Topological mechanism of polymer nucleation and growth - The role of chain sliding diffusion and entanglement

Masamichi Hikosaka, Kaori Watanabe, Kiyoka Okada, Shinichi Yamazaki

Research output: Contribution to journalReview articlepeer-review

52 Citations (Scopus)

Abstract

Direct evidence of nucleation during the induction period of nucleation from the melt is obtained for the first time by means of small angle X-ray scattering (SAXS). This confirmed that the induction period of crystallization from the melt corresponds to the process of nucleation, not to that of spinodal decomposition. This success is due to a significant increase in the scattering intensity (Ix) from the nuclei (104 times as large as is normal), which was achieved by adding a nucleating agent (NA) to a "model polymer" of polyethylene (PE). Ix increased soon after quenching to the crystallization temperature (Tc) and saturated after the induction time (τi). Lamellae start stacking later than the τi. Power laws of the molecular weight (Mn) dependence of the primary nucleation rate (I) and the growth rate (V) of PE, i.e., I or V ∝ Mn-H where H is a constant, were found for both morphologies of folded chain crystals (FCCs) and extended chain crystals (ECCs). As the power law was also confirmed on isotactic polypropylene (iPP), universality of the power law is suggested. It is to be noted that the power H increases significantly with increase of the degree of order of the crystal structure. The power law confirms that the topological nature of polymer chains, such as chain sliding diffusion and the chain entanglement within the interface between the nucleus and the melt or those within a nucleus, adopts a most important role in the nucleation and growth of polymers. This is theoretically explained by improving the "chain sliding diffusion theory" proposed by Hikosaka. Entanglement dependence of the nucleation rate I is qualitatively obtained for the first time by changing the number density of entanglement (νe) within the melt. An experimental formula of I as a function of νe was obtained on PE, I(νe) ∝ exp(-γνe) where γ is a constant.

Original languageEnglish
Pages (from-to)137-186
Number of pages50
JournalAdvances in Polymer Science
Volume191
Issue number1
DOIs
Publication statusPublished - Dec 1 2005
Externally publishedYes

Keywords

  • Crystallization
  • Degree of supercooling
  • Entanglement
  • Extended chain crystal (ECC)
  • Folded chain crystal (FCC)
  • Growth
  • Growth rate
  • Induction period
  • Melt relaxation
  • Molecular weight
  • Nucleation
  • Nucleation rate
  • Nucleus
  • Optical microscope (OM)
  • Polyethylene

ASJC Scopus subject areas

  • Chemical Engineering(all)
  • Organic Chemistry
  • Polymers and Plastics

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