Pyrene-labeled poly(ethylenimine) (PEI) containing different amounts of pyrene per polymer were prepared by reductive amination of PEI with 1-pyrenecarboxaldehyde. Aqueous solutions of the pyrene-labeled PEI (PEI-Py) exhibit typical pyrene monomer and excimer emission, and the excimerto-monomer ratio I E/IM decreases with decreasing Py content of the macromolecule. The excimer emission arises from preassociated pyrene aggregates. Both the monomer and excimer emission intensities increase with decreasing pH of the solution. A decrease in pH of the solution from pH ) 10 to pH ≈ 1.5 led to approximately a 100-fold increase in IM, whereas IE increased just 2-to 3-fold. A major feature of this system is the quenching of the Py fluorescence by amino groups of the PEI. This quenching depends on the degree of protonation of these groups. Model experiments with pyrenemethanol show that triethylamine is 20 times more effective as a quencher than diethylamine in water, implying that most of the quenching in PEI is due to the tertiary amine groups. More interesting is the relative insensitivity of the excimer emission to this quenching process. This selective quenching may be due to the lower energy of the excimer state or the environment of the preassociated pyrenes in the polymer.

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The synthesis, characterization, and properties of colloidal nanostructures in hydrocarbon media are reported. These sterically stabilized structures are unusual in that the stabilizing arms are attached to the particle by photoactive groups, and the arms can be cleaved through irradiation, leading to photoinduced flocculation. In the first step of the synthesis, cross-linked poly(butyl methacrylate) (PBMA) latex particles with controlled functionality (−COOH and −OH groups) were prepared by emulsion polymerization. The purified PBMA latex was neutralized with Cs2CO3 and then transferred to an organic medium (dimethylformamide), where it was converted to lipophilic nanoparticles through chemical modification with 2-bromo derivatives of long-chain 1-phenylalkyl ketones or nitrobenzyl ether derivatives of polyisobutylene. The particles can be dispersed in hydrocarbon solvents. Irradiation leads to flocculation, except that in the presence of hydrocarbon-soluble polymers bearing amino groups, the unprotected particles can be intercepted and flocculation inhibited. These particles serve as an interesting model for precursors to sludge formation in motor oil.

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Since vicinal diols present in carbohydrates may form perborate esters with hydrogen peroxide and borax, such species were loaded onto peroxide bleached and unbleached mechanical pulps. These species were shown to act as slow solid-state oxidizing bleaching agents capable of partially restoring, in the dark, the brightness losses induced on mechanical pulps during direct outdoor and indoor irradiation. More specifically, bleached TMP handsheets were impregnated at pH 9.5 with a mixture comprised of 2 % borax and 1 % hydrogen peroxide. These samples were then irradiated with indoor direct sunlight for 5 hours followed by a dark bleaching period of about 7 hours. At the end of this period brightness readings were recorded and the cycle was repeated, thus simulating indoor handling of paper products. For a 33 hour of cumulative direct indoor sunlight irradiation, the percentage stabilization offered was about 70 %.When a similar solution was used to impregnate unbleached TMP samples, a brightness gain of about 10 ISO points was obtained without using any heat for the bleaching stage. While repeated irradiation and dark storage cycles, over a cumulative period of 37 hours, resulted in approximately 3 points of brightness losses, the initial brightness gains due to bleaching were maintained. The application of perborates possibly offers a potential solution to thermal reversion issues that face most mechanical pulp mills.