15 research outputs found
Self-Healing of a Cross-Linked Polymer with Dynamic Covalent Linkages at Mild Temperature and Evaluation at Macroscopic and Molecular Levels
A lot
of self-healing materials using dynamic bonding systems have
been reported, while the focus is mainly on the macroscopic self-healing
behavior such as visually recognizable healing. Because the healing
originates from microscopic chemical reactions of the dynamic bonds,
evaluation of the reactions in the materials is necessary for elucidation
of the healing mechanisms and development of the healing ability.
Herein, we demonstrated self-healing of a cross-linked polymer with
diarylbibenzofuranone (DABBF)-based dynamic covalent linkages at mild
temperature and investigated the healing behavior from both macroscopic
and microscopic viewpoints. The macroscopic behavior was inspected
by mechanical tests, and the linkage reaction (equilibrium) was evaluated
by electron paramagnetic resonance measurements. These assessments
revealed that the healing is strongly dependent on temperature, which
is attributable to synergism between changes in the chain mobility
and in the equilibrium of the incorporated linkages. These findings
would be applicable to other dynamic bonding systems
Multicolor Mechanochromic Polymer Blends That Can Discriminate between Stretching and Grinding
Mechanochromic
polymers, which react to mechanical force by changing
color, are expected to find applications in smart materials such as
damage sensors. Although numerous types of mechanochromic polymers
have been reported so far, developing mechanochromic polymers that
can recognize different mechanical stimuli remains a formidable challenge.
Materials that not only change their color in response to a mechanical
stimulus but also detect its nature should be of great importance
for practical applications. In this paper, we report our preliminary
findings on multicolor mechanochromic polymer blends that can discriminate
between two different mechanical stimuli, i.e., stretching and grinding,
by simply blending two mechanochromic polymers with different architectures.
The rational design and blending of two mechanochromic polymers with
radical-type mechanochromophores embedded separately in positions
adjacent to soft or hard domains made it possible to achieve multicolor
mechanochromism in response to different stimuli. Electron paramagnetic
resonance and solid-state UV–vis measurements supported the
mechanism proposed for this discrimination
Thermally Healable and Reprocessable Bis(hindered amino)disulfide-Cross-Linked Polymethacrylate Networks
A facile
approach to polymethacrylate networks that contain thermally
exchangeable bisÂ(2,2,6,6-tetramethylpiperidin-1-yl)Âdisulfide (BiTEMPS)
cross-linkers is reported, and the easily inducible healability and
reprocessability of the obtained networks are discussed. The free
radical polymerization of BiTEMPS cross-linkers and hexyl methacrylate
(HMA) monomers afforded insoluble and colorless networks of polyÂ(hexyl
methacrylate) (PHMA) films, whose structures were characterized after
de-cross-linking via thermal BiTEMPS exchange reactions with added
low-molecular-weight BiTEMPS. Swelling experiments and stress-relaxation
measurements at elevated temperatures revealed the contribution of
BiTEMPS as a polymer chain exchanger both in the gels and in the bulk.
The BiTEMPS-cross-linked PHMA networks showed damage healability and
repeatable reprocessability in the bulk by simple hot pressing at
120 °C under mild pressure (∼70 kPa). These results should
grant facile access to various vinyl polymer networks with on-demand
malleability
Polymer–Inorganic Composites with Dynamic Covalent Mechanochromophore
Polymer–inorganic
composites with diarylÂbibenzoÂfuranone
(DABBF) moieties, dynamic covalent mechanochromophores, were prepared,
and their mechanochromic behavior was systematically investigated.
The central C–C bonds in DABBF moieties can be cleaved by mechanical
force to form the corresponding stable blue radicals, which can be
quantitatively evaluated by electron paramagnetic resonance (EPR)
spectroscopy. One controversial issue but attractive property in the
DABBF system is the equilibrium between the activated and deactivated
states. Although the deactivation process decreases the sensitivity
of some equilibrium mechanophores, the equilibrium has rarely been
considered when establishing molecular and/or material design of these
systems. Herein, a rational macromolecular design to suppress the
deactivation of activated dynamic mechanophores and improve sensitivity
by limiting their molecular motion is proposed. Polymer–inorganic
composite materials with rigid networks prepared from DABBF alkoxysilane
derivatives exhibited significant activation of the incorporated DABBF
linkages by grinding, with sensitivities more than 50 times as high
as that of DABBF monomers. The increased sensitivity is due to the
effective transmission of mechanical force to the DABBF moieties in
the network structures and suppression of the recombination of the
generated radicals by the rigid frameworks. Furthermore, when the
rigid frameworks were incorporated into elastomers as inorganic hard
domains, the DABBF mechanophores at the interface between the organic
and inorganic domains were preferentially activated by elongation
Polymer–Inorganic Composites with Dynamic Covalent Mechanochromophore
Polymer–inorganic
composites with diarylÂbibenzoÂfuranone
(DABBF) moieties, dynamic covalent mechanochromophores, were prepared,
and their mechanochromic behavior was systematically investigated.
The central C–C bonds in DABBF moieties can be cleaved by mechanical
force to form the corresponding stable blue radicals, which can be
quantitatively evaluated by electron paramagnetic resonance (EPR)
spectroscopy. One controversial issue but attractive property in the
DABBF system is the equilibrium between the activated and deactivated
states. Although the deactivation process decreases the sensitivity
of some equilibrium mechanophores, the equilibrium has rarely been
considered when establishing molecular and/or material design of these
systems. Herein, a rational macromolecular design to suppress the
deactivation of activated dynamic mechanophores and improve sensitivity
by limiting their molecular motion is proposed. Polymer–inorganic
composite materials with rigid networks prepared from DABBF alkoxysilane
derivatives exhibited significant activation of the incorporated DABBF
linkages by grinding, with sensitivities more than 50 times as high
as that of DABBF monomers. The increased sensitivity is due to the
effective transmission of mechanical force to the DABBF moieties in
the network structures and suppression of the recombination of the
generated radicals by the rigid frameworks. Furthermore, when the
rigid frameworks were incorporated into elastomers as inorganic hard
domains, the DABBF mechanophores at the interface between the organic
and inorganic domains were preferentially activated by elongation
Polymer–Inorganic Composites with Dynamic Covalent Mechanochromophore
Polymer–inorganic
composites with diarylÂbibenzoÂfuranone
(DABBF) moieties, dynamic covalent mechanochromophores, were prepared,
and their mechanochromic behavior was systematically investigated.
The central C–C bonds in DABBF moieties can be cleaved by mechanical
force to form the corresponding stable blue radicals, which can be
quantitatively evaluated by electron paramagnetic resonance (EPR)
spectroscopy. One controversial issue but attractive property in the
DABBF system is the equilibrium between the activated and deactivated
states. Although the deactivation process decreases the sensitivity
of some equilibrium mechanophores, the equilibrium has rarely been
considered when establishing molecular and/or material design of these
systems. Herein, a rational macromolecular design to suppress the
deactivation of activated dynamic mechanophores and improve sensitivity
by limiting their molecular motion is proposed. Polymer–inorganic
composite materials with rigid networks prepared from DABBF alkoxysilane
derivatives exhibited significant activation of the incorporated DABBF
linkages by grinding, with sensitivities more than 50 times as high
as that of DABBF monomers. The increased sensitivity is due to the
effective transmission of mechanical force to the DABBF moieties in
the network structures and suppression of the recombination of the
generated radicals by the rigid frameworks. Furthermore, when the
rigid frameworks were incorporated into elastomers as inorganic hard
domains, the DABBF mechanophores at the interface between the organic
and inorganic domains were preferentially activated by elongation
Self-healing and shape-memory polymers based on cellulose acetate matrix
The creation of self-healing polymers with superior strength and stretchability from biodegradable materials is attracting increasing attention. In this study, we synthesized new biomass-derived cellulose acetate (CA) derivatives by ring-opening graft polymerization of δ-valerolactone followed by the introduction of ureidopyrimidinone (Upy) groups in the polymer side chains. Due to the semicrystalline aliphatic characteristics of the side chain poly(δ-valerolactone) (PVL) and quadruple hydrogen bonds formed by the Upy groups, the stretchability of the resulting polymers was significantly enhanced. Moreover, the shape memory ability and self-healing property (58.3% of self-healing efficiency) were successfully imparted to the polymer. This study demonstrates the great significance of using biomass sources to create self-healing polymers. This paper describes the first successful demonstration of self-healing polymers with superior strength and stretchability from a biodegradable material, cellulose acetate (CA). We initially introduced the ureidopyrimidinone (Upy) groups in the side chains of CA. However, the resulting polymer was not soluble and processable. In order to solve this issue, a new strategy based on the ring-opening graft polymerization of δ-valerolactone followed by the introduction of ureidopyrimidinone (Upy) groups was adopted. Due to the semicrystalline aliphatic characteristics of the side chain poly(δ-valerolactone) (PVL), the resulting polymers were soluble and processable. In addition, the quadruple hydrogen bonds formed by the Upy groups enhanced the stretchability of the resulting polymers. Moreover, the shape memory ability and self-healing property were successfully achieved due to the presence of PVL and Upy. The developed new strategy can be applied to a variety of polymers including biomass-based polymers and materials.</p
Synthesis of Vinylic Macromolecular Rotaxane Cross-Linkers Endowing Network Polymers with Toughness
Macromolecular rotaxane cross-linkers
having two radically polymerizable
vinyl groups (RCs) were first synthesized and used to prepare network
polymers. A crown ether/<i>sec-</i>ammonium-type pseudorotaxane
initiator having an OH terminal-containing axle and a crown ether
wheel with a vinyl group was subjected to the living ring-opening
polymerization of δ-valerolactone followed by end-capping with
a bulky isocyanate to yield a polyester axle-tethering macromolecular
[2]Ârotaxane cross-linker (RC). Rotaxane cross-linked polymers (RCPs)
were prepared by the radical polymerization of <i>n</i>-butyl
acrylate in the presence of RCs (0.25, 0.50 mol %). The properties
of the RCPs and covalently cross-linked polymers (CCPs) were characterized
mainly by mechanical properties. Both fracture stress and strain values
of RCPs were much higher than those of CCPs, probably owing to the
increased network homogeneity by the rotaxane cross-link. The hybrid-type
RCPs obtained from a mixture of RC and covalently connected cross-linker
(CC) showed poorer mechanical properties similar to that of CCPs,
indicating the importance of RCs in increasing the toughness of the
network polymers
Triggered Structural Control of Dynamic Covalent Aromatic Polyamides: Effects of Thermal Reorganization Behavior in Solution and Solid States
Thermally
rearrangeable aromatic polyamides (TEMPO-PA) and random
copolyamides (TEMPO-PA-COOH) incorporating alkoxyamine moieties in
the main chain were synthesized, and the effects of thermal reorganization
behavior on their solution and solid-state structures were investigated.
The hydrodynamic radius in solution decreased as the solution temperature
increased because of the dissociation of the alkoxyamine unit. Additionally,
the dry density of the thin films decreased as the fabrication temperature
increased because of the suppression of polymer aggregation caused
by the thermally induced radical crossover reaction. In addition,
at the film surface of the random copolyamide containing hydrophobic
TEMPO and hydrophilic 3,5-diaminobenzoic acid (DABA) units, the hydrophilicity
decreased as the fabrication temperature increased. This is because
hydrophobic TEMPO and hydrophilic DABA units tend to be discretely
aggregated near the film surface to minimize the surface energy and
suppress the hydrogen bonding via a radical crossover reaction during
the thin-film fabrication process. The present study clearly shows
that both the solution structure and the solid-state molecular aggregation
structure of the dynamic covalent polymers can be easily controlled
by a thermal trigger, and it provides a new method for controlling
the higher-order structure of polymer solutions and solids
Network Reorganization of Dynamic Covalent Polymer Gels with Exchangeable Diarylbibenzofuranone at Ambient Temperature
Reversible bonds
and interactions have been utilized to build stimuli-responsive
and reorganizable polymer networks that show recyclability, plasticity,
and self-healing. In addition, reorganization of polymer gels at ambient
temperature, such as room or body temperature, is expected to lead
to several biomedical applications. Although these stimuli-responsive
properties originate from the reorganization of the polymer networks,
not such microscopic structural changes but instead only macroscopic
properties have been the focus of previous work. In the present work,
the reorganization of gel networks with diarylbibenzofuranone (DABBF)-based
dynamic covalent linkages in response to the ambient temperature was
systematically investigated from the perspective of both macroscopic
and microscopic changes. The gels continued to swell in suitable solvents
above room temperature but attained equilibrium swelling in nonsolvents
or below room temperature because of the equilibrium of DABBF linkages,
as supported by electron paramagnetic resonance measurements. Small-angle
X-ray scattering measurements revealed the mesh sizes of the gels
to be expanded and the network structures reorganized under control
at ambient temperature