Method for producing catalysts having increased strength and decreased volume reduction

Abstract

A series of four novel diamine-based benzoxazines containing aliphatic spacer groups in their structures were synthesized by the condensation of formaldehyde, phenol and aromatic diester diamine obtained by reduction of their precursor dinitro compounds. The four aromatic diamines synthesized are ethane-1,2-diyl bis (4-aminobenzoate), butane-1,4-diyl bis (4-aminobenzoate), hexane-1,6-diyl bis (4-aminobenzoate), and octane-1,8-diyl bis (4-aminobenzoate). The chemical structures of diamine benzoxazines are confirmed by Fourier-transform infrared (FTIR) and nuclear magnetic resonance spectroscopy (1H and 13C NMR). The curing properties with respect to the basic benzoxazine structure of the monomer were studied by differential scanning calorimetry (DSC). The softening points, onset of cure temperatures and the heat of polymerization have all decreased with increasing spacer length. DSC of polybenzoxazines indicated decrease of glass transition temperature (Tg) with increasing spacer length. The thermal behavior of polybenzoxazines was studied by thermo gravimetric analysis (TGA). Higher Td5 and Td10 values were obtained by polybenzoxazines with longer spacer groups but an inversion in thermal stability was observed after Td10. The derivative thermo gram of polybenzoxazine indicated a two stage degradation process due to chain cleavage at Mannich bridge as well as breakdown of polymer chain respectively. The char yield at 700 °C has decreased with increasing spacer length from 47% to 27%. The mechanical properties of glass cloth coated polybenzoxazines were evaluated with dynamic mechanical analysis (DMA). The storage modulus of the composite laminate of polybenzoxazine has increased with increasing spacer group which could be due to improvement in adhesion between fibers and resin with increasing flexibility of the resin.