Polyesters which contain maleate groups

Details Polyesters which contain maleate groups Polyesters which contain maleate groups

2000-08-03

2002-02-26

Yoon, Tae H. (Department: 1714)

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

Synthetic resins

From carboxylic acid or derivative thereof

C528S297000, C528S306000

Reexamination Certificate

active

06350849

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a method of producing polyesters which comprise maleate groups in their main chain.
BACKGROUND OF THE INVENTION
Polyesters which comprise unsaturated groups within their main chain constitute a class of reactive polymers which are very important industrially for numerous fields of application. Thus they are used, optionally after further modification, as styrene-containing solutions for lacquers, printing inks and adhesives, and are used in particular as casting resins for the production of fibre-reinforced components of all types.
They are produced by the condensation polymerisation of mixtures of saturated and unsaturated cyclic anhydrides, or of the corresponding dicarboxylic acids, with diols and optionally with small amounts of polyols at high temperatures, under basic or acidic catalysis. A multiplicity of polyesters can be produced by correspondingly selecting the condensation polymerisation conditions and the type and composition of the materials used. Maleic anhydride, maleic acid or fumaric acid are essentially used as the unsaturated component.
As a consequence of the condensation polymerisation conditions, the major part of the maleate esters which are incorporated by condensation isomerises to form fumarate ester groups. Hitherto, this was even desirable, and the aim was to effect isomerisation as completely as possible, since the aromatic vinyl compounds., preferably styrene, which were used almost exclusively as reactive thinners, copolymerise significantly more rapidly with fumarates than with maleates.
The choice of diols is also restricted to just a few compounds, such as ethylene glycol, propylene glycol-1,2 and oligoethers thereof, and to longer chain branched diols, such as neopentyl glycol and 2,2,4-trimethylpentanediol-1,3, which are added in small amounts. Diols which contain methyl groups are required so that the polyesters dissolve in styrene and in order to improve the material properties of the finished products.
A review of the chemistry and uses of unsaturated polyesters is give, for example, by A. Fradet and P. Arlaud in Comprehensive Polym. Sci., Volume 5, pages 331 to 344 (1989), and by T. J. Mao in the Encyclopedia of Polymer Science and Engineering, Volume 15, pages 167 to 178 (1989).
For many areas of application, it is necessary to replace styrene, which is very volatile and constitutes an industrial health hazard, by other less volatile reactive thinners which constitute less of an industrial health hazard. Acrylates, methacrylates, vinyl ethers and vinyl esters are suitable reactive thinners. In contrast to styrene, however, these compounds exhibit a significantly lower reactivity for polymerisation with fumarate groups, and often copolymerise or crosslink better with maleates. Thus WO 90/10660 describes the photochemical, radical-initiated curing of polyesters, which comprise terminal maleate groups, by polyfunctional vinyl ethers, wherein the polyesters are produced in a multi-stage reaction.
DD 256516 relates to the formation of low molecular weight bismaleic acid monoesters from maleic anhydride and diols of symmetrical structure under defined reaction conditions. Products of this type are solid, difficultly soluble, and contain terminal acidic groups via which they can be reacted further, but where there is a risk of isomerisation of the double bond.
It is also known that polyesters can be formed from maleic anhydride and simple epoxides, preferably epichlorohydrin, propylene oxide and butylene oxide. This reaction has been described by Akimoto et al. in J. of Polym. Sci., Volume 11, page 2247 et seq. (1973), by W. Kuran et al. in PL 121261, and by R. Herold in U.S. Pat. No. 3,538,043, for example, and is based on the ring-opening polymerisation of epoxides with anhydrides, as described by J. Luston and F. Vass in Adv. in Polym. Sci., Volume 56, page 91 et seq. (1984).
Examples of initiators which are used for polymerisation reactions of this type include alkali metal salts, halides, complex salts and acetylacetonates of transition metals, or tertiary amines, often in combination with diols, polyether diols or dicarboxylic acids. A common feature of reactions which employ initiators such as these is the restriction thereof to short-chain olefine epoxides. In no case is there any mention of the configuration of the double bonds in the main chain.
Moreover, with all these known initiators it is not possible to prevent the formation of homopolymers of the epoxides used.
In contrast, V. Bagrel et al. in U.S. Pat. No. 5,019,643 describe the formation of alternating polyesters from cyclic dicarboxylic anhydrides and epoxides which comprise at least 8 carbon atoms, in the presence of Ti(IV) diketone—complexes in hydrocarbons. In contrast to alkali metal salts, tertiary amines and N-heterocycles, it is claimed that these complex catalysts are capable of preventing the complex secondary reactions which occur between maleate double bonds and the aforementioned initiators, particularly alkali metal salts or tertiary amines. However, due to the restriction to epoxides comprising 8 or more carbon atoms which is cited in the above patent, it is obviously not possible to incorporate short-chain epoxides by polymerisation,
SUMMARY OF THE INVENTION
The underlying object of the present invention is to provide a simple method of producing polyesters which exclusively contain maleate groups in their polymer chain. The object is also to provide polyesters of this type which exhibit greater variability as regards different side groups compared with conventional polyesters, which practically only contain methyl side groups. It should thereby be possible to vary the dissolution properties and reactivity of polymers with reactive thinners and the mechanical properties of the resulting crosslinked products within wide limits.
The present invention relates to a method of producing polyesters comprising maleate groups in their main chain, which is characterised in that a mixture comprising
a) one or more &agr;,&bgr;-unsaturated anhydrides, selected from the group consisting of maleic anhydride, maleic anhydride derivatives, and precursors of maleic anhydride and maleic anhydride derivatives which are converted into maleic anhydride or maleic anhydride derivatives during polymerisation,
b) one or more epoxides comprising 2 to 25 carbon atoms, wherein the ratio of the amount of epoxide or epoxides to the amount of anhydrides cited in a) and b) is at least 1:1, preferably further
a-2) one or more aromatic, cycloaliphatic or aliphatic carboxylic anhydrides, most preferably up to 99-mol % of the anhydrides with respect to the total amount of components a) and a-2),
is copolymerised in the presence of 0.01 to 5 mol-% of a Zn
2+
carboxylate with respect to the total amount of anhydride(s) and epoxide(s), at a temperature from 50 to 120° C.
DETAILED DESCRIPTION OF THE INVENTION
The invention is based on the surprising observation that zinc(II) carboxylates are suitable initiators for the ring-opening polymerisation of saturated and unsaturated cyclic anhydrides with epoxides of all types, wherein the number of carbon atoms in the epoxides can be between 2 and 25, preferably between 4 and 18.
Examples of &agr;,&bgr;-unsaturated anhydrides which can be used in the method according to the invention include maleic anhydride, methylmaleic anhydride (citraconic anhydride), dimethylmaleic anhydride and phenylmaleic anhydride. Apart from the aforementioned maleic anhydrides, precursors of maleic anhydrides or precursors of maleic anhydride derivatives which are converted into maleic anhydride or maleic anhydride derivatives during polymerisation can also be used in the method according to the invention. One example thereof is itaconic anhydride, which during polymerisation is converted practically completely into methylmaleic anhydride, which is incorporated as such by polymerisation.
In addition, one or more aromatic, cycloaliphatic or aliphatic carboxylic anhydrides, preferably up to 99 mol-% of components a) and a-2) w

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