Conclusion on Solid-State NMR Investigations

As described, solid-state H, and NMR provide quite a detailed picture of the motions occurring in glassy BPA-PC. 

The main chain exhibits, at room temperature, an isotropic rotational motion with 10° rms at a frequency around 105 Hz, also showing a wide distribution of frequencies. 

The carbonyl motions of the carbonate group can be accounted for by considering jumps between two sites, corresponding to a rotation around an axis perpendicular to the C = O bond in the plane formed by the three oxygen atoms, with an angle of 40° between the two sites, over which is superimposed a rotation of 15° about the C = O bond. This latter motion requires a main-chain reorientation motion. 

In conclusion, it is unambiguous from the soHd-state NMR investigations that phenyl ring motions are involved in the mechanical p transition of BPA-PC. Additional support for this statement comes from the fact that the position and shape of the mechanical dynamic loss, G , can be weU simulated by using the activation parameters and the WUhams-Watts exponent deduced from the analysis of the phenyl ring motions [34], as shown in Fig. 53. 

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