Structure development in aromatic polycyanurate networks modified with hydroxyl-terminated polyethers

A series of polycyanurate networks (PCN), based on the dicyanate of bisphenol A monomer (DCBA), was synthesized in the presence of different contents of hydroxyl-terminated polyethers (PEth), such as polyoxypropylene glycol (PPG) and polyoxytetramethylene glycol (PTMG). We studied the influence of the nature of the oligomeric modifier, initially miscible with DCBA, on the chemical structure, glass transition behaviour, phase morphology and mechanical properties of modified PCN. The possibility of PEth incorporation into the PCN structure through mixed cyanurate ring formation is discussed. A maximum PEth incorporated content of 0.1 mol of PEth per mol of DCBA irrespective of PEth type has been detected. Dynamic mechanical thermal analysis (DMTA) analysis showed the formation of multiphase polymer compositions due to microphase separation of the components occurring during DCBA/PPG curing. The formation of very finely divided morphologies with highly interpenetrated phases, i.e. a PCN-rich phase, a mixed phase of PCN/PPG components and a PPG-rich phase was determined. On the other hand, all PCN/PTMG cured compositions exhibited a single, broad glass transition that shifted to lower temperature as the modifier content was increased and the experimental Tg versus modifier content showed a slight positive deviation from the Fox equation for miscible polymer systems. It can be concluded that the PCN and the PTMG have a higher degree of compatibility than PCN and PPG. The introduction of small additions of modifier (<10 wt%) allow production of the thermosets with high Tg and good strength properties.