Orientation of the diphenylene propane unit in stretched polycarbonate from two-dimensional magic-angle-spinning NMR

Two-dimensional magic-angle-spinning (2D-MAS) NMR has been used to measure the orientation parameter, P₂, of the diphenylene propane unit in bisphenol-A polycarbonate oriented by stretching to various extension ratios,, atT=295K andT= 403 K.P₂ is proportional to the birefringencen, with a maximum birefringencen₀= 0.189. There is some evidence that the order parameterP₂ of the DPP units with respect to the chain axis deviates from unity.n₀ is therefore expected to be different from the birefringence,n₀, of perfectly aligned chains of polycarbonate. The experimental results obtained forP₂() are compared to those predicted by the aggregate model.