Issue 17, 2014

Stability of star-shaped RAFT polystyrenes under mechanical and thermal stress


Well-defined three-arm and four-arm star polymers designed via a Z-group approach carrying trithiocarbonate functionalities at the core are prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization featuring molecular weights of Mn,SEC = 156 kDa, Đ = 1.16 (3-arm) and Mn,SEC = 162 kDa, Đ = 1.15 (4-arm) based on multi-angle laser light scattering (MALLS) detection, respectively. The star-shaped polystyrenes are subjected (in bulk) to thermal stress in the temperature range between 140 and 200 °C from 10 minutes up to 96 h. The thermally treated 3-arm and 4-arm star polymers are analyzed via size exclusion chromatography (SEC) to quantify the degradation process at variable temperatures as a function of time under an argon atmosphere. Cleavage rate coefficients of the star polymers are deduced as a function of temperature, resulting in activation parameters for the cleavage process, i.e. Ea = 131 kJ mol−1; A = 3.93 × 1011 s−1 (Mn,SEC = 156 kDa, Đ = 1.16, 3-arm star) and Ea, = 134 kJ mol−1; A = 9.13 × 1011 s−1 (Mn,SEC = 162 kDa, Đ = 1.15, 4-arm star), respectively. Processing of the star-shaped polymers is mimicked via a small scale counter rotating twin screw extrusion to achieve nonlinear shear and elongation flow under pressure. Furthermore, a rheological assessment via the linear shear deformation region (small amplitude oscillatory shear, SAOS) allows for a correlation of the processing conditions with the thermal degradation properties of the star polymers in the melt. Zero shear viscosity (η0) as a criterion of the degradation process is measured in the rheometer and correlated to the weight-average molecular weight, Mw.

Graphical abstract: Stability of star-shaped RAFT polystyrenes under mechanical and thermal stress

Supplementary files

Article information

Article type
05 Apr 2014
06 May 2014
First published
08 May 2014
This article is Open Access
Creative Commons BY license

Polym. Chem., 2014,5, 5009-5019

Stability of star-shaped RAFT polystyrenes under mechanical and thermal stress

O. Altintas, M. Abbasi, K. Riazi, A. S. Goldmann, N. Dingenouts, M. Wilhelm and C. Barner-Kowollik, Polym. Chem., 2014, 5, 5009 DOI: 10.1039/C4PY00484A

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