Conformational studies of polycyanurates: a study of internal stress versus molecular structure

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 Youngʹs 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 (Tg) of the polycyanurates well, although the calculated Tg values are slightly overestimated when compared with the empirical data, presumably due to the ‘perfect’ nature of the simulated network.