Synthesis And Characterization Of High Strength Polyimides

This dissertation consists of two parts:Part one: A series of high molecular weight polyimide (PI) precursors, poly(p-phenylene biphenyltetracarboxamic acid) (BP-PAA), were synthesized from 3, 4, 3',4'- biphenyltetracarboxylic dianhydride (BPDA) and p-phenylenediamine (PDA) by using intense mechanical stirring at the low temperature. The highest intrinsic viscosity, 7.6 dL/g, was measured by using the precursor BP-PAA synthesized in the condition of 10% by weight reacting substances in DMAc and at -5℃. Nanofibers of poly(p-phenylene biphenyltetracarboximide) (BP-PI) was obtained by electrospinning the solution of BP-PAA in DMAc and imidizing the as-electeospun BP-PAA nanofibers. The average diameter of the PI nanofibers was about 200 nm.The imidization condition of converting BP-PAA into BP-PI was investigated by using FT-IR spectroscope and by establishing relationships between the imidizing temperature as well as staying time at different temperature and the mechanical performance of PI film. The result showed that when molecular weight was no significant different, the higher the imidization degree of BP-PAA, the better the mechanical performance of the BP-PI film was. The highest tensile strength and modulus were respectively 960 MPa and 20.1 GPa for BP-PI film and 650 MPa and 15 GPa for electrospun BP-PI nanofiber mats or membranes. In addition, the heating-resistance of the BP-PI was measured to be 565°C in air and 603°C in nitrogen by 5% by weight degradation. Dynamic mechanical analysis of the PI film showed that the glass transition temperature and storage modulus of BP-PI thin filmswere respectively 330℃ and more than 18 GPa.Part two: a series of similar high molecular weight PI precursors, poly(p-phenylene biphenyltetracarboxamic-co-oxydiphthaldicarboxamic acid) (BOP-co-PAA) were synthesized from 3, 4, 3',4'- biphenyltetracarboxylic dianhydride (BPDA) ,4,4'- oxydiphthalic anhydride (ODPA) and p-phenylenediamine (PDA) at low temperature. The as-synthesized PI precursor solution was used to make BOP-co-PI thin films by solution-cast and consequent heat imidization.Mechanical performance of BOP-co-PI showed that the elongation to break of...