Fluorene end-labeled polystyrene was prepared by atom transfer radical polymerization with 9-bromofluorene as the initiator. Reactions were carried out in bulk or tetrahydrofuran solutions at temperatures of 80 8C or above. Analysis by gel permeation chromatography indicated that the polymers formed had low polydispersities with molecular weights consistently 2-5 times higher than calculated based on monomer-to-initiator ratios. Coupling of two fluorenyl radicals, formed by activation of the 9-bromofluorene, was found to compete with initiation, leading to the higherthan-expected molecular weight values while giving rise to a fluorene dimer. UV-vis spectrometry indicated near-quantitative fluorene labeling of the polystyrene. V V C 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2657-2665, 2005

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Summary: Polystyrene with high amounts of end‐labeling was synthesized using initiating systems comprised of conventional radical initiators and 2,7‐dibromofluorene or other fluorene derivatives in an adaptation of reverse atom transfer radical polymerization (RATRP). Benzoyl peroxide (BPO) or 2,2′‐azoisobutyronitrile (AIBN) were decomposed and allowed to react with 2,7‐dibromofluorene, 2‐bromofluorene, or fluorene in the presence of ligand‐bound CuX2 allowing for abstraction of the 9‐H from the fluorenyl species and the establishment of an equilibrium between the subsequent active radical and the dormant alkyl halide. Gel permeation chromatography (GPC) traces indicated CuCl2‐catalyzed reactions produced polymers possessing narrow polydispersity index (PDI) values <1.3 with AIBN and 2,7‐dibromofluorene systems, while analogous reactions catalyzed using CuBr2 were less controlled (PDI > 1.7). Analysis of the polymers using UV‐vis spectroscopy and UV‐GPC demonstrated competition between initiation from both the conventional radical initiator and fluorenyl species generating polymers end‐labeled with both the 2,7‐dibromofluorene and isobutyronitrile groups. Fluorene or 2‐bromofluorene as co‐initiators led to lowered amounts of end‐labeling, but the polymers generally possessed lower PDI values compared to 2,7‐dibromofluorene systems. magnified image

In this work, we study three aluminum oxides (alpha, gamma, boehmite) and various oxidized metallic aluminum powders to observe their dehydration and decomposition behavior using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and scanning electron microscopy (SEM). We find that a temperature increase to the aluminum oxides (aluminas) reduces physically adsorbed water molecules to reveal the presence of hydroxyl groups. All three aluminas contained bridged hydroxyls located at 3670 cm−1; we found additional surface hydroxyls, which varied based on the oxidation state of the aluminum atom. Oxidized metallic aluminum powders that were aged resulted in similar behavior; however, the results differed depending on the method of aging. We find that naturally aged aluminum (NA-Al) powders with heavy oxidation in the form of the tri-hydroxide decomposed and did not reveal any detectable surface hydroxyl peaks. When aged using artificial methods (AA-Al), we find both surface hydroxyls, including bridged hydroxyls at 3670, 3700, and 3730 cm−1, and a remaining boehmite-like surface. These results show that metallic aluminum powders can be tailored for specific applications, regardless of age. It also elucidates different ways to pre-process the powders to control the surface oxide layer, corroborated by comparison with the models oxides studied herein.

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