Rheology of Polydisperse Star Polymer Melts: Extension of the Parameter‐Free Tube Model of Milner and McLeish to Arbitrary Arm‐Length Polydispersity

Abstract

Summary: This paper considers the extension of the parameter‐free tube model of Milner and McLeish for stress relaxation in melts of monodisperse star polymers to star polymers whose arms have a continuous molecular weight distribution such as the Flory distribution in the case of star‐nylons and star‐polyesters. Exact expressions are derived for the relaxation spectrum and the relaxation modulus for star polymers having an arbitrary continuous arm‐length distribution. For a Flory distribution a comparison is made with results of dynamic measurements on a melt of 8‐arm poly(ε‐caprolactone) (PCL) stars. An excellent quantitative agreement over a large frequency range is found, however, only if one treats, in contrast with the original parameter‐free tube model approach, the entanglement molecular weight that determines the relaxation spectrum as a fitting parameter independent of the entanglement molecular weight of the linear PCL. This discrepancy is not in anyway related to the polydispersity in arm‐length, but a consequence of the thermorheological complexity of the PCL stars. A similar discrepancy has been observed for hydrogenated polybutadiene stars, as described by Levine and Milner.Measured and calculated storage moduli G′ as a function of frequency ω.magnified imageMeasured and calculated storage moduli G′ as a function of frequency ω.

Aliphatic polyester polymer stars: synthesis, properties and applications in biomedicine and nanotechnology

“…In addition, Grazing Incidence Small Angle X-ray Scattering (GISAXS) is used to determine the mechanism of thermal pore generation in organosilicate thin films loaded with PCL star polymers, 151 while the rheology of these PCL stars is modelled with the Milner-McLeish methodology. 152 As in the ROP of lactide, the ROP of e-caprolactone is widely mediated by a Sn(Oct) 2 catalyst. Alternative catalysts for the preparation of PCL star polymers include: (a) lipase enzyme Novozym 435 from Candida antarctica, 94,153,154 131,132 and Y(dbmp) 3 , 140,141 and (c) organic catalysts including aromatic acids, 118 fumaric acid 123 and DMAP.…”