SELECTIVE OBSERVATION OF THE INTERFACE OF HETEROGENEOUS POLYCARBONATE POLYSTYRENE BLENDS BY DYNAMIC NUCLEAR-POLARIZATION C-13 NMR-SPECTROSCOPY

Heterogeneous blends of [3,3'-C-13(2)]polycarbonate and [ul-ring-C-12(6)]polystyrene were formed by serial film casting. The polystyrene phase of each blend was homogeneously doped with 2 % by weight of a bis(diphenylene)phenylallyl free-radical complex with benzene. Proton polarization enhanced by dynamic nuclear polarization was generated in the polycarbonate phase by dipolar coupling to electrons in the polystyrene phase under 39-GHz microwave irradiation at the difference of the electron and proton Larmor frequencies. Proton magnetization was then transferred to carbons under matched, spin-lock conditions for detection with chemical-shift selectivity by magic-angle spinning C-13 NMR spectroscopy. The C-13 signal from polycarbonate arises exclusively from chains which are at the polycarbonate/polystyrene interface. Signals from bulk polycarbonate were suppressed by differencing techniques. Attempts at direct polarization transfers from electrons in the polystyrene phase to carbons in the polycarbonate phase failed.