Investigation of the Solution Behavior of Organosoluble Aromatic Polyimides

Abstract

Two high-molecular-weight organosoluble aromatic polyimides having the same diamine, 2,2'-(trifluoromethyl)-4,4'-diaminobiphenyl diamine (PFMB), but different dianhydrides, 2,2'-bis(trifluoromethyl)-4,4',5,5'-biphenyltetracarboxylic dianhydride (HFBPDA) and 2,2'-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), were prepared via one-step polycondensation reactions. Molecular weight fractionation of these two polymers was carried out and the polyimide fractions possess successively lower weight-average molecular weights. Intrinsic viscosity data from both sets of polyimide fractions gave the MarkHouwink-Sakurada constants of these two polyimides, which reflect differing chain rigidity in tetrahydrofuran (THF) solutions. The MHS relations are [q] = 5.24 x 10-4 M0.65 and [q] = 3.77x 97 for 6FDA-PFMB and HFBPDA-PFMB, respectively. The physical meanings of these constants are discussed using the intrinsic viscosity data of these two polyimides in varying solvents. The persistence lengths are calculated based on the viscosity and molecular weight results using Bohdanecky's approach and they were calculated to be 6.6 and 2.0 nm for HFBPDA-PFMB and 6FDA-PFMB, respectively. The experimental results indicate that the fully aromatic HFPBDA-PFMB is more rigid in THF solutions compared with 6FDA-PFMB. However, both of these polyimides are far from possessing true rigid-rod character. Plots of the weight-average molecular weight against the elution volume depict the differences in chain stiffness, and hence in hydrodynamic volume, between samples. Examination of the hydrodynamic volume of these polymers provides evidence that they both subscribe rather well to hydrodynamic theory at high molecular weights but that the stiffer HFBPDA-PFMB shows deviation at lower values.

Improving the high temperature tribology of polyimide by molecular structure design and grafting POSS

“…Several molecular chains of PI1 and PI2 with degree of polymerization of 1, 2, 3, 4, 5, 8, 10, 20, 30 were obtained. It can be seen from Figure 2 that when the number of repeat units was between 2 and 10, the densities of PI1 and PI2 were stable between 1.2 and 1.4 g/cm 3 and the solubility parameters were ranged from 21 (J/cm 3 ) 1/2 to 25 (J/cm 3 ) 1/2 , which was consistent with the experimental results 29–31 . However, when the number of repeat units was greater than 10, overlong chains of molecules bent and clashed with each other, which made the densities and solubility parameters deviate greatly from the actual values.…”

Organo-Soluble Polyimides: Synthesis and Polymerization of 2,2‘-Bis(trifluoromethyl)-4,4‘,5,5‘-Biphenyltetracarboxylic Dianhydride

“…Although this could be due to differences in molecular weight, it is likely that they are to some degree an indication that the polymers possess more extended conformations in the solutions. Evidence for this hypothesis is provided by the fact that the persistence lengths of 6FBPDA−PFMB is 6.6 nm compared to 2.0 nm for 6FDA−PFMB in THF. , …”