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Phthalonitrile resms, as a type of high performance thermosetting materials, have been widely studied in the past decades, due to the outstanding combination of properties such as thermal
and oxidative-thermal stability, low water uptake and flame-retardance.lHowever,thepolymerization of the neat resin is extremely sluggish, thus limiting their application.2 0n the other hand, phenylethynyl end-capped thermosetting resins have also received much attention.3 The derived polymers exhibit unique thermal and dimensional stability, excellent chemical resistance and mechanical properties, which offer promise for advanced composites application. However, the
intensively curing exothermic effect of the phenylethynyl-based resins was an unbeneficial
characteristic for fabrication of thick composite sections. In this study, the model compound with
both phthalonitrile and phenylethynyl groups 3PN3PEODPA, the phthalonitrile or phenylethynyl
end-capped imide compounds (3PNOPDA or 3PEODPA) were synthesized from 4, 4''-oxydiphthalic
anhydride (ODPA) with 4-(3-aminophenoxy) phthalonitrile or 3-phenylethynyl aniline by
imidization of chemical dehydration (SCHEME l), with an aim to combine their own curing
characteristics, which may offer a new tWe of resin systems with adjustable processability and
tailored properties. The theological behavior of the imide compounds was studied by dynamic
oscillation employing a TA Instruments AR-2000ex theometer in conjunction with an environmental
testing chamber for temperature control. In FIGURE l, storage modulus is shown as a function of
time at 330 0C for the three imide compounds. All of the samples exhibited a melt viscosity ofless
than 0.1 Pa.s at 330 0C. When held at 330 0C for a period of time, the melt viscosity of the
compound 3PN3PEODPA with both phenylethynyl and phthalonitrile groups increased, while that of
3PNODPA is very low, and maintained at about 0.1 Pa.s for a relatively long time. Interestingly,
through a comparative study of the theological behavior of 3PEODPA and 3PN3PEODPA, we could
find that the trend of thermal polymerization rate of 3PN3PEODPA slowed down significantly
compared with the neat compound 3PEODPA. The results also revealed that there is a moderate
large process window, which is helpful in the fabrication of large size composite sections. These
results offer promise for seeking new approach to design high performance thermosetting materials. |
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