Ionic effects on the behavior of thermoresponsive PEO-PNIPAAm block copolymers

Ian M. Henderson, Peter G. Adams, Gabriel A. Montaño, Walter F. Paxton

Research output: Contribution to journalArticlepeer-review

13 Scopus citations


The temperature-dependent aggregation and recovery of the copolymer poly(ethylene oxide)22-b-poly(N-isopropylacrylamide)29 with a C12 end-cap in aqueous solutions of salts and acids are investigated. Salt solutions affected the critical aggregation temperature of the copolymer in a manner predictable according to the Hofmeister series, with the kosmotropic adipic ion lowering the critical aggregation temperature and the chaotropic iodide raising it. Also, both salts and acids increased the size of copolymer aggregates formed with heating, due to the electrostatic shielding of aggregated structures provided by the electrolytes. Additionally, the presence of ionic additives caused a thermohysteretic increase in the size of copolymer aggregates with temperature cycling. The transitions of polymer structure with increasing temperature were surprisingly sharp with the C12 end-cap present, and particularly broad in samples in which the end cap had been cleaved. This observation suggested that the hydrophobic end group was responsible for imparting some degree of order to the polymer at low temperatures, which allowed for rapid reconfiguration with increasing temperature. Finally, in addition to the transitions expected from the least critical solution temperature behavior of the polymer blocks, we have observed an unexpected additional transition which we attribute to the contraction of the poly(ethylene oxide) chains of the copolymer aggregates at higher temperatures. This work illustrates the importance of considering the environment and composition of thermoresponsive block copolymers in certain applications, particularly in solutions with even modest electrolyte concentrations (1-10 mM), as it can have a profound effect on transition temperatures and morphology.

Original languageEnglish (US)
Pages (from-to)507-516
Number of pages10
JournalJournal of Polymer Science, Part B: Polymer Physics
Issue number7
StatePublished - Apr 1 2014
Externally publishedYes


  • NIPAAm
  • aggregate
  • copolymers
  • ethylene oxide
  • salt
  • thermohysteresis
  • thermoresponsive

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Physical and Theoretical Chemistry
  • Polymers and Plastics
  • Materials Chemistry


Dive into the research topics of 'Ionic effects on the behavior of thermoresponsive PEO-PNIPAAm block copolymers'. Together they form a unique fingerprint.

Cite this