writer：E.-S. Zhang, X.-M. Dai, Y.-L. Zhu, Q. Chen, Z.-Y. Sun, X.-P. Qiu, X.-L. Ji
keywords：Associating behavior, Polyimide
source：期刊
specific source：Polymer, 141, 11: 166-174 (2018)
Issue time：2018年
An associating polymer generally contains a small fraction of strongly interacting groups that can form stable aggregates. In this study, a novel soluble polyimide (PI) (6FDA-TFDB) sample with high molecular weight is synthesized; it contains a large fraction of relatively weak interacting groups. Investigation on the solution property and scaling law relationship between η0-ηs and volume fraction shows that this sample exhibits the behavior of associating polymer; this behavior fits the theory of unrenormalized sticky Rouse model and sticky reptation model in a broad volume fraction region, and the scaling exponents in different volume fraction ranges and the critical volume fractions are determined. Moreover, when the volume fraction is above ?* (overlap volume fraction), abnormal shear thinning phenomenon occurs. Oscillation frequency experiment for concentrated polyimide solutions demonstrates that the polyimide solution tends to become a gel above the critical volume fraction due to numerous weak dipole-dipole and π-π interactions. In the UV–Vis spectra, absorption peak shows a red shift with volume fraction, demonstrating that aggregates form in concentrated polyimide solution. Synchrotron radiation small-angle X-ray scattering (SAXS) experiment reveals the appearance of domain, which comes from the aggregates of PI segments. Finally, combined with the quantum chemical calculation, one model based on relatively weak interaction (i.e., dipole-dipole and π-π interactions) from chemical units of polyimides is proposed to explain the associating behavior of high molecular weight polyimide in solution and the shear thinning phenomenon. This study broadens the range of associating polymers.