Details of Dynamic Mechanical Properties of Dendritic Poly(ether ketone)s in Conjunction with their Highly Branched Structure and Degree of Branching

Abstract

Full Paper: To investigate the effects of unique hyperbranched structure on viscoelastic properties, three fluoroterminated hyperbranched poly(ether ketone)s (HPEKs) with different degrees of branching (i. e., 0.49; HPEK49, 0.62; HPEK62, and 0.67; HPEK67) and the analogous linear poly(ether ketone) (LPEK), whose chemical structure and molecular weights were similar to those of HPEKs, were synthesized and characterized. From the analysis of plots of the dynamic loss modulus G99(x) versus the storage modulus G9(x) of the individual polymers, it was confirmed that the amount of entanglements between polymer molecules decreased as the degree of branching increased, exhibiting a nearly Newtonian behavior particular for the HPEK with degree of branching of 0.67 (HPEK67). Furthermore, the G99(x) versus G9(x) plots indicated the narrowing of molecular weight distribution and/or shortening of branches with increasing degree of branching, being shown to shift the curves from lower to higher G99(x) values. From the master curves of HPEKs obtained by the time-temperature superposition principle, it was investigated that the rubbery plateau region and the crossover of G9(x) and G99(x) started to disappear at a critical value (A 0.62 ‐ 0.67) of the degree of branching, indicating a nearly Newtonian or little entanglement flow. Moreover, it could be predicted from the tendency of the shift factor aT, obtained from the master curve, that the molecular mobility and temperature dependence of individual HPEKs increased as the degree of branching increased. The shift factors of HPEKs fit with the Williams-LandelFerry (WLF) equation resulted in a more temperature dependent non-Arrhenius behavior than that of LPEK as the degree of branching increased, implying a fragile amorphous polymer. From the nonlinear curve fittings of shift factors by the Vogel-Tamman-Fulcher (VTF) equation, it was further quantified that the HPEKs were more fragile than the LPEK and the fragility increased with increasing degree of branching, which indicated that the branching structure induced the fragility in the materials.