Chain packing in linear phenol-polycarbonate by 13C{2H} REDOR

Interchain packing in [carbonyl-C-13, phenol-H-2]phenol-substituted bisphenol A polycarbonate ( I a totally amorphous polymer by X-ray powder diffraction) has been characterized by C-13{H-2} rotational-echo double-resonance (REDOR) NMR measurements on a 10 Angstrom distance scale. Differences in the REDOR dephasing rates of the centerband and spinning sidebands of the carbonyl carbon resonance prove the presence of local orientational order, Approximately 70% of the repeat units are locally ordered. For the most tightly packed pairs of chains, the phenol H-2 of one chain is 4-5 Angstrom from the carbonate C-13 of the other chain, and the interchain H-2-C-13 dipolar vector has an orientation of approximately 30degrees (azimuthal) and 70degrees (polar) in the carbonyl carbon chemical shift tensor reference frame. The REDOR determination of these packing parameters is model-independent. Both random and chain-pair models were generated to describe the chain packing, but only the chain-pair model was consistent with the REDOR distance and orientation results.