| Polymer blending often relies on reactive compatibilization to create stable mixtures of two otherwise immiscible polymers. In reactive compatibilization, a small number of polymer chains in each phase is functionalized. During blending, these functionalized chains react at the interface to form block or graft copolymers that stabilize the mixture. Several factors may affect the rate of reaction during compatibilization: external convection that creates interfacial area between the polymer phases, diffusion of the reactive polymer chains through the bulk to the interface, and the chemical reaction that occurs between different functional groups. This thesis details model experiments that separate these factors to pinpoint the most important to reactive compatibilization.; Forward recoil spectrometry (FRES) was used to monitor the diffusion and reaction of model end-functional polymers at a polystyrene/poly(methyl methacrylate) interface in the absence of external convection. FRES concentration profiles indicated the reaction kinetics as a function of reactant concentration, and reactant and matrix molecular weight. In all cases, the reaction required several hours to attain a steady state, and was much slower than expected from diffusion-controlled kinetics. Furthermore, a novel sample geometry directly revealed that the reactive chains diffused several hundred nanometers in minutes and sampled the interface many times before significant interfacial reaction occurred. Thus, in situ copolymer formation is limited by the movement of the reactive chains near the interface, rather than the diffusion of the chains through the bulk. The interface likely represents an enthalpic barrier to reaction, because the reactive chains must experience many unfavorable contacts with the other phase for reaction to occur.; Additional model experiments subjected reactive multilayer samples to both pure shear and extensional flows using available rheometers, as well as intensive mixing in a small cup-and-rotor mixer. The results of these experiments indicate that external convection changes the reaction time scale from hours to minutes, and suggest that the barrier to reaction posed by the interface can be overcome by applying large deformations at a high rate. |
