Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – From carboxylic acid or derivative thereof
Reexamination Certificate
2001-04-23
2002-08-27
Acquah, Samuel A. (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
From carboxylic acid or derivative thereof
C528S275000, C528S301000, C528S302000, C528S308000, C528S308600, C524S780000, C524S783000
Reexamination Certificate
active
06441125
ABSTRACT:
The invention relates to an improved process for the preparation of a copolyether ester. Copolyether esters are thermoplastic elastomer polymers built up of hard polyester segments of repeating units derived from at least one alkylene glycol and at least one aromatic dicarboxylic acid or an ester thereof and soft segments derived from a polyalkylene oxide glycol. Such a copolyether ester is generally prepared by a process involving the combining in the melt of at least one alkylene glycol, at least one aromatic dicarboxylic acid or an ester thereof and the polyalkylene oxide glycol. If an ester of an aromatic dicarboxylic acid is started from, for instance the dimethyl ester of terephthalic acid, then first a transesterification reaction takes place upon which the alkylene glycol and the polyalkylene oxide glycol take the methyl position in the aromatic dicarboxylic acid ester, with the methanol, which is volatile under the transesterification reaction conditions, being separated off. If the aromatic dicarboxylic acid is present in place of the ester, then esterification with the glycols takes place directly. Subsequently, polycondensation of the ester to yield polyester, in the case specified here copolyether ester, takes place under reaction conditions that are generally different from those of the transesterification or esterification. The polycondensation in the melt is then continued until a polycondensate with the desired molecular weight is obtained.
In a number of cases, especially if the polyalkylene oxide glycol is based on propylene oxide, the polycondensate must then be subjected to solid-phase post-condensation in order to achieve a sufficiently high molecular weight. For the softer copolyether esters the polycondensation is also much slower than for the harder copolyether ester that contain less soft segment.
It has proved possible to shorten the time needed to obtain a desired molecular weight in the melt condensation process by using a catalyst. Various catalysts have been developed for this; in practice, complex titanium compounds, in particular titanium tetrabutoxide (TBT), have found the widest application.
In U.S. Pat. No. 3,801,547 A and U.S. Pat. No. 4,687,835 A besides TBT salts of a bivalent metal, in particular magnesium acetate and calcium acetate are used as cocatalysts. In said patent publications other combinations of titanium and magnesium are also mentioned, for instance Mg[HTi(OR
6
]
2
where R=alkyl, and other complex titanates obtained from alkaline earth metal alkoxides and titanate esters. No reasons are given for the use of such combinations of a bivalent metal compound with the titanium compounds. The molar ratio of titanium to bivalent metal is generally 2:1.
In spite of the presence of said catalyst combinations, the state of the art processes take quite some time or lead, as for instance stated in Example 2 of U.S. Pat. No. 3,801,547-A at most to a copolyether ester having a minimum melt flow index (MFI) of 5.1 g/10 min. Polyether esters with such a high MFI can be used for only a limited number of processing techniques.
By using chain branching, for instance by alcohols or acids with a functionality of three or higher, for instance trimethylol propane or trimellitic acid, the time needed to reach a certain molecular weight can be shortened also, or a copolyether ester with a lower MFI can be obtained, see U.S. Pat. No. 4,205,158-A. However, the resulting branched copolyether esters have inferior elastic and fatigue properties, making them less suitable for use in, for instance, bellows in automotive applications under more extreme conditions.
Another process by which the problem of the low reaction rate in the preparation of the softer copolyether ester types can be obviated comprises partial replacement of the terephthalic acid by isophthalic acid, so that a lower polyalkylene oxide segments content is needed for a certain shore D hardness, while the hard segments content, which promotes a higher polycondensation rate, increases. However, this process has the drawback that the melting point of the copolyether ester is substantially lower than that of the corresponding copolyether ester that is based entirely on terephthalic acid, while moreover the glass transition temperature is higher. Particularly in applications at higher temperatures and extremely low temperatures, for instance under the bonnet, these iso- and terephthalic acid based copolyether esters prove less suitable. In addition, the elongation at break is lower.
The aim of the invention was therefore to find a process that offers the advantage of an increased polycondensation rate while it does not have the above-mentioned drawbacks, or only to a very limited extent.
The inventors have now found, very surprisingly, that when the ratio of titanium to bivalent metal in the catalyst combination is chosen to be substantially lower than the value of 2 that has so far been customary, for instance 1.6 or even lower, the polycondensation time for a given viscosity is substantially shortened and it proves possible to produce, without solid-phase post-condensation, copolyether ester that is suitable for, inter alia, injection moulding applications, but contains substantially less chain branching agent, or even no chain branching agent at all, than copolyether esters obtained in the melt according to the state of the art as described in U.S. Pat. No. 4,205,158-A.
The process according to the invention for the preparation of a copolyether ester with hard polyester segments of repeating units derived from at least one alkylene glycol and at least one aromatic dicarboxylic acid and soft segments derived from at least one polyalkylene oxide glycol, which comprises polymerization by polycondensation in the melt of at least one aromatic dicarboxylic acid, at least one alkylene glycol and at least one polyalkylene oxide glycol in the presence of a catalyst based on a combination of titanium and a bivalent metal in a single compound or a combination of titanium and bivalent metal containing compounds, is characterized in that the molecular ratio of titanium to bivalent metal is at most approximately 1.6, preferably at most 1.5.
The best results are achieved when the molecular ratio of titanium to bivalent metal is approximately 1.
Within the group of bivalent metals in particular the alkaline earth metals, for instance magnesium, barium and calcium, and zinc are very suitable. Magnesium is preferred. Preferably, the titanium and the bivalent metal are combined in two separate compounds. The compounds already referred to in the introduction are in principle eligible for use in the process according to the invention. However, the invention is not limited to these.
Preferably, the titanium is used in the form of a metal organic compound, for instance in the form of a titanium alkoxide, for instance TBT, or a titanium ester. The bivalent metal is preferably used in the form of a compound that is soluble in the reaction mixture, for instance in the form of an acetate, preferably magnesium acetate. The concentration of the catalyst in the reaction mixture may vary within broad limits; in general the useful activity is within a range of 0.01 wt. %-1 wt. % of TBT, relative to the terephthalic acid or terephthalate used. Preferably, the content lies between 0.03 and 0.3 wt. % TBT. Below a value of 0.01 wt. % TBT no effect is generally noticeable, and at a content of higher than 1 wt. % a polycondensate is obtained that is unsuitable for solid-phase post-condensation. Generally speaking, in the copolymerization of copolyether esters on the basis of polybutylene oxide diol or polyethylene oxide diol a smaller amount of catalyst will suffice than in the copolymerization of copolyether esters on the basis of polypropylene oxide diol. The same holds for the harder copolyether ester types, for which likewise a smaller amount of catalyst needs to be applied than for the softer types.
The titanium containing compound and the bivalent metal containing compound can simultaneously, or optional
Bonte Geert I. V.
Dijkstra Krijn
Warnier Jean M. M.
Werumeus Buning Gerard H
Acquah Samuel A.
DSM N. V.
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