Bin
Mo, Huanhuan Liu, Xiangdong Zhou, Youliang Zhao*,
“Facile synthesis of photolabile dendritic-unit-bridged hyperbranched graft
copolymers for stimuli-triggered topological transition and controlled release
of Nile red”, Polym.
Chem., 2015, 6, 3489–3501 (DOI:
10.1039/C5PY00132C).
http://pubs.rsc.org/en/content/articlelanding/2015/py/c5py00132c
Different from hyperbranched star-like polymers
and dendritic brushes, dendritic-unit-bridged hyperbranched graft copolymers
(DHGCs) with branching point linked branches and linear grafts can be regarded
as a new subclass of hyperbranched-graft-linear copolymers. This study aims at the
synthesis and properties of photocleavable DHGCs comprising oligomeric branches
composed of poly(ethylene glycol) methyl ether acrylate (PEGA) units, linear
poly(ε-caprolactone) (PCL) grafts and o-nitrobenzyl ester
(ONBE) moieties in the dendritic unit. Based on a multifunctional inimer
3-((2-acryloyloxymethyl-2-hydroxymethyl) propionyloxy)methyl-2-nitrobenzyl
4-cyano-4-(phenylcarbonothioylthio)pentanoate (ANCP), functional DHGCs were
controllably synthesized via two step reactions. RAFT
copolymerization afforded hyperbranched poly(ANCP-co-PEGA) (PAP), followed by CL polymerization to
achieve PAP-g-PCL. Upon photo-cleavage, hyperbranched PAP was converted
into linear polymers, and PAP-g-PCL was readily degraded into mixtures of linear,
star and graft polymers. With increasing UV irradiation time, the PAP-g-PCL micelles were
gradually evolved into vesicles and multicompartment vesicles due to
photo-triggered cleavage and reaggregation. Upon normal and on-demand UV irradiation,
the release kinetics for controlled release of Nile red from copolymer
aggregates could be tuned in a wide range, revealing the great potential in
smart drug delivery systems. This study affords a versatile method to construct
photolabile DHGCs, which opens up a new route to explore unique properties of
novel topological copolymers.