In situ synthesis of thermoresponsive 4-arm star block
copolymer nano-assemblies by dispersion RAFT polymerization
Qu, YQ (Qu, Yaqing)[ 1 ] ; Chang, XY (Chang, Xueying)[ 1 ] ; Chen, SL (Chen, Shengli)[ 1 ] ; Zhang, WQ (Zhang, Wangqing)[ 1,2 ]
POLYMER
CHEMISTRY, 2017, 8(22): 3485-3496
DOI: 10.1039/c7py00508c
WOS:000402732500011
Abstract
Well-defined
4-arm star block copolymer nanospheres of
[poly(N-isopropylacrylamide)-block-polystyrene](4) [(PNIPAM-b-PS)(4)]
containing a hydrophobic core of the polystyrene (PS) block and a
thermo-responsive corona of the 4-arm star poly(N-isopropylacrylamide) (PNIPAM)
were prepared by dispersion RAFT polymerization employing a tetrafunctional
macro-RAFT agent of tetra(trithiocarbonate)-terminated
poly(N-isopropylacrylamide) [(PNIPAM-TTC)(4)]. The size of the 4-arm star
(PNIPAM-b-PS)(4) nanospheres increases with the increasing degree of
polymerization (DP) of the PS block, whereas it decreases with the DP of the
star PNIPAM increasing. A comparison between the 4-arm star (PNIPAM-b-PS)(4)
nanospheres and the linear poly(N-isopropylacrylamide)-block-polystyrene
(PNIPAM-b-PS) nanospheres is made. It is found that the 4-arm star
(PNIPAM-b-PS)(4) nanospheres and the linear PNIPAM-b-PS nanospheres have a
similar particle size when the DPs of the PS and PNIPAM blocks in the star and
linear block copolymers are close to each other. Interestingly, the topology of
PNIPAM is found to exert influence on its thermo-responsive phase transition,
and the (PNIPAM(122)-b-PS110)(4) 4-arm star block copolymer nanospheres have a
lower critical solution temperature (LCST) lower than the PNIPAM(118)-b-PS125
linear block copolymer nanospheres. At temperatures above LCST of the
(PNIPAM(122)-b-PS110)(4) nanospheres, the 4-arm star PNIPAM chains deposit on
the PS core to form raspberry-like nanospheres, in which the dehydrated 4-arm
star PNIPAM chains form dispersed microdomains on the PS core. This synthesis
of (AB)(4) 4-arm star block copolymer nano-assemblies is believed to be
efficient and is helpful to study how the topology of PNIPAM affects the
thermo-responsive phase transition.
