Cangxia Li, Huanhuan Liu, Dandan Tang, Youliang Zhao*, “Synthesis,
postmodification and fluorescence properties of reduction-cleavable
core-couplable miktoarm stars with a branched core”, Polym.
Chem., 2015, 6, 1474–1486.
http://pubs.rsc.org/en/content/articlelanding/2015/py/c4py01495b
Novel amphiphilic (PEG)
m(PCL)
n (m ≈ n ≈ 23) miktoarm stars with a
disulfide-linked epoxy-functionalized branched core were controllably
synthesized via three step reactions comprising
self-condensing vinyl polymerization via reversible addition–fragmentation
chain transfer, epoxy-carboxyl coupling reaction and ring-opening
polymerization. The star copolymers were characterized by 1H NMR spectra, GPC-MALLS, DSC and
reduction-triggered degradation. Postpolymerization modification
via epoxy-carboxyl/phenol
coupling reactions allowed attaching dual-reactive functionalities including
coumarin, alkyne and alkyl bromide onto the branched core. In water and
THF–water mixtures, a coumarin-modified star copolymer could aggregate into
some intriguing morphologies including hyperbranched micelles and large vesicles
due to the influence of solvent polarity on aggregation behaviors. Owing to the
differences in the isolation of fluorophores from solvents and restricted
molecular motion, coumarin-functionalized stars exhibited adjustable
fluorescence properties in water and THF–water mixtures, and their aqueous
solution had a maximum quantum yield (ΦF =
44.2%). The solutions of star copolymers and their reduction-cleaved copolymers
were of different hydrodynamic diameters, and the ΦF(star)/
ΦF(cleaved copolymer) values were 1.85 (in THF),
3.00 (in water) and ranged between 1.29 and 2.58 in THF–water mixtures,
revealing that the aggregation behaviors and fluorescence properties were
strongly dependent on polymeric architecture, location of fluorophores and
solvent polarity. Our study affords a versatile method to construct functional
miktoarm stars with a multi-reactive branched core, and coumarin-functionalized
star copolymers may have a great potential as solvent polarity and reduction
dual-sensitive imaging materials in “green” ink, coatings and nanocarriers for
biomedical applications.