No abstract

Various difluoro functionalized aromatic 1,3,5-triazine monomers were prepared. A series of poly(1,3,5-triazine−ether)s was synthesized by polycondensation with 4,4‘-hexafluoroisopropylidenebis[phenol]. The polymers have excellent thermal stability and are amorphous with glass transition temperatures in the range 190−250 °C. In order to examine the potential application these polymers may possess for use in organic electroluminescent devices, the redox properties were studied by cyclic voltammetry. It was found that the monomers have high electron affinities and reach LUMO values in the range of −2.7 to −3.1 eV. This opens the possibility to utilize 1,3,5-triazine-containing materials as electron injecting/hole blocking layer in LEDs. Initial LED results are in accordance with these high electron affinities.

Previous fundamental work on the solvent properties of carbon dioxide by the research groups of McHugh, DeSimone, Johnston, and Eckert has been used as a road map for the design of materials that will be miscible with CO2 at relatively moderate pressures. In this initial work, judicious side chain functionalization of an oligomeric silicone has been shown to produce a material whose phase behavior in CO2 resembles that of a fluorinated polyether. The phase behavior results are quite dramatic in that addition of only five ester-functional side chains to the silicone polymer lowers the cloud point curve at 22 °C by 2500 psi. It was also observed that addition of simple alkyl side chains raises the cloud point pressures of the silicone in CO2. This latter observation is consistent with results on the phase behavior of poly(n-alkyl acrylates) in CO2 that showed that increasing alkyl content (i.e., increasing alkyl chain length) also raises cloud point pressures.

Molecular recognition in Langmuir monolayers at the air−water interface as a function of headgroup orientation and substrate using isotherms and in-situ Fourier transform infrared (FT-IR) reflection spectroscopy has been investigated. Isotherm measurements show that urea and 2,4,6-triaminopyrimidine (TAP) are specifically bound to barbituric acid lipid monolayers. As expected, TAP causes a larger shift in the limiting area of the isotherms than urea due to steric requirements. The peak positions of the CH stretching vibrations of the barbituric acid lipids indicate that the alkyl chains of barbituric acid lipids 1−3 are in a close-packed all-trans conformation both before and after the recognition process. The complexation of TAP is monitored in situ using external reflection FT-IR spectroscopy through shifts of the conformation-sensitive carbonyl frequencies in the head group region, while no shifts in the carbonyl peaks are observed when urea recognizes the lipid monolayers.

A series of low molecular weight dimeric 1,3,5-triazine ethers with high glass transition temperatures is synthesized from 2-(4-fluorophenyl)-4,6-diphenyl-1,3,5-triazine and various bisphenols. The thermal and electrochemical properties of these materials are examined using differential scanning calorimetry and cyclic voltammetry, respectively. The glass transition temperatures (T g ) are in the range of 106-144°C, and all of them have similar thermal stability and show no weight loss up to 380°C in thermogravimetric measurements. Some of these dimers form stable glasses which do not recrystallize on annealing at or above the T g . Cyclic voltammetry studies reveal that these compounds undergo reversible reduction between -2.09 and -2.27 V vs ferrocene/ferrocenium as internal standard which correspond to LUMO values between -2.5 and -2.7 eV, respectively. The application of one of these dimeric ethers as a hole-blocking/electron-transport material in organic light-emitting devices is demonstrated.