Total-molecular-weight-dependent Rouse dynamic of ultra-small branched star poly(ε-caprolactone)s as a single coarse-grain unit

The extremely small branched effects on molecular dynamics are investigated using well-defined star poly( e -caprolactone)s containing ultra-small branches (USB-SPCLs) as a model system. USB-SPCLs interestingly show total-molecular-weight-dependent glass transitions regardless of the molecular architecture parameters, such as the number and length of branches, whereas typical star polymers with polymeric large branches show the end-group-concentration-dependent glass transitions. The viscoelasticity of USB-SPCLs does not depend exponentially on the individual branched molecular weight, as observed in typical star polymers, and instead follows the modified Mark–Houwink power law and the Bueche-modified Rouse model for unentangled linear polymers. The flow activation energy and the longest Rouse relaxation time of USB-SPCLs show that the individual branches of USB-SPCL are dynamically equivalent and that a whole USB-SPCL molecule moves with a simple uni-motion. These results suggest that a whole USB-SPCL molecule presumably acts as a dynamically-equivalent single coarse-grain unit because of the extremely small branches on the scale of 20–40 atoms.