A theoretical study of structural defects in conjugated polymers

Accurate ab-initio calculations are performed for pyrrole and thiophene oligomers bonded through α and β carbons. The thermodynamical stabilitiy of all possible binding types including the branched forms of tetramers and pentamers are compared. Employing the probabilities obtained from these calculations, a Monte Carlo type growth scheme is applied to predict branching as functions of the chain length and temperature. A high degree of branching for polypyrrole is reported whereas the linear chains dominate the structure of polythiophene.