One intellectual problem in polymer research - The coil-to-globule conformation transition of flexible chains

Xiao Dong Ye, Ke Jin Zhou, Chi Wu

Research output: Contribution to journalArticle

2 Scopus citations

Abstract

A macromolecule consists of many repeating units connected via covalent bonds. Such a chain connectivity results in some unique physical properties and related problems of macromolecules. In this review, we will clarify one intellectual problem that is absent in small molecular systems; namely, small molecules only have soluble and insoluble two states; in 1960's, theorists predicted that even in its soluble state a flexible linear polymer chain can change its conformation from a swollen random coil to a collapsed globule as the solvent quality varies from good to poor. Since the end of 1970's, experimentalists tried hard to confirm such a coil-to-globule transition. However, a stable single-chain collapsed globule had not been experimentally observed up to the middle of 1990's. This unsolved problem has long puzzled many researchers. One theorist even claimed in 1993 that a thermodynamically stable single-chain collapsed globule cannot be observed with our modern instruments and current sample preparation technique. In China, the late Professor Renyuan Qian and some researchers started to study some single-chain problems in the end of 1980's. In 1993, our laboratory used a novel approach to attack such a problem by successfully preparing and using some narrowly distributed high-molar mass linear thermally sensitive water-soluble homopolymers. In 1995, we observed this long-predicted coil-to-globule transition by using laser light scattering. Further, we discovered a novel "molten globule" state during the coil-to-globule transition and revealed that there is no additional knotting and entanglement inside individual single-chain globules. We also studied, for the first time, the opposite globule-to-coil transition and found an unexpected hysteresis in comparison with the coil-to-globule transition, which is related to the formation of additional intrachain hydrogen bonds inside the collapsed globular state. Finally, we investigated the chain folding kinetics by using the infrared pulsed laser-induced temperature jump and unearthed that the coil-to-globule transition has two distinct kinetic stages: the nucleation (formation of small "pearls" made of a limited number of collapsed chain segments along the chain), in dependent of the chain length; and the coarsening (merging of "pearls"). After persisting for nearly twenty years, we have essentially concluded the study of this important intellectual problem in modern polymer physics and revealed some of its related unique physical properties.

Original languageEnglish (US)
Pages (from-to)1389-1399
Number of pages11
JournalActa Polymerica Sinica
Issue number9
DOIs
Publication statusPublished - Sep 20 2017

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Keywords

  • Chain conformation
  • Flexible linear polymer chain
  • Laser light scattering
  • Polymer solution
  • Thermally sensitive water-soluble polymer

ASJC Scopus subject areas

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

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