| Aromatic polyimides have become integral materials in many industries since they can be engineered to have low coefficients of thermal expansion (CTE), low dielectric constants ({dollar}varepsilon{dollar}), high thermal and thermo-oxidative stability, good solvent resistance and excellent mechanical properties. Traditionally, polyimides have been processed from their precursor poly(amic acid) (PAA) form and then converted into the final imidized state by either chemical or thermal cyclodehydration. However, there has been increasing interest in soluble aromatic polyimides which can be processed from their fully imidized form. This provides the benefits of fewer processing steps, less complicated storage concerns and fewer flaws in the films, fibers, etc., produced from them.; Under investigation in this study is one novel soluble, aromatic polyimide HFBPDA-PFMB. This polyimide is prepared from the condensation of 2,2{dollar}spprime{dollar}-bis(trifluoromethyl)-4,4{dollar}spprime{dollar},5,5{dollar}spprime{dollar}- biphenyltetracarboxylic dianhydride (HFBPDA) and 2,2{dollar}spprime{dollar}-(trifluoromethyl)-4,4{dollar}spprime{dollar},-diaminobiphenyl diamine (PFMB). The results from this work are paralleled with those from an already well-known polyimide 6FDA-PFMB, which is created from the condensation of 2,2{dollar}spprime{dollar}-bis(3,4 dicarboxyphenyl)-hexafluoropropane dianhydride (6FDA) and PFMB. The hexafluoropropane linkage in 6FDA-PFMB increases its flexibility with respect to HFBPDA-PFMB. Not only is the flexibility increased but this aliphatic group adds a sharp bend in the backbone as a result of the bond angle of the sp{dollar}sp3{dollar} hybridized carbon. This geometry further decreases the linearity along the backbone in contrast to HFBPDA-PFMB.; We are taking this opportunity to study some of the solution characteristics of HFBPDA-PFMB and 6FDA-PFMB in order to try to determine their chain rigidity. Specifically, we examined whether these segmented rigid-rod polymers subscribe to the size exclusion chematography (SEC) universal calibration, their Mark-Houwink-Sakurada constants, persistence lengths and unperturbed dimensions. The results obtained from this work are necessary for the continuing characterization of polymers in this family whose number and application is ever increasing.; These polyimides have proven to be useful in certain optical applications. For instance, these polymers have been found to be important components in liquid crystal displays where they act as negative birefingence compensation films. These films dramatically increase the viewing angles of the displays. We have investigated the relation between the molecular weight and the film optical properties such as birefringence. |
