Study On Novel Phthalide-containing Bismaleimides And Modified Resin Systems Derived Therefrom

Bismaleimides, one of the most promising classes of high performance thermosetting resins, are known for their excellent processability and balance of thermal, electrical and mechanical properties. Howerver, the common BMI monomers are of high melting temperature and poor solubility in common organic solvents, and the cured resins have high inherent brittleness due to their high crosslink density and rigid molecular networks. These shortcomings restrict their application in high-tech fields. In order to overcome them, the molecular design "methodology was used to introduce phthalide group and flexible ether linkages into bismaleimide structure with the aim of improving the processability and enhancing the fracture toughness of the corresponding cured without sacrificing thermostability and mechanical properties.A series of chain-extended bismaleimides containing phthalide cardo structure was designed and synthesized in this paper. One monomer with high properties was selected and blended with other thermosetting resins, such as2,2'-diallyl bisphenol A (DABPA), N,N'-(4,4'-diphenylmethane)bismaleimide (MBMI), epoxy (E-51), in order to obtain preferable resin with excellent balance of properties. The main research works in this thesis are as follows.Firstly, three novel phthalide-containing bismaleimide monomers, i.e.,3,3-bis[4-(4-male-imidophenoxy)phenyl]phthalide (PPBMI),3,3-bis[4-(4-maleimido phenoxy)-3-methylphenyl]-phthalide (MPBMI),3,3-bis[5-isopropyl-4-(4-maleimidophenoxy)-2-methylphenyl]phthalide (IPBMI), were synthesized based on phenolphthalein, o-cresolphthalein and thymolphthalein, respectively. The chemical structures of the monomers were confirmed by1H and13C nuclear magnetic resonance spectroscopy (NMR) and Fourier transform infrared spectroscopy (FTIR). These monomers exhibit good solubility in common organic solvents, enabling an easy solution processing. Thermal curing behavior of these monomers was investigated by differential scanning calorimetry (DSC), displaying broad exothermic peaks and large thermal processing windows. Thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA) were used to characterize the thermal stability and thermal mechanical properties of the cured BMI resins and the results exhibit the heat resistance and thermal stability were decreased along with growing bulk of the alkyl substituent. The water absorption tests of the cured products demonstrate the chemical structure exerted materially effect on moisture resistance. Based on the study of aforementioned properties, the relationships between structure and properties were discussed simultaneously.The copolymerization systems of PPBMI/DABPA were prepared, and their cure kinetics and cure cycle were analyzed by DSC. The FTIR was employed to investigate the cure mechanism under200℃. DMA, TGA, mechanical properties and water uptake measurement were used to monitor the effect of the change in the PPBMI/D ABPA molar ratio on the various properties. The results indicate the storage modulus (G'), glass transition temperature (To), thermostability and char yield were increased and the water uptake was reduced with the increase of PPBMI in the PPBMI/D ABPA systems.PPBMI was introduced into the MBMI/DABPA system, and the effect of MBMI/PPBMI molar ratio on the properties of the modified resins was investigated at the molar ratio of maleimide to allyl groups of1:0.87. As the PPBMI content was increased, the G' in the rubbery region and To were decreased, but the thermal stability and moisture resistance were enhanced. The flexural strength and impact strength firstly increased and then decreased, but the flexural modulus always increased with increasing PPBMI content. The fracture micrographs exhibited some defects in the cured networks with higher PPBMI content.The PPBMI/DDS/E-51co-curing systems were prepared, and the resin systems were divided into E-51modified PPBMI/DDS systems and PPBMI modified E-51/DDS systems on the basis of the different fundamental ingredients. The cure mechanism of modified resins was analyzed by means of FTIR and DSC, the results indicate that the E-51modified PPBMI/DDS systems have different cure mechanism depending on composition of modified systems and the main reaction occurring during the cure of PPBMI modified E-51/DDS systems include epoxy cure and Michael addition between PPBMI and DDS. DMA, TGA, mechanical properties and water uptake measurement were used to study the properties of two modified resins. For E-51modified PPBMI/DDS systems, heat resistance, thermostability and moisture resistance were decreased with increasing content of E-51, but the impact strength was improved. For PPBMI modified E-51/DDS systems, heat resistance decreased, but thermal stability, moisture resistance, flexural strength and modulus were enhenced as an increase of PPBMI; the impact strength firstly increased and then decreased with the PPBMI content and the5%PPBMI modified system showed maximum value.