A theoretical study of structural defects in conjugated polymers

Accurate ab-initio calculations are performed for pyrrole and thiophene oli gomers bonded through alpha and beta carbons. The thermodynamical stabiliti y of all possible binding types including the branched forms of tetramers a nd pentamers are compared. Employing the probabilities obtained from these calculations, a Monte Carlo type growth scheme is applied to predict branch ing as functions of the chain length and temperature. A high degree of bran ching for polypyrrole is reported whereas the linear chains dominate the st ructure of polythiophene.