Process for preparation of polyester-based polymers

Details Process for preparation of polyester-based polymers Process for preparation of polyester-based polymers

2001-06-19

2003-12-16

Acquah, Samuel A. (Department: 1711)

Stock material or miscellaneous articles

Coated or structually defined flake, particle, cell, strand,...

Particulate matter

C528S275000, C528S279000, C528S280000, C528S281000, C528S283000, C528S285000, C528S286000, C528S298000, C528S302000, C528S308000, C524S706000, C524S711000, C524S765000, C524S767000

Reexamination Certificate

active

06663961

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a novel process for preparing polyester-based polymers. More particularly, the present invention relates to a novel and advanced process for preparing polyester-based polymers by using a composite polymerization catalyst which was prepared by reacting titanium compounds and cobalt compounds in the solution containing at least one alcohol.
2. Description of the Background Art
Polyester-based polymers, for example, polyethylene terephthalate (PET), polybutylene terephthalate (PBT) and/or polyethylene naphthalate (PEN), which are currently industrially manufactured, have high degrees of crystallinity, higher softening points and numerous other superior properties in terms of mechanical strength, resistance to gas permeability, chemical resistance, thermal resistance, weather resistance and electrical insulation, etc. Thus, they are widely used for manufacturing high quality films, bottles, high strength fibers and other industrial materials.
There are two steps in industrial preparations of polyesters such as PET and/or PEN. The first step is to make esterified low molecular weight compounds by reacting diacid or derivatives of diacid with glycols. The product of this step in making PEN is bis(beta-hydroxyethyl)naphthalate or their low molecular weight prepolymers (hereinafter referred to as “esterified compounds”). The product of this step in making PET is bis(beta-hydroxyethyl)terephthalate or their low prepolymers.
The first step is performed by means of either a direct esterification or an ester-interchange reaction which is called as transesterfication also. In the ester-interchange reaction, dimethyl terephthalate (DMT) or 2,6-naphthalene dicarboxylic acid dimethylester (2,6-NDC) is reacted with ethylene glycol (EG) in the presence of a catalyst such as zinc acetate [Zn(OAc)
2
] or manganese acetate [Mn(OAc)
2
] at reaction temperatures ranging from 180 to 260° C. and the side product, that is methanol, is removed. In case of direct esterification reaction, TPA (terephthalic acid) or 2,6-naphthalene dicarboxylic acid (2,6-NCDA) is mixed with ethylene glycol (EG) and reacted at the temperatures ranging from 200~280° C. under atmospheric pressure or under slight pressure and the side product, that is water, is removed. Thereafter in the second step, the synthesized, esterified compounds are polycondensed in the presence of a polymerization catalyst such as antimony trioxide (Sb
2
O
3
) at higher reaction temperatures ranging from 280 to 300° C. under reduced pressure (generally less than 1.0 torr) in order to prepare the high molecular weight polymers.
Currently, in the case of PET, the direct esterification method is mostly used, which uses the TPA as a starting material. But in the case of preparing PEN, because of the high cost, the ester-interchange reaction method is mostly adopted. Meanwhile, PBT can also be prepared by a similar method except that 1,4-butanediol is used instead of EG.
Generally, a reaction catalyst is employed to accelerate and smoothly advance a reaction in preparing polyester. These catalysts include a variety of metal compounds of antimony, titanium, germanium, tin, zinc, manganese, lead and the like.
However, it is well known that the color and the thermal stability of the resulting polyester, especially, PEN, and the reaction rate considerably depend on the catalysts employed. The reactions for preparing polyester are carried out at high temperatures for an extensive period in the presence of catalysts containing metals. Thus, several undesirable side reactions that result in coloring the polymer product yellow and increasing the amount of diethylene glycol and the concentration of terminal carboxylic groups above their optimum levels are accompanied in preparing high molecular weight polyesters. Yellowish color and excessive amount of diethylene glycol deteriorate the physical properties of the polyester such as the melting point, strength and the like. Therefore, it is important to prepare polyester that can exhibit good color and superior physical properties at a higher reaction rate.
Currently, antimony compounds, especially, antimony trioxide, are mostly used as industrial polycondensation catalysts due to its acceptable catalytic activity and moderate price.
But since antimony trioxide is not solved well in ethylene glycol and in reaction intermediate for preparing polyester, it tends to precipitate during the reaction and it cause the resulting color of the polyester to become gray or yellow-green and less transparent. These effects are more distinct when the amount of the catalyst added is increased or the reaction temperature is raised to improve the production rate.
In order to overcome the above-mentioned problems, there have been several methods using catalysts to produce polyester exhibiting good color and superior physical properties by reducing the esterification reaction time and the polycondensation reaction time. However, many of the proposed methods could not overcome the above-mentioned problems: a method of using catalyst as a solution prepared by dissolving antimony trioxide with cobalt compound and phosphorous compound together in ethylene glycol (Japanese Laid Open Patent Publication No. 53-51295) and a method in which a compound of antimony is used with an organic acid (Japanese Laid Open Patent Publication No. 60-166320) were attempted. However, these methods fail to reduce both the esterification reaction time and the polycondensation reaction time. And they also caused several problems in the physical properties of the prepared polyesters in that the color of the prepared polymer is light yellow and the content of diethylene glycol or terminal carboxylic groups is not reduced sufficiently.
Also, as a method to improve the color and physical properties of the prepared polymer, there have been known a method in which compounds of cobalt and alkali metal are used with a compound of antimony (Japanese Laid Open Patent Publication No. 58-117216), a method in which a compound of antimony is used with a compound of tin (Japanese Laid Open Patent Publication No. 49-31317), and a method in which antimony compound, tin compound and compounds of cobalt and alkalimetal, phosphorous compounds are used together (Japanese Laid Open Patent Publication No. 62-265324). However, these methods are incapable of improving the color and transparency, physical properties of the prepared polymer significantly. And these methods fail to provide any important advantage in reducing the reaction time.
Meanwhile, by previous inventions made by the present inventors, problems of preparing polyesters, especially PET, have been overcome by using titanium compound and antimony compound together (U.S. Pat. No. 5,286,836) or by using a composite catalyst containing additional tin compound along with titanium compound and antimony compound (U.S. Pat. No. 5,714,570)
However, a marked difference between the preparation of PEN and PET exists. For instance, the reactant, 2,6-NCDA has a lower solubility in EG because of higher molecular weight and smaller crystal size of 2,6-NDCA than TPA. Therefore, it is not possible to feed the slurry prepared by mixing 2,6-NCDA and EG in similar molar ratio as in PET preparation (generally, EG/TPA=1.1~2.5) into the reactor.
Since the naphthalene ring structure of 2,6-NDCA or 2,6-NDC is more liable to become colorized by impurities than the benzene ring structure of PET, careful selection of catalyst is very critical to attain good colored product. And because PEN has a higher melt viscosity, it requires a higher polymerization temperature than PET. However, higher temperature makes PEN be colored and more liable to degradation. To overcome this problems, efficient catalyst is essential to reduce the reaction time in preparing the polymer
Although several methods to overcome these problems have been proposed, those were not so successful in shortening the reaction time or in improving the product quality.
SUMMAR

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