On the Z5.8‐dependence of viscosity of polymer rings over the range 15 < Zw ≤ 300 of the entanglement number

Abstract

AbstractDynamic moduli G* and zero‐shear viscosity ηo,ring data in both melt and solution states were reported for putative cyclic poly(3,6‐dioxa‐1,8‐octanedithiol) (RDODT) with molecular weights ranging from 43 to 556 kg/mol. Measurements over wide temperature ranges provide up to 18 decades of reduced frequency to characterize RDODT melts and solutions with Zw = Mw/Me,lin from 23 to 300, where Mw is the weight average molecular weight and Me,lin ≈ 1850 g/mol is the entanglement molecular weight of the linear counterparts (LDODT). The G* of all the seven RDODT melts and eight of their solutions with Zw > 15 all have a rubbery plateau with the plateau moduli about same as GNo of the corresponding LDODT. The value Zw ≈ 15 marks the threshold for the change in scaling of ηo,ring from the Rouse‐like ηo,ring ∼ Zw1.0 to a much stronger dependence of ηo,ring ∼ Zw5.8 for Zw up to 300. Such a Zw5.8‐dependence has not been seen before in cyclic polymers and cannot be accounted for by current theoretical models for cyclic polymers. The Coupling Model had been used before to explain the Mw3.4 ‐dependence of linear entangled polymers and the stronger Mw ‐dependence of multi‐arm star branched polymers. It is applied to cyclic RDODT melts and solutions and the results provide an explanation of the observed Zw5.8‐dependence of ηo,ring.