Rheological behavior of reactive miscible polymer blends: Influence of mixing and annealing before crosslinking

We followed crosslinking reactions in the blends of two miscible reactive polymers by either torque rheometry or dynamic rheological measurements. Functional polymers with controlled glass‐transition temperatures (T_g's), chain lengths, and number of reactive groups per chain were synthesized by bulk radical polymerization. The blends were prepared either in a batch mixer or directly in the parallel plate geometry of a dynamic rheometer. Because of the low T_g of the blend components, it was possible to separate the mixing step from the crosslinking reaction, which was followed by small amplitude dynamic measurements at a higher temperature. The kinetics of the crosslinking reaction were determined by the study of the variations of the storage modulus (G′) as a function of the reaction time. In this study, we focused on investigating the influence of blend composition, crosslinking reaction temperature, and amount of shear generated during the mixing step on the reaction kinetics. The influence of annealing time after the preshear step was also investigated. We found that the mixing procedure in the internal mixer produced homogeneous blends for which G′ was dependent on the reaction time. Moreover, the reaction rate increased as the temperature and the chain functionality increased. A first approach showed that reduced variables could be defined from G′ and reaction time with the initial concentration of the functional units to obtain a master curve independent of the species concentration. For blends prepared directly between the parallel plates of the dynamic rheometer, G′ and the subsequent reaction rate were strongly dependent on the amount of shear generated during the mixing step. However, at high enough shear, the blend was perfectly mixed and the increase in G′ versus reaction time was comparable to that obtained for the blend prepared in the internal mixer. Surprisingly, the higher the annealing time was, the lower the increase in G′ was. However, we could explained this by considering the fact that the reaction started during the annealing step, which therefore, led to a thin crosslinked layer, which prevented any further diffusion of the polymer chains. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 1978–1995, 2005