  We propose a theoretical approach to quantitatively account for the role of
entanglement in the nucleation of polymer melts, which is the unique feature of
polymer differentiated from small molecules. By performing molecular dynamics
simulations, we obtain the nucleation barriers of polymer systems with
different entanglement densities, which exhibits an opposite trend compared to
the prediction of the classic nucleation theory (CNT). To amend the deficiency
of the CNT in polymer crystallization, we introduce the entanglement free
energy to reflect the role of entanglement in polymer nucleation. Specifically,
the polymer nucleation not only involves free energies of monomers inside and
on the surface of a nucleus as considered in the CNT, but also affects the
entanglement network around the nucleus. Our theoretical approach provides a
reasonable interpretation for the unsolved nucleation phenomena of polymers in
simulations and experiments.

Soft Condensed Matter