Molecular Motions Involved in the Secondary Transitions of BPA-PC

Conclusion on the Molecular Motions Involved in the Secondary Transitions of BPA-PC 

Various experimental techniques (dielectric relaxation, dynamic mechanical analysis, 1H, 2H and 13C solid-state NMR) have been used for investigating the secondary transitions of BPA-PC, and the block copolymers of BPA and TMBPA carbonates as well as compatible blends of BPA-PC and TMBPA-PC. They have provided lots of information on the motions of methyl, phenyl ring and carbonate units in bulk BPA-PC. The effect of intermolecular packing has also been clearly evidenced. 

Atomistic modelling leads to a more detailed description of the motions and yields a clear insight on the extent of intra- and intermolecular cooperativity. 

By combining all the results, a comprehensive picture of the motions occurring in bulk BPA-PC is reached. At very low temperatures, the first motions to occur are the rotations of the methyl groups of the isopropylidene unit around the C3 axis. The activation energy associated with this y transition is around 8 kj mol-1. 

At higher temperatures, around - 100 °C at 1 Hz, the ft transition involves motions of both carbonates and phenyl rings, accompanied by main-chain reorientation, which can be described in more details as follows. 

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