Study On Synthesis And Properties Of Phosphorous/nitrogen-containing Flame Retardant Epoxy Resin

Epoxy resins are widely used as structural adhesives, coatings, and advanced composite matrices in the aerospace and electronic industries because of their high tensile strength and modulus, low shrinkage on cure, high adhesion to many substrates, excellent chemical and corrosion resistance, and good dimensional stability. The flammability of epoxy resins, however, is a major hazard in their applications.Therefore, many flame retardants have been developed to improve their flame retardancy. Among them, organophosphorous compounds, generating negligible amounts of toxic gas and smoke, have demonstrated high efficiency as flame retardants for epoxy polymers. The research work of this dissertation is mainly involving the synthesis, application and mechanism about the phosphorous-containing, nitrogen- containing or phosphorous-nitrogen epoxy resins.There are five parts in this dissertation: introduction; synthesis and characterize of an novel phosphorous-containing biphenol DPODB and its application as flame- retardant in epoxy resin; synthesis and application of an novel curing agent used for epoxy resins bearing N-(4-hydroxyphenyl) maleimide (HPM); study on properties and mechanism about curing reaction of a self-intumescent flame retardant epoxy resin cured with an new phosphorous-nitrogen phenolic resins; investigation on thermal decomposition performance and mechanism about cured epoxy resins with different elements; conclusions. Among the organophosphorous flame retardants, phosphorinane compounds with higher thermal stabilities have been in great favor for phosphorous-containing epoxy resin, and many investigations have been done about them. A novel phosphorous- containing biphenol, 2-(5,5-dimethyl-4-phenyl-2 -oxy-1,3,2-dioxa- phosphorin-6-yl)1, 4-benzenediol(DPODB), was prepared by the addition reaction between 5,5-dimethyl-4- phenyl-2-oxy-1,3,2-dioxaphos-phorinane phosphonate (DPODP) and p-benzoquinone ( BQ ). The compound (DPODB) was used as a reactive flame-retardant in o-cresol formaldehyde novolac epoxy resin (CNE) for electronic application. The structure of DPODB was confirmed by FTIR and NMR spectra. Thermal properties of cured epoxy resin were studied using differential scanning calorimetry (DSC) and thermal gravimetric analysis (TGA). The flame-retardance of cured epoxy resins was tested by UL-94 vertical test and achieved UL-94 vertical tests of V-0 grade (nonflammable). The most studied approach to toughen epoxy resin was the use of polyimides which have high degree of thermal stability, excellent mechanical properties and chemical resistance. In this study, we made another approach to prepare an novel epoxy/polyimide cured resins, in which the curing agent is a maleimide-functional novolac copolymer resin synthesized through the copolymerization of HPM with phenol and formaldehyde. The modified epoxy films excellent solvent resistance; The tensile measurements of the films showed that, with the increase of the maleimide content, tensile properties of the film increased but were not changed significantly which reflects their independence on the HPM content on the film within the ratios used in this study. The thermal properties and thermal degradation behaviors of the PMF-CNE cured epoxy resins were also studied thermogravimetric analysis. Extremely high thermal stability (above 380℃) and high char yields (700℃48.6%) were observed for the PMF-CNE (o-cresol novolac epoxy)-based resins. Thermo gravimetric analysis also showed the increase of the thermal stability with the increase of the maleimide content.phosphorous-nitrogen intumescent flame retardants especially self-intrumescent flame retardant have been attracting so many interests in the fields of compound flame retardant, for the reason that their better compatibility, better flame retardance, good solvent resistance and tensile properties.Through the electrophilic addition reaction of -P(O)-H and C=C, a series of novel phosphorus-containing phenolic resins bearing maleimide (P-PMFs) were synthesized and used as curing agent for preparing high performance and flame retardancy epoxy resins. The structure of the resin was confirmed with FTIR and elemental analysis. Thermal properties and thermal degradation behaviors of the thermosetted resin was investigated by using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The epoxy resins exhibited high glass transition temperature (143-156℃) , goof thermal stability (>330℃) and retardation on thermal degradation rates. High char yields (700℃52.9%) and high limited oxygen indices (30.6-34.8) were observed, indicating the resins'good flame retardance for the P-PMFs/CNE cured resins. The developed resin may be used potentially as"green"in electronic fields.The thermal degradation property of flame-retarded systems was investigated by means of FTIR. It is found that the thermal decomposition process is closely related to the structure of polymers, the types of flame-retarded elements and the structure of elements. TG and FTIR results demonstrate that the flammability and thermal stability of the system are all improved as a results of cross-linking in the process of thermo-oxidative degradation. The C=N bonds appeared and took part in the cross-linking reaction in the higher temperature, which contrast to the appearance of phosphorate groups in the lower temperature during the decomposition process of phosphorous-nitrogen intumescent flame retarded epoxy systems. The possible composition of intumescent char of phosphorous-nitrogen epoxy systems was suggested based on the XPS measurement. It was found that there was NOP group appeared during the decomposition process and the char yields is in proportion to the rate of NOP. Moreover, the morphology of char residues was examined by SEM.Moreover, the dynamic research is another important point in this dissertation. FTIR, dynamic TG and DSC were used to calculate the active energy and other kinetics parameters of curing reaction with various methods, and asserted their mechanistic function of thermal decomposition. The mechanistic function of curing reaction was also investigated by in-situ FTIR.