Journal
JOURNAL OF DISPERSION SCIENCE AND TECHNOLOGY
Volume 33, Issue 1-3, Pages 287-292Publisher
TAYLOR & FRANCIS INC
DOI: 10.1080/01932691.2011.561699
Keywords
Double hydrophilic block copolymers; micelle; nanoaggregates; RAFT
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Funding
- Iketani Science and Technology Foundation
- Kawanishi Memorial Shinmaywa Education Foundation
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Heat and salt induced aggregation of three well-defined double hydrophilic block copolymers (DHBCs) of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and N-isopropylacrylamide (NIPAM) with constant chain length of the PAMPS block (with number-average degree of polymerization, DPn = 61) and varying chain length of the PNIPAM block with DPn = 11, 23, and 34 synthesized via reversible addition-fragmentation chain transfer (RAFT) controlled radical polymerization was investigated by turbidity, dynamic light scattering (DLS) and H-1 NMR measurements. In the presence of salt or with an increase in temperature, the diblock copolymers form micelles with a PNIPAM core and PAMPS corona. The heat and salt induced aggregation in dilute aqueous solutions dependant on the molecular characteristics of the DHBC (DPn of the PNIPAM block) was observed. The DHBC becomes amphiphilic as the PNIPAM block loses hydrophilicity at higher temperature above its lower critical solution temperature (LCST). Furthermore, the presence of salt induces salting out effect of the uncharged PNIPAM block. The diblock copolymer thus forms nanosized aggregates at a high temperature or in the presence of salt. These aggregates may be multiple aggregates due to inter-micellar aggregation of the spherical core-corona micelles.
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