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 T_g 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 T_g 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 T_g for this polymer is 180 °C; the onset of T_g from our empirical DSC measurement is ca. 177 °C, and the extrapolated value of T_g 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 T_g 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.