Effect of carbon fiber volume fraction on 6H to 4H-SiC polytype transformation

In this study, polycrystalline α-SiC composed of 55.7?wt.% 6H-SiC, 35.1?wt.% 4H-SiC with different volume fractions of carbon fibers (0–5–10–15–20%) was successfully sintered by spark plasma sintering technique at 2000°C and 35?MPa of applied pressure. The micrographs obtained from scanning electron microscopy revealed that the sintered samples were composed of equiaxed SiC grains. Results indicated that the presence of carbon fibers retarded the SiC densification process, decreased their relative densities and increased their porosity. Additionally, according to quantitative phase analysis by the Rietveld method during the sintering step, it was found that the 6H to 4H transformation has taken place. Increasing the carbon fibers content accelerated this trend as the sample containing 20?vol.% carbon fiber was consisted of 85.5?wt.% 4H-SiC.     

The Evolution of the Total Synthesis of Rocaglamide

The complex flavagline, (?)‐rocaglamide, possesses a synthetically intriguing tricyclic scaffold with five contiguous stereocenters and also exhibits potent anticancer, anti‐inflammatory and insecticidal activity. This full account details distinct approaches to (±)‐ and (?)‐rocaglamide utilizing Brønsted acid catalyzed and asymmetric Pd⁰‐catalyzed Nazarov chemistry developed in our laboratory, respectively. The successful asymmetric synthesis revealed unforeseen mechanistic complexity that required adjusting our strategy to overcome an unanticipated racemization process, an unusual reversible ring‐cleavage step and a very facile trialkylsilyl group migration.     

Synthesis of new graft copolymers containing polyisobutylene by a combination of the 1,1‐diphenylethylene technique and cationic polymerization

The synthesis of macroinitiators for the cationic polymerization of isobutylene via radical polymerization is presented. The 1,1‐diphenylethylene system was used to obtain macroinitiators consisting of 4‐chloromethylstyrene and methyl methacrylate units. The resulting polymers were used for the cationic polymerization of isobutylene, yielding graft copolymers that were characterized by gel permeation chromatography and NMR. The dependence of the molar mass and polydispersity on the temperature and monomer concentration was studied. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3725–3733, 2002