Chain Dynamics in Bulk BPA-PC

A method for the detailed atomistic modelling of amorphous glassy polymers has been developed [50] and appUed to atactic polypropylene. 

The model system is a cube of glassy polymer with 3D periodic boimd-aries, filled with chain segments at a density corresponding to the experimental value for the considered polymer. The entire contents of the cube are formed from a single parent chain with the chemical structure of the polymer. The cube can thus be considered as part of an infinite medium, consisting of displaced images of the same chain, as shown on Fig. 58. 

The initial guess structure is subjected to a total energy minimisation by sHghtly modifying the internal rotation angles in order to reach a microscopic structure in a mechanical equilibrium, i.e. corresponding to a true potential energy minimum. 

The quasi-static modelling of chain dynamics [51] involves starting with an energy-minimised structure in which one degree of freedom is selected 

In the case of BPA-PC [51], the chosen micro structures had cube-edge lengths of 18.44 A and a degree of polymerisation of 35 (Mw = 4532). There are 485 atoms or atom groups in each cube (methyl groups are represented as spherical pseudo-atoms). The force field [46] has fixed bond lengths and fixed 

In order to investigate the intra- and intermolecular cooperativity associated with phenyl and carbonyl motions in glassy BPA-PC, it is interesting to perform dynamic molecular modelling in bulk. Two different modelling approaches have been used to yield information on the nature of cooperativity. 

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