Synthesis and 'schizophrenic' micellization of double hydrophilic AB 4 miktoarm star and AB diblock copolymers: Structure and kinetics of micellization

Zhishen Ge, Yuanli Cai, Jun Yin, Zhiyuan Zhu, Jingyi Rao, Shiyong Liu

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114 Citations (Scopus)

Abstract

Poly(N-isopropylacrylamide) (PNIPAM)-based tetrafunctional atom transfer radical polymerization (ATRP) macroinitiator (1b) was synthesized via addition reaction of mono-amino-terminated PNIPAM (1a) with glycidol, followed by esterification with excess 2-bromoisobutyryl bromide. Well-defined double hydrophilic miktoarm AB4 star copolymer, PNIPAM-b-(PDEA)4, was then synthesized by polymerizing 2-(diethylamino)ethyl methacrylate (DEA) via ATRP in 2-propanol at 45°C using 1b, where PDEA was poly(2- (diethylamino)ethyl methacrylate). For comparison, PNIPAM-b-PDEA linear diblock copolymer with comparable molecular weight and composition to that of PNIPAM-b-(PDEA)4 was prepared via reversible addition - fragmentation chain transfer (RAFT) polymerization. The pH- and thermoresponsive 'schizophrenic' micellization behavior of the obtained PNIPAM 65-b-(PDEA63)4 miktoarm star and PNIPAM 70-b-PDEA260 linear diblock copolymers were investigated by 1H NMR and laser light scattering (LLS). In acidic solution and elevated temperatures, PNIPAM-core micelles were formed; whereas at slightly alkaline conditions and room temperature, structurally inverted PDEA-core micelles were formed. The size of the PDEA-core micelles of PNIPAM 65-b-(PDEA63)4 is much smaller than that of PNIPAM70-b-PDEA260. Furthermore, the pH-induced micellization kinetics of the AB4 miktoarm star and AB block copolymers were investigated by the stopped-flow light scattering technique upon a pH jump from 4 to 10. Typical kinetic traces for the micellization of both types of copolymers can be well fitted with double-exponential functions, yielding a fast (τ1) and a slow (τ2) relaxation processes. τ1 for both copolymers decreased with increasing polymer concentration. τ2 was independent of polymer concentration for PNIPAM65-b-(PDEA63)4, whereas it decreased with increasing polymer concentration for PNIPAM 70-b-PDEA260. The chain architectural effects on the micellization properties and the underlying mechanisms were discussed in detail.

Original languageEnglish
Pages (from-to)1114-1122
Number of pages9
JournalLangmuir
Volume23
Issue number3
DOIs
Publication statusPublished - 2007 Jan 30

ASJC Scopus subject areas

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

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