Rotational isomeric-state approximation for the unperturbed dimensions of a POLA polyester

Rotational isomeric-state theory has been applied to investigate chain configurations of a polyester prepared from 4′,5-(1,1,3-trimethyl-3-phenylindan) dicarboxylic acid and 2,2-bis(4′-hydroxyphenyl) propane (POLA polyester). Independent conformations for each repeat monomer unit of the chain have been assumed in the calculations of the unperturbed dimensions. Rotations about the oxygen-phenylene-carbon (O? ?? C) bonds are considered to be free with twofold symmetric potentials. The trans and cis conformations of the carbonyl-phenylene-carbon (O?C? ?? C) and the indan-carbonyl residues are assumed to have equal probability. Two rotational states, trans and cis, are assigned to the ester C? O bonds. Calculation of the reduced unperturbed dimensions (〈r₀²〉/M)_∞ with conformations thus assigned for the bonds in the repeat unit, and comparison with experiment (0.72 ± 0.02 Ų/g) indicate that the conformation in the ester C? O bonds is predominantly trans. An equation for the conformational potential as a function of rotational angle about the ester C? O bond has been formulated using data on potential barriers for low molecular weight compounds. This equation, yielding a potential difference between the cis the trans isomers of 2.5–3.0 kcal/mole, is in good agreement with the prediction made from the calculation of the unperturbed dimensions where a cis/trans ratio of 0.01 for the ester C? O bonds was obtained.