Rheo-mechanical and rheo-optical characterisation of ultra high molecular mass poly(methylmethacrylate) in solution

This paper presents rheo-mechanical and rheo-optical experimental characterisation of ultra-high molecular mass poly(methylmethacrylate) in solution. A set of ultra-high molecular mass (up to 2 x 10(7) g/mol) poly(methylmethacrylate), obtained in a previous work by B. Simionescu, was used together with a commercial set of lower molecular mass samples in order to cover two decades of molecular mass range. Two solvents were selected, toluene and N,N-dimethylformamide and the concentration was fixed at 2% (wt/wt). All the measurements were performed at 298 degreesK. A complete rheo-mechanical characterisation, both in dynamic mode and in steady shear rate, was performed. In a second step, rheooptical techniques were able to measure the flow-induced birefringence, dichroism and the associated orientation angles. Using the experimental data obtained in this paper, we have derived the stress optical coefficients and shown that they are independent of shear rate and molar mass. We also explore the normal stress behaviour of the solutions tested. (C) 2000 Elsevier Science Ltd. All rights reserved.