Chain Packing in Linear Phenol−Polycarbonate by 13C{2H} REDOR

Abstract

Interchain packing in [carbonyl-13C, phenol-2H]phenol-substituted bisphenol A polycarbonate (a totally amorphous polymer by X-ray powder diffraction) has been characterized by 13C{2H} rotational-echo double-resonance (REDOR) NMR measurements on a 10 A 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 2H of one chain is 4−5 A from the carbonate 13C of the other chain, and the interchain 2H−13C dipolar vector has an orientation of approximately 30° (azimuthal) and 70° (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 orienta...