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A new class of macrocyclic lanthanide complexes, Ln/DTPA-PDA-C(sub n), is developed for cellular labeling and magnetic resonance imaging (MRI) applications. These agents, combining with 3-dimensional MRI microscopy, have broad applications in imaging cell movement and localization in different biological systems in vivo.

A poly(methyl methacrylate)-intercalated graphite oxide/poly(methyl methacrylate) nanocomposite was prepared by emulsion polymerization of methyl methacrylate in the presence of graphite oxide (GO). GO was synthesized by the oxidization of natural graphite powder with KMn[O.sub.4] in concentrated sulfuric acid. The functional groups and microstructure of the oxidized graphite and the composite were carefully characterized by use of X-ray diffraction, infrared, transmission electron microscopy, and elemental analysis. The electrical conductivity and mechanical properties were also measured. Polym. Eng. Sci. 44:2335-2339, 2004. © 2004 Society of Plastics Engineers., INTRODUCTION Conducting polymer composites have been extensively studied because of their potential applications in batteries, antistatic, electromagnetic shielding, electrorheological fluids, and other applications (1-8). Since natural graphite (NG) has high [...]

Michel-addition polymerization of disulfide-based diacrylate and equimolar N-methyl ethylenediamine (MEDA) has formed ABB' type intermediates. The poly(amino ester)s have stimuli-sensitive disulfide bonds in the backbone that can be cleaved under dithiothreitol (DTT), affording these poly(amino ester)s with potential applications.

By combination of high trapping free radical efficiency of the thioketone and resonance of the allylic radical, a new type of mediating agent, 1,3,3-triphenylprop-2-ene-1-thione (TPPT) has been successfully synthesized, and then is used to study controlled free radical polymerization of methacrylates. Very stable TPPT radicals at the end of poly(methyl methacrylate) (PMMA) are detected in the polymerization of MMA using TPPT and AIBN as the control agent and initiator. The MALDI-TOF MS spectra are used to identify terminal groups of the resultant poly(glycidyl methacrylate) (PGMA), and major component of the obtained polymer has the structure, (CH3)2(CN)C-PGMA-C7H9O3. Chain extension reaction tests ascertain formation of the dead polymers during the polymer storage and purification process of the polymers. Owing to very slow fragmentation reaction of the TPPT-terminated polymethacrylate radical and addition reaction of this radical with a primary radical, the growing chain radicals are difficult to be regenerated, leading to an unobvious change of the molecular weight with monomer conversion. The molecular weights of polymers can be controlled by the ratios of monomer/initiator and TPPT/initiator. However, the first order kinetics of the polymerization and the polymers with narrow polydispersity are obtained, and these phenomena are discussed. This study provides useful information on how to design a better controlling agent. [ABSTRACT FROM AUTHOR]

We investigated the effects of molecular weight and film thickness on the crystallization and microphase separation in semicrystalline block copolymer polystyrene- block-poly(L-lactic acid) (PS- b-PLLA) thin films, at the early stage of film evolution (when T < T < T) by in situ hot stage atomic force microscopy. For PS- b-PLLA 1 copolymer which had lower molecular weight and higher PLLA fraction, diffusion-controlled break-out crystallization started easily. For PS- b-PLLA 2 with higher molecular weight, crystallization in nanometer scales occurs in local area. After melting of the two copolymer films, islands were observed at the film surface: PS- b-PLLA 1 film was in a disordered phase mixed state while PS- b-PLLA 2 film formed phase-separated lamellar structure paralleling to the substrate. Crystallization-melting and van der Waals forces drove the island formation in PS- b-PLLA 1 film. Film thickness affected the crystallization rate. Crystals grew very slowly in much thinner film of PS- b-PLLA 1 and remained almost unchanged at long time annealing. The incompatibility between PS and PLLA blocks drove the film fluctuation which subsequently evolved into spinodal-like morphology. [ABSTRACT FROM AUTHOR]

A water-soluble, biodegradable and fluorescent hyperbranched poly(amidoamine) with mannose groups on their surface (M-HPAMAM) has been successfully prepared, and the synthetic strategy includes Michael addition polymerization of diacrylamide with 1-(2-aminoethyl)piperazine and, subsequently, surface modification with mannosamine. The photoluminescence of M-HPAMAM was enhanced significantly due to the surface mannose groups. Incubation of E. coliwith M-HPAMAMs yielded brightly fluorescent bacteria clusters, but the fluorescent intensity of the aqueous solution lowered. This indicates that the M-HPAMAMs have strong affinity with bacteria due to their polyvalent interactions. Based on the size and the amount of bacteria clusters formed, the bacteria with the concentrations higher than 102cfu/mL can be detected. [ABSTRACT FROM AUTHOR]

A facile and versatile method to prepare mesoporous core-shell nanostructures with a reversibly switchable nanoshell is reported. Reversible addition-fragmentation chain transfer (RAFT) functionalities were anchored to the exterior surface of mesoporous silica nanoparticles (MSNs), forming RAFT agent coated MSNs. RAFT polymerization was then conducted to graft a poly(acrylic acid) (PAA) shell onto the exterior surface of MSNs, producing novel smart nanocontainers with a MSN as the container and a pH-responsive PAA nanoshell as a smart nanovalve. The PAA nanovalve can control the access of guest molecules to and from the MSN nanocontainer. This core-shell nanostructure should have potential applications in drug and gene delivery. [ABSTRACT FROM AUTHOR]

The preparation of exquisite hierarchical worm-like silica nanotubes by a simple sol–gel method is successfully achieved for the first time. Poly(2-(dimethylamino)ethyl methacrylate)-grafted multiwall carbon nanotubes (MWNT-g-PDMAEMA) were used as a sacrificial template, subsequent hydrolysis and polycondensation of tetraethoxysilane-produced MWNT–silica nanocomposites with lots of silica nanowires arranged on their surfaces. The length of the silica nanowires can be controlled by the deposition time of silica. After the templates were removed by calcination in air, hierarchical worm-like silica nanotubes with some of the characteristics of mesoporous materials, such as large surface area, multiple pore distribution and large pore volume, were obtained. [ABSTRACT FROM AUTHOR]

Three-armed star-shaped poly(ester amine) was synthesized by Michael addition polymerizations of equal molar ratio of ethylene glycol diacrylate (EGDA) and piperazine (PZ) in the presence of a small amount of multifunctional monomer, 1,3,5-triacryloylhexa-hydro-1,3,5-triazine (TT) in CHCl3. When the polymerization proceeded almost completely, the molecular weight of the polymers formed were determined by the feed molar ratio of difunctional monomer to multifunctional monomer, and the molecular weight distribution (Mw/Mn) approached the theoretical value (Mw/Mn =1+1/f). The mechanism of the polymerization was investigated by ¹H NMR and Gel permeation chromatography (GPC). The monomer concentration and the molar ratio of difunctional monomers/multifunctional monomer played an important role in the polymerization. [ABSTRACT FROM AUTHOR]

The atom transfer radical dispersion polymerization of 4-vinylpyridine (4VP) in an ethanol/H2O mixture displayed two stages of polymerization; the first stage is the formation of a diblock copolymer with the polymerization rate of 1.21 mol·L-1·h-1before 1 h of polymerization, and the second is the main polymerization in micelles formed from the aggregation of the resultant block copolymers with the polymerization rate of 0.009 mol·L-1·h-1. The 2-bromoisobutyryl-terminated poly(ethylene glycol) methyl ether used in the polymerization acts as both a stabilizer and an initiator. The stable micelles with functional core were synthesized by a one-pot strategy via atom transfer radical dispersion copolymerization (ATRDCP) of 4VP and N,N‘-methylenebisacrylamide (MBA) in an ethanol/H2O solution for the first time. In the initial stage of polymerization, 4VP and MBA were copolymerized to form a block copolymer, PEG-b-(4VP-co-MBA), with pendent unreacted vinyl groups, and after phase separation at a critical chain length of P4VP-co-PMBA, the cross-linking reaction and polymerization occurred at the same time, resulting in cross-linked micelles. The volume ratio of ethanol/H2O had a big influence on the ATRDCP. An increase in the relative amount of ethanol in the solvent mixture will increase the solubility of P4VP in the polymerization system, the phase separation will be postponed, and the critical chain length of 4VP blocks at the phase separation becomes longer. As a result, the particles size and the 4VP content in the resultant micelles increase. The Au/polymer composite nanoparticles were successfully prepared by complexation of P4VP with HAuCl4and following reduction with NaBH4. [ABSTRACT FROM AUTHOR]

Heteroarm H‐shaped terpolymers, [(poly(L‐lactide))(polystyrene)]poly(ethylene oxide)[(polystyrene)(poly(L‐lactide))], [(PLLA)(PS)]PEO[(PS)(PLLA)], in which PEO acts as a main chain and PS and PLLA as side arms, have been successfully prepared via combination of reversible addition–fragmentation transfer (RAFT) polymerization and ring‐opening polymerization (ROP). The first step is the synthesis of the PEO capped with one terminal dithiobenzoate group and one hydroxyl group at every chain end, [(HOCH2)(PhC(S)S)]PEO[(S(S)CPh)(CH2OH)] from the reaction of carboxylic acid with ethylene oxide. Then, the RAFT polymerization of styrene (St) was carried out using [(HOCH2)(PhC(S)S)]PEO[(S(S)CPh)(CH2OH)] as RAFT agent and AIBN as initiator, and the triblock copolymer, [(HOCH2)(PS)]PEO[(PS)(CH2OH)], was formed. Finally, the heteroarm H‐shaped terpolymers, [(PLLA)(PS)]PEO[(PS)(PLLA)], were produced by ROP of LLA, using triblock copolymer, [(HOCH2)(PS)]PEO[(PS)(CH2OH)], as macroinitiator and Sn(Oct)2 as catalyst. The target products and intermediates were characterized by 1H NMR spectroscopy and gel permeation chromatography. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 789–799, 2007 [ABSTRACT FROM AUTHOR]

Characterizes poly(styrene-b-p-nitrophenyl methacrylate using atom transfer radical polymerization method. Concentration level of chain radicals; Preparation of hexa-armed stars; Application of unimolecular micelles.

Describes the synthesis and characterization of well-defined block copolymers. Atom transfer radical polymerization; Macromolecular initiator; Structure of block copolymer; Analysis of molecular weight and molecular weight distribution using gel permeation chromatograph.

Discusses the effects of monomer structure of cyclic ketene acetals on the behavior of controlled radical ring-opening polymerization. Conditions and results of free radical ring-opening polymerization; Polymerization mechanism.

A facile strategy for control of the polymer topologies can be achieved simply by tuning the feed molar ratio of catalyst to transfer agent in the controlled radical polymerization. [ABSTRACT FROM AUTHOR]

The copolymerization Of styrene (St) with maleic anhydride (MAh) under gamma radiation at room temperature in the presence of benzyl dithiobenzoate (BDTB) was found to display "living" nature evidenced by constant concentration of chain radicals during the copolymerization, linear evolution of molecular weights with conversion and narrow molecular weight distribution (M[sub w]/M[sub n] = 1.23-1.35). The compositional analysis and the sequence structural information of the copolymers obtained from DEPT (Distortionless Enhancement by Polarization Transfer) experiments demonstrate that the copolymers obtained also possess strictly alternating structure. [ABSTRACT FROM AUTHOR]