Study On The Design And Synthesis Of Branched Phthalonitrile Resin And Composites

Phthalonitrile(PN)resins and its composites have been widely used in aerospace,electronics,shipbuilding and other fields.Wave-transparent composites are the key materials for high-speed aircraft.With the development of high technology and military industry,higher requirements have been put forward for dielectric stability in wide temperature domain,thermal and mechanical properties of wave-transparent composites.This thesis is based on the requirements for resin-based wave-transparent composites for aircraft at the speed of 4 Mach or less and the response to the reported problem that phthalonitrile resin cannot take both thermal performance and into account processing performance.Therefore,for the standpoint of molecular structure design,the rigid trifunctional monomer and branched structure are introduced,the resin have excellent thermal stability after cued;By adjusting the structure of the trifunctional monomer,it is to endow the resin compatible excellent temperature resistance and good processability.Then,a series of resin-based fiber-reinforced composites with high temperature resistance,low dielectric constant,wide temperature range(from room temperature to 500?)stable dielectric properties,and excellent mechanical properties are prepared by combining the resin and reinforcing fibers.The main work of this thesis are as follows:In order to improve the thermal properties of phthalonitrile resins.Using the "one-pot,two-step" method,the first step is to use the "A2+B3" method to obtain hydroxyl-terminated branched structures from Biphenyl(BP)and trihalide containing phenyl-s-triazine structure(TFPT).In the second step,4-nitrophthalonitrile were used for end-capping to obtain branched PN oligomers.Through the first step of reactant concentration and reactant feed ratio(n(BP)/n(TFPT)),the structures and properties of the oligomers were adjusted.With the concentration of the reactants increasing,the minimum viscosity of the neat oligomers gradually increased.With the molar ratio of biphenol increasing,the minimum viscosity of the neat oligomers gradually decreased.Using DDS as curing agent,combining the processability of the oligomers and the thermal properties of the cured networks,when concentration of the reactants are 0.10 g/mL,n(BP)/n(TFPT)=3.6,the resin have 5%weight loss temperature(Td5%N2)as high as 575?,the weight retention at 1000?(Cy1000)is 74.1%,the 5%weight loss temperature(Td5%Air)in air is 548?.The glass transition temperature of composites exceed 500?.The branched structures bearing the rigid phenyl-s-triazine endow the PN resin outstanding thermal properties.Different bisphenols(hydroquinone,resorcinol,1,6-naphthalene diphenol,2,6naphthalene diphenol)are used to synthesize branched PN oligomers with TFPT,and the rheological processability of the oligomers,the thermal properties of the cured networks,the mechanical properties and the dielectric properties of the composites are studied.The processing temperature window of oligomers containing resorcinol range from 125? to 235?,exhibiting wide processing window.After the optimal curing procedure,the structures of the cured networks are mainly triazine rings and isoindole structures.The cured resins exhibite several properties(Td5%N2,546?566?;Cy1000,66.5%?70.8%;Td5%Air,533?).After the cured resins are subjected to thermal oxygen aging,the mass retention rates range from 54?76 wt%.The Tg of composites are exceeding 500?.The composites of flexural strength and interlaminar shear strength,which containing hydroquinone structure of resin then reinforced by glass fiber,could reach 705 MPa and 46 MPa,respectively.The quartz fiber reinforced composites have excellent wide temperature range dielectric stability,from room temperature to 500?,the dielectric constant only increase 0.10(from 3.40 to 3.50),and the dielectric loss only increase 0.003(from 0.003 to 0.006).The high-performance composites are expected to be applied in high-temperature environments and high-tech fields such as national defense and military industry.In order to balance the thermal properties and processability of PN resins.The trifunctional structures containing rigidity and flexibility are introduced into the PN oligomers.By introducing the bisphenol structures,the branched PNs containing the benzoyl structure are obtained.Studies have shown that the oligomers have good solubility in tetrahydrofuran and acetone,which provide convenience for the preparation of wet prepregs.Among them,the oligomer containing 1,6-naphthalenediol structures has a gel time of 55 min at 200?,exhibiting good processability.The cured resins possess excellent thermal properties(Td5%N2,512?553?;Cy1000,71.4%?75.9%).After the cured resins are subjected to thermal oxygen aging,the mass retention rates ranged from 78?87 wt%.The Tg of composites are exceeding 500?.The flexural strength of the quartz composite could reach 530 MPa,the interlaminar shear is as high as 32 MPa.When the oligomer contained hydroquinone structures,the flexural strength of the quartz fiber reinforced composite is 530 MPa,and the interlaminar shear strength is 28 MPa;the dielectric constant is only increased by 0.22(from 3.24 to 3.46),and dielectric loss is only increased by 0.003(from 0.004 to 0.007).The wide temperature range dielectric stability of composites are better than that of the dielectric composites that have been reported so far.The branched PN resins containing bio-based furan structure are synthesized.The rheological properties of the oligomers,the thermal properties of the cured networks,the mechanical properties and the dielectric properties of the composites are investigated.Results have shown that the gel time of oligomers containing different triphenol structures are different.Among them,the processing temperature window of the oligomer containing methylene triphenol structure is 165?226?,and the gel time is 50 min at 180 ?.After the cured resins are subjected to thermal oxygen aging,the mass retention rates range from 81?83 wt%.The resins containing the structures of phenyl-s-triazine have excellent thermal properties(Td5%N2,531?;Cy1000,76.7%;Td5%Air,529?).The Tg of composite is over 500?.The wide temperature range dielectric stable of the composites are excellent,from room temperature to 500?,the dielectric constant fluctuate 0.08(from 3.53 to 3.61),and the dielectric loss only increased by 0.002(from 0.006 to 0.008).It provides new idea for the design of high valueadded bio-based materials in thermosetting resins and functional composites.