Covalent triazine networks

It can be assumed that two separate networks with no covalent bonds between the UPR and the cyanate-based triazine network are formed. The possible addition of terminal hydroxyls from the unsaturated polyester to the —C = N bonds in BPA/DC is rather improbable as the addition of alcohols to cyanates, leading to iminocarbonate derivatives (Scheme 8), only occurs in the presence of strong alkali catalysts [134], The cyanate cyclotrimerization has been evidenced from disappearance of the 2230 and 2270 cm-1 and the appearance of 1370 and 1560 cm-1 absorption bands in the infrared spectra of the crosslinked IPN. 

BET = Brunauer-Emmett-Teller CMON = covalent metal-organic networks CTF = covalent triazine-based framework DCQNI = A,A -dicyanoquinodiimine DEF = A,A-diethylformamide DMA = A,A-dimethyl-acetamide FP-TRMC = flash-photolysis time-resolved microwave conductivity HHT = 2,3,6,7,10,11-hexa-hydroxytriphenylene M-CAT = metal-catecholate PSM = postsynthesis modifications PXRD = powder X-ray diffraction TCNQ = tetracyanoquinodimethane TOF = time-of-flight TTF = tetrathiafulvalene. 

Recently, a few papers [221-228] on PCN networks, modified by montmoril-lonite (MMT) silicate nanolayers, were published. Data on structure and mechanical and thermal properties of these nanocomposites were obtained. The 2D shape of MMT nanolayers, the enormous interfacial area, and strong PCN-MMT interactions, due to both covalent bonding between cyanate groups and the functional groups of MMT surface as well as between triazine rings and A1 and Si atoms (charge transfer interactions), provided the enhancement of some PCN properties in the nanocomposites. Well-dispersed MMT additive resulted in the substantial increase in fracture toughness and crack resistance of PCN [223,225], better thermal stability, and reduced coefficient of thermal expansion [221]. 

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