Polymer dynamics at low molecular weight of poly(butylene oxide) star polymers†

Abstract

Star polymers are an interesting class of polymers to study based on their shape and dynamics. We use complementary techniques to study the polymer dynamics of star polymers with shorter side chains and compare them with linear counterparts. Using dielectric spectroscopy and rheology allows the extraction of the critical molecular weight using two different approaches. Furthermore, the reduction of the dielectric normal mode relaxation time shows a temperature as well as molecular weight dependent factor. Based on our dielectric spectroscopy results and taking as the limiting case based on theory, a temperature of T = 201.5 K is required which translates into a corresponding factor of for low molecular weight, i.e., M_w < M_c. Fast field cycling NMR together with rheology allowed us to conclude that both techniques track the dynamics of the entire star polymer rather than the dynamics of single arm like dielectric spectroscopy. This is especially seen as the dynamic moduli of linPBO8.5 and starPBO3.7 overlap and therefore have the same relaxation time.