Stimuli-responsive
light-emitting polymers (SRLEPs) have many promising
applications. However, the synthesis of SRLEPs from nonconjugated
and water-soluble monomers remains a challenge. Herein, for the first
time, nonconjugated luminescent polymers with an upper critical solution
temperature (UCST) in aqueous solution are reported. The polymer is
synthesized through copolymerization of a strong hydrogen-donating
monomer, acrylic acid (AAc), and a strong hydrogen-accepting monomer, N-vinylcaprolactam (NVCL). The polymer–polymer hydrogen-bonding
rigidifies the chain conformation and enhances the clustering of the
heteroatoms and carbonyl groups, resulting in an improved clusteroluminescence.
Meanwhile, the polymer–polymer hydrogen bonding also brings
in dynamic chain association that can be switched with temperature,
yielding a UCST-type thermoresponsiveness in aqueous solution. This
work demonstrates a novel and facile method of designing SRLEPs through
tailoring the hydrogen bonds in the polymer. The properties of clusteroluminescence
and thermoresponsiveness of the AAc–NVCL copolymers may render
themselves with applications as temperature-sensitive biosensing.
Polymer–protein
hybrids have been extensively used in biomedical
fields. Polymers with upper critical solution temperature (UCST) behaviors
can form a hydrated coacervate phase below the cloud point (T
cp), providing themselves the opportunity to
directly capture hydrophilic proteins and form hybrids in aqueous
solutions. However, it is always a challenge to obtain a UCST polymer
that could aggregate at a high temperature at a relatively low concentration
and also efficiently bind with proteins. In this work, a UCST polymer
reactive with proteins was designed, and its temperature responsiveness
and protein-capture ability were investigated in detail. The polymer
was synthesized by the reversible addition–fragmentation chain
transfer (RAFT) polymerization of acrylamide (AAm) and N-acryloxysuccinimide (NAS). Interestingly, taking advantage of the
partial hydrolysis of NAS into acrylic acid (AAc), the obtained P(AAm-co-NAS-co-AAc) polymer exhibited an excellent
UCST behavior and possessed good protein-capture ability. It showed
a relatively higher T
cp (81 °C) at
a lower concentration (0.1 wt %) and quickly formed polymer–protein
hybrids with high protein loading and without losing protein bioactivity,
and both the polymer and polymer–protein nanoparticles showed
good cytocompatibility. All the findings are attributed to the unique
structure of the polymer, which provided not only the strong and stable
hydrogen bonds but also the quick and mild reactivity. The work offers
an easy and mild strategy for polymer–protein hybridization
directly in aqueous solutions, which may find applications in biomedical
fields.
Poly(N-acryloyl glycinamide) (PNAGA)
can form
high-strength hydrogen bonds (H-bonds) through the dual amide motifs
in the side chain, allowing the polymer to exhibit gelation behavior
and an upper critical solution temperature (UCST) property. These
features make PNAGA a candidate platform for biomedical devices. However,
most applications focused on PNAGA hydrogels, while few focused on
PNAGA nanoparticles. Improving the UCST tunability and bio-interfacial
adhesion of the PNAGA nanoparticles may expand their applications
in biomedical fields. To address the issues, we established a reactive
H-bond-type P(NAGA-co-NAS) copolymer via reversible addition–fragmentation chain transfer polymerization
of NAGA and N-acryloxysuccinimide (NAS) monomers.
The UCST behaviors and the bio-interfacial adhesion toward the proteins
and cells along with the potential application of the copolymer nanoparticles
were investigated in detail. Taking advantage of the enhanced H-bonding
and reactivity, the copolymer exhibited a tunable UCST in a broad
temperature range, showing thermo-reversible transition between nanoparticles
(PNPs) and soluble chains; the PNPs efficiently bonded proteins into
nano-biohybrids while keeping the secondary structure of the protein,
and more importantly, they also exhibited good adhesion ability to
the cell membrane and significantly inhibited cell-specific propagation.
These features suggest broad prospects for the P(NAGA-co-NAS) nanoparticles in the fields of biosensors, protein delivery,
cell surface decoration, and cell-specific function regulation.
The
design of thermoresponsive luminescent polymers with both a
tunable upper critical solution temperature (UCST) and a tunable color
is of great challenge. Herein, a series of thermoresponsive copolymers
with UCST and aggregation-induced emission (AIE) behaviors are prepared,
and a color-shifting fluorescent system based on the energy conversion
between the AIE polymers and fluorescent dyes is constructed. The
copolymers are prepared from acrylamide and 6-(4-vinylphenyl)-2,4-diamino-1,3,5-triazine
(VPhDT). Benefitting from VPhDT, an AIE-active monomer that can provide
multiple hydrogen bonds and enhance association of the polymer chains,
the obtained copolymers exhibit both UCST and AIE behaviors in aqueous
solutions. Utilizing the AIE copolymers as the donor and fluorescent
dyes as the acceptors, color-shifting fluorescent systems that can
emit blue, green, and red lights are established. The color-shifting
fluorescent systems also exhibit tunable luminescent intensities and
colors with the stimuli of temperature and pH. Such a color-shifting
fluorescent system may have promising applications in the fields of
temperature sensors and information displays.
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