ether unit in the product 
was 1.0 mole %. The reaction time required from the start of reaction to 
the completion of this step was 11 hours. 
EXAMPLE 3 
In a 3-liter reactor equipped with a stirrer, a thermometer and a 
fractionating column were placed 1,488 g (16.9 moles) of ethylene 
carbonate, 968 g (10.7 moles) of 1,4-butanediol, 544 g (4.6 moles) of 
1,6-hexanediol and 30 mg of lead acetate and they were subjected to 
reaction at a temperature of 130.degree. C. at a pressure of 
2.0.times.10.sup.3 Pa to 5.3.times.10.sup.3 Pa (15 mmHg to 40 mmHg) for 10 
hours. In this case, the ethylene glycol produced as a by-product and 
unreacted ethylene carbonate were distilled out of the top of the 
fractionating column, and in the cold trap, it was found that 2.2 mole % 
based on the 1,4-butanediol fed of tetrahydrofuran was produced. The 
number average molecular weight of the product in the reactor at this time 
was measured by GPC to find it to be about 380. 
Subsequently, the pressure was returned to normal pressure, the 
fractionating column was removed to make direct evacuation possible, and 
thereafter, the temperature was adjusted to 140.degree. C., at which 
unreacted diol was taken out at a pressure of 5.3.times.10.sup.2 Pa to 
8.0.times.10.sup.2 Pa (4 mmHg to 6 mmHg) for 1.5 hours until the diol 
concentration in the reaction system became 0.6% by weight. Subsequently, 
the temperature was adjusted to 140.degree. C. to 150.degree. C., at which 
ethylene carbonate was continuously added to the reaction system at a rate 
of 100 g per hour at a pressure of 5.3.times.10.sup.2 Pa to 
1.3.times.10.sup.3 Pa (4 mmHg to 10 mmHg) for 4 hours and subjected to 
reaction. In this case, the ethylene glycol produced as a by-product was 
distilled out together with unreacted ethylene carbonate. In the cold 
trap, THF was produced in a proportion of 1.3 mole % based on the 
1,4-butanediol fed. At this time, in the reactor, 1,264 g of a copolymeric 
polycarbonate diol was produced, and the number average molecular weight 
thereof was 2,560 (hydroxyl value=43.8 mg.multidot.KOH/g). As a result of 
analysis, the ether unit in the product was 0.9 mole %. The total amount 
of THF produced as a by-product from the initial stage of the reaction was 
3.5 mole % of the 1,4-butanediol fed. The reaction time required from the 
start of reaction to the completion of this step was 15.5 hours. 
COMATIVE EXAMPLE 1 
In a 3-liter reactor equipped with a stirrer, a thermometer and a 
fractionating column were placed 1,584 g (18 moles) of ethylene carbonate, 
1,440 g (16 moles) of 1,4-butanediol and 30 mg of lead acetate and they 
were subjected to reaction at a temperature of 130.degree. C. at a 
pressure of 2.3.times.10.sup.3 Pa to 4.7.times.10.sup.3 Pa (17 mmHg to 35 
mmHg) for 10 hours. In this case, the ethylene glycol produced as a 
by-product and unreacted ethylene carbonate were distilled out of the top 
of the fractionating column, and in the cold trap, it was found that 2.4 
mole % based on the 1,4-butanediol fed of tetrahydrofuran was produced. 
The number average molecular weight of the product in the reactor at this 
time was measured by GPC to find it to be about 400. Subsequently, the 
pressure was returned to normal pressure, the fractionating column was 
removed to make direct evacuation possible, and then, the temperature was 
adjusted to 140.degree. C., at which unreacted diol was taken out at a 
pressure of 5.3.times.10.sup.2 Pa to 8.0.times.10.sup.2 Pa (4 mmHg to 6 
mmHg) for 0.5 hour until the diol concentration in the reaction system 
became 10% by weight. Subsequently, the temperature was adjusted to 
140.degree. C. to 150.degree. C., at which ethylene carbonate was 
continuously added to the reaction system at a rate of 100 g per hour at a 
pressure of 5.3.times.10.sup.2 Pa to 1.3.times.10.sup.3 Pa (4 mmHg to 10 
mmHg) over 4 hours and subjected to reaction. The number average molecular 
weight of the product at this time was 820 (hydroxyl value=136.8 
mg.multidot.KOH/g). Ethylene carbonate was further continuously added to 
the reaction system at a rate of 100 g per hour over 4 hours and subjected 
to reaction. 
In this case, the ethylene glycol produced as a by-product was distilled 
out together with unreacted ethylene carbonate. In the cold trap, THF was 
produced in a proportion of 3.2 mole % based on the 1,4-butanediol fed. At 
this time, in the reactor, 1,286 g of polytetramethylene carbonate diol 
was produced, and the number average molecular weight thereof was 1,065 
(hydroxyl value=105.4 mg.multidot.KOH/g). As a result of analysis, the 
ether unit in the product was 2.1 mole %. The total amount of THF produced 
as a by-product from the initial stage of the reaction was 5.6 mole % 
based on the 1,4-butanediol fed. The reaction time required from the start 
of reaction to the completion of this step was 18.5 hours. 
COMATIVE EXAMPLE 2 
In a 3-liter reactor equipped with a stirrer, a thermometer and a 
fractionating column were placed 1,593 g (18.1 moles) of ethylene 
carbonate, 1,481 g (16.5 moles) of 1,4-butanediol and 30 mg of lead 
acetate and they were subjected to reaction at a temperature of 
130.degree. C. at a pressure of 2.3.times.10.sup.3 Pa to 
4.7.times.10.sup.3 Pa (17 mmHg to 35 mmHg) for 10 hours. In this case, the 
ethylene glycol produced as a by-product and unreacted ethylene carbonate 
were distilled out of the top of the fractionating column, and in the cold 
trap, it was found that 2.4 mole % based on the 1,4-butanediol fed of 
tetrahydrofuran was produced. The number average molecular weight of the 
product in the reactor at this time was measured by GPC to find it to be 
about 400. Subsequently, the pressure was returned to normal pressure, the 
fractionating column was removed to make direct evacuation possible, and 
then, the temperature was adjusted to 140.degree. C., at which unreacted 
diol was taken out at a pressure of 5.3.times.10.sup.2 Pa to 
8.0.times.10.sup.2 Pa (4 mmHg to 6 mmHg) for 1 hour until the diol 
concentration in the reaction system became 3% by weight. Subsequently, 
400 g of ethylene carbonate was added in one portion, and thereafter, the 
temperature was adjusted to 140.degree. C. to 150.degree. C., at which the 
ethylene glycol produced as a by-product was distilled out together with 
unreacted ethylene carbonate while the degree of vacuum was gradually 
elevated from 3.3.times.10.sup.3 Pa to 5.3.times.10.sup.2 Pa (from 25 mmHg 
to 4 mmHg). When 2 hours passed from the start of the reaction, the 
distillation of ethylene carbonate became unobserved. At this time, the 
concentration of the ethylene carbonate in the reaction system was 0.6% by 
weight, and the number average molecular weight of the product was 680 
(hydroxyl value=127.5). The reaction was further conducted for 4 hours 
while the ethylene glycol produced as a by-product was distilled out at a 
pressure of 5.3.times.10.sup.2 Pa (4 mmHg). In the cold trap, THF was 
produced in a proportion of 2.6 mole % based on the 1,4-butanediol fed. 
The number average molecular weight of the product in the reactor was 995 
(hydroxyl value=112.8 mg.multidot.KOH/g). As a result of analysis, the 
ether unit in the product was 2.6 mole %. The total amount of THF produced 
as a by-product from the initial stage of the reaction was 4.9 mole % 
based on the 1,4-butanediol fed. The reaction time required from the start 
of reaction to the completion of this step was 17 hours. 
COMATIVE EXAMPLE 3 
In a 3-liter reactor equipped with a stirrer, a thermometer and a 
fractionating column were placed 1,584 g (18 moles) of ethylene carbonate, 
1,440 g (16 moles) of 1,4-butanediol and 30 mg of lead acetate and they 
were subjected to reaction at a temperature of 130.degree. C. at a 
pressure of 2.3.times.10.sup.3 Pa to 4.7.times.10.sup.3 Pa (17 mmHg to 35 
mmHg) for 10 hours. In this case, the ethylene glycol produced as a 
by-product and unreacted ethylene carbonate were distilled out of the top 
of the fractionating column, and in the cold trap, it was found that 2.5 
mole % based on the 1,4-butanediol fed of tetrahydrofuran was produced. 
The number average molecular weight of the product in the reactor at this 
time was measured by GPC to find it to be about 400. Subsequently, the 
pressure was returned to normal pressure, the fractionating column was 
removed to make direct evacuation possible, and then, the temperature was 
adjusted to 140.degree. C., at which unreacted diol and ethylene carbonate 
were taken out at a pressure of 5.3.times.10.sup.2 Pa to 
8.0.times.10.sup.2 Pa (4 mmHg to 6 mmHg) for 1 hour until the diol 
concentration in the reaction system became 1.5% by weight or less. 
Subsequently, the temperature was elevated from 140.degree. C. to 
180.degree. C., the degree of vacuum was gradually raised from 
2.7.times.10.sup.3 Pa (20 mm Hg) and reaction was effected for 4 hours 
while 1,4-butanediol was distilled out. However, the decomposition of the 
product was violent, the degree of vacuum did not rise, and the number 
average molecular weight of the product did not rise to higher than 850 as 
a result of measurement by GPC. Moreover, as a result of analysis, the 
ether unit in the product was 1.3 mole %. The amount of THF produced as a 
by-product at this time was 8.8 mole % based on the 1,4-butanediol fed. 
Incidentally, the total amount of THF produced as a by-product from the 
start of reaction was 11.3 mole % based on the 1,4-butanediol fed. 
FIELD OF UTILIZATION IN INDUSTRY! 
According to this invention, there can be economically advantageously 
produced a polycarbonate having terminal hydroxyl groups which is useful 
as a starting material for polyurethane in an emulsion, a coating, a 
thermoplastic elastomer, a paint, an adhesive or the like.