Biodegradable aliphatic copolyester and method of preparing...

Details Biodegradable aliphatic copolyester and method of preparing... Biodegradable aliphatic copolyester and method of preparing...

2000-02-10

2001-01-30

Acquah, Samuel A. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

From carboxylic acid or derivative thereof

C528S272000, C528S275000, C528S279000

Reexamination Certificate

active

06180751

ABSTRACT:

BACKGROUND OF THE INVENTION
This invention relates to a biodegradable aliphatic copolyester and a method of preparing same.
As biodegradable plastics, aliphatic polyesters are promising. In particular, much attention has been paid on polybutylene succinate or modified products thereof because of their high mechanical strengths and suitable melting point. From the standpoint of industrial application, however, known biodegradable aliphatic polyesters are not fully satisfactory.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an industrially applicable, biodegradable aliphatic copolyester which has good mechanical strengths and good moldability.
Another object of the present invention is to provide a method which can produce biodegradable aliphatic copolyester in a simple, industrially acceptable manner.
In accomplishing the foregoing object, there is provided in accordance with one aspect of the present invention an aliphatic copolyester comprising a plurality of first ester units each represented by the following formula (I):
—CO—[R
1
]
t
—CO—O—R
2
—O—  (I)
wherein R
1
represents a divalent aliphatic group having 1-12 carbon atoms, R
2
represents a divalent aliphatic group having 2-12 carbon atoms and t is an integer of 0 or 1, and a plurality of second ester units each represented by the following formula (II):
wherein R
1
and t are as defined above and R
3
represents an aliphatic group having 6-22 carbon atoms, the molar ratio of said first ester unit to said second ester unit being 90:10 to 99.9:0.1.
In another aspect, the present invention provides a method of preparing an aliphatic copolyester, comprising reacting an aliphatic diester of the following formula (III):
R
4
O—CO—[R
1
]
t
—CO—OR
5
  (III)
wherein R
1
represents a divalent aliphatic group having 1-12 carbon atoms, R
4
and R
5
each represent an alkyl group having 1-4 carbon atoms and t is an integer of 0 or 1, with an aliphatic glycol of the following formula (IV)
HO—R
2
—OH  (IV)
wherein R
2
represents a divalent aliphatic group having 2-12 carbon atoms, and with a monoacylated glycerin of the following formula (V):
wherein R
3
represents an aliphatic group having 6-22 carbon atoms,
said aliphatic glycol and said monoacylated glycerin being used in amounts of 90-110 moles and 0.05-10 moles, respectively, per 100 moles of said aliphatic diester.
The present invention also provides an aliphatic copolyester obtained by the above method.
Other objects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiments to follow.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
The copolyester according to the present invention has first and second ester units. In the first ester unit of the formula (I):
—CO—[R
1
]
t
—CO—O—R—O—  (I)
R
1
represents a linear or cyclic divalent aliphatic group, such as an alkylene, having 1-12 carbon atoms, preferably 2-6 carbon atoms. Examples of the divalent aliphatic groups include methylene, ethylene, propylene, butylene, hexylene, octylene, dodecylene, cyclohexylene and cyclohesanedimethylene. The symbol t is an integer of 0 or 1. When t is 0, the first ester unit is represented by
—CO—CO—O—R
2
—O—,
and when t is 1, the first ester unit is represented by
—CO—R
1
—CO—O—R
2
—O—,
The symbol R
2
of the formula (I) represents a linear or cyclic divalent aliphatic group, such as an alkylene, having 2-12 carbon atoms, preferably 2-6 carbon atoms. Examples of the divalent aliphatic groups include methylene, ethylene, propylene, butylene, hexylene, octylene, dodecylene, cyclohexylene and cyclohexanedimethylene.
In the second ester unit of the formula (II):
R
1
and t have the same meaning as above. The symbol R
3
represents a linear or cyclic aliphatic group, such as an alkyl or alkenyl, having 6-22 carbon atoms, preferably 8-18 carbon atoms. Examples of the aliphatic groups include hexyl, octyl, nonyl, decyl, dodecyl, lauryl, stearyl, behenyl, dodecenyl, cyclohexylene and cyclohexanedimethylene. The particularly preferred aliphatic groups are those derived from natural fatty acids.
It is important that the molar ratio of the first ester unit to the second ester unit should be 90:10 to 99.9:0.1. When the molar ratio is smaller than 90:10, namely when the molar fraction of the second ester unit is greater than 0.1, the copolyester becomes brittle and easily gelled. On the other hand, when the molar ratio is greater than 99.9/0.1, namely when the molar fraction of the second ester unit is smaller than 0.001, the copolyester fails to exhibit satisfactory mechanical strengths. The second ester units are present in the copolyester at random.
The aliphatic copolyester of the present invention generally has a number average molecular weight of at least 10,000, preferably at least 30,000. The upper limit of the number average molecular weight is generally about 1,000,000.
The aliphatic copolyester may be produced by reacting an aliphatic diester of the following formula (III):
R
4
O'CO—[R
1
]
t
—CO—OR  (III)
with an aliphatic glycol of the formula (IV):
HO—R
2
—OH  (IV)
and with a monoacylated glycerin of the formula (V):
The aliphatic diester of the formula (III) may be, for example, a dialkyl ester, such as dimethyl ester, diethyl ester, dipropyl ester or dibutyl ester, of an aliphatic dicarboxylic acid such as succinic acid, adipic acid, suberic acid, sebacic acid or dodecanedicarboxylic acid.
The aliphatic glycol of the formula (IV) may be, for example, ethylene glycol, propylene glycol, 1,4-butanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, polyethylene glycol or polypropylene glycol. The aliphatic glycol is generally used in an amount of 90-110 moles, preferably 95-105 moles, per 100 moles of the aliphatic diester.
The monoacylated glycerin of the formula (V) may be obtained by reaction of glycerin with a saturated or unsaturated fatty acid R
3
COOH in which R
3
is an aliphatic group having 6-22 carbon atoms, preferably 12-18 carbon atoms. Illustrative of suitable aliphatic acids are caproic acid, caprylic acid, lauric acid, myristic acid, stearic acid, behenic acid, oleic acid, erucic acid, linoleic acid, linolenic acid and arachidonic acid. The monoacylated glycerin is generally used in an amount of 0.05-10 moles, preferably 0.1-5 moles, per 100 moles of the aliphatic diester.
The reaction, namely condensation, of the aliphatic diester, aliphatic glycol and monoacylated glycerin is preferably carried out in the presence of a conventional ester exchange catalyst. The reaction is generally performed at a temperature so that the hydroxyl compounds R
4
OH and R
5
OH produced as by-products can exist as a gas in the reaction system. When R
4
OH and R
5
OH are each methanol, for example, the reaction is generally performed at 100-300° C., preferably 120-250° C. The reaction pressure is generally under a reduced pressure, an ambient pressure or a pressurized condition of up to 0.5 kg/cm
2
G. An ambient pressure or a reduced pressure is preferably adopted. It is preferred that the reaction be performed using a reactor equipped with a distillation tower for removing the hydroxyl compounds R
4
OH and R
5
OH from the reactor as soon as they are produced.
The reaction may be carried out in two, first and second stages. In the first stage, low molecular weight condensation products having a number average molecular weight of 500-10,000, preferably 1,000-5,000, are formed at a relatively lower temperature but at a temperature sufficient for R
4
OH and R
5
OH to exist as a gas. In the second stage, the condensation products are further condensed to form a high molecular weight copolyester having a number average molecular weight of at least 10,000. The second stage is preferably performed at a relatively higher temperature and a lower pressure as compared with the first stage, so that the removal of an aliphatic glycol produced as a by-product is expedited.
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