JPH0321634A - Polyestercarbonate copolymer and production thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a polyester carbonate copolymer and a method for producing the same, and more particularly, to a polyester carbonate copolymer and a method for producing the same.
Glass transition temperature (Tg) measured by DSC)
The present invention relates to a polyester carbonate copolymer which has a single peak and can yield a rod-shaped body having excellent transparency, heat resistance and mechanical strength, and a method for producing the same.

Technical background of the invention and its problems Resin compositions consisting of polyesters such as polyethylene terephthalate and polycarbonates have been known from many prior art documents [for example, Japanese Patent Publication No. 36
-14035 publication, JP-A-52-51445 publication,
JP-A-53-51248, JP-A-54-1837
Publication No. 5, JP-A-55-145751, JP-A No. 5
No. 7-16137, Japanese Patent Publication No. 58-18391, j. W. Barlov et at. Author, Jour
al of'^ppl1ed Polymer Sc1e
nce. Vo1.23.85-99 (1979) and III! lul Vang et at. Author, Makr
omolekulre Chesle Rapid Co
mmunicat1ons, Vol. 7,255-25
9 (198B)].

In these prior art documents, attempts have been made to prepare compositions with excellent transparency from polyester and polycarbonate; Kosho 58-18
Publication No. 391 discloses that a composition with excellent transparency can be achieved only in a composition containing polyester as a main component or a composition containing polycarbonate as a main component. These prior art documents also state that when the blending ratios of polyester and polycarbonate are close to equal amounts, a resin composition with excellent transparency cannot be obtained. Although the composite soles mainly composed of polyester disclosed in these prior art documents have good transparency, they are inferior in properties such as heat resistance and impact resistance, and the appearance of the molded products is subject to sink marks and There is a problem in that it tends to warp. In addition, although compositions containing polycarbonate as the main component have good transparency and excellent heat resistance,
There is a problem that properties such as chemical resistance stability, stress crack resistance, and melt fluidity are inferior.

Furthermore, in the prior art document, It 1 tl u i
W a n g e Lat. Author, Makroiol
ekulre Chem1e Rapid Coa+m
unjcat1on. Vo1.7.255-259(1
No. 98B) discloses that a resin composition containing polyester and polycarbonate in approximately equal amounts is transparent and has a single glass transition temperature. However, all of the resin compositions disclosed in this prior art document have a problem that they have a low molecular weight and poor mechanical strength such as impact resistance, and cannot be used as a shaped material.

Purpose of the Invention The present invention aims to solve the problems associated with the prior art as described above, and has excellent mechanical properties such as impact resistance and stress crack resistance, heat resistance, and transparency. The object of the present invention is to provide a polyester carbonate copolymer with excellent melt flowability during molding and a method for producing the same.

Summary of the Invention The polyester carbonate copolymer according to the present invention has ethylene terephthalate as its main constituent unit and has an intrinsic viscosity [η] of 0.6 as measured at 25°C in O-chlorophenol.
dg/g or less of alkylene terephthalate oligomer [I] 20 to 80% by weight and 2.2-bis(4-hydroxyphenyl)propane as the main constituent units, and the intrinsic viscosity measured at 25°C in 0-chlorophenol. A polyester carbonate copolymer obtained by polymerizing a mixture consisting of 20 to 80% by weight of carbonate oligomany [II] having [η] of 0.6 dg/g or less, Intrinsic viscosity [η] measured in chlorophenol at 25°C is 0.4~
1.2 dR/g, a glass transition temperature (Tg) of 80 to 140'C, and a single peak.

Further, the method for producing a polyester carbonate copolymer according to the present invention includes 20 to 80% by weight of the above alkylene terephthalate oligomer [I] and 20 to 80% by weight of the alkylene terephthalate oligomer [I].
The above carbonate oligomer [II] is blended, melted and stirred, and a polycondensation reaction is carried out while removing volatile components under reduced pressure.

DETAILED DESCRIPTION OF THE INVENTION The polyester carbonate copolymer and the method for producing the same according to the present invention will be explained in detail below.

First, the polyester carbonate copolymer according to the present invention will be explained.

Alkylene terephthalate oligomer [I1] The alkylene terephthalate oligomer [I] used in the present invention is composed of dicarboxylic acid component units and diol component units, and usually has a content of ethylene terephthalate units of 50 to 100 mol%. Alkylene terephthalate oligomer [I] is used, and among them, alkylene terephthalate oligomer [I1] having a content of 70 to 100 mol % of ethylene terephthalate structural units is preferably used.

In the present invention, the main dicarboxylic acid component unit constituting the alkylene terephthalate oligomer [I] is a terephthalic acid component unit, but it contains a small amount of other aromatic dicarboxylic acid component units in addition to the terephthalic acid component unit. You may do so. Specific examples of aromatic dicarboxylic acid component units other than terephthalic acid fractional units include dicarboxylic acid fractional units such as isophthalic acid, phthalic acid, and naphthalene dicarboxylic acid. Further, the main diol fractional unit constituting the alkylene terephthalate oligomer [I] is an ethylene glycol fractional unit, but it may contain a small amount of other diol component units in addition to the ethylene glycol component unit. Preferred diol component units other than ethylene glycol component units include 1,3-propanediol, 1,4-butanediol, neopentyl glycol, cyclohexanediol, cyclohexanedimethanol, 1,4-bis (β−
hydroxyethoxy)benzene, 1,3-bis(β-hydroxyethoxy)benzene, 2,2-bis(4-β-monohydroxyethoxyphenyl)propane, bis(4-β
Examples include diol component units having 3 to 15 carbon atoms such as -hydroxyethoxyphenyl) sulfone.

In addition, the alkylene terephthalate oligomer [I]
In addition to the above aromatic dicarboxylic acid fractional units and diol fractional units, the composition may contain a small amount of polyfunctional compound fractional units as required. Specifically, the polyfunctional compound component units include trimellitic acid, trimesic acid, and! Aromatic polybasic acids such as 9.3',5,5°-tetracarpoxydiphenyl, aliphatic polybasic acids such as butanetetracarboxylic acid, phloroglucin, 1.2,4.5-
Aromatic polyols such as tetrahydroxybenzene, aliphatic polyols such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol,
A certain unit of a polyfunctional compound such as oxybocarboxylic acid such as tartaric acid and malic acid may be mentioned.

In the alkylene terephthalate oligomer [I],
The amount of terephthalic acid component units is usually 50 to 100 mol%, preferably 70 to 100 mol%, and the amount of aromatic dicarboxylic acid component units other than terephthalic acid component units is usually 0.
~50 mol%, preferably O~30 mol%, ethylene glycol fractional units, usually 50 to 100 mol%, preferably 70 to 100 mol%, diol component units other than ethylene glycol fractional units But usually 0 to 50
mol % Preferably in an amount of 0 to 30 mol %, and polyfunctional compound or fractional units usually in an amount of 0 to 2 mol %, preferably 0 to 30 mol %
Preferably, it is present in an amount of 1 mol%.

Specifically, the method for producing the alkylene terephthalate oligomer [1] includes direct polycondensation of an aromatic dicarboxylic acid containing terephthalic acid as a main component and a diol containing ethylene glycol as a main component to produce an alkylene terephthalate oligomer. or a method of producing an alkylene terephthalate oligomer by transesterifying an aromatic dicarboxylic acid diester whose main component is a terephthalic acid diester such as dimethyl terephthalate with a diol whose main component is ethylene glycol. However, any method can be adopted. Among these methods, the direct polycondensation method is preferred because it yields alkylene terephthalate oligomers with excellent hue and transparency.

In addition, as a catalyst during polycondensation, catalysts commonly used in polycondensation reactions such as antimony compounds, titanium compounds, and germanium compounds can be used, but among these, germanium compounds such as germanium oxide and tetraalkoxygermanium are used. However, it is preferable because an alkylene terephthalate oligomer having an excellent hue can be obtained.

In addition, the intrinsic viscosity [η] (value measured at 25°C in 0-chlorophenol) of the alkylene terephthalate oligomer [I] used in the present invention is usually 0.6 dil/
g or less, preferably 0.55d4? /g or less, more preferably 0.56D/tr or less.

In the present invention, alkylene terephthalate oligomer [I
] is 100% by weight of the total weight of alkylene terephthalate oligomer [I] and carbonate oligomer [II]
, usually 20 to 80% by weight, preferably 25 to 7% by weight.
It is used in an amount of 5% by weight, more preferably 30-70% by weight. Alkylene terephthalate oligomer [11
When the amount of is more than 80% by weight, the polyester carbonate copolymer has a glass transition temperature (T g ) that is lower than the glass transition temperature ( T g ) of polyalkylene terephthalate.
＞, the heat resistance tends to decrease and the mechanical strength such as impact resistance tends to decrease. On the other hand, when the amount of alkylene terephthalate oligomer [I] is less than 20% by weight, the polyester carbonate copolymer tends to have lower fluidity, and also has lower chemical resistance, stress crack resistance, etc. arise.

Carbonate oligomer [n1 Carbonate oligomer used in the present invention [II]
is a carbonate oligomer whose main constituent unit is 2,2-bis(4-hydroxyphenyl)propane [bisphenol A], and in the present invention, 2,2-bis(
Carbonate oligomer [I
I] is used, in particular, the content of 2,2-bis(4-hydroxyphenyl)propane structural units is 70 to 100.
mol % of carbonate oligomer [1 is preferably used.

In the present invention, the carbonate oligomer [II3 is
In addition to the 2.2-bis(4-hydroxyphenyl)propane component unit, it may contain a small amount of other aromatic diol component units. Specifically, other aromatic diol component units other than the 2.2-bis(4-hydroxyphenyl)propane component unit include 2.2-bis(4-hydroxy-3.5-dimethylphenyl). ) propane, bis(4-
hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl>ethane, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxy-
3.5-jethylphenyl)propane, 2.2-bis(
4-Hydroxy-8.5-dibropylphenyl)propane, 1.1-bis(4-hydroxyphenyl)cyclohexane, bis(4-hydroxyphenyl)ketone, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl) -hydroxyphenyl)thioether, bis(4-hydroxyphenyl)sulfone, and 4.4°-dihydroxybiphenyl.

Further, the carbonate oligomer [II] may contain a small amount of aliphatic diol component units in addition to the aromatic diol fractional units. Specific examples of aliphatic diols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, neobentyl glycol, cyclohexanediol, cyclohexanedimethanol, 1,4-bis(β -hydroxyethoxy)
Benzene, t,a-bis(β-hydroxyethoxy)benzene, 2,2-bis(4-β-hydroxyethoxyphenyl)propane, bis(4-β-hydroxyethoxyphenyl)sulfone, etc. Examples include diol component units having 3 to 15 units.

In addition to the aromatic diol component units and aliphatic diol component units, the carbonate oligomer [■] may contain a small amount of polyfunctional compound component units as required. Specifically, the unit of polyfunctional compound is phloroglucin%'l. 2.4.5-
Aromatic polyols such as tetrahydroxybenzene, aliphatic polyols such as glycerin, trimethylolethane, trimethylolpropane, pentaerythritol,
Trimellitic acid, trimesic acid, 3,3°, 5.5°-
Aromatic polybasic acids such as tetracarpoxydiphenyl, aliphatic polybasic acids such as butanetetracarboxylic acid, tartaric acid,
Examples include component units such as oxybocarboxylic acids such as malic acid.

In the carbonate oligomer [II], the 2,2-bis(4-hydroxyphenyl)propane fraction unit is usually 50 to 100 mol%, preferably 70 to 100 mol%. The amount of aromatic diol component units other than (4-hydroxyphenyl)propane component units is usually 0 to 50 mol%, preferably 0 to 30 mol%, and aliphatic diol component units and polyfunctional compounds. The component unit is usually 0 to 2 mol%, preferably 0 to 1 mol%
Preferably, it is present in an amount of .

Specifically, the method for producing the carbonate oligomer [n] includes interfacial polymerization of a diol whose main component is 2,2-bis(4-hydroxyphenyl)propane and phosgene. or a method of producing a carbonate oligomer by transesterifying a diol component mainly composed of 2,2-bis(4-hydroxyphenyl)propane with a carbonic acid diester. Can be adopted. The above carbonate oligomer [
[II] by the transesterification method, antimony compounds, titanium compounds,
Catalysts commonly used in transesterification reactions, such as germanium compounds and tin compounds, can be used, but among these, tin compounds such as stannous acetate and stannous oxalate, germanium oxide, tetraalkoxygermanium, etc. germanium compounds are preferably used.

Furthermore, the carbonate oligomer [1
] of intrinsic viscosity [η] (25°C in 0-chlorophenol
) is usually 0.6dρ/g or less, preferably 0.556II/g or less, more preferably 0,5
dρ/g or less.

In the present invention, the carbonate oligomer [II] is usually 20 to 80% by weight, preferably 25 to 75% by weight, based on 100% by weight of the total weight of the alkylene terephthalate oligomer [I] and the carbonate oligomer [II].
More preferably, it is used in an amount of 30 to 70% by weight.

When the amount of carbonate oligomer [1] reaches 20% by weight, the glass transition temperature (Tg') of the polyester carbonate copolymer approaches the glass transition temperature (Tg) of polyalkylene terephthalate, and the heat resistance decreases. There is also a tendency for mechanical strength such as impact resistance to decrease.

On the other hand, the amount of carbonate oligomer [II] is 80% by weight
If it exceeds this, the polyester carbonate copolymer tends to have lower fluidity, chemical stability, stress crack resistance, etc.

Polyester carbonate copolymer The polyester carbonate copolymer according to the present invention is obtained by polymerizing the above alkylene terephthalate oligomer [I] and carbonate oligomer [n], as described below.

Such polyester carbonate uses an alkylene terephthalate oligomer having a content of 100% ethylene terephthalate structural units as an alkylene terephthalate oligomer, and a content of 2,2-bis(4-hydroxyphenyl)broban structural units as a carbonate oligomer. When a carbonate oligomer having 100% is used, it mainly contains the following structural units in the following amounts.

1) Bisphenol A bonding mode content ffi (mol%) Preferably 20 to 40 mol% Total 100 mol% 2) Terephthalic acid bonding mode Total 100 mol% Polyester carbonate copolymer as described above according to the present invention The intrinsic viscosity [η] measured in 0-chlorophenol at 25°C is usually 0.4 to 1.2 di)/g, preferably 0.5 to 1.1 dρ/g, more preferably 0.
6 to 1.0 di)/g. The intrinsic viscosity [η] of the polyester carbonate copolymer is 0.4 dD/g
If it is less than 10%, mechanical strength such as impact resistance of the polyester carbonate copolymer tends to decrease, and stress crack resistance etc. tend to decrease. On the other hand, 1.2d#/
If it exceeds g, the melt fluidity of the polyester carbonate copolymer tends to decrease and the moldability tends to decrease.

Further, the polyester carbonate copolymer according to the present invention has a glass transition temperature (Tg) of 80 to 140°C as measured by a differential scanning calorimeter (DSC), and has a single peak. When the glass transition temperature (Tg) of the polyester carbonate copolymer becomes less than 80°C, the polyester carbonate copolymer
As Tg) approaches the glass transition temperature (Tg) of polyalkylene terephthalate, heat resistance tends to decrease. On the other hand, if the glass transition temperature (Tg) of the polyester carbonate copolymer exceeds 140°C, it approaches the glass transition temperature (Tg) of polycarbonate, and chemical resistance, stress crack resistance, etc. tend to decrease. Further, even if the glass transition temperature (Tg) of the polyester carbonate copolymer is within the above range, if the polyester carbonate copolymer has two or more peaks, the transparency tends to decrease.

Further, the haze of the double-thickness oval plate made of the polyester carbonate copolymer according to the present invention is usually 25% or less, preferably 20% or less, and more preferably 15%. The polyester carbonate copolymer according to the present invention has excellent transparency.

In addition, in addition to the alkylene terephthalate oligomer [I] and carbonate oligomer [II], the polyester carbonate copolymer according to the present invention may optionally contain a phosphorus stabilizer such as trimethyl phosphate or triphenyl phosphate, In addition, various additives such as conventionally known inorganic fillers, lubricants, slip agents, antiblocking agents, antistatic agents, antifogging agents, and pigments can be included within the range that does not impair the object of the present invention.

Method for producing a polyester carbonate copolymer Next, a method for producing a polyester carbonate copolymer according to the present invention will be explained.

First, the alkylene terephthalate oligomer [I] and the carbonate oligomer [II] constituting the polyester carbonate copolymer are prepared by the production method described above.

Such alkylene terephthalate oligomer N]
Before use, it is dried in an atmosphere such as dry air, dry nitrogen, or under reduced pressure, for example, at 140° C. for 15 hours or more. In addition, carbonate oligomers [II
Similar to the alkylene terephthalate oligomer [I], it is also dried in an atmosphere such as dry air, dry nitrogen, or under reduced pressure, for example, at 120° C. for 15 hours or more.

Next, 20 to 80% by weight of dry alkylene terephthalate oligomer [I] and 20 to 80% by weight of carbonate oligomer [II] were mixed, and then put into a reaction tank equipped with a stirring device and operable under reduced pressure. The mixture is melted and stirred, and the polycondensation reaction is carried out while removing volatile components under reduced pressure.

In addition, during the above mixing, if necessary, phosphorus stabilizers such as trimethyl phosphate and triphenyl phosphate, as well as conventionally known inorganic fillers, lubricants, slip agents,
Various additives such as antiblocking agents, antistatic agents, antifogging agents, and pigments can be added within the range that does not impair the purpose of the present invention.

The reaction temperature conditions for carrying out the above polycondensation reaction are usually 260 to 300°C, preferably 265 to 295°C.
℃, more preferably within the range of 270 to 290℃. Further, the reduced pressure condition is usually 0.1 to 300 mmHg, preferably 1 to 200 a+sHg.

The melting and stirring time varies depending on the temperature conditions, but is usually 0.5 to 15 hours, preferably 1 to 10 hours. In addition, when the viscosity of the reaction product increases with the passage of stirring time, it is appropriate to carry out the polycondensation reaction while gradually raising the temperature within the above reaction temperature range.

Furthermore, in the present invention, catalysts commonly used in polycondensation reactions such as titanium compounds, antimony compounds, tin compounds, and germanium compounds can be used as polycondensation catalysts during polycondensation. Tin compounds such as stannous acetate and stannous oxalate, and germanium compounds such as germanium oxide and tetraalkoxygermanium are preferably used.

After the completion of the polycondensation reaction, the reaction product is taken out from the reaction tank under pressure in the form of a strand and recovered by a conventional method such as cutting to obtain a transparent polyester carbonate copolymer.

Effect of the invention The polyester carbonate copolymer according to the invention has 0
- Intrinsic viscosity [η] measured at 25°C in chlorophenol
is 0.4 to 1,2d,Q/g, and the glass transition temperature (
T g) is 80 to 140°C and has a single peak, so W = mechanical properties such as impact resistance and stress crack resistance, heat resistance and melt flowability during shaping, especially impact strength. ing.

Therefore, the polyester carbonate copolymer according to the present invention can be used for applications such as molding materials.

Further, the polyester carbonate copolymer according to the present invention is useful as a compatibilizing agent for a polymer, for example, a compatibilizing agent for a polyester such as polyalkylene terephthalate and a polycarbonate.

According to the method for producing a polyester carbonate copolymer according to the present invention, alkylene terephthalate oligomer [
I] and carbonate oligomer [II] are blended in the above-mentioned specific ratio, melted and stirred, and the polycondensation reaction is performed while removing volatile components under reduced pressure, so it has excellent properties and is suitable for molding materials, etc. A polyester carbonate copolymer is obtained which can be used for various purposes.

EXAMPLES The present invention will be explained below with reference to Examples, but the present invention is not limited to these Examples.

The alkylene terephthalate oligomer [I] and carbonate oligomer [II] used in the Examples and Comparative Examples were manufactured by the method shown in the Synthesis Example.

Note that the intrinsic viscosity [η] of the polyester carbonate copolymer and the like was measured at 25° C. in 0-chlorophenol. The glass transition temperature of the polyester carbonate copolymer was determined by measuring the temperature increase rate and temperature decrease rate at 1.0° C./min using a differential scanning calorimeter.

In addition, the thermal properties and mechanical strength of polyester carbonate copolymers are determined according to JIS K 13719, JIS K
It was measured according to standard measurement methods such as 6911 and JIS K 8719.

Furthermore, the transparency of the polyester carbonate copolymer was measured using an NDI1-20D hazemeter manufactured by Nippon Denshoku Kogyo ■.

[Synthesis Example ~ 1] 706 parts by weight of diphenyl carbonate and bis(
After 502 parts by weight of 4-hydroxyphenyl)propane was added and melted at 240°C, 0.05 parts by weight of titanium tetra(isoproboxide) was added to the reaction tank and reacted for 4 hours under N2 atmosphere. Furthermore, after stirring for 1 hour under a reduced pressure condition of 2 mm Hg, the reaction product was taken out from the reaction tank, cooled, and then pulverized and dried to obtain 671 parts by weight of carbonate oligomer.

The intrinsic viscosity [η] of the obtained carbonate oligomer is 0
．． 08 dN/g, and the number average degree of polymerization was 3.

[Synthesis Example-2] 1734 parts by weight of terephthalic acid and 713 parts by weight of ethylene glycol were stirred at 260°C under 2 atm for 4 hours.

Thereafter, 0.3 parts by weight of germanium dioxide, 0.3 parts by weight of tetraethylammonium hydroxide and 0.4 parts by weight of methyl acid phosphate were added, and the mixture was heated to 260°C.
After the reaction was carried out under 1 atm for 2 hours, the reaction product was extracted and cooled, and then pulverized and dried to obtain 1500 parts by weight of ethylene terephthalate oligomer.

The intrinsic viscosity of the obtained ethylene terephthalate oligomer [η is 0.09 d. l2/g, and the number average degree of polymerization was 3.

Example-1 In a reaction tank equipped with a stirring device and a device for condensing the fraction distilled off by operating under reduced pressure,
50 parts by weight of the carbonate oligomer obtained in Synthesis Example 2, 50 parts by weight of the ethylene terephthalate oligomer obtained in Synthesis Example 2
part by weight and 0.1 part by weight of stannous oxalate, and heated to 270°C under a nitrogen atmosphere to melt the mixture. The system was heated to about 2 am from atmospheric pressure over about 30 minutes while stirring. Reduce the pressure to Hg and further reduce the pressure to 270°C to 29°C.
Stirring was continued for about 3 hours at 0° C. under a vacuum of about 2 1+11 H g. After completing the above heat treatment, the system was returned to atmospheric pressure with nitrogen, and then the mixture was extracted into strands while pressurized with nitrogen and cut into particles with a cutter to obtain a transparent polyester carbonate copolymer.

The obtained polyester carbonate copolymer is transparent, and its intrinsic viscosity [η] is 0.60 dfl/g,
The glass transition temperature (Tg) was 104°C. moreover,
Approximately 270% of this granular polyester carbonate copolymer
A test piece was prepared by press molding at °C, and the bending strength, flexural modulus, Izod impact strength (notched, 23 °C), and haze were measured.

The results are shown in Table 1.

Examples 2 to 5 In Example 1, as shown in Table 1, the amount of ethylene terephthalate oligomer used was 70 parts by weight, 60 parts by weight, 40 parts by weight, and 30 parts by weight, and the amount of carbonate oligomer was changed accordingly. A polyester carbonate copolymer was obtained in the same manner as in Example 1, except that the amounts used were 30 parts by weight, 40 parts by weight, 60 parts by weight, and 70 parts by weight, and its physical properties were evaluated.

The results are shown in Table 1.

The main structural units and their content contained in the polyester carbonate copolymer obtained in Example 4 are as follows:
It was as follows.

Binding mode of bisphenol A 2) Binding mode content of terephthalic acid (mol%) Comparative example-1 In Example-1, the amounts of ethylene terephthalate oligomer and carbonate oligomer were each 9
Example - except that the parts were 0 parts by weight and 10 parts by weight.
A transparent polyester carbonate copolymer was obtained in the same manner as in Example 1. The intrinsic viscosity [η] of the obtained polyester carbonate copolymer was 0.58 dI1/g. Further, the glass transition temperature (Tg) was 78° C., although only one peak of absorption was observed, and there was almost no difference between the glass transition temperature and the glass transition temperature of polyethylene terephthalate.

Claims (2)

[Claims] (1) The main constituent unit is ethylene terephthalate, and o-
Mainly composed of 20-80% by weight of alkylene terephthalate oligomer [I] whose intrinsic viscosity [η] measured at 25°C in chlorophenol is 0.6 dl/g or less, and 2,2-bis(4-hydroxyphenyl)propane. A polyester carbonate obtained by polymerizing a mixture consisting of 20 to 80% by weight of a carbonate oligomer [II] having an intrinsic viscosity [η] of 0.6 dl/g or less when measured in o-chlorophenol at 25°C. A copolymer, the copolymer has an intrinsic viscosity [η] of 0.4 to 0.4 as measured at 25°C in o-chlorophenol.
1.2 dl/g, and the glass transition temperature (Tg) is 80
A polyester carbonate copolymer characterized by having a temperature of ~140°C and a single peak. (2) 20 to 80% by weight of alkylene terephthalate oligomer [I] and 20 to 80% by weight of carbonate oligomer [II] are blended, melted and stirred, and a polycondensation reaction is carried out while removing volatile components under reduced pressure. 2. The method for producing a polyester carbonate copolymer according to claim 1, which comprises: