# US 7,465,782 B2 · Method for making polybenzobisoxazole containing fiber

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- Number: US 7,465,782 B2
- Document ID: US7465782B2
- Status: Granted
- Kind: B2
- Application number: 11/180,239
- Filed: 2005-07-13
- Published: 2007-01-18
- Granted: 2008-12-16
- Earliest claimed: 2005-07-13
- Assignees: E.I. du Pont de Nemours and Company
- Inventors: Kiu-Seung Lee
- Web page: https://patentgrep.com/patent/US7465782B2

## CPC

- C08G 73/22: Polybenzoxazoles
- C08G: MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS

## Abstract

A method of making polybenzobisoxazole containing fiber by use of a non-polybenzobisoxazole polymer, hydroxylating the polymer, forming the polymer into a fiber and heating the fiber wherein ring closure occurs in the hydroxylated polymer.

## Claims

### Claim 1

A method of making polybenzobisoxazole containing fiber comprising the steps of:
a) forming a polymer solution comprising a solvent and a polymer having the structure:
wherein
Ar1 is
Ar2 is
b) contacting the polymer solution of a) with a oxidizing agent in the presence of an alkyl carboxylic acid which provides oxygen atoms to hydroxylate at least a portion of Ar1, in forming a hydroxylated polymer with ortho hydroxyl groups,
c) forming a fiber from the hydroxylated polymer of step b),
d) heating the fiber to form ring closure of at least a portion of ortho-hydroxyl groups.

### Claim 2 (depends on 1)

The method of claim 1 wherein Ar1 is:

### Claim 3 (depends on 2)

The method of claim 2 wherein Ar2 is:

### Claim 4 (depends on 1)

The method of claim 1 wherein Ar1 is:

### Claim 5 (depends on 4)

The method of claim 4 wherein Ar2 is:

### Claim 6 (depends on 1)

The method of claim 1 wherein the oxidizing agent is nitrosulfuric acid, lead tetracetate or sodium nitrate.

### Claim 7 (depends on 6)

The method of claim 6 wherein the oxidizing agent is nitrosulfuric acid.

### Claim 8 (depends on 1)

The method of claim 1 wherein the alkyl carboxylic acid is formic acid or acetic acid.

### Claim 9 (depends on 8)

The method of claim 8 wherein the alkyl carboxylic acid is acetic acid.

### Claim 10 (depends on 1)

The method of claim 1 wherein the heating is in a range from 170 to 280 degrees Celsius.