Predicting the macromolecular structure and properties of lignin and comparison with synthetically produced polymers

Determining the structure of the plant polymer lignin is not feasible because of the heterogeneous structure of this polymer and the difficulties encountered in its extraction. Therefore, computational chemistry can provide information, which may otherwise be unavailable. Based on experimental results, computational chemistry was used to mimic the processes involved in lignin formation. Synthetic polymers also were prepared from the three major lignin precursors and their physical properties were shown to give good correlation with computational models constructed to represent these polymers. Both computational and experimental results, demonstrated that the higher the degree of methoxylation, the more flexible the polymer and this was shown to be dependent on the type of inter-unit linkage. Using the same experimentally derived parameters, a model was constructed to represent a generalised lignin. This model was shown to be a flexible, closely packed structure and this was attributed to the predominance of 8-O-4 linkages, which allowed closer stacking of the aromatic rings.