Addition–fragmentation chain transfer: Molecular weight distributions and retardation in the system methyl methacrylate/methyl α‐(bromomethyl)acrylate

A detailed investigation of addition–fragmentation chain transfer (AFCT) in the free‐radical polymerization of methyl methacrylate (MMA) in the presence of methyl α‐(bromomethyl)acrylate (MBMA) was carried out to elucidate mechanistic details with efficient macromonomer synthesis as an underlying goal. Advanced modeling techniques were used in connection with the experimental work. Curve fitting of simulated and experimental molecular weight distributions with respect to the rate coefficient for addition of propagating radicals to MBMA (k_add) over 60–120 °C resulted in E_add = 21.7 kJ mol^?1 and A_add = 2.18 × 10⁶ M^?1 s^?1 and a very weak temperature dependence of the chain‐transfer constant (E_add ≈ E_p). The rate coefficient for fragmentation of adduct radicals at 60 °C was estimated as k_f ≈ 39 s^?1 on the basis of experimental data of the MMA conversion and the concentration of 2‐carbomethoxy‐2‐propenyl end groups. The approach developed is generic and can be applied to any AFCT system in which copolymerization does not occur and in which the resulting unsaturated end groups do not undergo further reactions. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2640–2650, 2004     

Endoscopic Observation of Tissue by Narrowband Illumination

We propose a new illumination method for a medical endoscope: narrow band imaging (NBI), in which the spectral bandwidth of the filtered light is narrowed. To confirm how the spectral specifications of the filtered light influence a reproduced image, an experiment was conducted observing the endoscopic images of the back mucosa of a human tongue. In addition, the effect of NBI on endoscopic images was investigated through preliminary clinical tests in colonoscopy and upper gastrointestinal endoscopy. It has been shown that NBI can enhance the capillary pattern and the crypt pattern on the mucosa. These patterns are useful features for diagnosing an early cancer.     

Analysis of Spectral Reflectance Using Normalization Method from Endoscopic Spectroscopy System

Objective assessment of gastrointestinal mucosal color is extremely important in the endoscopic diagnosis of digestive tract disease. In this paper, we propose a method to clarify the spectral characteristics of gastric and colon cancer. A large number of spectral reflectance data of mucous membrane are measured by the endoscopic spectroscopy system (ESS) in the National Cancer Center Hospital East, Kashiwa, Japan and the Department of Internal Medicine, Self-Defense Force Center Hospital, Tokyo, Japan. We assume that early cancer appears primarily in the spectral data of short wavelength, because it is usually present in a superficial cell where short wavelength light is scattered more strongly than long wavelength light. To identify the features in the short wavelength components, the spectral reflectance was divided by the reflectance of a long wavelength. We investigated the possibility of distinguishing early cancer from normal spectral data through statistical analysis, employing the projection axis as the mean difference between them. Early cancer and normal spectral data were projected on the projection axis, and the Student’s T-test was applied to evaluate the mean of the distribution between these data.     

Enantioselective spiro ene-carbocyclization of 1,6-enynes catalyzed by tropos rhodium(I) complex with skewphos ligand

A tropos rhodium(I) complex having skewphos ligand is shown to be a highly enantioselective catalyst for asymmetric ene-type carbocyclization of 1,6-enynes with tri-substituted olefins to control quaternary stereogenic centers or spiro-rings.     

Basic study of the gelation of dimethacrylate‐type crosslinking agents

An investigation was made of the gelation of dimethacrylate‐type crosslinking agents in view of an application for separation media. The study mainly centered on a crosslinking agent, glycerol dimethacrylate (GDMA), which is relatively hydrophilic because of a hydroxyl group in the middle of its structure. The gelation of GDMA was compared with that of other hydrophobic crosslinking agents such as ethylene glycol dimethacrylate and 1,6‐hexanediol dimethacrylate. The diluents used in the study were toluene, toluene with methanol, and cyclohexanol. The gelation was observed in real time with a charge coupled device camera and dynamic light scattering (DLS). Also, the separated dry gels were extensively characterized with scanning electron microscopy, BET (N₂ absorption and desorption isotherm), and Fourier transform infrared. DLS analysis showed a stronger molecular interaction of GDMA gelation in toluene, whereas this interaction was much weaker in an alcoholic solvent such as toluene with methanol or cyclohexanol. This indicated that GDMA gelation might proceed through hydrogen bonding as well as a crosslinking reaction of vinyl groups. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 949–958, 2006     

Pressure response of Raman spectra of water and its implication to the change in hydrogen bond interaction

In situ Raman spectroscopic measurements of water in the region of OH vibration were conducted up to 0.4 GPa at 23 and 52 degrees C. The frequencies of the decomposed OH stretching bands initially decreased with increasing pressure, reached a minimum at 0.15 GPa and increased up to 0.3 GPa and then decreased, which corresponds to the variations of the strength of hydrogen bonding. This variation was observed at 23 degrees C, but not at 52 degrees C, which suggests a change in pressure dependence on the hydrogen bond interaction between these two temperatures. Based on the equilibration model between hydrogen-bonded and nonhydrogen-bonded molecules, the present experimental results indicate that the pressure variation of the viscosity depends on the ratio of hydrogen-bonded molecules, rather than the strength of hydrogen bonding between molecules.     

Preparation and physical properties of flame retardant acrylic resin containing nano-sized aluminum hydroxide

Poly(methylmethacrylate) (PMMA) shows high strength and transparency but is a flammable material. In this study, the surface of aluminum hydroxide was modified with methacrylate containing phosphoric acid moieties before dispersion in MMA, and organic-inorganic nano-hybrid materials were obtained by bulk polymerization in the presence of the surface-modified aluminum hydroxide. The resulting hybrid materials retained the high transparency of PMMA, with transparency values similar to that of pure PMMA. Moreover, the flame resistance of the hybrid materials was improved in comparison with that of pure PMMA, with depression of the horizontal burning rate becoming a maximum at an inorganic content of 3 wt%. These results suggest that the use of aluminum hydroxide surface-modified with phosphoric acid groups is an efficient method for obtaining good performance fire-resistant polymer materials.     

Changeable reactivity of ketyl radicals derived from 2-bromomethyl-2-(3-butenyl)benzocyclic-1-alkanones depending on electron transfer conditions employed

Photoinduced electron transfer reaction of 2-bromomethyl-2-(3-butenyl)benzocyclic-1-alkanones with amines afforded 5-exo radical cyclization products while electron transfer reaction with samarium diiodide produced cyclopropanols.