Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-03-09
2002-07-09
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C528S272000, C528S274000, C528S481000, C528S487000, C528S503000
Reexamination Certificate
active
06417266
ABSTRACT:
TECHNICAL FIELD
This invention relates to a process for preparing an aliphatic polyester, which is a biodegradable polymer useful as a substitute for any general-purpose resin, from an aliphatic dihydric alcohol and an aliphatic dicarboxylic acid by solid-phase polymerization in the presence of a non-metallic volatile catalyst. More particularly, it relates to a process which can manufacture an aliphatic polyester of high stability by using a non-metallic volatile catalyst and without employing any special step for its removal.
BACKGROUND ART
The disposal of waste matter has recently come to be discussed in conjunction with the protection of the environment. If molded or processed products of general-purpose high molecular materials are buried as waste matter, there arise problems, as they are not degradable by micro-organisms, etc., but remain semi-permanently as foreign matter in the environment, while the dissolution of additives, such as a plasticizer, therefrom causes the pollution of the environment.
It has also been pointed out that if they are incinerated as waste matter, a large amount of heat produced by their combustion damages the incinerator, and that the smoke and gases resulting from their combustion may cause air pollution, the destruction of the ozone layer, global warming, acid rain, etc.
Under these circumstances, polyhydroxycarboxylic acids such as polylactic acid, polyglycolic acid, poly-3-hydroxybutyric acid and polycaprolactone, and aliphatic polyesters such as polyethylene succinate, polybutylene succinate and polyethylene adipate have recently come to draw a great deal of attention for research and development activities.
As regards the aliphatic polyesters, there are a process in which an aliphatic polyester having a high molecular weight is obtained by reacting a diisocyanate with the ends of a polymer in the molten state, as disclosed in Japanese Patent Appln. Laid-Open No. 189822/1992 or 189823/1992, and a process in which an aliphatic polyester having a high molecular weight is obtained by a dehydration condensation reaction using an organic solvent without using any diisocyanate, as disclosed in U.S. Pat. No. 5,401,796.
There is also known a process for preparing an aliphatic polyester by solid-phase polymerization. Japanese Patent Appln. Laid-Open No. 34843/1996 discloses a process in which an aliphatic polyester having a high molecular weight is produced by crystallizing an aliphatic polyester having a relative viscosity of 1.5 or above and subjecting it to solid-phase polymerization at a temperature lower than its melting point in an inert gas atmosphere, or at a reduced pressure.
The catalyst disclosed therein is a compound of a metal such as titanium, germanium, antimony, magnesium, calcium, zinc, iron, zirconium, vanadium, lithium, cobalt or manganese, and is used in the form of a metal alkoxide, acetylacetonate, oxide, complex or hydroxide, an organic acid salt, etc. There is no statement teaching the use of any non-metallic volatile catalyst in the form of an organic sulfonic acid type compound.
It is known that if metallic catalyst remains active in a polyester, the polyester has its molecular weight lowered by heat during a molding process, and is not satisfactory in moldability or heat resistance. In order to ensure the stability of a polyester, therefore, it is usual practice to add a catalyst deactivator, such as phosphoric or phosphorous acid, or a polymer stabilizer to deactivate the catalyst in a polyester, or remove the catalyst from the polyester in case of using a metallic catalyst.
Any such additive is easy to add to a polyester in a polymerization system if it is made by solution or melt polymerization, but if it is made by a solid-phase process, an additional step is required for melting a solid polymer before adding any such additive to it, and complicates the process. In either event, there is undesirably obtained a polyester containing any such additive, and a deactivated catalyst.
The removal of the catalyst is preferable to the addition of any additive in that no undesirable material remains in the polyester, but requires operation and equipment differing entirely from those employed for polymerization, and thereby adds a step complicating the preparation process of the polyester.
It is, therefore, an object of this invention to provide a process which makes it possible to prepare an aliphatic polyester of high stability from an aliphatic dihydric alcohol and an aliphatic dicarboxylic acid without requiring any special step for catalyst removal.
DISCLOSURE OF THE INVENTION
We, the inventors of this invention, have made a careful study of the problems as pointed out above in connection with the prior art, and found that an aliphatic polyester of high stability can be made from an aliphatic dihydric alcohol and an aliphatic dicarboxylic acid without requiring any special step for catalyst removal if it is made by solid-phase polymerization using a volatile catalyst.
Thus, the process of this invention is defined according to [1] to [8] below.
[1] A process for preparing an aliphatic polyester, wherein a crystallized aliphatic polyester prepolymer formed from an aliphatic dihydric alcohol and an aliphatic dicarboxylic acid and having a weight-average molecular weight (Mw
1
) falling within the range defined by a formula (1) is caused to undergo solid-phase polymerization in the presence of a volatile catalyst to make an aliphatic polyester having a weight-average molecular weight (Mw
2
) falling within the range defined by formulas (2) and (3):
2×10
3
≦Mw
1
≦1×10
5
(1)
5×10
4
≦Mw
2
≦1×10
6
(2)
Mw
1
<MW
2
(3)
[2] A process for preparing an aliphatic polyester according to [1] wherein the residual catalyst percentage R, as defined by a formula (4), is 50% or below:
R[%]=C
A
[ppm]÷C
B
[ppm]×100 (4)
wherein R is the residual catalyst percentage [%] as a measure for the difference in catalyst content between before and after the solid-phase polymerization, C
B
[ppm] is the theoretical catalyst content of the aliphatic polyester in the case where all of the catalyst introduced into the reaction system before and/or during solid-phase polymerization remains in the polyester, as calculated by a formula (5), and C
A
[ppm] is a final catalyst content in the aliphatic polyester calculated by a formula (6);
C
B
[ppm]=W
B
[g]÷W
P
[g]×10
6
(5)
wherein W
B
[g] is the total weight of the catalyst introduced into the reaction system before and/or during solid-phase polymerization, and W
P
[g] is the final weight of the polyester;
C
A
[ppm]=W
A
[g]÷W
P
[g]×10
6
(6)
wherein W
A
[g] is the final weight of the catalyst in the polyester, and W
P
[g] is the final weight of the polyester.
[3] A process for preparing an aliphatic polyester according to [1] or [2], wherein the prepolymer is a polybutylene succinate prepolymer formed from succinic acid and 1,4-butanediol, and the polyester is polybutylene succinate.
[4] A process for preparing an aliphatic polyester according to [1] or [2], wherein the volatile catalyst is an organic sulfonic acid.
[5] A process for preparing an aliphatic polyester according to [4], wherein the organic sulfonic acid is at least one compound selected from the group consisting of methanesulfonic, ethanesulfonic, 1-propanesulfonic, benzenesulfonic, p-chlorobenzenesulfonic, and m-xylene-4-sulfonic acids.
[6] A process for preparing an aliphatic polyester according to [4] or [5], wherein the final catalyst content of the aliphatic polyester is from 0 to 300 ppm in terms of the sulfur content.
[7&rs
Ajioka Masanobu
Hiraoka Shoji
Kimura Hiroshi
Kotaki Yasushi
Ogawa Shinji
Acquah Samuel A.
Mitsui Chemicals Inc.
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