Bismaleimides comprising mesogenic groups

Details Bismaleimides comprising mesogenic groups Bismaleimides comprising mesogenic groups

1999-12-27

2001-01-02

Powers, Fiona T. (Department: 1626)

Organic compounds -- part of the class 532-570 series

Organic compounds

Heterocyclic carbon compounds containing a hetero ring...

C544S372000

Utility Patent

active

06169186

ABSTRACT:

This invention relates to new bismaleimides comprising mesogenic groups and to methods of producing them.
Polymeric networks with liquid crystalline properties are materials which are potentially of interest, since they are capable of preferentially exhibiting outstanding mechanical and optical properties in their oriented state. Amongst the optical properties of networks of this type, the change in birefringence and the direction of polarisation in electric, mechanical and magnetic fields, which are utilised for the storage and display of information, e.g. in polymer network LCDs, should be emphasised in particular. In thermally crosslinked materials a refinforcement by liquid crystalline phases results in an increase in the modulus of elasticity, in the bending and fracture strength, and in hardness.
Mesogenic compounds are suitable for the synthesis of liquid crystalline crosslinking agents. Mesogenic compounds such as these are mainly aromatic compounds comprising at least two benzene rings, which are linked para to each other by suitable groups, such as ester-(—COO—), amide (—CONH—) or azomethine (—CH═N—) groups for example, wherein the terminal aromatic rings are each substituted in the para position in relation to these linking groups by an —OH, —COOH or —NH
2
group.
In order to attain liquid crystalline properties, the mesogens generally also have to be linked to suitable spacer chains via the aforementioned reactive —OH, —COOH or —NH
2
groups. The liquid crystals which are thus formed exhibit what are predominantly nematic textures under the polarising microscope.
If the spacer chains of the mesogens which were schematically described above have functions at their ends which are capable of crosslinking, such as acrylate, vinyl ether or glycidyl ether—groups for example, liquid crystalline compounds of this type are self-crosslinking or are capable of crosslinking with other reactive compounds by copolymerization. Their solubility in solvents, compatibility with the oligomeric and polymeric reactants and the liquid crystalline temperature ranges depend on the length of the linear aliphatic spacers, which may have a length corresponding to 1 to 30, preferably 3 to 20 CH
2
groups. Due to the spacer chains, the mesogens which form the liquid crystalline phase are isolated from the crosslinking sites, which is advantageous for the formation and for the capacity of orientation of the mesogenic phase. Examples thereof include liquid crystalline diglycidyl ethers, such as those described by D. J. Broer et al. in Macromolecules, 26, 1244-47 (1993) and by B. Koscielny et al. in Polymer Bulletin, Vol. 32 (5-6), 529-36 (1994), as well as diacrylate and divinyl ethers, such as those described by R. A. M. Hikmet et al. in Macromolecules 28, 3313-27 (1995) and in Polymer, 34, 1736-40 (1993).
As essential characteristic property for the existence of liquid crystallinity is the length/diameter ratio of the individual molecule, which should reach or exceed a value of 5. When the above mesogens are used, the resulting networks also predominantly exhibit nematic behaviour.
The industrial use of liquid crystalline crosslinking agents for the synthesis of mesogenic networks has hitherto foundered because of the costly synthesis of compounds of this type, which cannot be employed in an economically and technically feasible manner on an industrial scale. Multistage syntheses using protective groups are necessary in many cases, as described, for example, by M. Ando and T. Uryu in J. Polymer Science, Part A, 28, 2575-84 (1990) for liquid crystalline diacrylates. This publication describes the general procedure which was known hitherto for the synthesis of crosslinking agents of this type, which consists of reacting previously prepared bifunction mesogens, which comprise aromatically bonded para-substituted reactive —OH, —COOH or —NH
2
groups or halogen atoms, mainly fluorine, bromine or iodine, in a Williamson ether synthesis with an excess of an &agr;,&ohgr;-dihalo- or dihydroxyalkane, whereby the polyalkylene chains which are necessary as spacers are introduced. If &agr;,&ohgr;-dihydroxyalkanes are used, an OH function generally has to be protected by a suitable reversible protective group before di-substitution. A reaction with compounds which contain a group which is capable of polymerization is not effected until the end, optionally after the removal of the protective groups.
The groups which are employed as crosslinking groups are frequently those which are only capable of reacting with themselves or with a limited selection of other groups. Examples include the aforementioned acrylate, methacrylate and vinyl ether functions, which crosslink in addition polymerization reactions with compounds which contain groups of the same type or similar groups, or such as glycidyl ethers, which react with few other compounds, such as dicarboxylic acids, anhydrides or diamines. Moreover, liquid crystalline crosslinking agents which comprise said active crosslinking groups always require initiators or catalysts in order to initiate the reaction.
The object of the present invention was to identify liquid crystalline crosslinking agents which can be produced in as simple a manner as possible, and which can be produced in a simpler, less costly manner, even on an industrial scale, than the mesogenic crosslinking agents known hitherto, which could only be obtained in laboratory syntheses. At the same time, the object was to identify a method which was equally suitable for the production of as many different products as possible which differ only as regards their mesogen and by the length of their spacer group, so as to produce suitable products for as many areas of application as possible. In order to achieve this object, the number of reaction steps required for the formation of liquid crystalline crosslinking agents have had to be significantly reduced and the few steps which were required must proceed with a high yield and be only slightly dependent, or not dependent at all, on the structure of the reactants.
The present invention relates to bismaleimides comprising mesogenic groups, which consist, corresponding to formula (I) given below, of two reactive terminal maleimide groups which are linked via linear or singly alkyl-substituted alkylene chains A, which are linked to an aromatic mesogen M via ester, amide or ether groups,
wherein A independently represents an alkylene chain comprising 3 to 20 CH
2
groups, wherein one C atom of each alkylene chain A can be chiral due to alkyl substitution, X independently represents —C(O)O—, —C(O)NH— or —O—, and M represents a mesogen consisting of at least two rings including an aromatic or a heterocyclic ring, which are linked para to each other by single bond, —CH
2
—CH
2
—, —CH═CH—, —C≡C—, ester (—COO—), amide (CONH—), methylstilbene (—C(CH
3
═CH—), azomethine (—CH═N—), azine (—CH═N—N═CH—), azo (—N═N—) or azoxy (—N(O)═N—) groups, and which can be mono- or di-substituted by alkyl groups, wherein the terminal aromatic rings are each substituted in the para position to these linking groups by an O or NH group of X, and R independently represents an H atom, an alkyl group comprising 1 to 8 C atoms, a phenyl ring or a halogen atom.
Unless otherwise stated, the term “alkyl” denotes a hydrocarbon group comprising 1 to 5 carbon atoms, such as methyl, ethyl, propyl, butyl and pentyl, including the isomers thereof. Methyl is preferred.
The bismaleimides of formula (I) according to the invention can be produced from maleimidoalkylcarboxylic acids, the single-stage synthesis of which is described in EP-A-0 847 991, by linking the acid chlorides thereof, which can be obtained in a simple manner and in good yield, with difunctional aromatic mesogens.
Therefore, the present invention further relates to a method of producing bismaleimides comprising mesogenic groups of general formula (I) as defined above, in which X represents —C(O))— or —C(O)NH—, wherein maleimidoalkylcarboxylic acids of general formula
wherein R and A a

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