Kinetics of crystallization mechanisms in poly(3-hexylthiophene) and poly(9,9-dihexylfluorene-alt-2,5-didodecyloxybenzene) conjugated polymers

Abstract

Conjugated polymers are perceived as promising materials for emerging applications in energy and environment. Kinetics of crystallization processes in conjugated polymers may not only model the processes but also helps in revealing their mechanisms. This paper gives an account of the kinetic investigation on crystallization processes in two known conjugated polymers, poly(3-hexylthiophene) (P3HT) and poly(9,9-dihexylfluorene-alt-2,5-didodecyloxybenzene) (PF6OC12) under non-isothermal conditions by employing the advanced polymer crystallization kinetics approach. Kinetic study suggests that both P3HT and PF6OC12 crystallize by following fairly single-step nucleation and diffusion phenomena. In addition, the diffusion activation energies of P3HT and PF6OC12 obtained are compared and conform to the universal activation energy value of the segmental jump during the diffusion processes in polymers. Nevertheless, while PF6OC12 pursues two-dimensional (2D) growth of spherulites, P3HT on the other hand, follows a rather complex crystallization mechanism. It is noteworthy that the glass transition temperatures of both the conjugated polymers are more or less the same. The obtained kinetic parameters are interpreted in terms of their plausible physical meanings. A thermodynamic expression to determine the transition entropy of polymer crystallization is also derived and discussed.