No abstract

A multiple aromatic ether linked phthalonitrile was synthesized and characterized. The oligomeric phthalonitrile monomer was prepared from the reaction of an excess amount of bisphenol A with 4,4′‐difluorobenzophenone in the presence of K2CO3 as the base in an N,N‐dimethylformamide/toluene solvent mixture, followed by end capping with 4‐nitrophthalonitrile in a two‐step, one‐pot reaction. The monomer properties were compared to those of the known resin 2,2‐bis[4‐(3,4‐dicyanophenoxy)phenyl]propane after being cured in the presence of bis[4‐(4‐aminophenoxy)phenyl]sulfone. Rheometric measurements and thermogravimetric analysis showed that the oligomeric phthalonitrile resin maintained good structural integrity upon heating to elevated temperatures and exhibited excellent thermal properties along with long‐term oxidative stability. The ether‐linked phthalonitrile resin absorbed less than 2.5% water by weight after exposure to an aqueous environment for extended periods. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4136–4143, 2005

An improved synthetic method has been developed for oligomeric aromatic ether ketone‐based phthalonitrile (PN) resins. A new curing additive was studied that lowers the cure temperature of the PN resin to around 150 °C and compared to the traditional high‐temperature aromatic diamine. Mechanical and thermo‐oxidative analyses of polymeric samples from both systems were determined and compared under various curing conditions. The PN polymer exhibited low water absorption regardless of the chosen cure system. Published 2014. This article is a U.S. Government work and is in the public domain in the USA. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 1662–1668

Using an atomic-force microscope* (AFM), we have studied the attractive and adhesive forces between a cantilever tip and sample surfaces as a function of sample surface energy. The measured forces systematically increased with surface energy. The AFM is very sensitive; changes in the surface forces (i.e., attraction and adhesion) of monolayer-covered samples could be clearly discerned when only the surface group of the monolayer film was changed from -CH3 to -CF3.PACS numbers: 68.35.Md, 62.20.PnThe atomic-force microscope 1 (AFM) has been used primarily to image the surfaces of insulating materials 2 " 6 with nanometer-scale resolution. The principal component of an AFM is a small cantilever which measures the force between a tip attached to the cantilever and the surface of interest. The force is determined by multiplying the measured cantilever deflection by the calibrated spring constant of the cantilever. Recording the deflection of the cantilever as a function of sample position generates a force map, or image, of the surface.Recently, the AFM has also been used to investigate the mechanical properties of materials including atomicscale friction, 7 elasticity, 8 and surface forces. 8,9 The dependence of the AFM surface-force measurement on tip-sample geometry and materials properties has not been studied systematically until now. In this study, cantilever tip size and shape are measured with a scanning electron microscope before and after use, and the composition, structure, and cleanliness of the sample surfaces are characterized using infrared reflectionabsorption spectroscopy. Sample surface energies are determined by contact angle measurements. We measure the attractive and adhesive forces between a tungsten tip and a variety of surfaces, and find the forces detected by AFM increase with sample surface energy. The attractive force results are compared to van der Waals forces calculated for a sphere approaching a flat surface. 10 Derjaguin-Muller-Toporov (DMT) adhesion theory 11,12 is used to analyze the adhesive forces. We estimate the contact area between tip and sample at zero applied load, and discuss the implications for tribology and imaging.Our instrument employs a "double cross" cantilever which constrains the motion of the tip to the z direction (normal to the sample surface). The cantilever has an effective spring constant of 50 ±10 N/m and its deflection is measured with a tunneling microscope. The tunneling microscope was operated in the constantcurrent mode, well below its maximum slew rate. Therefore, the force between the tunneling tip and cantilever was constant, and was ignored in our calculations. De-tails of the instrumentation are described elsewhere. The AFM measurements were done in a glove box under dry nitrogen. The partial pressure of water in the dry box was determined by dew-point measurements to be less than 1 /im of mercury. This is more than 3 orders of magnitude lower than the humidity required for nanometer capillary condensation. 10 As a result the measured attractive forc...

A series of low-melting phthalonitrile oligomers were prepared in which variable-length multiple aromatic ether linkages interconnect the terminal phthalonitrile units. These materials were designed to address the need for a processable resin system with good high-temperature properties. The melt-processable oligomers are obtained using a modified-Ullman ether reaction between a bisphenol and a dihalobenzene to form a hydroxyl-terminated oligomeric intermediate that is endcapped by reaction with 4-nitrophthalonitrile. Viscosity measurements show that the phthalonitrile oligomers are polymerized at a moderate temperature (200°C) using the typical aromatic diamine curing additives, bis[4-(4-aminophenoxy)phenyl]sulfone and 1,3-bis(3-aminophenoxy)benzene. The oligomeric phthalonitrile/diamine mixtures exhibit a low complex melt viscosity (0.01-0.1 Pa s) at 200°C. Differential scanning calorimetric analysis is used to follow the polymerization as the oligomeric phthalonitrile/diamine mixtures are heated to elevated temperatures. Thermal and dynamic mechanical properties of thermally-cured oligomeric phthalonitrile polymers are systematically evaluated and compared with those of two other high temperature thermosetting phthalonitrile polymers, 4,4~-bis(3,4-dicyanophenoxy)biphenyl and 1,3- bis(3,4-dicyanophenoxy)benzene. After thermal treatment at 425°C for 8 h, the oligomeric phthalonitrile polymers exhibit char yields of 70% when heated to 1000°C in flowing nitrogen and decomposition temperatures in excess of 500°C when heated in either flowing nitrogen or air. Rheometric measurements indicate that the fully cured oligomeric phthalonitrile polymers do not soften or exhibit a glass transition temperature upon heating to 450°C. Overall, studies on the phthalonitrile oligomers and the corresponding polymers reveal an attractive combination of processability, thermal and thermo-oxidative stability and good dynamic mechanical properties for these materials

No abstract

No abstract

Unidirectional carbon fiber‐reinforced phthalonitrile composite panels were fabricated by prepreg consolidation with bis[4‐(4‐aminophenoxy)phenyl]sulfone (p‐BAPS) as the phthalonitrile curing additive. Rheometric measurements and elevated‐temperature, short beam shear tests were used to evaluate the cure of the composite as a function of the cure and postcure conditions. These techniques revealed that a fully cured phthalonitrile composite was obtained when the composite was heated at 375°C for 8 hours. Room‐temperature mechanical properties of the cured composite were then evaluated using short beam shear, tension, and flexural tests. The results are compared with those obtained by curing the phthalonitrile with 1,3‐bis(3‐aminophenoxy)benzene (m‐APB). The data indicate that substitution of p‐BAPS for m‐APB has little effect on the mechanical properties of the cured composite. Elevated‐temperature, short beam shear studies up to 371°C show that the cured phthalonitrile composite retains approximately 70% of its room‐temperature apparent interlaminar shear strength. The composite also retains 70% of its room‐temperature storage modulus up to 450°C. Polym. Compos. 25:554–561, 2004. © 2004 Society of Plastics Engineers.