Process to polymerize AB-PBO monomer phosphate salts
AssigneeThe Dow Chemical Company
InventorsWilliam J. Harris, Zenon Lysenko, Carl W. Hurtig
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Abstract
AB-polybenzoxazole monomer, such as 3-amino-4-hydroxybenzoic acid, can be synthesized in high yields from a hydroxy-benzoic acid or related compound in a three-step process of (1) nitration, (2) hydrolysis of the ester, and (3) reduction of the nitro moiety. The monomer is conveniently recovered as a phosphate salt in high purity by precipitating and recrystallizing from a phosphoric acid solution. The monomer may be polymerized in high concentrations in polyphosphoric acid containing high levels of P.sub.2 O.sub.5 to yield a high molecular weight polymer without dehydrohalogenation.
Claims13
A process for synthesizing a polybenzazole polymer without a dehydrohalogenation step said process comprising the steps of:
- (1) mixing a phosphate salt of an AB-PBO monomer with a polyphosphoric acid containing at least 80 percent P.sub.2 O.sub.5 by weight at the commencement of the reaction in a concentration of monomer to polyphosphoric acid that is chosen such that the solution resulting from polymerization contains at least 7 weight percent polymer and less than 30 weight percent polymer under non-oxidizing conditions to form a polymerization mixture:
- and
- (2) maintaining the polymerization mixture at a temperature and under conditions suitable to cause the AB-PBO monomer to form polymer for a period of time sufficient to form a polybenzazole polymer containing AB-PBO mer units.
Dependencies are inferred from the claim text.