SYNOPSISLiving cationic polymerization of alkoxyethyl vinyl ether [ CH, = CHOCH,CH,OR R CH, (MOVE), C2H5 (EOVE) ] and related vinyl ethers with oxyethylene units in the pendant was achieved by 1-(isobutoxy)ethyl acetate ( 1)/Etl.5AlC1,.5 initiating system in the presence of an added base (ethyl acetate or T H F ) in toluene at 0°C. The polymers had a very narrow molecular weight distribution (A?,,,/A?,, = 1.1-1.2) and the M,, proportionally increased with the progress of the polymerization reaction. On the other hand, the polymerization by 1/EtA1C12 initiating system in the presence of ethyl acetate, which produces living polymer of isobutyl vinyl ether, yielded the nonliving polymer. When an aqueous solution of the polymers thus obtained was heated, the phase separation phenomenon was clearly observed in each polymer at a definite critical temperature ( T p s ) .For example, Tps was 70°C for poly(MOVE), and 20°C for poly(E0VE) (1 wt % aqueous solution, M n -2 X l o 4 ) . The phase separation for each case was quite sensitive (AT,, = 0.3-05°C) and reversible on heating and cooling. The T,, or AT,, was clearly dependent not only on the structure of polymer side chains (oxyethylene chain length and w-alkyl group), but also on the molecular weight (A?,, = 5 X lo3-7 X lo4) and its distribution. 0

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A stoichiometric SiC‐polycrystalline fiber (Tyranno SAR) shows excellent heat‐resistance up to 2000°C and relatively high strength around 3 GPa. However, presently, the higher strength has been eagerly required to extend the application field. To achieve increase in the strength, we have to perfectly understand the dominating factors of the strength. We specified the dominating factors (defects) by detecting the first fracture surface and the fracture origin. This type of fiber was found to contain several types of defects, and showed that the strength was decreased in inverse proportion to one‐half power of the defect size. The causes of the defects were clarified by an actual experimental analysis and calculation results. Tyranno SA was produced by a conversion process from an amorphous Si‐Al‐C‐O fiber to SiC polycrystalline structure accompanied by a release of CO gas. During the conversion process, undesirable change in the composition (vaporization of SiO gas), which causes an increase in the residual carbon (one of defects), occurs. To prevent the vaporization of SiO gas, we newly developed a favorable condition by shifting the equilibrium state of the conversion process, and then could remarkably reduce both an abnormal SiC grain growth and the residual carbon.