DYNAMIC NUCLEAR-POLARIZATION ENHANCED NUCLEAR-MAGNETIC-RESONANCE OF POLYMER-BLEND INTERFACES

Heterogeneous blends of [3,3'- C-13(2)]polycarbonate and [uniform-ring -C-12(6)]Polystyrene were formed by serial film casting. The polystyre ne phase of each blend was homogeneously doped with 2% by weight of a bis (diphenylene)phenylally] free-radical complex with benzene. Proton polarization enhanced by dynamic nuclear polarization was generated i n the polycarbonate phase by dipolar coupling to electrons in the poly styrene phase under 39 GHz microwave irradiation at the difference of the electron and proton Larmor frequencies. Proton magnetization was t hen transferred to carbons under matched spin-lock conditions for dete ction with chemical-shift selectivity by magic-angle spinning C-13 nuc lear magnetic resonance. The C-13 Signal from polycarbonate arises exc lusively from chains which are at the polycarbonate-polystyrene interf ace. Signals from bulk polycarbonate were suppressed by differencing t echniques. The dominant mechanism of polarization transfer from the el ectrons in the polystyrene phase to the protons in the polycarbonate p hase is by direct polarization transfer. The interface signal arises f rom a 60 angstrom region which is 2% of the film thickness. As monitor ed by dynamic nuclear polarization selected dipolar rotational spin-ec ho C-13 nuclear magnetic resonance, polycarbonate chains have less mot ion at the interface than in the bulk.