Syntheses, Cure Behaviors, Properties And Applications Of Nitrogen-containing Flame-retardant Epoxy Resins And Hardeners

In this dissertation, series of novel nitrogen-containing epoxy resins and curing agents were synthesized for preparation of the advanced flame-retardant epoxy thermosets, which meet the requirements of environmental protection (non-halogen, lead-free). These nitrogen-containing structures are as follows: isocyanurate, triazine, aromatic azomethine and phthalazinone. The structure-properties relationships of the resulting epoxy thermosets were discussed systematically and intensively. The curing kinetics and mechanism of these epoxy systems were also investigated intensively in the first time in detail.Thermal properties such as glass transition temperature (T_g), initial decomposition temperature (T_d,5wt.%) char yield in 850℃(Y_c) and integral procedure decomposition temperature (IPDT) were evaluated by DSC and TGA methods;the storage modulus (G'), Loss tangent (Tan 5) and Coefficient of thermal expansion (CTE) of these epoxy thermosets were obtained by DMA and TMA methods;flame retardancy of these epoxy thermosets were obtained by UL94 test and Limited Oxygen index (LOT).1. A novel nitrogen-containing epoxy resin was firstly synthesized by an addition reaction between triglycidyl isocyanurate (TGIC), which is heat-resistant and has high nitrogen content, and XPF resin, which has unsymmetrical and hydrophobic structure. Investigation on the synthetic kinetics of XT resin showed that the reaction conversion depended on the polarity of the solvent. In addition, FD resin containing DOPO structure was synthesized for preparation of flame-retardant epoxy thermosets.Avrami method is suitable for calculating the kinetic parameters up to the gel point at least for XT/DDS curing system. The apparent activation energy (E_a) for isothermal cure process was in agreement with that for nonisothermal cure process. E_avalue in the early stage (78.5-81.0 KJ/mol) was about three times than that in the later stage (23.3-26.5 KJ/mol). The kinetic results from Avrami theory may present a combined effect of all factors, which is helpful to understand the cure technique for XT resin.The cured XT/FD/DICY thermosets containing isocyanurate, xylene and cyclophosphate structure had high 7g (>150°C), high 7d,5wt%(>300oC), high storage modulus (above 15000MPa), and low CTE (24/163). XT/FD/DICY thermoset could reach the UL94 V-0 rating when the phosphorus content was 1.25 wt. % and nitrogen content was 4.0 wt. %, while FD/DICY thermoset (phosphorus content was 2.5 wt. %) only achieved the UL94 V-1 rating. This result showed that isocyanurate structure and phosphorus structure exhibited a synergistic effect on flame retardancy.2. New triazine-containing curing agents, MPF1 and MPF2, which have amino and hydroxyl groups in their moleculars, were synthesized by one-step method and two-step method respectively.Because MPF1 have amino and hydroxyl groups in its molecular, the dynamic DSC curve of MPF1/E51 had two obvious exothermal peaks. Based on the results of Kissinger method, we deduced that the first peak resulted from the reaction of amine and epoxide, and the second peak resulted from the reaction of the hydroxyl and epoxide, and their Ea's were 70.5 and 86.5KJ/mol respectively. The Model compound MoPF were designed and synthesized, and cure behavior of MoPF/E51 confirmed above deduction. Furthermore, Ea calculated by isoconversional method was in agreement with the above results (69.8 and 89.4KJ/mol respectively).Due to the introduction of triazine structure, Epoxy/MPFl (MPF2) thermoset had very high Tg (even reach 190°C), high T± 5wt o/o(320 - 360°C), high char yield (above 30 wt. %), high Storage modulus (above 16000 MPa) and low CTE (e.g. FD3.0/MPF1 was 42/174). The cured MPF1 (MPF2)/FD could reach UL 94 V-0 rating even containing low phosphorus (1.94 wt. %). There was no linear relation between nitrogen and phosphorus content in the FD/MPF1 thermoset with LOI, however theaddition of nitrogen and phosphorus content with LOI showed a better linear relation (linear correlation coefficient was 0.99), which indicated the nitrogen and phosphorus in the thermoset had an obvious significant synergistic effect.3. Novel hybrid Epoxy/n-PN (novolac phenol formaldehyde resin)/HM3 systems were firstly prepared by sol-gel method. And the characteristic of these new epoxy systems lies in the dual reactivity of n-PN with epoxy resin and HM3.The resulting Epoxy/n-PN/HM3 hybrid thermoset had CH2OAr, NCH2OCH2N and NCH2N segments from the investigation by DSC and in situ FTIR method. The reaction rate of the epoxy/curing agents' addition reaction and HM3 self-condensation reaction might result in different physical structures of the resulting thermoset.Yc and IPDT of the cured E51/n-PN thermoset and HM3 self-condensation thermoset were very low, which were about 14 wt. % and 664 688 °C respectively, But the cured E5 l/n-PN/HM3 thermosets had excellent properties (7d) 5wt. % > 320°C, Yc= 24-35 wt. %, IPDT= 873-1164°C). The cured FDA1-PN/HM3 thermosets with low phosphorus content (1.76-1.30 wt. %) and HM3 content (5wt. %) had high LOI (above 40) and achieved UL94 V-0 rating.4. Three novel aromatic bisphenol curing agents containing rigid (azomethine and/or phthalazinone structures) and flexible aromatic ether structures were synthesized.Investigation on the curing kinetic of azomethine-containing bisphenol/E51 showed that the main reaction was the addition reaction of hydroxyl and epoxy groups, and the main structure of the resulting polymers was poly (hydroxyethers). In addition, the reactivity towards oxirane group of the mixed curing agents bisphenol/diamine was stronger than their individual reactivity towards oxirane groups. They exhibited significant associated effect on their reactivity.The cured ternary epoxy thermosets exhibited high Tg (127-170°C), high 7d,5wt.% (over 329°C), high IPDT values (732-1230°C), high LOI's (beyond 28.4) without any loss of toughness. The linear relationships of char yield, LOI and the content of CH=N structure were found in the resulting epoxy thermosets. DMA results showedthat the crosslinking density of these ternary epoxy thermosets decreased dramatically with increasing bisphenol content, G' of the thermosets containing more bisphenol segments decreased to zero after T% transition, and this was close to the dynamic mechanical characteristic of thermo plastic. In addition, Bisphenol/FD thermoset had very high Tg (157°C), high LOI (35) and reached UL94 V-l rating.The cure behaviors of diamine, DAP (has unsymmetrical structure) were investigated by DSC and in situ FTIR method. Ea were 73.8, 77.4 and 73.3KJ/mol calculated by Kissinger, Ozawa and isoconversional method respectively. The non-linear relationship of ￡aand a calculated by isoconversional method might result from the unequal reactivity of amines of DAP.The cured DAP/DPP/E51 (FD) had excellent thermal properties (Tg= 157-204 °C, rd>5wt.% > 350°C, Yc= 23-49 wt. %, IPDT= 845-1770°C) due to the introduction of phthalazinone and/or azomethine moieties. The cured DAP/FD thermoset had high T% (157°C), high 10/(50.8), and low CTE (67/298) and achieved UL94 V-0 rating.The overall properties of the ternary epoxy thermoset mainly depended on the content of bisphenol, and by changing the molar ration of diamine/bisphenol, we can adjust the structures and properties of the resulting epoxy thermosets.