Synthesis and aggregation behavior of thermally responsive star polymers

Robert H. Lambeth, Subramanian Ramakrishnan, Ryan Mueller, John P. Poziemski, George S. Miguel, Larry J. Markoski, Charles F. Zukoski, Jeffrey S. Moore

Research output: Contribution to journalArticlepeer-review

Abstract

To mimic the three-dimensional (3-D) globular architecture resulting from the precise positioning of hydrophobic/ hydrophilic domains (blocks) of naturally occurring proteins, water-soluble linear and star homopolymers of N,N′-dimethylacrylamide (DMA) were synthesized with prescribed molecular weights via reversible addition-fragmentation chain transfer (RAFT) polymerization and subsequently used as macro chain transfer agents for block copolymerization with N-isopropylacrylamide (NIPAM). For the star block copolymers, the interior block consisted of NIPAM while the exterior block was DMA. Since polyNIPAM thermally switches from hydrophilic to hydrophobic, the 3-D solution conformations of the polymers were studied as a function of temperature using differential scanning calorimetry (DSC), static light scattering (SLS), and dynamic light scattering (DLS). The polymers were observed to form monodisperse aggregates in an aqueous pH 4 buffer solution when heated above the lower critical solution temperature (LCST) of polyNIPAM. The temperature at which the polymers aggregated and the size of the aggregates were dependent on the NIPAM block length and the core architecture. A simple model based on an optimal area per headgroup was used to analyze our experimental findings and was useful for predicting the final size and molecular weight of the aggregates formed.

Original languageEnglish (US)
Pages (from-to)6352-6360
Number of pages9
JournalLangmuir
Volume22
Issue number14
DOIs
StatePublished - Jul 4 2006

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Surfaces and Interfaces
  • Spectroscopy
  • Electrochemistry

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