Single BPA-PC Chain

Since the late 1960s, BPA-PC has been studied by various atomistic modelling approaches molecular mechanics or quantum mechanics, either ab initio or semi-empirical. The references about these studies are given in [46]. 

The repeat unit of BPA-PC is shown in Fig. 54 in the conformation where all the torsion angles are zero, corresponding to a fully planar structure. 

Such a repeat unit can be modelled by considering the conformational characteristics of the fragment molecules, diphenyl carbonate (DPC) and 2,2 diphenyl propane (DPP), shown in Figs. 55 and 56, respectively. 

In spite of ab initio calculations performed on these molecules [47], more detail can be found in the semi-empirical quantum mechanics approach developed in [48]. The most relevant results will be described. 

The optimised geometry of DPP has C2 symmetry. The phenyl rings are both tilted by 48.1° relative to the Cp - Q - Cp plane (where Cp denotes the phenyl carbon linked to Ci) X-ray data give 55°. 

---

At this point, we will comment on how this procedure generalizes to other polymers. The other case that was considered by us [28,30,32,175,176] was concerned with bisphenol-A-polycarbonate (BPA-PC) (cf. Fig. 5.1). While for PE we had a correspondence that five chemical repeat units correspond to one effective bond of the bond fluctuation model, for BPA-PC the mapping ratio was inverse - one chemical repeat unit was mapped onto three effective bonds One must consider, however, the very different sizes of the chemical repeat units while for PE this is a single CH2 group, in BPA-PC the repeat unit involves 12 C-C or C-0 bonds along the backbone, and the end-to-end distance of the repeat unit is of the order of 10 A. Thus in this case also one effective bond corresponds to a group of four successive covalent bonds along the backbone of the chain, and a lattice unit corresponds to about 2.03 A [175],... 

---