9 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
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
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
Enhancing Mechanochemical Activation in the Bulk State by Designing Polymer Architectures
Mechanoresponsive
polymers can have attractive functions; however,
the relationship between polymer architecture and mechanoresponsiveness
in the bulk state is still poorly understood. Here, we designed well-defined
linear and star polymers with a mechanophore at the center of each
architecture, and investigated the effect of molecular weight and
branched structures on mechanoresponsiveness in the solid state. Diarylbibenzofuranone,
which can undergo homolytic cleavage of the central C–C bond
by mechanical force to form blue-colored radicals, was used as a mechanophore
because the cleaved radicals could be evaluated quantitatively using
electron paramagnetic resonance measurements. We confirmed that longer
polymer chains induce mechanochemical activation more effectively
and found that, in the bulk state, the star polymers have higher sensitivity
to mechanical stress compared with a linear polymer having similar
molecular weight arm segment
Enhancing Mechanochemical Activation in the Bulk State by Designing Polymer Architectures
Mechanoresponsive
polymers can have attractive functions; however,
the relationship between polymer architecture and mechanoresponsiveness
in the bulk state is still poorly understood. Here, we designed well-defined
linear and star polymers with a mechanophore at the center of each
architecture, and investigated the effect of molecular weight and
branched structures on mechanoresponsiveness in the solid state. Diarylbibenzofuranone,
which can undergo homolytic cleavage of the central C–C bond
by mechanical force to form blue-colored radicals, was used as a mechanophore
because the cleaved radicals could be evaluated quantitatively using
electron paramagnetic resonance measurements. We confirmed that longer
polymer chains induce mechanochemical activation more effectively
and found that, in the bulk state, the star polymers have higher sensitivity
to mechanical stress compared with a linear polymer having similar
molecular weight arm segment
Mechanochromic Dynamic Covalent Elastomers: Quantitative Stress Evaluation and Autonomous Recovery
Stress evaluation in polymeric materials
is important in order
to not only spot danger in them before serious failure, but also precisely
interpret the destructive mechanism, which can improve the lifetime
and durability of polymeric materials. Here, we are able to visualize
stress by color changes, as well as quantitatively estimate the stress
in situ, in segmented polyurethane elastomers with diarylbibenzofuranone-based
dynamic covalent mechanophores. We prepared films of the segmented
polyurethanes, in which the mechanophores were incorporated in the
soft segments, and efficiently activated them by mechanical force.
Cleavage of the mechanophores during uniaxial elongation and their
recovery after the removal of the stress were quantitatively evaluated
by in situ electron paramagnetic resonance measurements, accompanied
by drastic color changes
Mechanochromic Dynamic Covalent Elastomers: Quantitative Stress Evaluation and Autonomous Recovery
Stress evaluation in polymeric materials
is important in order
to not only spot danger in them before serious failure, but also precisely
interpret the destructive mechanism, which can improve the lifetime
and durability of polymeric materials. Here, we are able to visualize
stress by color changes, as well as quantitatively estimate the stress
in situ, in segmented polyurethane elastomers with diarylbibenzofuranone-based
dynamic covalent mechanophores. We prepared films of the segmented
polyurethanes, in which the mechanophores were incorporated in the
soft segments, and efficiently activated them by mechanical force.
Cleavage of the mechanophores during uniaxial elongation and their
recovery after the removal of the stress were quantitatively evaluated
by in situ electron paramagnetic resonance measurements, accompanied
by drastic color changes