Viscoelastic relaxation and molecular mobility of hyperbranched Poly(ε-caprolactone)s in their melt state

The dynamic viscoelastic relaxation behavior and the molecular mobility of a series of hyperbranched poly(epsilon-caprolactone)s (HPCLs) possessing molecular architectural variation and their linear counterpart, linear poly(E-caprolactone) (LPCL), were characterized and evaluated in conjunction with their specific molecular architectures which are the different lengths of the linear backbone segments and the different relative degrees of branching (DBs). The relative DBs, determined by the branching ratio values, were in decreasing order of HPCL-5 > HPCL-10 > HPCL-20. Dynamic viscoelastic relaxation measurements exhibited unentangled behavior for HPCLs compared to the apparently entangled linear, and the parallel G'(omega) and G(omega) curves were observed for the HPCLs, while the LPCL exhibited a typical curve. The melt dynamics of HPCLs was observed to be complex. This characteristic dynamic behavior of HPCLs, particularly incorporating the shorter segments, can be seen to be another example of gellike power-law relaxation of hyperbranched systems. The correlation time, tau(c), was determined from the G(omega) and the empirical Havriliak-Negami (HN) equation, which provided a unique means to evaluate the molecular mobility. Further insights to the correlation times with the Arrhenius equation provided novel information about the temperature-dependence of the molecular mobility and the activation energy, E-a. The molecular mobility of three HPCLs was found to be higher than that of LPCL, and was observed to enhance with decreasing lengths of oligo(E-caprolactone) segments and increasing relative DB.