## Abstract

The molecular weight (M_{n}) dependence of the primary nucleation rate (I) of folded chain single crystals (FCSCs) of polyethylene (PE) was studied. A power law for the nucleation rate, I ∝ M_{n}^{-2.4}, was found. The FCSCs were formed by isothermal crystallization from the melt into an ordered phase (=orthorhombic phase). A new experimental method was established to obtain reliable I, which has been difficult in the case of heterogeneous nucleation for long years. The degree of supercooling (ΔT) dependence of I fits well with the theoretical I given by classical nucleation theory, I = I_{0} exp(-ΔG*/kT) ∝ D exp(-C/ΔT^{2}), where I_{0} is proportional to the topological diffusion coefficient of polymer chains (D), ΔG* is the free energy for forming a critical nucleus, k is the Boltzmann constant, T is temperature, and C is a constant. It is found that ΔG* (∝C) does not depend on M_{n}, while I_{0} decreases with increase of M_{n}, from which it is concluded that formation of a critical nucleus is not controlled by M_{n}, while only topologic diffusion of polymers is controlled by M_{n}, i.e., I ∝ D(M_{n}). Similar power laws of PE were already found by the present authors on I of extended chain single crystals (ECSCs), i.e., I ∝ M_{n}^{-1.0}, and on the lateral growth rates (V) of ECSCs and FCSCs, V ∝ M_{n}^{-0.7} and V ∝ M_{n}^{-1.7}, respectively. ECSCs were formed by isothermal crystallization from the melt into a disordered phase (=hexagonal phase). Therefore, it is concluded that a common power law, I, V ∝ D(M_{n}) ∝ M_{n}^{-H} of PE is confirmed, irrespective of nucleation or growth and irrespective of crystalline phases, ordered or disordered phases. It is to be noted that the power H depends on the degree of order of the crystalline phase, from which it is concluded that both nucleation and growth are controlled by the "topological" diffusion of polymer chains within interface between a nucleus (or crystal) and the melt and/or within the nucleus. The "topological" diffusion is related to chain sliding diffusion and disentanglements.

Original language | English |
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Pages (from-to) | 6985-6991 |

Number of pages | 7 |

Journal | Macromolecules |

Volume | 35 |

Issue number | 18 |

DOIs | |

Publication status | Published - Aug 27 2002 |

## ASJC Scopus subject areas

- Organic Chemistry
- Polymers and Plastics
- Inorganic Chemistry
- Materials Chemistry