Study Of Phenylethynyl-terminated Polyether P-polyimide Matrix Resins And Its Carbon Fiber Composites

The matrix resin of composite can be divided into thermoplastic polymer and thermosetting polymer.The thermoplastic polymer has excellent mechanical and heat-resistance properties,but the higher molecular weight of it leads to a high melt viscosity and poor solubility,which makes it difficult to process.On the contrary,the thermosetting polymer with relatively low molecular weight usually contains reactive groups in structure which can trigger off crosslinking reaction under external stimulation.After crosslinking,the molecular weight of the thermosetting resin rises,and the thermal stability and mechanical strength are greatly improved,such as epoxy resin and PMR resin.Polyimide is a kind of high-performance material with properties of high-temperature resistance,high-strength,insulation,low thermal expansion coefficient and non-toxicity.In 1990s,NASA planned to introduce phenylacetylene groups into polyimide to synthetize high-performance thermosetting matrix resin for preparing composites with carbon fiber.The results showed that phenylacetylene groups can balance between processing,thermal and mechanical properties of polymers which have attracted more and more attentions of people to study it.Nowadays,the Resin transfer Molding(RTM)is the preferred technology for the preparation of large components because of its low processing cost and high production efficiency,which solves the problem of high cost in the preparation of advanced composites.However,RTM requires the resins to have low melt viscosity and high melt viscosity stability,so the research of high performance polymers with low melt viscosity have become an important topic.Form now on,for decreasing the melt viscosity of resins,introducing asymmetric and irregular structure,bulk pendants,branched configuration into polymer structure can be effectively ways.However,The synthesis of monomers containing these structures are very complicated,and accordingly,difficult to realize in real production.The design idea of this paper is to prepare phenylethynyl-terminated polyimide which have excellent processability before curing,and own high thermostability and mechanical property after curing.Meanwhile,monomers are easily available.The diamine monomer with para-polyether structure was selected in the experiment.The monomer is easy to obtain,simple in preparation and low in cost.Moreover,the ether bond in polymer can effectively improve the flexibility of molecular chain,reducing the melt viscosity of polymer,and then achieving the goal of easy processingIn this paper,two kinds of diamine monomers,2,2-Bis[4-(4-aminophenoxy)phenyl]hexafluoropropanane(6FBAPP)and2,2-Bis[4-(4-aminophenoxy)phenyl]propane(BAPP)were selected as diamine monomers to polymerize seperately with4,4’-oxydiphthalic anhydride(ODPA)and 4-phenylethylphthalic anhydride(PEPA)to prepare phenylethynyl-terminated polyether p-polyimide.The comprehensive properties of this kind of polyimide were evaluated,and then the influence of the introduction of fluorine on the oligomers was studied by comparing the fluorine-free oligomers.The results showed that these kind of polyimides had lower melt viscosity.The melt viscosity of Oligo-6F-2 and Oligo-2 were underneath 5Pa?s and the viscosity was still stable at 310℃after 1 h,indicating that Oligo-6F-2 and Oligo-2 were suitable for RTM technology.All oligomers have excellent solubility in organic solvents which will satisfy the requirement of more processing technology.After curing,the T_g of the resins were improved greatly,the T_g of Oligo-6F-2 was 276℃,which is higher than PETI-5(270°C).The thermogravimetric temperature at 5%of Oligo-6F-2 was above520℃,anditstensilestrengthwasabove80MPa.The phenylethynyl-terminated polyether p-polyimide possessed excellent comprehensive properties,of which fluorizated series resins owned more outstanding in solubility and thermal propertiesAfter the evaluation of resins,according to the existing experimental conditions in the laboratory,we selected Oligo-6F-4 and Oligo-4 as the resin matrix to prepare the composites,and the mechanical properties of the composites were tested.The result showed that the mechanical properties of CF-4 and CH-4 were excellent.Then the aging test of composite was carried out.A series of mechanical properties tests showed that the aging test had no effect on the composite,which meant the binding ability of resin and fiber was excellent which has been further proved by scanning electron microscope(SEM).