Rheological study of mixing in molten polymers: 2-mixing of reactive systems

Three reactive polymer systems have been examined with a new mixing device adapted on a classical rheometer in order to investigate reactive mixing situations encountered in polymer blends. After having characterized the bulk polymerization of epsilon-caprolactone (epsilon-CL), the polymerization of 40 wt% of epsilon-caprolactone into a copolymer of ethylene and vinyl acetate (EVA) was run into the rheo-mixer. The kinetics of the reaction in dispersed media was observed slightly different from that in bulk since the characteristic time of epsilon-caprolactone diffusion into EVA is much lower than its time of mixing. On the other hand, it was observed that the molecular weight distribution of the poly(epsilon-caprolactone) is broader in dispersed media ((M) over bar (w) = 15,000 g mole(-1), I-p = 2.6) than in bulk ((M) over bar (w) = 17,000 g mole(-1), I-p = 1.6). A broadening of the molecular weight distribution in dispersed media was pointed out due to the fact that epsilon-CL monomer is partitioned between the EVA and PCL phases leading to a non-homogeneous concentration of monomer in the reactive phase. The polycondensation of 40 wt% of a epoxy-amine system into a polystyrene matrix was also investigated and the morphology of the resulting material examined. A gradient of structure and conversion was detected in a blend obtained from the assembly of two initially non-reactive layers. The gradient reveals that the amine diffuses faster than the epoxy leading to non-stoichiometry of the reactive functions across the sample. When the blend was polymerized under shear, the kinetic of the reaction remained unchanged regardless the level of shear. However, the morphologies were significantly different, pointing out the importance of the coalescence and droplet deformation phenomena. Spherical droplets were observed at 0.15 s(-1) elongated droplets and fibers at 1.5 and 15 s(-1). (C) 2004 Elsevier Ltd. All rights reserved.