A new parameter set (RDA-DR2.21_Inv) is shown to reproduce both the geometries and the physical and mechanical properties of three polycyanurates based on 2,2-bis(4-cyanatophenyl)propane, 1,1-bis(4-cyanatophenyl)ethane and 1,3-bis(4-cyanatophenyl-1-(1-methylethylidene))benzene. The results show a trend of internal stress within the molecule caused by varying backbone structure. The simulated Young's modulus of elasticity decreases in the order: 1,1-bis(4-cyanatophenyl)ethane > 2,2-bis(4-cyanatophenyl)propane > 1,3-bis(4-cyanatophenyl-1-(1-methylethylidene))benzene (from 31.11 to 14.33 GPa). Molecular dynamics simulations, carried out on 1,1-bis(4-cyanatophenyl)ethane and 1,3-bis(4-cyanatophenyl-1-(1-methylethylidene))benzene, reproduce the empirical glass transition temperatures (T-g) of the polycyanurates well, although the calculated T-g values are slightly overestimated when compared with the empirical data, presumably due to the 'perfect' nature of the simulated network.