Study On Novel Bismaleimides Containing Fluorene Cardo Group And Modified Resin Systems Derived Therefrom

Bismaleimide as a kind of high performance thermosetting resin has many excellent properties such as temperature resistance, mechanical performance and excellent processing properties. It is widely used in aerospace, machinery, electronics and other fields. However, because of its rigid and symmetrical structure, the common BMI (MBMI) generally possesses poor solubility in common organic solvents and higher melting temperature. The cured resins have high inherent brittleness due to their rigid molecular networks and high crosslink density. These shortcomings have considerably restricted the BMI applications as high performance resins. In order to overcome these shortcomings, novel bismaleimide monomers containing fluorene cardo structure and ester bond or aryl ether bond were designed and synthesized. The new BMIs are expected to possess the processability and solubility while maintaining good thermal stability, and the cured BMI resins have high impact toughness.A series of chain extended BMI monomers containing fluorene cardo group was designed and synthesized in this paper. The monomer with high properties was selected and blended with other thermosetting resins, such as 2,2'-diallylbisphenol A (DABPA), MBMI and epoxy (E-51), so as to gain preferable resins with excellent performance. The main research works in this thesis are as follows.Firstly, two novel BMI monomers (PEFBMI, MEFBMI) containing fluorene cardo structure and ester bond were synthesized using 9,9-bis(4-hydroxyphenyl)fiuorene and its derivative as raw materials by four steps. The chemical structures of the intermediate products and the target monomers were confirmed from FTIR, NMR and elemental analysis. Both monomers obtained were readily soluble in common organic solvents. The curing behavior of the monomers investigated by different scanning calorimetry (DSC) indicated that the alkyl substituent in the new monomer improve its melting point and reduce the reaction activity of BMI double bond. Dynamic mechanical analysis (DMA) and thermogravimetric analysis (TGA) results showed that the thermal mechanical properties and thermal stability of the cured resins were decreased by the alkyl substituent. The water absorption experiment demonstrated the chemical structure materially effect on the moisture resistance of the cured resins. On the basis of aforementioned properties, the relationship between the structure and the properties of two monomers was discussed at the same time.Secondly, two novel BMI monomers (PFBMI, MFBMI) containing fluorene cardo group and aryl ether linkage based on 9,9-bis(4-hydroxyphenyl)fluorene and its derivative were designed and synthesized. The chemical structures of the monomers were confirmed by FTIR, NMR and element analysis. Both monomers obtained were readily soluble in acetone and chloroform, enabling an easy solution processing. DSC results showed that both monomers possess lower melt points and large thermal processing windows indicating excellent machining performance. The BMI resins based on these new monomers had good thermal stability and thermal mechanical properties seen from the TGA and DMA results. The water absorption tests of the products demonstrated the water absorption of the resins was decreased by the alkyl substituent. On the basis of aforementioned properties, the relationship between the structure and the properties of two monomers was discussed at the same time.The copolymerization systems of PFBMI/DABPA with different molar ratios (PD87, PD100 and PD120) and MFBMI/DABPA with equal molar ratio (MD100) were prepared. The curing behavior of all these resins and the curing kinetic parameters of PD100 system were studied by DSC. The curing mechanism of PD100 system under 200? was studied carefully by FTIR. DMA, TGA and water absorption tests were employed to investigate the thermal properties and moisture resistance of these resins. The results indicated that with the content of PFBMI increase, the heat resistance, thermal stability and glass transition temperature of cured PD systems all increased, but the water absorption decreased significantly. The thermal stability and glasstransition temperature of MD100 system was lower, while the water absorption was higher than that of PD100 system.PFBMI monomer was introduced into MBMI/DABPA system, and the effect of different molar ratio of PFBMI and MBMI on the properties of the copolymer resins were studied at the molar ratio of maleimide group to allyl group of 1:0.87. Research results showed that with the content of PFBMI increase, the storage modulus of the cured resins in glassy state increased while in rubber state decreased, the glass transition temperature also decreased. The maximum thermal decomposition temperature maintained stable, the thermal stability and the carbon residue rate increased. The flexural modulus and flexural strength, the impact strength of the systems increased at first and then decreased with the content of PFBMI increased, and the maximum increase of the impact strength was 35%. The fracture morphology showed some internal defects caused by higher content of PFBMI.PFBMI modified E-51/DDS copolymers were prepared by introducing PFBMI into E-51/DDS system at the molar ratio of E-51 to DDS of 1:1. The effect of PFBMI content on the various properties of the PFBMI/E-51/DDS copolymers was investigated. Research results showed that the heat resistance, thermal stability and the moisture resistance of PFBMI/E-51/DDS resins all improve with the content of PFBMI increased. The flexural modulus gradually increased, while the flexural strength and the unnotched impact strength increased slightly at first and then gradually decreased. The 5% PFBMI modified system showed the maximun value.