Property Studies Of Polyimide And Polyimide/MMT Films Based On Polyamic Acid Salt Precursor

Polyimide (PI) has been intensively studied since the1960s for their excellentthermal stability and high mechanical properties, along with their super chemicalresistance and electrical properties. Owing to these outstanding properties, PI are beingused for a variety of applications such as aerospace programs, automobile and electricalindustries, coatings applications, etc. However, traditional preparation approach of PI bypoly amic acid (PAA) precursors contains some disadvantages, such as, deep harm tothe environment owing to the volatilization of the toxic polar solvents mentioned above,high thermal imidization temperature and low hydrolytic stability of PAA precursors. Toovercome these drawbacks, considerable attention has been drawn to the salt of PAA,poly (amic acid) ammonium salt (PAAS), as precursor of PI.In this paper, the synthesis and properties of PAAS precursors and PI films fromPAAS precursors with different amounts of TEA were studied. Moreover, smectite claysas layered silicates are considered to be good candidates for the preparation oforganic-inorganic nanocomposites because they can be broken down into nanoscalereinforcing material. So, we use smectite clays as reinforcing material to improve themechanical and thermal properties of PI films derived from PAAS precursors. The mainresearch content and conclusions are as follows:(1)A series of new PAAS precursors were prepared by incorporating differentamounts of triethylamine (TEA) into terpolymer PAA. The chemical structure of PAASfilms was confirmed by1H NMR and FT-IR spectroscopy. Mechanical properties,intrinsic viscosities and solubility of PAAS precursors were examined, respectively. Itwas found that the intrinsic viscosity of PAA solution obviously decreased with storagetime during30days, while no distinct changes were observed in the intrinsic viscosityof the PAAS (the mole ratio of TEA/Repeating unit of PAA=2/1) solution after90days. The results suggested that hydrolytic stability of the PAAS films was significantlyimproved as compared with that of PAA film due to the polyelectrolyte structure ofPAAS.(2) Thermal stability and mechanical properties of PI films derived from PAA andPAAS with different amounts of TEA were studied. It was found that mechanicalproperties of PI films depended on the mole ratio of TEA/PAA. With the increase of theratio of TEA/PAA, tensile strength of PI films derived from different PAAS precursorsdecreased from162.5to144.5MPa. The elongation at break had the similar tendency:from9.97%to6.63%. In addition, thermal stability of PI films from PAAS also hasslight losses compared with those of PI film obtained from PAA.(3) Polyimide/organic clay (PI/OMMT) composite films were prepared to improvethermal stability and mechanical properties of PI films from PAAS. PI/OMMT hybridswere prepared by in-situ polymerization. Tensile properties measurements of PI/OMMTfilms indicated that the addition of3wt.%of OMMT increased the tensile strength of PIfilm up to163.9MPa, which is ca.12.8%higher than the pristine PI film from PAASprecursors. TGA showed that the PI/OMMT films have higher decompositiontemperatures and thermal stability in comparison with the original PI film from bothPAA and PAAS precursors.