Preparation and characterization of thermally responsive block copolymer micelles comprising poly(N-isopropylacrylamide-b-DL-lactide)

Fukashi Kohori, Kiyotaka Sakai, Takao Aoyagi, Masayuki Yokoyama, Yasuhisa Sakurai, Teruo Okano*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

265 Citations (Scopus)


The thermally sensitive block copolymer, poly(N-isopropylacrylamide-b-dl-lactide) (PIPAAm-PLA), was synthesized by ring-opening polymerization of dl-lactide initiated from hydroxy-terminated poly (N-isopropylacrylamide) (PIPAAm). A PIPAAm bearing a single terminal hydroxyl group was prepared by telomerization using 2-hydroxyethanethiol as a chain-transfer agent. Successful preparation of PIPAAm and the PIPAAm-PLA block copolymer was verified by gel permeation chromatography (GPC) and 1H-NMR spectroscopy. Polymeric micelles were prepared from block copolymers using a dialysis method. Their solutions showed reversible changes in optical properties: transparent below a lower critical solution temperature (LCST) and opaque above the LCST. Dynamic light scattering measurements were used to observe the formation of micellar structures approximately 40 nm in diameter, which do not change between 20°C and 30°C. Above the LCST, polymer micelles aggregated, a phenomenon found to be reversible since the aggregates dissociated again by cooling below the LCST. Further observations using atomic force microscopy (AFM) confirmed this behaviour. The properties of this block copolymer system are interesting from both applied and fundamental perspectives, particularly for active targeting as drug carriers. Copyright (C) 1998 Elsevier Science B.V.

Original languageEnglish
Pages (from-to)87-98
Number of pages12
JournalJournal of Controlled Release
Issue number1
Publication statusPublished - 1998 Oct 30


  • Poly(DL-lactide)
  • Poly(N-isopropylacrylamide)
  • Polymeric micelles
  • Thermally sensitive

ASJC Scopus subject areas

  • Pharmaceutical Science


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