Monodisperse Cylindrical Micelles of Controlled Length with a Liquid‐Crystalline Perfluorinated Core by 1D “Self‐Seeding”

Precise control over the morphology and dimensions of block copolymer (BCP) micelles has attracted interest due to the potential of this approach to generate functional nanostructures. Incorporation of liquid crystalline (LC) block can provide additional ways to vary micellar morphologies, but the formation of uniform micelles with controllable dimensions from LC BCPs has not yet been realized. Herein, we report the preparation of monodisperse cylindrical micelles with a LC poly(2‐(perfluorooctyl)ethyl methacrylate (PFMA) core via a fragmentation‐thermal annealing (F‐TA) process, resembling the “self‐seeding” process of crystalline BCP micelles. The average length of the cylinders increases with annealing temperature, with a narrow length distribution (L_w/L_n<1.1). We also demonstrate the potential application of the cylinders with LC cores as a cargo‐carrier by the successful incorporation of a hydrophobic fluorescent dye tagged with a fluorooctyl group.     

Lanthanide-containing polymer nanoparticles for biological tagging applications: nonspecific endocytosis and cell adhesion

We describe the synthesis and characterization of element-encoded polystyrene nanoparticles with diameters on the order of 100 nm and a narrow size distribution. Individual particles contain ca. 10(3) chelated lanthanide ions, of either a single element or a mixture of elements. These particles were effectively internalized by nonspecific endocytosis into three cell lines associated with human leukemia. Using an assay based upon ICP-MS detection, we could monitor quantitatively cell adhesion induced by cell differentiation of THP-1 cells in response to phorbol ester stimulation (PMA) in single cell type or mixed cultures.     

Botryoidal assembly of cholesteryl-pullulan/poly(N-isopropylacrylamide) nanogels

Hybrid nanogels consisting of cholesteryl-modified pullulan (CHP) and poly(N-isopropylacrylamide) (PNIPAM) were synthesized by graft free-radical copolymerization of N-isopropylacrylamide (NIPAM) onto methacryloyl-substituted CHP nanogels (CHPMA) in water at 50 degrees C in the presence of a water-soluble free radical initiator. Depending on the initial NIPAM/CHPMA ratio, CHP-PNIPAM (CN) nanogels containing 30.8-84.8 wt % PNIPAM were obtained in the form of self-assembled nanoparticles with a hydrodynamic radius (Rh) of 69.0-116.0 nm in water kept at 20 degrees C. Hybrid nanogels of sufficiently high NIPAM content, such as the sample CN90, which contains 79.6 wt % NIPAM, exhibited a two-step response to changes in solution (3 mg/mL) temperature: a decrease in Rh from 93 to 57 nm as the temperature increased from 20 to 35 degrees C, followed by a sharp increase in Rh from 57 nm to 90 nm at 55 degrees C. Both steps in this temperature response were reversible. The multistep response to temperature of the CN nanogels was attributed to the morphology of the nanogels, which are seen as consisting of grape-like (botryoidal) clusters of associated native nanogels held together via cholesteryl cross-linking points and held together by the grafted PNIPAM chains.     

Long-term exposure to CdTe quantum dots causes functional impairments in live cells

Several studies suggested that the cytotoxic effects of quantum dots (QDs) may be mediated by cadmium ions (Cd2+) released from the QDs cores. The objective of this work was to assess the intracellular Cd2+ concentration in human breast cancer MCF-7 cells treated with cadmium telluride (CdTe) and core/shell cadmium selenide/zinc sulfide (CdSe/ZnS) nanoparticles capped with mercaptopropionic acid (MPA), cysteamine (Cys), or N-acetylcysteine (NAC) conjugated to cysteamine. The Cd2+ concentration determined by a Cd2+-specific cellular assay was below the assay detection limit (<5 nM) in cells treated with CdSe/ZnS QDs, while in cells incubated with CdTe QDs, it ranged from approximately 30 to 150 nM, depending on the capping molecule. A cell viability assay revealed that CdSe/ZnS QDs were nontoxic, whereas the CdTe QDs were cytotoxic. However, for the various CdTe QD samples, there was no dose-dependent correlation between cell viability and intracellular [Cd2+], implying that their cytotoxicity cannot be attributed solely to the toxic effect of free Cd2+. Confocal laser scanning microscopy of CdTe QDs-treated cells imaged with organelle-specific dyes revealed significant lysosomal damage attributable to the presence of Cd2+ and of reactive oxygen species (ROS), which can be formed via Cd2+-specific cellular pathways and/or via CdTe-triggered photoxidative processes involving singlet oxygen or electron transfer from excited QDs to oxygen. In summary, CdTe QDs induce cell death via mechanisms involving both Cd2+ and ROS accompanied by lysosomal enlargement and intracellular redistribution.     

Thermal decomposition of amide and imide derivatives of maleated polyethylene

The thermal decomposition behavior of six derivatives of maleated polyethylene was investigated by high‐resolution pyrolysis gas chromatography–mass spectrometry. The results revealed that substituents attached to maleated polyethylene as amides formed from secondary amines were significantly less stable than imides formed from primary amines. Morpholine amide and N‐methylaniline amide derivatives of maleated polyethylene underwent significant decomposition at 160 °C and substantial decomposition at 200 °C. In contrast, the imide derivatives of maleated polyethylene were stable for long periods of time at elevated temperatures. Following 2 min of heating, the first traces of decomposition were detected at 200 °C for the 2‐aminoanthrancene imide derivative, at 255 °C for the 2‐phenethylamine imide, and at 280 °C for the 9‐aminomethylphenanthrene imide. With the exception of the 9‐aminomethylphenanthrene imide, all other derivatives decomposed to form the corresponding amine as the single most significant volatile product. The most likely explanation for this result is that the polymer contained small amounts of succinamic acid that did not close to form the imide. We concluded that the imide was stable even to 315 °C and that the amine was lost from β‐carboxyamide groups present in the sample. In the 9‐aminomethylphenanthrene imide derivative, we observed no loss of amine. Instead, we observed an alternative fragmentation process yielding 9‐methyl phenanthrene. The dependence of the thermal stability of these various derivatives of maleated polyethylene has important implications for the design of reactive‐blending strategies for polyolefins with other functional polymers. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 730–740, 2000     

Synthesis,characterization, and stability of carbodiimide groups in carbodiimide‐functionalized latex dispersions and films

Cyclohexylcarbodiimidoethyl methacrylate (CCEMA) and t‐butylcarbodiimidoethyl methacrylate (t‐BCEMA) were prepared in a two‐step synthesis. These monomers were then used to prepare carbodiimide‐functionalized PBMA and PEHMA latex particles, employing two‐stage emulsion polymerization, with the carbodiimide–methacrylate monomers being introduced only in the second stage under monomer‐starved conditions. During emulsion polymerization, the carbodiimide moiety ( NCN ) was found to be unstable at pH 4, but stable when the pH of the dispersion was increased to 8, using NaHCO₃ as the buffer. Survival of  NCN group against hydrolysis during the polymerization, and during storage in the dispersion, was enhanced by using EHMA as the comonomer (more hydrophobic) and the t‐butyl carbodiimide derivative. The t‐butyl group provides more steric hindrance to the hydrolysis reaction. A decrease in the reaction temperature from 80°C to 60°C was also found to increase the extent of  NCN group incorporation during emulsion polymerization. Under ideal conditions, more than 98% of the  NCN groups in the monomer feed are successfully incorporated into the latex. When these latex particles are mixed with a  COOH containing latex and allowed to dry, polymer diffusion leading to crosslinking occurs. Films annealed at 60°C reach a gel content of 60% in 10 h. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 855–869, 2000     

Interface characterization in latex blend films by fluorescence energy transfer

Immiscible polymer blend films were formed by air drying aqueous dispersions containing mixtures of a high-T_g latex, poly(methyl methacrylate), and a film-forming low-T_g latex, poly(butyl methacrylate-co-butyl acrylate). Fluorescence energy transfer experiments were used to characterize the interfaces in these films, in which one component was labeled with a donor dye and the other with an acceptor. The quantum efficiency of energy transfer (Φ_ET) between the donors and acceptors is influenced by the interfacial contact area between the two polymer phases. As the amount of soft component in the blend is increased, Φ_ET approaches an asymptotic value, consistent with complete coverage of the hard polymer surface with soft polymer. This limiting extent of energy transfer is very sensitive to the total surface area in the film, with correspondingly more energy transfer at constant volume fraction for small hard particles. Some of the details of the energy transfer are revealed through a fluorescence lifetime distribution analysis. The presence of ionic surfactant (sodium dodecyl sulfate) in the dispersion from which the latex blend film is prepared reduces the cross-boundary energy transfer by 30%, which implies that in these films the surfactant decreases the interfacial contact. After annealing the surfactant-free blends above 100°C, we observe an increase in energy transfer, consistent with a broader interface between the two polymers. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1115–1128, 1998     

Analysis of polycyclic aromatic hydrocarbons by ion trap tandem mass spectrometry

An ion-trap mass spectrometer with a wave board and tandem mass spectrometry software was used to analyze gas chromatographically separated polycyclic aromatic hydrocarbons (PAHs) by using collision-induced dissociation (CID). The nonresonant (multiple collision) mode was used to determine the conditions for CID ionization of 18 PAHs. Unlike in electron impact (EI) analysis, the relative abundances of progeny ions of isomers were statistically different (using Student’s t-test) in CID analysis, thus making isomer identification by CID possible. For comparison, CID and EI were applied to the analysis of used motor oil. CID analysis was shown to be more sensitive than EI analysis of the used motor oil. Precision at the 10-ppb level for EI and CID showed relative standard deviations of 5. 2 and 7. 7%, respectively.     

Polymerizable anthracene derivatives for labeling emulsion copolymers

We describe the synthesis of three anthracene–methacrylate monomers [9‐methacryloxymethyl‐10‐methyl anthracene ( 4 ), 9‐methacryloxyethyloxymethyl‐10‐methyl anthracene ( 5 ), and 9‐methacryloxy‐10‐methyl anthracene ( 6 )] as well as their emulsion copolymers containing butylacrylate. When films prepared from latex dispersions containing 4 or 5 were heated, the anthracene (An) group was cleaved from the polymer at temperatures above 120 °C. Lower temperatures induced this reaction when strong acids were present. In 4 and 5 , the polymerizable group is connected to the An ring via a 9‐CH₂O? linkage. The cleavage reaction requires more stringent conditions when the connection involves a benzylic ether ( 5 ) instead of a benzylic ester. Polymers prepared from 6 , with an An? O? bond, were stable for 1 h at 150 °C in the presence of 0.5 wt % p‐toluene sulfonic acid. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1495–1504, 2001     

Polycarbonate particles and dye‐labeled particles by miniemulsion polymerization

We describe the synthesis of several different polycarbonate particles by miniemulsion polymerization. The monomers were allylmethyl carbonate (AlMeC), di(ethylene glycol) bisallylcarbonate (DBAC), and 4‐vinyl‐1,3‐dioxan‐2‐one [vinyl ethylene carbonate (VEC)]. For these polymerizations, higher monomer conversions were obtained with oil‐soluble initiators (azobisisobutyronitrile and benzoyl peroxide) than with a water‐soluble initiator (potassium persulfate). Benzoyl peroxide was particularly effective in yielding particles with a narrow size distribution. Although increasing amounts of a surfactant (sodium dodecyl sulfate) led to smaller particles, the choice of the monomer was the major determinant. For example, in polymerization reactions carried out at 85 °C with benzoyl peroxide as the initiator and with otherwise identical recipes, we obtained particle sizes of 181 nm with AlMeC, 296 nm with VEC, and 203 nm with DBAC. Fluorescent particles were synthesized with comonomers based on the benzothioxanthene nucleus. Because the dyes had poor solubility in the monomers, it was necessary to include typically 20 wt % bromobenzene or dichlorobenzene based on the monomer in the miniemulsion reaction mixture. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1999–2009, 2004