Mechanism of DNP-Enhanced Polarization Transfer Across the Interface of Polycarbonate/Polystyrene Heterogeneous Blends.

摘要

The same integrated intensity is observed for the interface-PC signal in PC(13C)/PS(12C/*) and PC(13C)/PS(2D/*) thin film blends in a Dynamic Nuclear Polarization (DNP)-difference experiment. This result proves that the dominant mechanism of polarization transfer from the electrons in the PS phase to the protons in the PC phase is by direct polarization transfer. The interface-PC signal intensity arises from a 60-A region which is 2% of the PC film thickness. Minor polarization transfer from the DNP-enhanced protons of PS to the PC protons across the PC/PS interface via H-H spin diffusion in PC(13C)/PS(12C/*) may also occur. Even in BDPA-doped homopolymers, the enhancement mechanism is mainly via direct solid-effect polarization transfer, a conclusion based on the similarity of the time dependence of the electron-proton polarization transfers for PS(*) and PS(2D/*).