Self-Assembly of a Diblock
Copolymer with Pendant
Disulfide Bonds and Chromophore Groups: A New Platform for Fast Release
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Abstract
An amphiphilic block copolymer comprising poly(ethylene
glycol)
(PEG) and poly(2-(methacryloyl)oxyethyl-2′-hydroxyethyl disulfide)
(PMAOHD) blocks was synthesized by atom transfer radical polymerization
(ATRP). Pyrenebutyric acid was conjugated to the block copolymer by
esterification, and a block copolymer with pendant disulfide bonds
and pyrenyl groups (PEG-<i>b</i>-P(MAOHD-<i>g</i>-Py)) was obtained. <sup>1</sup>H NMR and gel permeation chromatography
(GPC) results demonstrated the successful synthesis of the block copolymer.
The cleavage of the disulfide bonds and the degrafting of the pyrenyl
groups were investigated in THF and a THF/methanol mixture. Fluorescence
spectroscopy, GPC, and <sup>1</sup>H NMR results demonstrated fast
cleavage of the disulfide bonds by Bu<sub>3</sub>P in THF. Fluorescence
results showed the ratio of the intensity of the excimer peak to the
monomer peak decreased rapidly within 20 min. GPC traces of the block
copolymer moved to a long retention time region after addition of
Bu<sub>3</sub>P, indicating the cleavage of the disulfide bonds and
the degrafting of the pyrenyl groups. PEG-<i>b</i>-P(MAOHD-<i>g</i>-Py) can self-assemble into micelles with poly(MAOHD-<i>g</i>-Py) cores and PEG coronae in a mixture of methanol and
THF (9:1 by volume). The dissociation of the micelles in the presence
of Bu<sub>3</sub>P was investigated. After cleavage of the disulfide
bonds in the micellar cores, a pyrene-containing small molecular compound
and a block copolymer with pendant thiol groups were produced. Transmission
electron microscopy (TEM), dynamic light scattering (DLS), and <sup>1</sup>H NMR were employed to track the dissociation of the polymeric
micelles. All the techniques demonstrated the dissociation of the
micelles and the fast release of pyrenyl groups from the micelles