pH and ionic strength responsive polyelectrolyte block copolymer micelles prepared by ring opening metathesis polymerization

Abstract

Well‐defined amphiphilic block copolymers were prepared by ring opening metathesis polymerization and their stimuli responsive behavior of formed micelles in aqueous solution was investigated. The hydrophobic core of the micelles consists of either a poly[5,6‐bis(ethoxymethyl)bicyclo[2.2.1]hept‐2‐ene]‐block with a glass transition Tg at room temperature or a poly[endo,exo[2.2.1]bicyclohept‐5‐ene‐2,3‐diylbis (phenylmethanone)] with a Tg of 143 °C. For the polyelectrolyte shell, the precursor block poly[endo,exo[2.2.1]bicyclohept‐5‐ene‐2,3‐dicarboxyclic tert‐butylester] was transformed into the free acidic block by cleavage of the tert‐butyl groups using trifluoroacetic acid. Micellar solutions were prepared by dialysis, dissolving the copolymers in dimethyl sulfoxide which was subsequently replaced by water. All polymers form micelles with radii between 10 and 20 nm at a pH‐value below 5, where the carboxylic acid groups are in the protonated state. The block copolymer micelles show a strong increase of the hydrodynamic radius with increasing pH‐value, due to the repulsion among the formed carboxylate anions resulting in a stretching of the polymer chains. In this state, the micelles exhibit responsive behavior to ionic strength where a contraction of the micelles is observed as the carboxylate charges are balanced by sodium ions, whereas no changes of the hydrodynamic radius on addition of salt are observed at low pH. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1178–1191, 2009

Polymeric nanoparticles, micelles and polymersomes from amphiphilic block copolymer

“…The transformation changes the HLB value of the copolymers and results in the destabilization of the polymersome. Stubenrauch pH and ionic strength variations [132]. They prepared block copolymers containing 5,6-bis(ethoxymethyl)-bicyclo[2.2.1]hept-2-ene or endo, exo[2.2.1]bicyclohept-5-ene-2,3-diylbis(phenylmethanone), etc, as hydrophobic blocks, by using ROMP.…”

Facile synthesis of triple‐stimuli (photo/pH/thermo) responsive copolymers of 2‐diazo‐1,2‐naphthoquinone‐mediated poly(N‐isopropylacrylamide‐co‐N‐hydroxymethylacrylamide)

“…However, in the architectures bearing segmented monomer sequences, such as block and graft copolymers that are often found synthetically challenging, the LCST tends to be remained unchanged as that of PNIPAM 22–27. Meanwhile, the LCST behavior can also be affected by other factors, such as pH,28–31 solvent,32–35 ionic strength,36–40 and so forth, and these characters can be utilized to make “smart” materials 41–43…”

Synthesis of Miktoarm Branched Conjugated Copolymers by ROMPing In and Out

“…37 Polyelectrolyte block copolymers derived from 3 have been shown to form pH- and ionic strength-responsive micelles, which undergo a transition in size between pH 5 and 6. 38 Neutral aqueous solutions of P5-OH may be purified from the polynorbornene diblock by centrifuge filtration. At pH 3, P5-OH forms 45 ± 11 nm particles displaying a LCST at 20.5 °C, as determined by DLS and transmission measurements (Figure 4).…”