Dynamical heterogeneity and molecular mobility of hyperbranched poly(ether ketone)s with respect to the homologous linear

Hyperbranched poly(ether ketone) (HBPEK) with fluoro-end groups (F-HBPEK) was synthesized by a one-step polymerization reaction. Another HBPEK with different end groups, i.e. cyano-terminated HBPEK (C-HBPEK), was prepared by chemical modification of the fluorides in FHBPEK with cyanophenols. Through analysis by 19F nuclear magnetic resonance (NMR) spectroscopy, the degree of modification from fluorine to cyano groups was determined to be 71%. Furthermore, it was confirmed that the most of the cyano groups were substituted on to the terminal units rather than the linear units. Dynamical heterogeneity/homogeneity and corresponding molecular mobility of both F- and C-HBPEK were investigated by a solid-state 1H NMR spectroscopy. The results were then compared to those of linear analogous poly(ether ketone) (LPEK), which was prepared to investigate any difference in these two characteristics due to their structural dissimilarity. Analysis of 1H magnetization decay as a function of delay time determined the spin–lattice relaxation time in the rotating frame, T1ρ. The double-exponential decay of T1ρ relaxation of both F- and C-HBPEK indicated coexistence of dynamically heterogeneous phases on the basis of motional difference; each was assigned to be the linear and the branched/terminal phase, respectively. In contrast, the single decay in LPEK confirmed a dynamical homogeneity. From further measurements of T1ρs over the temperature range of 140–400 K, the correlation times, τcs, and the activation energies, Eas, were determined. The dynamics of the branched/terminal phase of HBPEKs was greatly affected by the nature of end-group modification. The molecular motion of the linear phase of HBPEKs was faster than that of LPEK, indicating that the hyperbranched structure was responsible for the higher molecular mobility than the linear structure.