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The Synthesis And Structure-Properties Study Of Polyimides With Side Chains Containing Biphenyl Unit

Posted on:2004-04-20Degree:DoctorType:Dissertation
Country:ChinaCandidate:X K LiuFull Text:PDF
GTID:1101360122965408Subject:Materials science
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Polyimides are a class of high performance polymers thatare widely used as high temperature insulators, coatings, adhesives and advanced composite matrices. Nevertheless, further research is necessary to develop new polyimide systems in order to enhance the desirable properties for various high technology applications. One area that has received considerable attention is the side chain modification and functionalization of high performance polyimides. Introducing functional groups into polyimide chains as substitutes is very interesting because they can be used to impart special functionality to polyimide as well as to improve processability. Thus the synthetic chemistry and structure-properties relationship of polyimides with functional side chains is of great interest.The studies in this dissertation have focused on the synthesis, characterization and structure-properties relationship of polyimides with various side chains. These objectives were accomplished by design various novel diamines containing biphenyl mesogenic unit, then several novel polyimides were prepared by polycondensation of diamine containing pendent group with various aromatic dianhydrides. Many fundamental questions related to the synthetic chemistry and and physics were studied, such as: the methodology of introducing side chains, the control of macromolecular structure and architecture, and the formation and control of ordered structure. The knowledge get out from the research of structure-properties relationship of polyimides can make good contribution to the development of high performance polyimides. And themethodology of side chain modification and functionalization of polyimides has made the polyimides prepared have a unique combination of processability and high strength, high modulus which is presently unavailable in common polyimides.In the second chapter, a series of novel diamines containing various side chains with biphenyl groups 2-(4-phenylphenoxy) ethyl 3,5-diaminobenzoate, 6-(4-phenylphenoxy)hexyl 3,5-diaminobenzoate, 6-(4-cyano-phenylphenoxy)hexyl 3,5-diaminobenzoate were synthesized using 3,5-dinitrobenzoic acid as starting material. All the monomers and the. intermediates were characterized by melt points, Fourier transform infrared and 'H nuclear magnetic resonance spectroscopy; the results were in good agreement with the proposed structures. Based on these newly synthesized diamine monomers, a series of polyimides with various side mesogenic units were prepared through classical two-step thermal imidization process or one-step high temperature solution imidization process. The influences of monomer adding mode, the imidization condition and imidization proceed on the resulted films were studied.It has been recognized that some physical properties of polymer are largely affected by not only the chemical structures but also the aggregate structure. The chemical change during imidization has been studied by many groups, while the aggregate change has seldom been researched. Thus we deepen our work to study the morphological feature and crystalline structure development during thermal imidization. The combination of FTIR, DSC, WAXD and POM studies is carried out to provide some new insight into the ordered phase formation during imidization process. Of particular interesting is the observation of new banded spherulites in the BTDA/MPDA polyimide samples. The imidization and crystallization occurred in a similar way at the initial stage of thermal treatment. Then the crystallization reached nearly complete after 8 minutes thermal treatment, meanwhile the PAA was only partial imidized. The banded spherulitic morphology was dramatically affected by the imidization condition and the molecular weight of polyimide. Too slow or tooquick heating rate leaded to the relative small polyimide spherulites and the banded became less identifiable, while samples of lower molecular weight formed degenerated banded spherulites. X-ray diffraction revealed the highly crystalline nature of BTDA-MPDA0.95 polyimides...
Keywords/Search Tags:Polyimide, Biphenyl unit, Banded spherulite Crystalline morphology, Phase structure, Phase transition, Structure-Properties relationship, Mechanical properties, Thermal stability, Solubility, Dimensional stability
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