GB811758A - Polybenzoxazoles and method of preparing the same - Google Patents

Abstract

Polybenzoxazoles are made by heating an amino-hydroxy-phenylalkanoic acid of the general formula <FORM:0811758/IV (a)/1> where R is a divalent hydrocarbon radical, or by heating a compound of the general formula <FORM:0811758/IV (a)/2> where R1 is a divalent hydrocarbon radical or a carbon-to-carbon bond with a substantially equimolecular quantity of a saturated aliphatic dicarboxylic acid or an ester thereof, at a temperature of from 100 DEG to 350 DEG C. in the absence of oxygen. The monomers may be co-condensed with polyamide-forming monomers, e.g. tetramethylene and hexamethylene diamine, if equimolecular quantities of dicarboxylic acids are present. In the examples, polybenzoxazoles are prepared from (i) 3-amino-4-hydroxyhydrocinnamic acid; (ii) 3-(3-amino-4-hydroxy phenyl)-3 methyl butyric acid; (iii) 5 - (3 - amino - 4 - hydroxyphenyl) - 5 - methyl hexonoic acid; (iv) 3,31-dihydroxybenzidine and sebacic acid; (v) 3,31-dihydroxybenzidine and sebacic, azelaic and suberic acid. Specifications 461,236, 461,237, [both in Group IV], and U.S.A. Specification 2,497,248 are referred to.ALSO:Amino-hydroxy phenyl alkanoic acids of the general formula <FORM:0811758/IV (b)/1> where R is a divalent hydrocarbon radicle, and compounds of the general formula <FORM:0811758/IV (b)/2> where R1 is a divalent hydrocarbon radicle or a carbon-to-carbon bond are prepared and used as intermediates in the preparation of polybenzoxazoles (see Group IV (a)). In the examples: (1) 4-hydroxybenzaldehyde is heated with malonic acid in the presence of pyridine to prepare 4-hydroxy cinnamic acid which is reduced to 4-hydroxy hydrocinnamic acid, nitrated with aqueous nitric acid to form 3-nitro-4-hydroxyhydrocinnamic acid which is reduced with hydrogen to yield 3-amino-hydroxyhydrocinnamic acid; (II) methoxybenzene is reacted with methallyl chloride in the presence of sulphuric acid to yield 4-chloro-tertiarybutyl methoxybenzene which is converted by a Grignard reaction to 3-(4-methoxyphenyl)-3-methylbutyric acid from which 3-(4-hydroxyphenyl)-3-methyl butyric acid is derived by reflux with an hydrobromic acid-acetic acid mixture, the resultant acid being nitrated and hydrogenated to yield 3-(3-amino-4-hydroxyphenyl)-3-methylbutyric acid; (III) methoxybenzene is alkylated with 5-methyl-5-hexenenitrile in the presence of hydrogen fluoride to yield 5- (4-methoxyphenyl) - 5 - methyl hexenenitrile which is refluxed with sulphuric acid and reacted with an hydrobromic acid-acetic acid mixture to yield 5-(4-hydroxyphenyl)-5-methylhexanoic acid which is nitrated and reduced with hydrogen to give 5 - (3 - amino - 4 - hydroxyphenyl - 5 - methylhexanoic acid; and (IV) 3,31-dihydroxybenzidine is made by demethylating o-dianisidine with aluminium chloride. Specifications 461,236, 461,237, [both in Group IV], and U.S.A. Specification 2,497,248 are referred to.