Randomly branched polycyanurates - modification of the network structure

Polycyanurates (poly(2,4,6-trisaroxy-1,3,5-triazines)) are built up through a step-growth polycyclotrimerization of difunctional aromatic cyanic acid esters and form an ideally trifunctional randomly branched network, where all initial cyanato groups are linked with the triazine branching units at full conversion. Results on modifications of the high network density of pure polycyanurates are reported for three types of comonomers: monofunctional cyanic acid esters, difunctional phenols and difunctional aromatic glycidyl ethers. Using the coreaction of mono- and difunctional aromatic cyanic acid esters, additional chain segments, dangling ends and low molecular weight compounds are built, the fractions of which are dependent on the initial admixture of the monofunctional compound and its relative reactivity. Therefore, the critical conversion at the gel point is shifted to higher values and the network density at full conversion decreases. The abstraction of phenols from intermediately formed iminocarbonic ester structures is utilized for the modification of the polycyanurate network through the coreaction of difunctional aromatic cyanic acid esters with phenols. It was found that the critical conversion and the network structure are dependent on all the initial amount of phenols, their reactivity and functionality. The modification with the help of glycidyl ethers is characterized by an insertion of the oxirane ring into the cyanurate and the succeeding reactions into isocyanurates and oxazolidinones. Depending on the initial mixture and the reaction conditions, a large spectrum of chemical and topological network structures can be obtained, what is demonstrated by both experimental and theoretical investigations.