Study On Synthesis And Properties Of Fluorenyl Cardo Polyimides

Polyimides are well known as high performance polymers for their excellent heat resistance,electrical insulating properties and mechanical characteristics,so they are widely used in the fields of electrical materials,adhesives,and composite fibers and film materials.However,they are generally insoluble and infusible in their fully imidized form,which would lead to processing difficulties;and this process of poly (amic acid)intermediate has several inherent problems such as emission of volatile byproducts(e.g.,H₂O)and storage instability etc.To overcome these problems,much research effort has been focused on synthesis of soluble,processable and heat-resistant novel polyimides in fully imidized form.The introduction of fluorenyl cardo groups into the backbone of polyimides is an effective approach for improving solubility and thereby processability of polyimides without sacrificing thermal properties.In this thesis,a series of fluorenyl Cardo polyimides were synthesized and the structure-property relationship was investigated. The research work includes five parts;1.Synthesis and characterization of soluble fluorenyl Cardo polyimides;2.Synthesis and properties of polyamide-imides containing fluorenyl Cardo structure;3.Synthesis and characterization of novel chain-extended bismaleimides containing fluorenyl Cardo structure;4.Studies on fluorenyl Cardo copolyimides;5.Synthesis and properties of fluorenyl Cardo polyesterimides.The main content is as follows;(1)Five fluorenyl cardo diamines with different alkyl substituents were synthesized and characterized.A series of fluorenyl cardo polyimides were prepared by "one step" polycondensation of these cardo diamines with the dianhydrides(4,4'-oxydiphthalic anhydride(ODPA),3,3'4,4'-benzophenonetetracarboxylic dianhydride(BTDA), 3,3',4,4'-biphenyl tetracarboylic dianhydride(BPDA)and pyromellitic dianhydride (PMDA))respectively.Most of fluorenyl cardo polyimides exhibited excellent solubility in common organic solvents such as m-cresol,chloroform(CHCl₃), tetrahydrofuran(THF),N-methyl-2-pyrrolidinone(NMP),N,N-dimethylacetamide (DMAC)etc and intrinsic viscosity in N,N-dimethylacetamide(DMAC)ranged from 0.31-1.00dL/g.Tg of polyimides based on ODPA decrease slightly with the number and size of alkyl substituents on fluorenyl cardo diamine,but Tg of all ODPA-typed polyimides exceed 310℃.The results show that the incorporation of noncoplanar structure led by the introducing alkyl substituents on fluorenyl cardo diamines improves the solubility of cardo polyimides in organic solvents without sacrificing thermal properties.(2)A series of alternating polyamide-imides(PAIs)with fluorenyl cardo structure was synthesized by "one-pot" polycondensation of cardo diamines,trimellitic anhydride and various aromatic diamines including p-phenylene diamine,m-phenylene diamine, 4,4'-oxydianiline,3,4'-oxydianiline,2,2-bis[4-(4-aminophenoxy)phenyl]propane, 2,2-bis[4-(3-aminophenoxy)phenyl]propane respectively using triphenyl phosphite as condensing agents.Most of the polyamide-imides having inherent viscosities of 0.38-0.88dL/g were readily soluble in a variety of organic solvents,such as NMP, DMAc,N,N-dimethylformamide(DMF),dimethyl sulfoxide(DMSO),pyridine,and THF etc.Polyamide-imides exhibited better solubility when alkyl substituents were incorporated.Moreover,the effects of the linkage of imide/amide(head to head,tail to tail)on the properties of polyamide-imides were also discussed.The glass-transition temperatures of these polymers were recorded between 235-448℃by DSC and 10%weight loss temperature of all polymers exceed 450℃in air. Compared with homo-polymimdes and copolymimdes,PAIs can evidently improve mechanical properties while maintaining excellent solubility,high Tg and thermal stability of fluorenyl cardo polyimides.The film with good mechanical properties could be also obtained even if very rigid PDA diamine was copolymerizied.These films had a tensile strength in the range of 43-111MPa,and an elongation at break in the range of 1.5%-7.1%.(3)Novel Fluorenyl Cardo chain extended bismaleimides(FCCEBMIs)were synthesized and characterized by reacting maleic anhydride with fluorenyl cardo diamine and different dianhydrides.All FCCEBMI monomers were readily soluble in a variety of organic solvents,such as NMP,DMAc,CHCl₃,methylene chloride (CH₂Cl₂),DMSO and THF etc compared with 9,9-bis(4-maleimidophenyl)fluorene. Curing process of FCCEBMIs was investigated by differential scanning calorimetry (DSC)and the cured products are stable up 430℃as the results of thermogravimetry analysis.The results show that the FCCEBMIs with imide structure improve significantly the solubility of bismaleimide in organic solvents without sacrificing thermal properties of cured bismaleimides. (4)A series of random copolyimides with fluorenyl cardo structure was synthesized by the introduction of fluorenyl cardo groups into the backbone of polyimides with lower Tg—YS-20,YS-30 and Ultem respectively.The results show that the introduction of fluorenyt cardo groups can;a.evidently increase Tg;b.partly improve the solubility but the effect is not outstanding;c.not decrease thermal stability;d.not decrease mechanical properties when the molar content of cardo group is low.(5)A dianhydride containing ester bond—9,9-bis[4-(3,4-dicarboxybenzoyloxy) phenyl]fluorene(BDPF)was synthesized and characterized.A series of fluorenyl cardo poly(ester-imide)s were prepared by polycondensation of BDPF with m-phenylene diamine,4,4'-oxydianiline,3,4'-oxydianiline,2,2-bis[4-(4-amino phenoxy)phenyl]propane,2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane, 1,6-hexamethylenediamine(HAD)respectively.Most of fluorenyl cardo poly(ester-imide)s exhibited excellent solubility in common organic solvents such as 1,2-dichlorobenzene(ODCB),CHCl₃,THF,DMAC,DMSO,NMP etc.The glass transition temperatures of these polymers were recorded between 199-283℃by DSC and 10%weight loss temperature of all polymers exceed 440℃in air.