Flame retardant compositions derived from difunctional carboxylic acids containing a halogenated thiophere ring and methods for their preparation

DETAILED DESCRIPTION OF THE INVENTION The flame-retardant polyesters of this invention are derived, at least in part, from mono- or dihalogenated thiophene dicarboxylic acids.
The dicarboxylic acids exhibit one or more of the following formulae ##SPC2## wherein X represents a chlorine or bromine atom, and m represents the integer 1 or 2.
PREPARATION OF HALOGENATED THIOPHENE DICARBOXYLIC ACIDS Halogenated 2, 5-thiophene dicarboxylic acids corresponding to formula I hereinabove are conveniently prepared by reacting the corresponding 2,3,4,5-tetrahalo- or 2,3,5-trihalothiophene (prepared by the halogenation of thiophene) with a stoichiometric amount or a slight excess of organolithium compound at low temperatures and in the presence of a cyclic or linear ether as the diluent.
The resultant organolithium derivative is then reacted with carbon dioxide using procedures described in the prior art.
The reaction is believed to follow the course outlined below for the tetrabrominated derivative: ##EQU1## Thiophene-3, 4-dicarboxylic acids can be prepared as described in U.
S.
Pat.
No.
2,744,917 from the corresponding formyl succinate and phosphorus pentasulfide, followed by hydrolysis of the resultant ester.
A method for preparing thiophene-2, 4-dinitrile is described in U.
S.
Pat.
No.
3,162,650.
The nitrile is readily hydrolyzed to the corresponding acid using known procedures.
INCORPORATION OF HALOGENATED THIOPHENE DICARBOXYLIC ACIDS INTO POLYMERS The dicarboxylic acids of this invention can be incorporated into the structure of synthetic polyesters derived from dicarboxylic acids and either diols or dihydric phenols.
Polyesters are prepared by reacting one or more aliphatic or aromatic dicarboxylic acids or suitable derivatives thereof, such as anhydrides or esters of the acids prepared using volatile monohydric alcohols containing between 1 and 5 carbon atoms, with one or more alkyl, aralkyl or cycloalkyl diols containing between 2 and 12 carbon atoms.
Suitable acids contain between 2 and 18 carbon atoms and include oxalic, malic, maleic, butanedioic, hexanedioic, octanedioic, and the isomeric cyclohexanedioic acids, the three isomeric phthalic acids, trimellitic acid, and the isomeric naphthalene dicarboxylic acids