Thermoresponsive amphiphilic symmetrical triblock copolymers with a hydrophilic middle block made of poly(N-isopropylacrylamide): Synthesis, self-organization, and hydrogel formation

Achille M. Bivigou-Koumba, Eckhard Görnitz, André Laschewsky, Peter Müller-Buschbaum, Christine M. Papadakis

Research output: Contribution to journalArticlepeer-review

51 Scopus citations

Abstract

Several series of symmetrical triblock copolymers were synthesized by the reversible addition fragmentation chain transfer method. They consist of a long block of poly(N-isopropylacrylamide) as hydrophilic, thermoresponsive middle block, which is end-capped by two small strongly hydrophobic blocks made from five different vinyl polymers. The association of the amphiphilic polymers was studied in dilute and concentrated aqueous solution. The polymer micelles found at low concentrations form hydrogels at high concentrations, typically above 30-35 wt.%. Hydrogel formation and the thermosensitive rheological behavior were studied exemplarily for copolymers with hydrophobic blocks of polystyrene, poly(2-ethylhexyl acrylate), and poly(n-octadecyl acrylate). All systems exhibited a cloud point around 30∈°C. Heating beyond the cloud point initially favors hydrogel formation but continued heating results in macroscopic phase separation. The rheological behavior suggests that the copolymers associate into flower-like micelles, with only a small share of polymers that bridge the micelles and act as physical cross-linkers, even at high concentrations.

Original languageEnglish
Pages (from-to)499-517
Number of pages19
JournalColloid and Polymer Science
Volume288
Issue number5
DOIs
StatePublished - Mar 2010

Keywords

  • Amphiphiles
  • Hydrogel
  • Lower critical solution temperature
  • Polymer micelle
  • Reversible addition fragmentation chain transfer (RAFT)
  • Triblock copolymers

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