Soap-free emulsion polymerization of poly(ethylene glycol)block-poly(N- isopropylacrylamide): Elucidation of specific reaction fields for quasi-living polymerization by time-resolved SANS

Ryuhei Motokawa, Satoshi Koizumi, Takeji Hashimoto, Masahiko Annaka, Takayuki Nakahira

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15 Citations (Scopus)

Abstract

Poly(ethylene glycol)-block-poly(N-isopropylacrylamide) (PEG-b-PNIPAAm) was synthesized by radical polymerization of N-isopropylacrylamide (NIPAAm) from the radically activated chain ends generated on PEG. The polymerization process was investigated by a conventional observation of molecular weight and its distribution as well as monomer conversion, CM(t), as a function of the polymerization time t and temperature Tp, by means of time-resolved GPC. The reaction fields in which the polymerization takes place were explored by time-resolved small-angle neutron scattering (SANS). The results elucidated the following characteristics on the temperature-dependence of the solution structure and, hence, the reaction fields: (i) at 15 ≤ T p (°C) ≤ 30, the solution is composed of swollen micelles in which PNIPAAm and PEG block chains form swollen cores and brushes emanating from the interface between them, respectively; and (ii) at 34 ≤ Tp (°C) ≤ 60, the solution is composed of dehydrated PNIPAAm cores (hard cores) and swollen PEG brushes with well-defined interfaces between them. As for (i) and (ii), the micelles were formed from a very early stage of the polymerization as CM being as small as 0.05, hence, yielding a "soap-free emulsion polymerization" field for NIPAAm. The results obtained in this work reveal that the hard-core micelle formation is the necessary and sufficient condition for the "quasi-living soap-free emulsion polymerization".

Original languageEnglish
Pages (from-to)752-764
Number of pages13
JournalMacromolecules
Volume43
Issue number2
DOIs
Publication statusPublished - Jan 26 2010

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Living polymerization
Soaps (detergents)
Emulsion polymerization
Neutron scattering
Polyethylene glycols
Micelles
Polymerization
Brushes
Free radical polymerization
Monomers
Molecular weight
Temperature
poly-N-isopropylacrylamide
N-isopropylacrylamide

All Science Journal Classification (ASJC) codes

  • Organic Chemistry
  • Polymers and Plastics
  • Inorganic Chemistry
  • Materials Chemistry

Cite this

Soap-free emulsion polymerization of poly(ethylene glycol)block-poly(N- isopropylacrylamide) : Elucidation of specific reaction fields for quasi-living polymerization by time-resolved SANS. / Motokawa, Ryuhei; Koizumi, Satoshi; Hashimoto, Takeji; Annaka, Masahiko; Nakahira, Takayuki.

In: Macromolecules, Vol. 43, No. 2, 26.01.2010, p. 752-764.

Research output: Contribution to journalArticle

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abstract = "Poly(ethylene glycol)-block-poly(N-isopropylacrylamide) (PEG-b-PNIPAAm) was synthesized by radical polymerization of N-isopropylacrylamide (NIPAAm) from the radically activated chain ends generated on PEG. The polymerization process was investigated by a conventional observation of molecular weight and its distribution as well as monomer conversion, CM(t), as a function of the polymerization time t and temperature Tp, by means of time-resolved GPC. The reaction fields in which the polymerization takes place were explored by time-resolved small-angle neutron scattering (SANS). The results elucidated the following characteristics on the temperature-dependence of the solution structure and, hence, the reaction fields: (i) at 15 ≤ T p (°C) ≤ 30, the solution is composed of swollen micelles in which PNIPAAm and PEG block chains form swollen cores and brushes emanating from the interface between them, respectively; and (ii) at 34 ≤ Tp (°C) ≤ 60, the solution is composed of dehydrated PNIPAAm cores (hard cores) and swollen PEG brushes with well-defined interfaces between them. As for (i) and (ii), the micelles were formed from a very early stage of the polymerization as CM being as small as 0.05, hence, yielding a {"}soap-free emulsion polymerization{"} field for NIPAAm. The results obtained in this work reveal that the hard-core micelle formation is the necessary and sufficient condition for the {"}quasi-living soap-free emulsion polymerization{"}.",
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