Curing and characterization of oxazolidone‐isocyanurate‐ether networks

Abstract

Oxazolidone-isocyanurate-ether networks were prepared by copolymerization of mixtures of DGEBA and toluene-2,4-diisocyanate (TDI) in presence of benzyldimethylamine (BDMA) as catalyst. Changes during curing and final properties of the cured materials were investigated by using DSC, FTIR/ATR, TMA, DMTA, TGA, and densitometry. The influence of the molar ratio of isocyanate to epoxide groups on the properties and curing were studied. The kinetics of curing was analyzed by means of an integral isoconversional nonisothermal procedure. The fractions of oxazolidone, isocyanurate, and ether groups present in the final network were evaluated and were found to be dependent on the initial isocyanate/epoxy ratio and curing conditions. By increasing the initial proportion of isocyanate the glass transition temperature, the thermal stability, the shrinkage, and the amount of isocyanurate rings increase, whereas the fraction of ether linkages and oxazolidones decreases. It was observed that the gelation is controlled by the formation of isocyanurate rings at the beginning of the curing.

Preparation and characterization of highly thermostable polyisocyanurate foams modified with epoxy resin

“…The EP‐PIR foams are prepared by reacting PAPI with DGEBA, and the mole ratio of [PAPI]/[DGEBA] is 2.5. According to previous reports, the curing temperature had a great influence on the chemical structure of the final EP‐PIR resins . Therefore, the EP‐PIR foams are postcured at 75°C, 100°C, 150°C, 180°C, and 220°C for 2 h. The FTIR spectra of EP‐PIR foams cured at different temperatures are presented in Figure , and the mole ratio of [PAPI]/[DGEBA] is 2.5.…”

“…The exothermic peak at 130°C is the trimerization of isocyanate to form isocyanurate rings, and a exothermic peak at around 170°C is related to the formation of oxazolidone rings by reaction between isocyanate and epoxy groups. Meanwhile, the exothermic peak at 220–240°C is due to the formation of oxazolidone rings by the reaction between isocyanurate and epoxy groups (Scheme ) . In Figure , the intensity of the exothermic peak at 130°C decreases with the decrease of the ratio of [PAPI]/[DGEBA].…”

Fabrication and evaluation of structural film adhesive using oxazolidinone modified novolac epoxy resin

“…Peak at 915 cm −1 , the signature of epoxy ring, indicated partial modification of EPN. Conversion of epoxy was calculated from FTIR [Figure (b,c)] by monitoring the change in the ratio of intensities of peaks at 915 and 1610 cm −1 corresponding to epoxy and C=C of benzene ring, respectively. It was found that 16.4% of epoxy reacted with –NCO.…”

Isocyanurate transformation induced healing of isocyanurate–oxazolidone polymers

“…Isocyanurate–oxazolidone (ISOX) polymers are prepared from the trimerization of isocyanates and their reaction with epoxides to produce two heat‐resistant heterocyclic rings, specifically isocyanurate and oxazolidone, respectively, and their use has been well known in high‐performance thermosets . The network structure of the ISOX polymers can be significantly altered by the ratio and type of diisocyanate and diepoxide reactants, the employed catalyst and the presence of solvents, the combination of which act to control the fraction of the isocyanurate crosslinks and oxazolidone chain extenders . While diisocyanate including methylene diphenyl diisocyanate, toluene diisocyanate (TDI), hexamethylene diisocyanate, and diepoxides such as bisphenol A diglycidyl ether, bisphenol F diglycidyl ether (DGEBF) have been the most extensively used reactants for the ISOX polymers, a number of catalysts have been explored for the polymerization including tertiary amines (NR 3 ) and imidazoles, quaternary ammonium halides, Lewis acids, alkoxides, and phenoxides of alkali earth metals .…”

“…During the initiation stage of the polymerization, the role of nucleophile, epoxide, and isocyanate was not accurately assigned. Some reports suggested that two different initiation mechanisms including zwitterions formed between the nucleophile and epoxide, and zwitterions formed between the nucleophile and isocyanate, which have reactivity dependent on temperature, are both active during the polymerization . Others later reported that the zwitterions formed between the nucleophile and isocyanate were the catalytic species as a specific amount of nucleophile alone was able to polymerize diisocyanate into isocyanurate polymer at 80 °C .…”