Synthesis And Characterization Of Heterocyclic Polyimides

Polyimide has so far the best thermal-performance among organic materials,the phenyl- heterocyclic groups could form conjugated, scalariform and semi-scalariform structure which gives its molecule strong hardness, high free rotatingenergy, and thus lead to high glass transformation temeperature, melting point andintenerate temperature, could retain its physical performance for a short periodunder temperature of 555℃, while under 300~C or even higher its performancecould be kept for a long time. The most developed synthetic route for theseimportant materials is the classical two-step method, the first step being thesynthesis of precursor, ie. poly(amic acid) (PA) from the reaction ofdiamine anddianhydride and the latter step being subsequent thermal or chemical imidizationof the poly(amic acid). Many studys have shown that the molecular weight of PAA,and distribution of molecular weight will affect PI's performance.Aromatic polyimides (PIs) are one of the most important class ofhigh-performance polymers. Due to their excellent electrical, thermal, and lowand/or high-temperature mechanical properties, PI have a wide range ofapplication in fields such like aeronautics, electrical system, and IT industry andhave played an important role. China started researching into polyimide in 1960s,after 30 Years of development the production of monomer's qutity as well as itsvariety has reached a certain level, but there's still a certain gap between foreigncountries in monomer's category and producing technology, also, the output ofmould plastic as well as composite material is rather low and still mainly used inavigation and war industry field. Certain gap also exists in production variety andperformances when compared with Dupont Company. With the rapid progress intechnology and production, PI with high thermal-resistance, stability, progressingfeasibility has become an novel developing orientation. Introducing soft groups into PI could improve its processing feasibility, also, certain functional propertycould be obtained at the same time.In this work, different kinds of monomers with groups such like aethergroups, katone groups, as well as sulphone groups have been chosen to synthesizepolyimides. The work canbe divided into 2 steps: the 1st step is the synthesis of PIwith different function groups, which has 3 processes: 1) Synthesis of PI withaether and katone groups. Mainly by two-step method, combined.with 1-stepmethod as well as co-condansation; 2) Synthesis of PI with sulphone groupsthrough 2-step method; 3) Synthesis of PI with katone as well as sulphone groupsthrough 2-step method. The 2nd step are characterization of PI. The resultant PIs'properties were tested with techniques such as intrinsic viscosity, IR, TGA, DSC,X-ray and so on. Then their performances are compared with fluorinated PI.The result shows that with the affect of hard groups in molecule, PI withaether and katone groups can obtain a excellent thermal-performance, while theirsolvency are not inproved so well as fluorinated PI. When concerning to thedifferent method in synthesizing, during one-step method there's still enoughsolvent at a high temperature which allows molecules to arrange in order, thusgives molecules its stiffiaess which lead to a high thermal-performance. PIsynthesised by two-step method has a thermal-performance slightly weaker thanone-step methods. Co-condensation can destroy the inerratic arrangement and thuslead to a decline in thermal-performance. When concerned with different functiongroups, PI with aether and katone groups has a relative better thermal-performance,sulphone group can improved its solvency while sulphone group plays the mainrole, but its thermal-performance declined. PI with heterocyclic groups canimprove solvency much better, with a thermal performance better than PI withsulohone groups while a bit lower than PI with aether-katone PI.