Chemical process for forming low molecular weight, fully cyclized heteroaromatic prepolymers under conditions which limit chain extension or branching is described. Exact procedures used in conducting chemical reaction are defined. Advantages of process over conventional methods are presented

Hughes, C. T.

Mchenry, R. J.

English

NASA Technical Reports Server

August 1972	 .	 B72-10473 
NASA TECH BRIEF 
Langley Research Center 	
-4r 
NASA Tech Briefs announce new technology derived from the U.S. space program. They are issued to encourage 
commercial application. Tech Briefs are available on a subscription basis from the National Technical Information 
Service, Springfield, Virginia 22151. Requests for individual copies or questions relating to the Tech Brief program may 
be directed to the Technology Utilization Office, NASA, Code KT, Washington, D.C. 20546. 
Process for Synthesizing and Formulating Condensed Ring Polymers 
A new method of synthesizing and formulating 
condensed ring polymers for use in moldings, laminates, 
and adhesives has been conceived with pyrrone polymers 
using a novel synthesis route. 
Previous work with condensed ring polymers has 
involved the formation of long chain, high molecular 
weight, highly soluble precursor polymers having flexible 
bonds and highly polar functional groups. These polymers 
were subsequently converted to an insoluble, rigid, 
cyclized heteroaromatic structure by thermal treatment 
which eliminated one or more molecules of water from 
the chain per-monomer-unit. These volatiles have to be 
removed to obtain a cured resin with optimum properties. 
An example of this process is the preparation of pyrrone 
polymers which have been synthesized with polyamide 
acid amine precursors. These precursors have been made 
by the reaction of aromatic five-ring dianhydrides with 
bis(o-diamines), which are thermally or chemically cyclo-
dehydrated to a heterocyclic ring system containing four 
or seven fused rings (depending on the dianhydride). 
The resulting polymer can have either a ladder or a semi-
ladder structure, and an even more rigid backbone chain 
than the polyimides. 
This new process forms low molecular weight, fully 
cyclized heteroaromatic prepolymers (or oligomers) 
under conditions which severely limit chain extension 
or branching. The oligomers are then more easily pro-
cessed in conventional fashion with less volatile for-
mation. The process is defined as follows: 
(a) A partially or fully cyclized prepolymer was pre-
pared with controlled molecular weight by reacting 
a large excess of comonomer A with comonomer 
B. The average molecular weight and distribution 
were controlled by the ratio of the monomers, 
the higher the ratio, the lower the average weight 
and the narrower the distribution. To prevent 
branching and promote cyclodehydration, the 
reaction was conducted at an elevated temperature
and in dilute solution. It was also essential to 
maintain the desired ratio of monomers during 
the entire reaction in order to prevent chain ex-
tension and possible gellation. The prepolymer 
contained end groups associated with comonomer 
A. 
(b) The above procedure was repeated with an excess 
of B relative to A to produce a prepolymer with 
end groups for comonomer B. 
(c) Solutions of the two prepolymer oligomers (either 
with or without comonomers) were then mixed 
in as short a time as possible at a relatively low 
temperature and precipitated immediately. A pow-
der was produced which was a molecular mixture 
of the two oligomers and which had a minimum 
of chain extension. Molecular mixing of the 
pyrrones at 450 K resulted in some chain exten-
sion although enough flow still remained to obtain 
good high pressure holdings. 
The advantages of this process, as exemplified by 
pyrrone polymers, are several-fold. The volatiles gener-
ated during final cure are reduced (relative to the poly-
amide acid amine precursor) thus making the moldings 
substantially more void free. In addition the molded 
pyrrone polymer had a higher flexural strength and 
modulus (especially at 500 K and higher) and sub-
stantially improved oxidation resistance. 
Note: 
The following documentation may be obtained from: 
National Technical Information Service 
Springfield, Virginia 22151 
Single document price $3.00 
(or microfiche $0.95) 
Reference: 
NASA CR-1633 (N70-35716), Preparation and 
Characterization of Low DP End-Capped Pyrrone 
Moldings
(rontinued overleaf) 
This document was prepared under the sponsorship of the National
	 Government assumes any liability resulting from the use of the 
Aeronautics and Space Administration. Neither the United States
	 information contained in this document, or warrants that such use 
Government nor any person acting on behalf of the United States
	 will be free from privately owned rights.
https://ntrs.nasa.gov/search.jsp?R=19720000472 2020-03-17T03:40:37+00:00Z
Patent status:	 Source: C. T. Hughes and R. J. McHenry of 
Title to this invention has been waived under the 	 AVCO Corporation 
provisions of the National Aeronautics and Space Act 	 under contract to 
[42 U.S.C. 2457 (1)] , to the AVCO Corporation, Lowell, 	 Langley Research Center 
Massachusetts 0 185 1	 (LAR-10423) 
B72-10473	 Category 04	 S


Process for synthesizing and formulating condensed ring polymers

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server