Highly monodisperse crosslinked polymethylmethacrylate microparticles by dispersion polymerization

Highly monodisperse polymethylmethacrylate (PMMA) microparticles crosslinked with carboxylic group-containing urethane acrylates (CUA) were produced by simple dispersion polymerization in methanol solution. In contrast to conventional crosslinkers, the CUA employed as a crosslinker was excellent for maintaining the monodispersity of PMMA microparticles even at moderate crosslinker concentrations (to about 5 wt%). It was believed that the CUA helped form the monomer-swellable surface of primary particles, because of the structurally long tetramethylene oxide groups in the molecule. Carboxylic groups in the molecular backbone resulted in larger primary particles by increasing the solubility of the monomer mixture in the medium. Owing to these larger primary particles, the crosslinked PMMA particles showed lower polymerization rates than the linear ones during particle growth. However, at high CUA concentrations (about 10 wt%), bimodal distributions were observed. This was attributed to the high crosslinking density of the primary particle surfaces. Therefore, monomer diffusion toward the polymer phase was restricted, resulting in more favorable secondary nucleation in the medium. Received: 12 May 1998 Accepted: 19 August 1998     

Electrorheological properties of carbon nanotube/polyelectrolyte self‐assembled polystyrene particles by layer‐by‐layer assembly

Sulfonated polystyrene (PS) particles were prepared by the sulfonation of PS microspheres with H₂SO₄. Then, composite particles were synthesized by layer‐by‐layer (LbL) self‐assembly with funtionalized multiwall carbon nanotubes (fMCNTs) and polyelectrolytes on sulfonated PS particles. The amount of fMCNTs on PS particles was adjusted by controlling the number of fMCNT layers by LbL self‐assembly. Composite particles were characterized by ζ‐potential analysis, scanning electron microscopy, and thermal analysis. The electrorheological (ER) properties of composite particles in insulating oil was investigated with varying the number of fMCNT layers under controlled electric fields. It was observed that the number of fMCNT layers was a critical factor to determine the ER properties of composite particles. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 1058–1065, 2008     

Improved properties of polyfluorenevinylenes by introduction of carbazole units

New electroluminescent polyfluorenevinylenes (PFV) copolymers with carbazole group, CzPFVs, have been synthesized by the GILCH polymerization. The carbazole groups were introduced as pendant to increase the electron rich ability of the copolymers. All CzPFVs exhibited absorption spectra with maximum peaks at around 417 nm. In the PL emission spectra of CzPFVs, maximum peaks around 463 nm and shoulder peaks around 490–500 nm were exhibited. By adjusting the feed ratios of carbazole groups in the CzPFVs, it is possible to have the higher current density and brightness, and the lower turn‐on voltage due to increasing hole injection ability. The maximum luminescence of CzPFV9 was 2003 cd/m² at 7 V. The introduction of carbazole contents in PFVs can enhance the device performance to result in stable PL and EL spectra with high current density and brightness due to the increased hole injection ability and reduced interchain interaction between polymer backbones. Especially, the 1:1 mixture of CzPFV10 and PVK didn't show aggregation effect in PL spectra even after annealing the thin film at 80 °C up to 60 min, since the interchain interaction among polymer backbones with fluorenevinylene units was reduced. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4407–4419, 2008     

Biocompatible microspheres based on acetylated polysaccharide prepared from water-in-oil-in-water (W1/O/W2) double-emulsion method for delivery of type II diabetic drug (exenatide)

Polysaccharide microspheres (PAMs) from acetylated pullulan were designed for the long-term delivery of peptide/protein drugs, as an alternative to a PLGA depot system. Three kinds of samples were obtained according to their different degrees of acetylation (0.8(PA1), 1.5(PA2), 2.3(PA3) acetyl groups in one glucose unit in pullulan), and then utilized to prepare a microsphere via a water-in-oil-in-water (W₁/O/W₂) emulsion method. The mean particle size of PAMs was shown to be in a range between 35 and 110 μm, as determined by a particle size analyzer. In order to evaluate their potential as a depot for protein/peptide delivery, exenatide, a drug used for the treatment of type II diabetes, was employed. The encapsulation efficiency of exenatide in PAMs was 69.1%, 80.4%, and 90.3% in PAM 1, PAM 2, and PAM 3, respectively. Although the release of exenatide from the PLGA microspheres evidenced a fast and high-burst behavior, PAMs evidenced a sustained release profile for 21 days. After 16 days, the released peptide was found to have a molecular weight almost identical to that of native exenatide, indicating that the stability of the peptide in the PAMs was maintained. The tissue reaction evidenced by the PAM was characterized by minimal foreign body reaction and minimal configurations of immune cells such as neutrophils and macrophages, but that of the PLGA microspheres was characterized by relatively elevated inflammation. On the basis of these results, we have concluded that the PAM may provide new insights into the development of new protein/peptide depots in long-term delivery.     

Autogenic synthesis of green- and red-emitting single-phase Pr(2)O(2)CO(3) and PrO(1.833) luminescent nanopowders

This Article reveals a rare synthesis of pure Pr(2)O(2)CO(3) (POC) nanopowder by thermolysis (700 °C) of a single chemical precursor in an autogenic reaction. The autogenic thermolysis of praseodymium acetate is a solvent-free, efficient, and straightforward approach yielding luminescent POC nanoparticles. The as-prepared POC nanopowder converted to PrO(1.833) (PO) powder via combustion. Methodical morphological, structural, and compositional characterizations of POC and PO powders are carried out, supported by mechanistic elucidation and the photoluminescent properties.     

Gas chromatography‐mass spectrometric method for the screening and quantification of illicit drugs and their metabolites in human urine using solid‐phase extraction and trimethylsilyl derivatization

A simple and rapid GC‐MS method has been developed for the screening and quantification of many illicit drugs and their metabolites in human urine by using automatic SPE and trimethylsilylation. Sixty illicit drugs, including parent drugs and their metabolites that are possibly abused in Korea, can be monitored by this method. Among them, 24 popularly abused illicit drugs were selected for quantification. Very delicate optimizations were carried out in SPE, trimethylsilylation derivatization, and GC/MS to enable such remarkable achievements. Trimethylsilylated analytes were well separated within 21 min by GC‐MS. In the validation results, the LOD of all the analytes were in the range of 2–75 ng/mL. The LOQ of the quantified analytes were in the range of 5–98 ng/mL. The linearity (r²) of the quantified analytes ranged 0.990–1.000 in each concentration range between 10 and 1000 ng/mL. The mean recoveries ranged from 62 to 126% at three different concentrations of each analyte. The inter‐day and inter‐person accuracies were within ?13.3～14.9%, and ?10.1～13.0%, respectively, and the inter‐day and inter‐person precisions were less than 12.9%. The method was reliable and efficient for the screening and quantification of abused illicit drugs in routine urine analysis.     

The Design of Polymer‐based Nanocarriers for Effective Transdermal Delivery

This study reports a facile and practical means to non‐invasively deliver biologically active ingredients through the skin using polymer‐based nanocarriers. For this, polymer nanocapsules were fabricated with different surface charges as well as glass transition temperatures and we observed their ability to deliver the encapsulated active ingredient, coenzyme Q10, through the skin layer. Direct imaging of a probe molecule, Nile Red, and a matrix polymer labeled with fluorescence moiety, Lucifer Yellow, allowed us to demonstrate that the probe molecule readily permeates into the deep skin, while the matrix polymer stays in the stratum corneum layer due to electrostatic interactions. Quantitative characterization of the penetrating amount of coenzyme Q10 using the Frantz cell method proved that, to achieve improved delivery efficiency, the nanocapsule should have a low glass transition temperature as well as positive surface charges.

     

\mathfrak D -parallelism of normal and structure Jacobi operators for hypersurfaces in complex two-plane Grassmannians

In this paper, we give non-existence theorems for Hopf hypersurfaces in complex two-plane Grassmannians $G_2(\mathbb{C }^{m+2})$ with $\mathfrak D $ -parallel normal Jacobi operator ${\bar{R}}_N$ and $\mathfrak D $ -parallel structure Jacobi operator $R_{\xi }$ if the distribution $\mathfrak D $ or $\mathfrak D ^{\bot }$ component of the Reeb vector field is invariant by the shape operator, respectively.     

Hopf hypersurfaces in complex two-plane Grassmannians with generalized Tanaka-Webster \mathfrak{D}^ \bot-parallel structure Jacobi operator

Regarding the generalized Tanaka-Webster connection, we considered a new notion of \(\mathfrak{D}^ \bot\) -parallel structure Jacobi operator for a real hypersurface in a complex two-plane Grassmannian G ₂(? ^m+2) and proved that a real hypersurface in G ₂(? ^m+2) with generalized Tanaka-Webster \(\mathfrak{D}^ \bot\) -parallel structure Jacobi operator is locally congruent to an open part of a tube around a totally geodesic quaternionic projective space ?P ⁿ in G ₂(? ^m+2), where m = 2n.     

Real hypersurfaces in complex two-plane Grassmannians with certain commuting condition II

Lee, Kim and Suh (2012) gave a characterization for real hypersurfaces M of Type (A) in complex two plane Grassmannians G ₂(? ^m+2) with a commuting condition between the shape operator A and the structure tensors φ and φ ₁ for M in G ₂(? ^m+2). Motivated by this geometrical notion, in this paper we consider a new commuting condition in relation to the shape operator A and a new operator φφ ₁ induced by two structure tensors φ and φ ₁. That is, this commuting shape operator is given by φφ ₁ A = A φφ ₁. Using this condition, we prove that M is locally congruent to a tube of radius r over a totally geodesic G ₂(? ^m+1) in G ₂(? ^m+2).