Reprocessable and degradable thermoset with high Tg cross-linked via Si-O-Ph bonds

The introduction of reversible covalent bonds makes some thermosets reprocessable and degradable. However, the low temperature at which the reversible reactions occur severely limits heat-resistant properties of these thermosets, and their glass transition temperatures (T(g)s) rarely exceed 200 degrees C. We propose a novel way to cross-link the benzoxazine resin [poly(P-mdes)] via dynamic Si-O-Ph bonds. The results show that the dynamic Si-O-Ph bonds are reversible only at high temperature, which enables poly(P-mdes) to be a high heat-resistant thermoset with its T-g (tan delta) reaching 301 degrees C. This T-g is much higher than those of all the known reprocessable thermosets so far. Besides, poly(P-mdes) can be repeatedly reprocessed under hot pressing conditions, and still retains 74.0% of the original tensile strength, even after the fourth reprocessing procedure. Under acidic conditions (pH = 1), poly(P-mdes) is also degraded, and thus can be recycled.