Three series of halogenated and non-halogenated polycyanurates are prepared in good yield and purity, and fully characterised. Many of the resulting polymers, formed at room temperature using phase transfer catalysis, can be cast into films with good resilience and high thermal stability (some examples suffer no mass loss when held isothermally at 190 degrees C and only display appreciable losses when held continuously at 300 degrees C). Char yields of 35-65% are achieved in nitrogen depending on backbone structure. Some problems were encountered with solubility, particularly with heavily halogenated dichlorotriazines, which limited molecular weights (M-n = 2000-4000 g mol(-1) depending on backbone structure) although when the phase volume ratio was altered to 0.25 higher molecular weights (M-n = 10,000-30,000 g mol(-1)) were possible. Best solubility was achieved by using aromatic diols with at least two equivalent phenylene units per dichlorotriazine unit. DSC reveals polymerisation exotherms with maxima at 190-260 degrees C (Delta H-p = 35-57 kJ/mol) followed by embrittlement and shrinkage (when heated to 300 degrees C). These phenomena may be due to the formation of poorly formed crystallites (activation energies span 155-380 kJ/mol) combined with thermal isomerisation. (c) 2013 Elsevier Ltd. All rights reserved.