Abstract
Recently, benzoxazine has been reported as a new class of high performance thermosetting resin with ring-opening reactivity, which has superior properties such as high heat-resistance, high glass transition temperature (Tg) and small volumetric shrinkage. Various poly-functionalized benzoxazines are prepared from corresponding phenol resins for studies of their properties - exothermic hardening behavior, thermal decomposition and thermo-mechanical properties after thermal curing. The benzoxazines exhibit exothermic hardening at the temperature from 230℃ to 250℃, from the results of differential scanning calorimetric analysis. Thermal decomposition of any cured benzoxazines commence in the vicinity of 300℃, despite their different structures in spacers. Benzoxazine with methylene substituent in phenol-spacers, reveal high residual weight over 50wt% at 700℃. In addition, the benzoxazine with metylene-spacer showed higher glass transition temperature (Tg). The crosslinking densities (ρ) were calculated from the results of dynamic mechanical analysis. Then, relationship between cross-linking density and thermo-mechanical properties were studied. Tg of benzoxazines were risen with increase of cross-linking density, in spite of their similar property on coefficient of thermal expansion. Storage modulus of Benzoxazines at temperature less than Tg was lowered with decrease of crosslinking density. The spacer constituted of benzoxazine structure which affected the modulus and glass transition temperature on the basis of results of dynamic mechanical analysis.
