Application of129Xe NMR to polymer blends

¹²⁹Xe NMR experiments on two different polymer blends are described. The first system, a blend of polypropylene (PP) and the copolymer of polypropylene and polyethylene (EP), shows separate domains of polypropylene and of the copolymer. The latter phase forms rubbery domains in the polypropylene matrix. The second system is the compatible blend of polyvinylidenefluoride and polymethylmethacrylate. For the incompatible blend two Xe resonances are found, one for Xe absorbed in the matrix and one for Xe in the rubbery EP phase. The chemical shift of the Xe absorbed in the rubbery phase can be related to the polyethylene content of the copolymer. The line widths and chemical shifts are affected by the polymer motions as a function of the temperature. Although the system has two very different glass transition temperatures, it is striking to see that upon approaching the polypropylene glass transition temperature the Xe resonance of Xe in the rubbery phase is also affected. Due to the dipolar interaction between Xe spins and polymer proton spins, cross-polarization experiments can be performed. This allows the measurement of correlated NMR spectra. The compatible blend shows only one line with a chemical shift proportional to the composition.