Page 292 - Academic Press Encyclopedia of Physical Science and Technology 3rd Polymer

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Encyclopedia of Physical Science and Technology En012c-604 July 26, 2001 16:2

Polymers, Thermally Stable 801

directed mainly toward the aerospace industry. Recently, Aliphatic, cycloaliphatic, and aromatic-substituted allyl
critical drawbacks to the use of PMR-15 have emerged nadic imides (LV) have been reported to produce ther-
which may limit its widespread commercial impact, moset resins by thermal homopolymerization as well as
including: being effective in bismaleimide comonomer blending.

CO CO CO CO
C(CF 3 ) 2 C(CF 3 ) 2
N N Ar N N
CO CO CO n CO
(LIV)
n = 0 or n = 1, Ar = C(CF 3 ) 2 ; ; ; O

CO CO
N R N
CO CO
(LV)
e.g., R = (CH 2 ) 6 ; CH 2

Carbon fiber matrix resins have been produced from
acetylene (ethynyl)-terminated prepolymers. Typically,
Thermid HR 600, imide oligomer (LVI,A = CO) cures
◦
in situ at 350 C to form a thermoset resin (T g > 350 C).
◦
Alternatives have been developed that improve the poor
processibility (low solubility and limited gel time of
3 min /250 C). For example, in Thermid FA 700 [LVI,
◦
A = C(CF 3 ) 2 ], solubility has been improved and gel time
increased on introduction of the hexafluoroisopropylidine
unit into the polymer chain.

CO A CO CO A C CH
O O
HC C N N N
CO CO CO
(LVI)
CO CO
C C C C
Problems associated with prepreg quality control and
N O N
CO CO
batch-to-batch variability. (LVII)
Microcracking of the resin matrix on thermal cycling

of carbon fiber laminates due to mismatch of Aromatic polyimides prepared from phenylethynyl-
fiber–resin thermal expansion coefficients. terminated imide monomers or oligomers (e.g., LVII)
Toxicity of the key methylene-dianiline (MDA)
demonstate many advantages over the ethynyl coun-
component. The fluorinated diamine (4-BDAF) terparts in their favorable processing and improved
(XLIV) has been used as a replacement both to reduce thermal/thermo-oxidative stability. In all of these systems,
the level of toxicity and to enhance the basic however, cyclotrimerization yields a complex of cross-
toughness of the resin. Improved processing linked structures rather than the predicted aromatic rings.
characteristics and higher operating temperatures than Indeed, the cure reaction mechanism is still little under-
for PMR-15 have been claimed for resins stood.
incorporating fluorine-containing groups in either R Commercial addition polyimides include the bis-
maleimides: Kinel 500 (molding resin), Kerimids, e.g.,
and/or A segments of the PMR system (LIII).
Compimid, Matrimid and Desbimid (filament wind-
Benzocyclobutene terminated imides (LIV) can be ho- ing/laminating resins); arylnadimides: e.g., P10, P13N,
mopolymerized in the melt to yield temperature-resistant P105A (solutions/molding resins); PMRs: e.g., PMR-15,
resins having a maximum of 24% weight loss after 200 hr PMR-11-50, LARC-160 and AFR 700B (solutions/carbon
at 371 C. These benzocyclobutenes have also produced fiber prepreg); and acetylene-terminated imides. Thermid
◦
modified resins by copolymerization with bismaleimides. HR-600 (molding resin, carbon fiber prepreg).