Preparation And Properties Of Novel Pyridine-containing Hyperbranched Polyimides And Their Nanocomposites With Functionalized Graphene

Polyimides(PIs)attract increasing attentions and continuous researches owing to their excellent mechanical,thermal,optical and dielectric properties.However,the further application researches of wholly aromatic PIs are extremely limited for their poor solubilities and melting behaviors.Various efforts have focused on the structural modification of linear PIs,such as incorporation of flexible linkages or other special structural units into the PIs backbones,or co-polycondensation,which can increase the disorder and winding of polymer chains,eventually achieve the goal of improving the solubilities or other properties.Furthermore,the design and synthesis of PIs with hyperbranched structure(hyperbranched polyimides,HBPIs)will not only maintain the advantages,but also endow the polymers with unique structural characteristic,physical and chemical properties,especially the numberous of terminal free groups,which will be able to provide convenience for their furthermulti-functionalization.Recently,the incorporation of various inorganic nanomaterials and PIs by hybrid or composite method is also found to be one of the most facile and effective approachs to improve the comprehensive performance or develop with new functions.In this paper,on the basis of brief introductions on the research progress of HBPIs,pyridine-containing PIs and graphene/PIs(GE/PIs)composites,together with the experienceof our previous works,two novel BB'2-type aromatic triamine monomers were synthesized firstly,and further used to prepare a series of HBPIs and co-HBPIs.Then various contents of fuctionalized GE were incorperated into co-HBPIs via in situ solution random copolycondensation or grafting reaction between the modified GO and the monomers or prepolymers.Thie particular work is as follows:1.A novel BB'2-type aromatic triamine monomers with symmetrical triarylsubstituted pyridine segments and prolonged flexible diphenyl ether linkages,2,4,6-tris[4-(4-aminophenoxy)phenyl]pyridine(TAPPP)was firstly synthesized and further employed to prepare a series of amine-terminated and anhydride-terminated pyridine-containing HBPIs by polycondensation with various commercial A2-type dianhydride monomers via a conventional two-step process of A2+BB'2 approach.The resulting HBPIs predominantly with amorphous structure,exhibited improved organo-solubilities in several strong polar aprotic solvents,good heat resistance and excellent thermal stabilities both in N2 and air.The obtained HBPIs films also showed high strength and modulus,considerable optical transparency,as well as low water absorption and neutral interface wettability.All of these properties varied from the dianhydride monomers used and the terminal groups.Meanwhile,another similar novel fluorinated BB'2-type aromatic triamine monomers,2,4,6-tris[4-(4'-amino-2'-trifluoromethylphenoxy)phenyl]pyridine(TATFPPP),and the corresponding fluorinated HBPIs(FHBPIs)were synthesized by the same methods.Comparing with HBPIs,the obtained similar FHBPIs presented higher crystallization and heat resistance,but lower thermal stabilities and organo-solubilities.2.A series of co-HBPIs films with various molar ratio of triamine and diamine were prepared by the copolycondensation of the novel BB'2-type aromatic triamine monomer(TAPPP)with flexible linkages containing comemercial diamine(ODA)and dianhydride(BPADA)via a conventional two-step process of A2+B2+BB'2 approach.The obtained co-HBPIs with different TAPPP contents,which held typical amorphous morphology,exhibited good thermal properties,improved mechanical properties,as well as low water absorption and slightly hydrophobic surface wettability.Heat resistance,mechanical strength and modulus,water absorption declined with the increase of ODA content,while thermal stability,mechanical toughness and surface hydrophobicity increased,except that the amorphous characteristic was no obvious changed.Furthermore,The heat resistance,mechanical strength and modulus of the similar fluorinated co-FHBPIs films,which were obtained by TATFPPP with the same method,were a little higher than the corresponding co-HBPIs films,but the mechanical toughness and thermal stabilities were less than the later ones.Meanwhile,the surface hydrophobicity of co-FHBPIs films were higher than the corresponding co-HBPIs films,but lower water absorption.3.Based on the above considerations,a series of GE/co-HBPIs nanocomposite films with various contents of fuctionalized GE,were obtained by incorporation of modified GO with excess MDI or ODA(GO-MDI or GO-ODA)into the co-HBPIs with better comprehensive performance,via in situ solution random copolycondensation or grafting reaction,together with synchronous thermal imidization and thermal reduction.It was found that the thermal,mechanical,hydrophobic,and gas barrier properties of the resulting GE/co-HBPIs nanocomposite films all had different degrees of improvement or enhancement,compared with the corresponding pure co-HBPIs films.Furthermore,the improvement or enhancement became more and more obvious with the content of GO-MDI or GO-ODA increasing.4.By contrast,all of the resulting GE/co-HBPIs nanocomposite films based on GO-MDI or GO-ODA,showed a typical amorphous structure.Meanwhile,the thermal,mechanical,hydrophobic and gas barrier properties of obtained nanocomposite films obtained by in situ random copolycondensation were all different degree higher than those obtained by in situ.grafting reaction.In addition,the obtained GE/co-HBPIs nanocomposite film based on'GO-ODA generally had a higher GE content and better comprehensive properties than those based on GO-MDI.The synthesis of this two novel triamine monomers and their HBPIs or co-HBPIs containing triarylsubstituted pyridine structure,lays a certain foundation for enriching the species of pyridine-containing polymers and developing multifunctional and multipurpose HBPIs materials.The facile and effective preparation method of homogeneous and high performance GE/HBPIs nanocomposite via in situ solution random copolycondensation or grafting reaction,and subsequent synchronous thermal imidization and thermal reduction,provides a possibility for developing multifunctional and multipurpose multifunctional and multipurpose advanced engineering or functional material based on PIs.