Developing poly(bis-benzoxazines) with improved fracture toughness. 1: Using molecular simulation to determine and predict structure-property relationships

The preparation and characterization of 6,6′-bis(3,4-dihydro-3-methyl-2H-1,3-benzoxazinyl)isopropane (1) and 6,6′-bis(3,4-dihydro-3-methyl-2H-1,3-benzoxazinyl)sulphone (2) using FTIR, 1H and 13C NMR spectroscopy and elemental analysis, is reported. Molecular simulation using both molecular mechanics and molecular dynamics techniques are reported for poly(bis-benzoxazine)s of both materials and the data compare well with literature values for the polymer of (1). The same methodology is extended to predict a Tg for the polymer of the newly-prepared, novel monomer (2), for which no published data currently exist. Preliminary measurements of the thermal behaviour, particularly the Tg values, of the monomers and polymers are made using differential scanning calorimetry (DSC). The latter show very good agreement for 6,6′-bis(3,4-dihydro-3-methyl-2H-1,3-benzoxazinyl)isopropane (an accepted literature value of Tg for this polymer is 180 °C; the onset of Tg from our empirical DSC measurement is ca. 177 °C, and the extrapolated value of Tg from simulation is 180 °C). In the case of the new monomer, 6,6′-bis(3,4-dihydro-3-methyl-2H-1,3-benzoxazinyl)sulphone, the predicted Tg from simulation lies in the range 120-150 °C (with an extrapolated value at 130 °C) and the empirical DSC measurement yields an onset value of ca. 117 °C.