MECHANISM OF DNP-ENHANCED POLARIZATION TRANSFER ACROSS THE INTERFACE OF POLYCARBONATE POLYSTYRENE HETEROGENEOUS BLENDS
MECHANISM OF DNP-ENHANCED POLARIZATION TRANSFER ACROSS THE INTERFACE OF POLYCARBONATE POLYSTYRENE HETEROGENEOUS BLENDS
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DOI：
10.1021/ma00042a007
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发表时间：
1992-08-03
期刊：
影响因子：
5.5
通讯作者：
SCHAEFER, J
中科院分区：
文献类型：
--
作者：
AFEWORKI, M;SCHAEFER, J
在DNP差分实验中，在PC(C-13)/PS(C-12/*)和(PC(C-13)/PS(2D/*))薄膜共混物中观察到相同的界面-PC信号的积分强度(样本记数见上一篇文章)。这一结果证明了从PS相的电子到PC相的质子的极化转移的主要机制是直接极化转移。界面-PC信号强度来自PC膜厚度的2%的60埃区域。通过PC(C-13)/PS(C-12/*)中的H-H自旋扩散，也可能发生DNP增强的PS质子通过PC/PS界面向PC质子的少量极化转移。即使在BDPA掺杂的均聚物中，增强机制也主要是通过直接固体效应极化转移，这一结论是基于PS(*)和PS(2D/*)的电子-质子极化转移的时间依赖关系的相似性。
In DNP difference experiments, the same integrated intensity is observed for the interface-PC signal in PC(C-13)/PS(C-12/*) and (PC(C-13)/PS(2D/*)) thin-film blends (see previous paper for sample notation). 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-angstrom 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(C-13)/PS(C-12/*) 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/*).