Thermosensitive diblock copolymer of poly(N-isopropylacrylamide) and poly(ethylene glycol) in water: Polymer preparation and solution behavior

Ryuhei Motokawa, Kanae Morishita, Satoshi Koizumi, Takayuki Nakahira, Annaka Masahiko

Research output: Contribution to journalArticle

122 Citations (Scopus)

Abstract

This investigation focused on the self-assembly of poly(N- isopropylacrylamide)-eZoc&-poly-(ethylene glycol) (PNIPA-block-PEG) in water. A quasi-living radical polymerization technique including a Ce(IV) ion redox system enabled us to prepare block copolymers with relatively narrow molecular weight distributions. We distinguish five regions in the phase diagram: a transparent sol, opaque sol, transparent gel, opaque gel, and syneresis. By examining the extent of changes in the spectroscopic properties of a fluorescence probe, pyrene, as a function of block polymer concentration and/or temperature, we determined the critical association concentration as well as the partition coefficient Kv for pyrene. The spectroscopic properties indicate that the hydrophobicity around the probe starts to increase far below the demixing line of the PNIPA-block-PEG, a remarkable finding which suggests that even in the temperature region below the LCST temperature of a PNIPA block (∼32°C), this block copolymer provides more space for a preferential transfer of pyrene molecules than a bulk water medium at a higher temperature. This result may be attributed to the action of water, which starts to behave as a selective solvent for PEG blocks; the PEG chains are more swollen with water than are the PNIPA chains. Dynamic light scattering measurements also indicate that contraction of the PNIPA block starts to occur around 18°C, which is consistent with results obtained by fluorescence measurements. By employing small-angle neutron scattering, it is also confirmed that microphase separation occurs above 17°C to form disordered micelles, which includes a range of states from (i) asymmetric swelling to (ii) micelle formation with only short-range liquidlike order. Above 30°C, network domains are formed as a result of macrophase separation due to dehydration of PNIPA blocks. As the temperature increased up to 40°C, the network domain is collapsed along a direction parallel to PNIPA-block-PEG interface, leading to increase in interfacial thickness and to macroscopic syneresis.

Original languageEnglish
Pages (from-to)5748-5760
Number of pages13
JournalMacromolecules
Volume38
Issue number13
DOIs
Publication statusPublished - Jun 28 2005

Fingerprint

Polyethylene glycols
Block copolymers
Polymers
Water
Pyrene
Micelles
Polymethyl Methacrylate
Sols
Gels
Temperature
Fluorescence
Microphase separation
Living polymerization
Dynamic light scattering
Molecular weight distribution
Hydrophobicity
Free radical polymerization
Neutron scattering
Dehydration
Self assembly

All Science Journal Classification (ASJC) codes

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

Cite this

Thermosensitive diblock copolymer of poly(N-isopropylacrylamide) and poly(ethylene glycol) in water : Polymer preparation and solution behavior. / Motokawa, Ryuhei; Morishita, Kanae; Koizumi, Satoshi; Nakahira, Takayuki; Masahiko, Annaka.

In: Macromolecules, Vol. 38, No. 13, 28.06.2005, p. 5748-5760.

Research output: Contribution to journalArticle

Motokawa, Ryuhei ; Morishita, Kanae ; Koizumi, Satoshi ; Nakahira, Takayuki ; Masahiko, Annaka. / Thermosensitive diblock copolymer of poly(N-isopropylacrylamide) and poly(ethylene glycol) in water : Polymer preparation and solution behavior. In: Macromolecules. 2005 ; Vol. 38, No. 13. pp. 5748-5760.
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