The Influence Of Substituents Of Diamine Moiety On Polyetherimide

Due to the excellent comprehensive properties,polyimides have widely used in microelectronics,aerospace,biomedicine,and other fields.However,the applications of polyimides in many aspects were restricted due to the low solubility,deep color,and poor processability of polyimides.Over the years,many designs of molecular structure have been usually adopted to prepare the novel polyimide with improved properties,and the results show that the substituent groups at the ortho-position(s)of the amino group in the diamine have a significant effect on the properties of the polyimide.Yet the effect of the substituent groups at the ortho-position(s)of the amino group has not been systematically explained due to the complex structure of the diamine monomer used in the literature.Therefore,in this paper,three kinds of diamine monomers containing substituted groups at the ortho-position of the amino group were designed and synthesized from simple alkylbenzene as raw materials,then a series of polyetherimide(PEI)containing substituted groups were synthesized by polymerization with bisphenol A type dianhydride(BPADA).Finally,the effect of the substituted groups at the ortho-position of the amino group on the properties of the polyimide has been assessed by comparing the properties of the prepared PEI with the model polymer Ultem 1000(PEI-1).The following research work was carried out.1.Synthesis of monomers.The dianhydride monomer(BPADA)was synthesized from bisphenol A and N-methyl-4-nitrophthalimide(NPI)via a three-step reaction of substitution,hydrolysis/acidification,and dehydration.Compared with the literature reports,the separation process was greatly simplified,and the yield was improved to 92%.The diamine monomers were synthesized via a two-step reaction,and the alkylbenzene was nitrated by the nitric acid-sulfuric acid system to obtain the dinitrolated alkylbenzene firstly,then the dinitro compounds were reduced by the hydrazine hydrate-ferric chloride reduction system to obtain the diamine monomers containing the alkyl groups at the ortho-position of the amino group.2.Synthesis,characterization,and properties of PEI containing cyclohexyl group at the ortho-position of the amino group.The PEI containing cyclohexyl group was prepared from BPADA and 4-cyclohexyl-1,3-phenylenediamine via polycondensation reaction.The measuring results of GPC,FT-IR,and ~1H NMR indicated that the PEI with the expected molecular structure and high molecular weight had been prepared successfully.The results of the properties test show that the solubility,T_g,and tensile strength have been improved;still,the optical properties and thermal stability decreased because of the introduction of cyclohexyl group at the ortho-position of the amino group.3.Synthesis,characterization,and properties of PEI containing alkyl groups at the ortho-position of the amino group.The PEIs containing alkyl groups were prepared from diamines(2,4,6-trimethyl-1,3-phenylenedi-amine and self-made diamines)and BPADA via polycondensation reaction.The measuring results of GPC,FT-IR,and ~1H NMR indicated that the PEI with the expected molecular structure and high molecular weight had been prepared successfully.And the results of properties tests show that the introduction of alkyl groups effectively improves the solubility,T_g,and tensile strength of the prepared PEI,yet reduces the thermal stability and optical properties.