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Plant Oil-Based Supramolecular Polymer Networks and Composites
for Debonding-on-Demand Adhesives
Anselmo del Prado, Diana Kay Hohl, Sandor Balog, Lucas Montero de Espinosa,
and Christoph Weder*
Adolphe Merkle Institute, University of Fribourg, Chemin des Verdiers 4, CH-1700 Fribourg, Switzerland
*
SSupporting Information
ABSTRACT: The stimuli responsiveness of supramolecular
polymers has recently been exploited for the development of
adhesives that can be (de)bonded on demand when heated or
exposed to UV light. However, it remains difficult to combine
competitive solid-state mechanical properties and very low
melt viscosity in one material. Here we report a new
supramolecular polymer adhesives platform based on soybean
oil as a multifunctional low-molecular-weight monomer
(∼1500 g/mol) and isophthalic acid (IPA) groups that
show hydrogen bonding and promote the formation of a
reversible network. The polarity difference between the
triglyceride backbone and the IPA groups leads to microphase
separation, and the crystalline IPA domains act as physical cross-links. Heating the polymer above the melting temperature of
the IPA-rich domains results in a dramatic viscosity reduction to 8 Pa·s at 120 °C. Once cooled to room temperature, the
material properties are fully recovered as a result of the reassembly of the supramolecular network. Single lap joint adhesive tests
performed at room temperature using glass and stainless steel substrates reveal shear strength values of 1.2 and 1.7 MPa,
respectively, and heat and UV light can be used as external stimuli to debond on command. In addition, composites were
prepared by adding 5 or 10 wt % microcrystalline cellulose (MCC) to the polymer, and this led to an increase of strength and
modulus below the glass transition by up to 80% and 170%, respectively. Because the introduction of MCC partially hinders the
crystallization of the matrix, the stiffness and tensile strength are reduced above the glass transition, while the elongation at
break is significantly increased.
KEYWORDS: supramolecular, stimuli responsive, reversible adhesive, noncovalent interactions, bonding and debonding on demand
■INTRODUCTION
Reversible adhesives with on-demand bonding and debonding
capabilities are considered useful for different applications,
including the repair of aged complex structural bonded
components,
1−3
the simplification of recycling processes by
facilitating the separation of different parts,
4,5
the temporary
bonding of pieces for maintenance or processing purposes,
6−8
and the painless removal of wound dressings
9−13
and dental
fixtures.
14
Hot melt adhesives are the most widely employed
type of materials that enable debonding-on-demand (DOD)
solutions.
15
However, they are based on high-molecular-weight
polymers and usually display high melt viscosity, which impacts
processing and removal after use. DOD properties can also be
imparted by combining high-molecular-weight polymers via
the introduction of heat-expandable fillers
16−19
or thermally,
optically, or catalytically
20
depolymerizable components.
21−25
More recently, stimuli-responsive polymers have been
considered as alternatives to hot melt adhesives for DOD
applications.
14,26−31
Despite the advances in the field, it has
remained a challenge to create easily processable adhesives that
combine excellent mechanical and adhesive properties during
use but which convert into an easily removable low-viscosity
liquid when a specific stimulus is applied. However, recent
studies on supramolecular polymers (SMPs) suggest that such
a combination of properties should be accessible by this class
of materials.
32
SMPs are based on noncovalently connected
monomers that are polymerized with the help of directional,
noncovalent interactions.
33,34
The dynamic nature of these
weak bonds allows for the reversible disassembly of SMPs on
command, i.e., when a suitable stimulus is applied.
35
This
approach has served as the basis for the development of
stimuli-responsive materials that display functions such as
thermal and light-induced healing,
36−39
shape memory
behavior,
40−42
or mechanochromism
43,44
and more recently
also for (de)bonding-on-demand applications.
32
A common strategy for the design of reversible adhesives
based on SMPs relies on the (dis)assembly of linear telechelic
polymers that are end-functionalized with two supramolecular
binding motifs; in such materials microphase separation into a
soft phase formed by the telechelics’backbones and a hard
Received: February 22, 2019
Accepted: April 29, 2019
Published: April 29, 2019
Article
pubs.acs.org/acsapm
Cite This: ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
© XXXX American Chemical Society ADOI: 10.1021/acsapm.9b00175
ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
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phase that is formed by the supramolecular binding motifs and
which serves as physical cross-linker is observed.
34,40,45,46
The
use of SMPs based on this architecture as reversible adhesives
is based on their capability to be thermally disassembled, and
the typically significant viscosity reduction facilitates debond-
ing on demand. For instance, Bosman and co-workers prepared
a telechelic poly(dimethylsiloxane) (PDMS) that was function-
alized with the well-known self-complementary quadruple H-
bonding ureidopyrimidone (UPy) motif.
47
Lap joints formed
by bonding two glass slides with this polymer were able to hold
a 1 kg weight for hours, they could be debonded by heating,
and the original adhesive properties could be restored by
rebonding and cooling. Similarly, Weder and co-workers
studied SMPs based on telechelic poly(ethylene-co-butylene)
that had been modified with either UPy motifs
48
or 2,6-bis(1′-
methylbenzimidazolyl)pyridine ligands, which allow for chain
extension by chelating metal ions.
36
In addition to thermal
(de)bonding on demand, these SMPs were shown to enable
light-induced de- and rebonding within seconds on account of
light−heat conversion by the binding motifs and optionally
added light−heat converters.
49
However, the telechelic nature
of the above supramolecular monomers and the rubbery nature
of the telechelic substrates used lead to relatively low strength,
stiffness, and adhesive strength. To improve these character-
istics, the groups of Long
50
and later Weder
51,52
investigated
poly(alkyl methacrylate)s with UPy side chains that function as
reversible supramolecular cross-links; however, as the back-
bones were of high molecular weight, the melt viscosity of such
materials is high. Another possibility that was reported by
Weder’s group is to create supramolecular networks based on
multifunctional monomers featuring a low-molecular-weight
core and three or more supramolecular binding motifs, such as
UPy or isophthalic acid groups, which can be assembled with
different bipyridines.
49,53
Such monomers assemble into highly
cross-linked SMP glasses with high storage modulus, but at the
same time these materials are brittle and on account of the
high content of binding motifs their viscosity is only
significantly reduced at high temperatures, which limits their
applicability and processability. Another strategy to combine
mechanical strength and low melt viscosity, reported in a series
of papers by Tournilhac, Leibler, and co-workers, is the use of
fatty acid-based supramolecular polymers either alone or
blended with hot melt adhesives.
54−56
Their general approach
involves the use of mixtures of fatty acids that provide the basis
for a soft phase, in combination with crystallizable blocks and
weakly binding hydrogen-bonding motifs. In these, the
crystalline parts provide competitive mechanical properties
and freeze the dynamic bonds, while above the melting
temperature monomer-like flow is observed as the weak
binding motifs are no longer connected via the crystalline
phase.
Herein, we show that an interesting combination of
properties can be accessed by SMP networks based on the
self-assembly of a soybean oil-derived multifunctional mono-
mer that carries only isophthalic acid as a H-bonding and π−π
stacking motif. The soybean oil derivative used as starting
material in this study is acrylated epoxidized soybean oil
(AESO), which has been already used as component of
different types of adhesives and composites, usually as cross-
linker but to our best knowledge never as the main component
in the formulation of supramolecular materials.
57−59
We show
that the combination of this low glass transition branched
structure, weak supramolecular cross-links, and nanophase
segregation effects provides access to a material with adequate
mechanical properties at room temperature and a very low
melt viscosity at 100−120 °C. In addition, we show that it is
possible to enhance the mechanical properties of this SMP by
adding microcrystalline cellulose (MCC) as a reinforcing filler.
Taking advantage of the weak bonds that maintain the network
structure, the synthesized materials were used as adhesives, and
temperature and UV light mediated (de)bonding was
demonstrated.
■EXPERIMENTAL SECTION
Materials. All chemicals were purchased from Sigma-Aldrich and
were used as received. 5-Mercaptoisophthalic acid was prepared
following a reported procedure,
60
which was modified as described
below.
Methods. 1H NMR (400 MHz) and 13C NMR (100.6 MHz)
spectra were recorded on a Bruker 400 MHz spectrometer in DMSO-
d6. Chemical shifts (δ) are reported in parts per million (ppm) relative
to the tetramethylsilane, even though the signal of residual DMSO
protons at 2.50 ppm was employed as internal reference. Mass
spectrometry (MS) analyses were performed as high-resolution
electrospray ionization (ESI) experiments on a Bruker FTMS 4.7T
BioAPEX II. Fourier transform infrared spectroscopy (FTIR) spectra
were acquired on a PerkinElmer Spectrum 65 spectrometer between
4000 and 600 cm−1with a resolution of 4 cm−1and 10 scans per data
point and on an attenuated total reflectance (ATR) device using
diamond/ZnSe as internal reflection element. Differential scanning
calorimetry (DSC) studies were performed with a Mettler-Toledo
STAR system under a nitrogen atmosphere, heating/cooling rates of
10 °C/min, in the range −50 to +150 °C, and using a sample mass of
∼5 mg. Thermal degradation studies were performed on a Mettler-
Toledo TGA/DSC STARe system at a heating rate of 10 °C/min
from 25 to 600 °C with samples of 10 mg in 40 μL aluminum
crucibles. The melting points (Tm) reported are the minimum values
of the corresponding heat capacity measured in the first heating cycle.
The crystallization temperatures (Tc) reported are the maximum
values in the heat capacity measured in the first cooling cycle. The
glass transition temperatures (Tg) reported are the midpoints of the
step change in the heat capacity measured in the first heating cycle.
Wide- and small-angle X-ray scattering (WAXS, SAXS) experiments
were conducted in vacuum and at ambient temperature using a
NanoMax-IQ camera (Rigaku Innovative Technologies, Auburn Hills,
MI). The scattering spectra (1d) shown have been processed using
standard procedures, and data are presented as a function of the
momentum transfer q=4πλ−1sin(θ/2), in which λ= 0.1524 nm is
the photon wavelength and θthe scattering angle. Rheological studies
were performed on a TA Instruments AR-G2 rheometer with 40 mm
parallel plates in oscillatory mode, using a Peltier element setup for
temperature control. The temperature-dependent viscosity measure-
ments were conducted between 25 and 120 °C, with heating/cooling
rates of 5 °C/min, at 10 rad/s and 0.1% strain. Frequency sweep
experiments were performed over a frequency range of ω= 0.05−100
rad/s at temperatures between 35 and 100 °Cin15°C increments.
Preparation of Polymer Films and Composites. AESOIPA (1
g) and microcrystalline cellulose (0, 5, and 10 wt %) were mixed in 10
mL of EtOH and sonicated for 30 min. The resulting mixtures were
cast into Petri dishes and were dried in a vacuum at room temperature
overnight. Polymer films were produced by compression molding the
resulting solids in a Carver CE press at 70 °C and applying 4 tons of
pressure for 3 min. The film thickness was controlled to 250−300 μm
by using poly(tetrafluoroethylene) film spacers. These films were used
for DMA and stress−strain experiments. Samples used in UV light
mediated thermal debonding experiments were based on materials
that also contained the UV stabilizer 2-(5-chloro-2H-benzotriazole-2-
yl)-6-(1,1-dimethylethyl)-4-methylphenol (available under the trade-
mark Tinuvin 326 from BASF). This additive was added to the
mixture of AESOIPA and microcrystalline cellulose in EtOH before
sonication, and the materials were processed as indicted above.
ACS Applied Polymer Materials Article
DOI: 10.1021/acsapm.9b00175
ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
B
Mechanical Testing. Dynamic mechanical analyses (DMA) and
stress−strain measurements were conducted in a tension film clamp
setup with a TA Instruments DMA Q800. DMA analyses were
performed at a heating rate of 5 °C/min, from 0 to 100 °C, at a
frequency of 1 Hz, and an amplitude of 5 μm. Stress−strain analyses
were performed at a constant temperature of 10 and 40 °C, with a
constant strain rate of 5%/min until sample failure. The shape of the
samples used for the mechanical analyses were rectangular with a
length of ≈10 mm, a width of 5.3 mm, and a thickness of 0.25 mm.
Creep experiments were performed on the same equipment at 10, 25,
and 40 °C. The strain was fixed to 0.04% for the experiment
conducted at 10 °C and to 5% for the experiments performed at 25
and 40 °C. The decay of the stress under constant strain was then
monitored as a function of time.
Adhesive Properties. Adhesive tests were performed at ambient
temperature on a Zwick/Roell Z010 tensile tester that was equipped
with mechanical gripping clamps and a 10 kN load cell. A strain rate
of 15 mm/min was applied. Single lap joints were fabricated using
glass or stainless steel substrates with a thickness of 1 mm. The bond
area was 20 ×25 mm2in the case of glass and 10 ×10 mm2in the
case of stainless steel. For adhesive experiments, the thickness of the
prepared thin films was reduced from 250−300 to ca. 90−100 μm, by
melting 30 mg (glass substrates) or 10 mg (stainless steel substrates)
of the respective material between the substrates. This was done by
placing the sandwich on a hot stage maintained at 100 °C, and the lap
joint was removed from the hot stage and pressed while cooling to
ambient temperature. Samples were tested within 1 h after bonding.
Debonding experiments were performed on the same instrument. In
this case, single lap joints were made with regular glass and stainless
steel with bond areas of 10 ×10 mm2. The applied stimuli for
debonding were either heat applied as hot air with a temperature of
ca. 100 °C (stainless steel) or UV light (glass) applied with a Hönle
Bluepoint 4 Ecocure UV lamp equipped with an optical fiber (λ=
320−390 nm, 1600 mW/cm2). For these experiments the samples
were subjected to a constant load of 20−23 N until debonding
occurred. In the case of the UV light mediated debonding
experiments, the surface temperature of the single lap joints was
measured with an Optris PI Connect infrared camera model PI 160
from Roth AG.
Synthesis of AESOIPA Monomer. Dimethyl 5-
((Dimethylcarbamothioyl)oxy)isophthalate (1). In a 100 mL
round-bottomed flask equipped with a magnetic stir bar, dimethyl
5-hydroxyisophthalate (5.00 g, 23.8 mmol) and 1,4-
diazabicyclo[2.2.2]octane (DABCO, 8.00 g, 71.4 mmol) were
dissolved in DMF (60 mL). Dimethylthiocarbamoyl chloride (3.80
g, 29.76 mmol) was added to the solution, and the reaction mixture
was stirred for 5 h at room temperature. The yellowish solution was
poured into distilled water (1 L) to precipitate a white powder, which
was filtered offand washed with distilled water until the washing
liquid was colorless and its pH neutral. The resulting solid was dried
under vacuum at 130 °C, and the title product was obtained as a
white solid (6.50 g, 92%). 1H NMR (400 MHz, DMSO-d6): δ= 8.35
(s, 1H, COOMe−C−CH−C−COOMe), 7.88 (s, 2H, CH−CO−
CH), 3.90 (s, 6H, 2 ×COOCH3), 3.36 (d, 6H, N(CH3)2). 13C NMR
(100.6 MHz, DMSO-d6): δ= 185.59 (−OCSNMe2), 164.68 (2 ×
COOMe), 154.99 (CH−CO−CH), 131.16 (2 ×C−COOMe),
128.07 (CH−CO−CH), 126.64 (COOMe−C−CH−C−COOMe),
52.68 (2 ×COOCH3), 38.72 (N(CH3)2). HRMS-ESI: [M + Na]+=
320.0560. Tm: 119.7 °C.
Dimethyl 5-((Dimethylcarbamoyl)thio)isophthalate (2). In a 50
mL round-bottomed flask equipped with a magnetic bar that was
purged with nitrogen and placed in a heating device, dimethyl 5-
((dimethylcarbamothioyl)oxy) isophthalate (1, 3.00 g, 10.10 mmol)
was heated to 215 °C for 3 h. The white solid melted and turned into
a brownish oil. After cooling to room temperature, a dark brown solid
was obtained. The product was purified by recrystallization from
MeOH (300 mL), and the title product was obtained in the form of
pale brown crystals (2.40 g, 80%). 1H NMR (400 MHz, DMSO-d6): δ
= 8.46 (s, 1H, COOMe−C−CH−C−COOMe), 8.19 (s, 2H, CH−
CS−CH) 3.91 (s, 6H, 2 ×COOCH3), 3.00 (d, 6H, N(CH3)2). 13C
NMR (100.6 MHz, DMSO-d6): δ= 164.67 (2 ×COOMe), 163.66
(−SCONMe2), 139.56 (CH−CS−CH), 131.02 (CH−CS−CH),
130.81 (2 ×C−COOMe), 129.78 (COOMe−C−CH−C−
COOMe), 52.69 (2 ×COOCH3), 36.66 (NCH3CH3), 36.47
(NCH3CH3). HRMS-ESI: [M + Na]+= 320.0557. Tm: 121.2 °C.
5-Mercaptoisophthalic Acid (IPASH) (3). In a 50 mL round-
bottomed flask equipped with a magnetic stir bar, dimethyl 5-
((dimethylcarbamoyl)thio)isophthalate (2, 3.00 g, 10.10 mmol) was
dissolved in EtOH (5 mL), and a 3 M aqueous NaOH solution (20
Scheme 1. Synthesis of IPASH (3) and the IPA-Functionalized Acrylated Epoxidized Soybean Oil AESOIPA (4)
a
a
Approximate chemical structures are shown for AESO and AESOIPA as commercial AESO is a mixture of triglycerides.
ACS Applied Polymer Materials Article
DOI: 10.1021/acsapm.9b00175
ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
C
mL) was added. The mixture was heated to 60 °C and stirred
overnight. After cooling to room temperature, the solution was
poured into a solution of 37% HCl and H2O (1:1 v/v, 100 mL) that
was cooled in an ice bath to precipitate a pale yellowish powder,
which was filtered offand washed with distilled water until the
washing liquid was pH neutral. The solid was then redissolved in
diethyl ether, the solution was filtered to remove insoluble impurities
and dried over MgSO4, the MgSO4was filtered off, and the solvent
was removed at reduced pressure. After drying under vacuum at 160
°C overnight, the title product was obtained as a yellowish powder
(1.80 g, 90%). 1H NMR (400 MHz, DMSO-d6): δ= 13.49 (broad
band, −COOH), 8.33 (s, 1H, COOH−C−CH−C−COOH), 8.27 (s,
2H, CH−CSH−CH). 13C NMR (100.6 MHz, DMSO-d6): δ= 165.62
(2 ×COOH), 137.00 (CH−CS−CH), 132.60 (2 ×C−COOH),
131.14 (CH−CS−CH), 128.97 (COOH−C−CH−C−COOH).
HRMS-ESI: [M + Na]+= 220.9883. Tm: 282.8 °C. Additional IR
data and 1H NMR comparison of compounds 1−3are shown in the
Supporting Information (Figures S1−S4).
Isophthalic Acid-Functionalized Soybean Oil (AESOIPA) (4). In a
50 mL round-bottomed flask equipped with a magnetic stir bar and a
reflux condenser, acrylated epoxidized soybean oil (AESO, approx-
imate structure shown in Scheme 1) (5.00 g, 4.04 mmol) was
dissolved in EtOH (6 mL). IPASH (3, 2.20 g, 11.3 mmol) and Et3N
(14 mL) were added, and the reaction mixture was stirred overnight
at 40 °C. The yellowish solution was then poured into a mixture of
aqueous HCl (40 mL 6 M) and ethyl acetate (80 mL). The organic
layer was separated off, and the aqueous phase was extracted with
ethyl acetate (3 ×50 mL). The organic layers were combined, washed
with distilled water, dried over MgSO4, and filtered, and the solvent
was removed at low pressure. The resulting solid was dried in a
vacuum at 70 °C overnight, yielding the title product as a yellowish
rubbery material (6.10 g, 85%). Because of the complexity of the 1H
NMR spectra (resulting from the fact that the commercial AESO is a
mixture of products), only the corresponding signals to the Michael
addition in the 1H NMR spectrum were analyzed and compared to
the commercial AESO (Figure S5). Commercial AESO contains ca.
2.45−2.65 mol of acrylate per mole of triglyceride. After the thiol−
Michael addition of IPASH to AESO, the acrylate signals (6.5−5.8
ppm) disappeared, and the modified AESOIPA shows new resonances
at 8.3−7.9 ppm, corresponding to the IPA motif, and in the range of
3.5−2.0 ppm, corresponding to the CH2after the addition to the α,β-
unsaturated ester (see the Supporting Information). ESI: [M + Na]+
= 1457 (Figure S6).
■RESULTS AND DISCUSSION
Isophthalic acid-functionalized soybean oil (AESOIPA) was
synthesized via thiol−Michael addition by reacting the
commercially available acrylated epoxidized soybean oil
(AESO) with 5-mercaptoisophthalic acid (IPASH), which
was synthesized by making minor modifications to a previously
reported protocol (Scheme 1 and Experimental Section).
60
Full conversion of the acrylate groups was indicated by the fact
that the number of IPA motifs per triglyceride (determined by
1H NMR spectroscopy; see Figure S5) matched the number of
acrylate groups in the parent AESO; i.e., AESOIPA had an IPA
number of 2.6. In sharp contrast to AESO, which is a viscous
oil, AESOIPA appears as a rubbery solid that can be readily be
melted and compression-molded into transparent, polymer-like
films (Figure 1 and Figure S7).
Small- and wide-angle X-ray scattering (SAXS-WAXS)
experiments were performed on AESOIPA, and for reference
purposes on the parent AESO, to investigate the reason for this
property contrast (Figure 1). The diffractogram of AESOIPA
shows a broad diffraction peak between q= 0.3−2nm
−1,
peaking at ∼1.5 nm−1, which indicates microphase segregation
with a characteristic length scale of ∼4 nm, arguably on
account of the formation of IPA-rich hard domains, which
segregate from the nonpolar soybean oil core. In addition, an
additional sharp band at q= 18.5 nm−1(3.4 Å) superimposing
the so-called amorphous halo suggests π−πstacking of the IPA
motifs within the hard phase, as previously observed in other
IPA derivatives.
61
The diffractogram of the parent AESO is
void of these diffraction maxima. Thus, the SAXS results
support the vastly changed mechanical properties of AESOIPA
(relative to AESO), as such hard domains provide physical
cross-links to the material (Figure 1).
62,63
Hydrogen bonding
between the acid groups in the isophthalic acid motifs are well
studied,
61,64,65
and infrared spectra are often used to probe
such interactions. In the infrared spectrum of the modified
AESOIPA, the band corresponding to the carbonyl groups of
the IPA motifs at 1685 cm−1is shifted to 1700 cm−1, while the
band corresponding to the carbonyl groups present in AESO,
shifted from 1725−1740 to 1710−1730 cm−1. In addition,
sharp bands appear in the region between 1575 and 1600
cm−1, which are characteristics of hydrogen bonds in
carboxylic acid compounds (Figure S8).
61
The nanophase
segregation of the polar IPA motifs from the nonpolar oily
phase could also be confirmed by differential scanning
calorimetry (DSC) of AESOIPA. A glass transition temper-
ature (Tg) is observed at ca. 25 °C, and the DSC trace also
shows an endothermic transition at ca. 88 °C, which is ascribed
to the melting point (Tm) of the IPA hard phase. This
interpretation is supported by the fact that the DSC cooling
trace shows a crystallization peak at 80 °C upon cooling from
the melt (Figure 2a and Table 1). The material displays
excellent solubility in ethanol, which also enables solvent
processing.
To expand the property matrix of AESOIPA, several
composites were prepared by mixing the supramolecular
polymer with microcrystalline cellulose (MCC).
66
MCC was
anticipated to disperse well in AESOIPA on account of
favorable interactions between its hydroxyl surface groups and
the IPA motifs. Thus, AESOIPA/MCC composites were
prepared by mixing AESOIPA and either 5 or 10 wt % MCC in
ethanol, sonicating the mixture for 30 min, and removing the
solvent under reduced pressure. The composites were then
compression molded into homogeneous films, whose thermal
and mechanical properties were investigated and compared to
those of the neat AESOIPA (Figure 2). The DSC traces of the
AESOIPA/MCC composites (Figure 2a,b and Table 1) are
similar to those of AESOIPA. While the Tgvalues are in the
same range (22−25 °C), the melting transitions were observed
at 65 and 62 °C for AESOIPA/MCC composites with 5 and
Figure 1. (a) Schematic illustrating the formation of a supramolecular
AESOIPA network and a picture of a film made from the material. (b)
SAXS−WAXS spectra of the parent AESO (green) and AESOIPA
(black).
ACS Applied Polymer Materials Article
DOI: 10.1021/acsapm.9b00175
ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
D
10 wt % MCC, respectively, i.e., at slightly lower temperatures.
The crystallization temperatures (Tc) are also lower (at ca. 60
°C) than for the neat AESOIPA. The decrease (and
broadening) of the melting and crystallization temperatures
in the composites suggests some interactions between the IPA
motifs and the hydroxyl groups of the MCC.
67,68
After establishing that AESOIPA is stable when heated in air
for 20 min to 150 °C(Figures S9 and S10), the mechanical
properties of AESOIPA and its MCC composites were studied
by dynamic mechanical analysis (DMA) and tensile testing
(Figure 2c,d and Table 1). The neat AESOIPA is fairly rigid
around and below ambient temperature, but the DMA trace
reveals a drastic drop of the storage modulus (E′) from ca. 1.4
GPa to 100 MPa between 20 and 70 °C, which is associated
with passing the glass transition, as observed by DSC. In
addition, a sharp modulus decrease above 70 °C and a failure
temperature at ca. 80 °C is observed, which corresponds to the
melting of the hard phase observed by DSC. The DMA trace
does not show a flat rubbery plateau but displays instead a
continuous modulus drop above Tg, which may indicate
progressive dissociation of the IPA binding motifs. Overall, the
DMA data are in agreement with the conclusions drawn from
the DSC results, i.e., that the crystalline hard domains of
AESOIPA maintain the structure of the polymer network
above its Tgby establishing physical cross-links. The DMA
traces of the AESOIPA/MCC composites show a very similar
behavior, but compared to the neat AESOIPA, the storage
moduli below Tgare considerably higher, which is explained by
the reinforcement provided by the MCC. Consistent with the
DSC data, the modulus drop and failure occur at lower
temperatures than in the neat AESOIPA. A much steeper
modulus drop is observed above Tg,reflecting again some
interactions between the IPA motifs and the MCC hydroxyl
Figure 2. Thermal and mechanical properties of AESOIPA (black) and AESOIPA/MCC composites with 5 wt % (blue) or 10 wt % (red) MCC.
(a, b) DSC heating and cooling traces of the as-prepared materials recorded with heating/cooling rates of 10 °C/min under a nitrogen atmosphere.
Traces are vertically shifted for clarity. (c) DMA traces recorded with a heating rate of 5 °C/min. (d) Stress−strain curves recorded at 25 °C with a
strain rate of 5%/min.
Table 1. Thermal and Mechanical Properties of Films Prepared from AESOIPA and AESOIPA/MCC Composites
Tg
a
(°C) Tc
a
(°C) Tm
a
(°C) E’at 10 °C
b
,
c
(MPa) E’at 25 °C
b
,
c
(MPa) failure T
b
(°C)
AESOIPA 25 80 88 1390 ±50 520 ±70 75−85
AESOIPA/MCC 5 wt % 24 60 65 2090 ±210 1200 ±140 60−70
AESOIPA/MCC 10 wt % 22 60 62 2670 ±200 1360 ±190 60−70
a
Determined by DSC.
b
Determined by DMA.
c
Results are averages of four measurements, and errors are standard deviations.
ACS Applied Polymer Materials Article
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ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
E
surface groups and a reduced perfection of network assembly
and phase segregation.
Tensile tests were performed at room temperature (18−22
°C), and because the Tgvalues of all materials are close to
room temperature, a modulus drop is observed, also at 10 °C
(Table 2,Figure 2d, and Figure S11). At 10 °C, the neat
AESOIPA displays a Young’s modulus of ca. 0.8 GPa, which
increased to 1 GPa upon incorporation of 10 wt % MCC. The
same effect was observed for the maximum stress, which was
measured to be 1 MPa for the neat polymer and 2.4 and 2.7
MPa for the 5 and 10 wt % MCC composites, respectively. At
10 °C, all materials were quite brittle, with an elongation at
break of 1% or less. A significant decrease of the Young’s
moduli was observed when the temperature was increased to
25 °C, i.e., 130 MPa for neat AESOIPA and 198 and 240 MPa
for the composites containing 5 and 10 wt % MCC,
respectively (Figure 2d and Table 2). At this temperature,
the maximum stress determined for the neat AESOIPA (1.9
MPa) was higher than that of the MCC composites (0.9 and
1.4 MPa), reflecting again a lower density of cross-linking hard
domains in the composites and revealing that this feature
outweighs the reinforcing effect of the MCC. All three
materials show a much higher elongation at break at 25 °C
than at 10 °C, in accordance with a change from glassy to
rubbery state. The MCC composites display a higher
elongation at break (40−50%) than the neat AESOIPA
(12%), perhaps on account of a larger fraction of a rubbery
amorphous phase. Overall, the drop of the stiffness and tensile
strength observed above the Tgin the AESOIPA/MCC
composites point to low melt viscosities, which is interesting
from a processing point of view and in the context of
debonding-on-demand applications. On the other hand, these
results suggest that to reinforce AESOIPA above its Tga non-
hydrogen-bonding reinforcing filler such as carbon nanotubes
or graphene would be preferable. Compared to previously
reported fatty acid-based supramolecular polymers,
54−56
AESOIPA and its MCC composites present a similar glassy
modulus, but their rubbery modulus and tensile strength are
somewhat lower, which, as discussed below, translates into
particularly low melt viscosities appropriate for the debonding-
on-demand application explored in this study.
Creep experiments were performed on the neat AESOIPA
films at 10, 25, and 40 °C to study the material’s behavior in
the glassy and elastic regime as well as in the transition phase.
The strain was fixed to 0.04% for the experiment conducted at
10 °C and to 5% for the experiments performed at 25 and 40
°C; this resulted in maximum stresses of 0.3 ±0.1, 1.2 ±0.3,
and 0.05 ±0.02 MPa, respectively. The decay of the stress
under constant strain was then monitored as a function of time
(Figure S12). Interestingly, at all temperatures significant creep
and rapid stress relaxation can be observed, which seems to
suggest that despite the formation of a crystalline hard phase
the network formation in AESOIPA is highly dynamic.
The rheological behavior of AESOIPA and its MCC
composites was analyzed with a temperature-controlled parallel
plate setup. Figure 3, which shows the temperature depend-
ence of the complex viscosity (η*) at a constant frequency of
10 rad/s and an oscillatory strain of 0.1%, reveals a significant
decrease in η*upon heating for all three materials. These
results mirror the modulus drop observed in DMA and are in
agreement with the disassembly of a supramolecular polymer
network into lower molecular weight species. AESOIPA
displays a very low complex viscosity of 8 Pa·s at 120 °C,
which suggests that it is largely dissociated into its low-
molecular-weight triglyceride constituents. The composites
display slightly higher viscosities (16 and 33 Pa·s) at the
indicated temperature on account of the presence of the
cellulosic filler. While it is difficult to compare the melt
viscosities of these materials with that of other previously
reported fatty acid-based supramolecular polymers as the
frequencies used for the measurement are different, it is
possible to conclude that the melt viscosities of AESOIPA and
its MCC composites are among the lowest reported. Indeed,
these materials present viscosities between 8 and 33 Pa·s, that
is, in the same order as for previously reported materials but in
most cases at lower frequency (10 rad/s vs 628−810 rad/
s)
55,56
and temperature (120 °C vs 180 °C).
55
Comparing the
melt viscosity of AESOIPA and its MCC composites with that
Table 2. Mechanical Properties of Films Prepared from AESOIPA and AESOIPA/MCC Composites
10 °C25°C
Young’s modulus
a
(MPa) maximum stress
(MPa) elongation at break
(%) Young’s modulus
a
(MPa) maximum stress
(MPa) elongation at break
(%)
AESOIPA 820 ±130 1.0 ±0.1 0.1 ±0.04 130 ±30 1.9 ±0.2 12 ±2
AESOIPA/MCC
5wt% 980 ±150 2.4 ±0.2 0.4 ±0.04 200 ±90 0.9 ±0.1 40 ±9
AESOIPA/MCC
10 wt % 1000 ±250 2.7 ±0.5 1.1 ±0.2 240 ±40 1.4 ±0.1 47 ±7
a
Calculated from the linear region in the strain regime of 0−0.4%. Results are averages of four measurements, and errors are standard deviations.
Figure 3. Complex viscosity of AESOIPA (black) and AESOIPA/
MCC composites with 5 wt % (blue) or 10 wt % (red) MCC at 50
and 120 °C. Data were recorded at 10 rad/s, 0.1% strain, and a
heating rate of 5 °C/min.
ACS Applied Polymer Materials Article
DOI: 10.1021/acsapm.9b00175
ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
F
of hot melt adhesives is not straightforward as the polymers
used in hot melt formulations have molecular weights of
typically above 10000 g/mol,
15
whereas AESOIPA is a mixture
of components with molecular weights below ca. 1500 g/mol.
In addition, low-molecular-weight additives such as tackifiers
and waxes are usually added to commercial hot melt
formulations to lower melt viscosity,
15,69−71
and such complex
mixtures cannot be compared to the neat AESOIPA studied
here. Perhaps a comparison with blends of a polyamide hot
melt adhesive (Mnof ca. 20000 g/mol) with a low-molecular-
weight supramolecular polymer (Mnof ca. 1000 g/mol) is
instructive.
54
The latter displayed low viscosities between 1
and 5 Pa·s, but at a higher temperature (160 °C vs 120 °Cin
this study) and much higher frequency (100 rad/s vs 10 rad/s
in this study), which suggests that the AESOIPA derivatives
reported here have melt viscosities that are comparable these
hot melt formulations.
The complex viscosity (η*) and the elastic (G′) and viscous
(G″) moduli were examined in dynamic mode as a function of
the angular frequency (ω) in the range of 0.05−100 rad/s in
the linear viscoelastic region at 0.1% strain. The time-
dependent properties were investigated at 50 °C, i.e., in the
rubbery regime, and are shown in Figure 4. The η*of
AESOIPA decreases with increasing ω, and the material
behaves like a viscoelastic solid, where G′dominates G″over
the whole frequency range (Figure 4, left). Upon addition of
MCC the material became more fluid-like, as evidenced by the
observation of a crossover angular frequency ωc, where G′=
G″(Figure 4, middle, right), consistent with the reduction of
the crystalline IPA phase (vide supra).
67,68
The 5 wt %
AESOIPA/MCC composite behaves like a viscoelastic liquid,
exhibiting terminal flow in a broad frequency range, and
turning weakly elastic at a turnover frequency of ω= 50 rad/s.
At low frequencies, the η*of the 5 wt % MCC composite was
about 1 order of magnitude lower than that of the neat
AESOIPA, further indicating that the hard domains of the
material are disrupted. The 10 wt % MCC composite was more
elastic, with ωshifted to a lower frequency of ω= 5 rad/s,
indicative of longer relaxation times at higher filler content.
The η*at low frequencies was higher compared to the lower
filler content material, arguably due to the filler content. In
addition, the 10 wt % composite showed a rubbery plateau at
high frequencies, evidencing that on short time scales the
material is partially cross-linked and behaves as a lightly
entangled polymer. Additional temperature-dependent dynam-
ic measurements confirm the solid-like behavior at a lower
temperature of 35 °C, where a plateau in the real part of the
modulus and a lower imaginary part G″can be observed. At T
>Tm,flow behavior becomes evident, as G″is proportional to
ωand G′, lower in value, shows a stronger ωdependency
(Figure S13). These observations are in agreement with the
thermal properties of the materials, as the Tmof the hard phase
of neat AESOIPA (88 °C) is well above the measuring
temperature (50 °C), while those of the MCC composites (65
and 62 °C) are somewhat closer.
To investigate the usefulness of these plant oil-based
supramolecular networks and composites as adhesives for
(de)bonding on-demand using thermal or light-based
activation, single lap joints were prepared by bonding two
glass or stainless steel substrates. All samples were prepared by
placing the polymer films between the substrates, heating the
sandwiches to 100 °C under compression with metallic clamps,
and cooling them to room temperature. Overlap areas of 20 ×
25 mm2and 10 ×10 mm2were used for glass and stainless
steel substrates, respectively. The thickness of the adhesive
layer in the bonded structure was checked with a micrometer
(ca. 90−100 μm for all samples). The adhesive properties were
quantitatively explored by lap shear tests at ambient temper-
ature using a tensile tester to apply uniaxial stress (Table 3).
The shear strength measured for the neat AESOIPA was 1.2
MPa for glass substrates and 1.7 MPa with stainless steel.
Similar values were determined for the composites with 5 wt %
MCC (1.0 MPa) and 10 wt % MCC (0.9 MPa) on glass, but
the shear strength increased significantly when steel was used
Figure 4. Frequency dependence of the elastic (●) and viscous (○) moduli and the complex viscosity (■) of neat AESOIPA (black) and
AESOIPA/MCC composites with 5 wt % (blue) or 10 wt % (red) MCC, all recorded at 50 °C.
Table 3. Shear Test Results of Glass and Stainless Steel
Single Lap Joints Bonded with AESOIPA and AESOIPA/
MCC Composites with 5 and 10 wt % MCC
a
shear strength (MPa)
AESOIPA AESOIPA/
MCC 5 wt % AESOIPA/
MCC 10 wt %
regular glass
substrates thermally
bonded 1.2 ±0.2 1.0 ±0.0 0.9 ±0.1
thermally
rebonded 1.3 ±0.1 1.0 ±0.1 1.0 ±0.1
stainless steel
substrates thermally
bonded 1.7 ±0.2 2.3 ±0.2 2.2 ±0.2
thermally
rebonded 1.7 ±0.2 2.4 ±0.4 2.1 ±0.2
a
Samples were subjected to a shear-test experiment until the bonds
failed and then rebonded using the original bonding protocol without
applying additional adhesive. Results are averages of three measure-
ments, and errors are standard deviations.
ACS Applied Polymer Materials Article
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G
(2.3 and 2.2 MPa, respectively) (Figures S14 and S15). All
samples failed through an adhesive mode (Figure S16),
indicating that there is a priori room for improvement by
formulation. To demonstrate the reversibility of these
supramolecular networks and composites, failed measured
samples were directly rebonded by applying the same heating/
cooling process described above. Indeed, the shear strength
remained constant through the two cycles for AESOIPA and
the two MCC composites.
The debonding on demand of lap joints bonded with neat
AESOIPA was investigated using heat and UV light (see
Videos S1,S2, and S3). In a first qualitative experiment (Video
S1), two metallic objects were thermally bonded, and multiple
release/rebond cycles were realized without any apparent loss
of properties (Table 3). In a second experiment (Video S2), a
small amount of AESOIPA containing 0.2 wt % of the UV light
absorber Tinuvin 326, which was added to increase the
absorption in the UV regime,
49,51,53,72
was placed on a glass
slide which was bonded with a metallic object by applying UV
light (λ= 320−390 nm, 1600 mW/cm2) through the glass
slide. After only 5 s of UV irradiation and a brief cooling period
(3−4 s), the metallic object was firmly bonded to the glass
support. The objects could be rapidly debonded by irradiation
with the same UV light source and without yellowing of the
supramolecular adhesive. In a third test (Video S3), the same
AESOIPA/Tinuvin 326 mixture was used to thermally bond a
single lap joint with two glass substrates (1 mm thickness).
The lap joint could hold a 200 g weight (∼2 N), and UV light
(λ= 320−390 nm, 1600 mW/cm2) triggered debonding could
be achieved in ca. 30 s. To obtain quantitative data, single lap
joint tests were performed with stainless steel and glass
substrates to evaluate heat and UV light as debonding stimuli,
and both neat AESOIPA and the AESOIPA/MCC composites
were used as adhesives. For the thermal debonding test, hot air
at a temperature of ca. 100 °C was applied, whereas for
debonding with UV light, a UV light source (λ= 320−390 nm,
1600 mW/cm2) was used. Optical debonding experiments
were performed with the neat AESOIPA as well as with a blend
containing 0.2 wt % of Tinuvin 326. All samples were mounted
in a tensile tester and placed under an initial constant force of
(20−23 N) before heat or light was applied to debond (Figure
5).
After the lap joints were mounted, the force was monitored
over time, and the time when failure occurred was recorded
and compared between the different materials. In the absence
of an external stimulus, neither creep nor failure was observed
within an hour. However, samples bonded with AESOIPA
failed after ca. 17 s upon exposure to heat, while those bonded
with the AESOIPA/MCC composites failed after 15 (5 wt %
MCC) or 12 s (10 wt % MCC). A similar behavior was
observed in the UV light mediated debonding experiments,
where the debonding occurred after 30−45 s for the Tinuvin
326-free samples. The debonding time was reduced to 20−30 s
when Tinuvin 326 was added. To monitor the temperature
induced by UV light exposure, surface temperature profiles of
the materials versus time were recorded with an IR camera
(Figure 6). The comparison shows that after 20 s of UV
irradiation the temperature of the materials with Tinuvin 326 is
around 20 °C higher than that of the materials without
Tinuvin 326, which illustrates the role of the additive in the
debonding process. Overall, the debonding temperatures
Figure 5. Debonding-on-demand experiments of lap joints bonded with the neat AESOIPA (black) and AESOIPA/MCC composites with 5 wt %
(blue) or 10 wt % MCC (red). An initial constant force of 20−23 N was applied, and the force was monitored as a function of time after (a) heat
was applied to the stainless steel substrates and (b) UV light (λ= 320−390 nm, 1600 mW/cm2) was focused on the lap joint bonded using
adhesives with (dashed lines) and without (solid lines) 0.2 wt % of the UV light absorber Tinuvin 326. A sample bonded with AESOIPA without
applying any stimuli was measured as a reference (orange). The vertical dashed line marks the start of the application of heat or UV light.
Figure 6. Surface temperature profiles of the neat AESOIPA (black)
and AESOIPA/MCC composites with 5 wt % (blue) and 10 wt %
(red) MCC with 0.2 wt % of Tinuvin 326 (dashed lines) and without
this light−heat converter (solid lines upon UV-irradiation (λ= 320−
390 nm, 1600 mW/cm2) applied on glass substrates. The maximum
values correspond to time points when the lamp was switched off.
ACS Applied Polymer Materials Article
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ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
H
observed are comparable with only small differences due to the
different response of the material to the external stimulus and
the corresponding heating rates.
■CONCLUSIONS
Taking advantage of the reversible and reconfigurable features
of supramolecular polymers, we have introduced a new
materials platform that displays an interesting composition of
adequate mechanical properties under ambient conditions and
a very low melt viscosity. This property combination was
accessed by coupling multiple weakly interacting IPA motifs
with a hydrophobic core and exploiting microphase
segregation between the triglyceride backbone and the IPA
groups. The domains formed by the latter act as physical cross-
links and stabilize the weak hydrogen bonds. The resulting
supramolecular networks are less brittle and show a lower melt
viscosity than previously investigated supramolecular polymer
networks,
72,73
and the IPA motif allows an effective
dissociation at relatively low temperatures (70−100 °C). The
addition of microcrystalline cellulose to the material further
increases strength and stiffness below the Tg. However, above
the Tgthe strength and stiffness decrease in the presence of
microcrystalline cellulose, but the toughness increases. Lap
joint adhesive tests performed at room temperature using glass
and stainless steel substrates revealed shear strength values
between 0.9 and 2.4 MPa, and heat and UV light were used as
external stimuli to mediate debonding on command.
■ASSOCIATED CONTENT
*
SSupporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acsapm.9b00175.
Analytic data (NMR, IR, and mass spectrometry) of
compounds 1−4, additional SAXS-WAXS, DSC, rheol-
ogy and adhesion data (PDF)
Video S1 (MP4)
Video S2 (MP4)
Video S3 (MP4)
■AUTHOR INFORMATION
Corresponding Author
*E-mail: christoph.weder@unifr.ch (C.W.).
ORCID
Anselmo del Prado: 0000-0003-2110-5621
Sandor Balog: 0000-0002-4847-9845
Christoph Weder: 0000-0001-7183-1790
Present Address
A.d.P.: Departamento de Qui ́
mica Orgá
nica, Facultad de
Ciencias, Universidad Autónoma de Madrid, 28049 Madrid,
Spain.
Notes
The authors declare no competing financial interest.
■ACKNOWLEDGMENTS
The authors gratefully acknowledge financial support from the
Swiss National Science Foundation (precoR Grant
20PC21_161565 to C.W. and Ambizione Grant
PZ00P2_154845 to L.M.E.) and the Adolphe Merkle
Foundation.
■REFERENCES
(1) Allies, V. R.; Zimmermann, W. D. Debondable cyanoacrylate
adhesive compositions. DE2612546A1, 1979.
(2) Kirsten, C.; Ferencz, A.; Hirthammer, M. Adhesives containing
activatable debonding agents and process for bonding and debonding.
DE19904835A1, 2000.
(3) Nijhuis, W. A. Multi-layer laminate structure with reversible
bonding. WO 2012143190 A1, 2012.
(4) Lu, Y.; Broughton, J.; Winfield, P. A review of innovations in
disbonding techniques for repair and recycling of automotive vehicles.
Int. J. Adhes. Adhes. 2014,50, 119−127.
(5) Banea, M. D.; Da Silva, L. F.; Campilho, R. D.; Sato, C. Smart
adhesive joints: An overview of recent developments. J. Adhes. 2014,
90,16−40.
(6) Wouters, M.; Burghoorn, M.; Ingenhut, B.; Timmer, K.;
Rentrop, C.; Bots, T.; Oosterhuis, G.; Fischer, H. Tuneable adhesion
through novel binder technologies. Prog. Org. Coat. 2011,72, 152−
158.
(7) Han, I. Y.; Song, H. G.; Park, S. W.; Ji-Seok, H. Debonder to
manufacture semiconductor and debonding method thereof. US
Patent 13/418795.
(8) Dittmers, H.-J.; Stock, J.; Thorns, D. Pressure-sensitive adhesive,
process for producing the same and its use. WO9412582A1, 1994.
(9) Chivers, R. A. Easy removal of pressure sensitive adhesives for
skin applications. Int. J. Adhes. Adhes. 2001,21, 381−388.
(10) Kirkbir, F. N.; Orosco, M. M.; Thompson, M. E.; Yu, X.;
Zhang, C. Reversible adhesives. EP 2625239 A2, 2012.
(11) Kasprzak, K. A. Method for removing tacky adhesives and
articles adhered therewith. DE3028780A1, 1983.
(12) Adler, M.; Kruh, D. Method and composition for removing
adhesive bandages. US 6063231 A, 2000.
(13) Webster, I. Adhesives. US 6184264 B1, 2001.
(14) Moszner, N.; Hirt, T.; Rist, K.; Salz, U.; Weder, C.; Fiore, G.;
Heinzmann, C.; Rheinberger, V. Dental materials based on
compounds having debonding-on-demand properties. US 9320686,
2016.
(15) Li, W.; Bouzidi, L.; Narine, S. S. Current research and
development status and prospect of hot-melt adhesives: A review. Ind.
Eng. Chem. Res. 2008,47, 7524−7532.
(16) McCurdy, R.; Hutchinson, A.; Winfield, P. The mechanical
performance of adhesive joints containing active disbonding agents.
Int. J. Adhes. Adhes. 2013,46, 100−113.
(17) Kim, D.; Chung, I.; Kim, G. Dismantlement studies of
dismantlable polyurethane adhesive by controlling thermal property. J.
Adhes. Sci. Technol. 2012,26, 2571−2589.
(18) Nishiyama, Y.; Uto, N.; Sato, C.; Sakurai, H. Dismantlement
behavior and strength of dismantlable adhesive including thermally
expansive particles. Int. J. Adhes. Adhes. 2003,23, 377−382.
(19) Keite-Telgenbüscher, K.; Junghans, M.; Dietz, B.; Dominikat,
U.; Domann, F.; Ellringmann, U. Heated planar element and method
for its attachment. US 8383997 B2, 2013.
(20) Sjong, A. Thermoplastic coating and removal using bonding
interface with catalytic nanoparticles. US 9481160, 2016.
(21) Sato, E.; Tamura, H.; Matsumoto, A. Cohesive force change
induced by polyperoxide degradation for application to dismantlable
adhesion. ACS Appl. Mater. Interfaces 2010,2, 2594−2601.
(22) Suyama, K.; Tachi, H. Direct rheological measurement of serial
photopolymerization and photodegradation processes of pressure-
sensitive adhesives composed of O-acyloxime-based photolabile
crosslinkers and butyl acrylate. Prog. Org. Coat. 2016,100,94−99.
(23) Wang, Y.-Z.; Li, L.; Du, F.-S.; Li, Z.-C. A facile approach to
catechol containing UV dismantlable adhesives. Polymer 2015,68,
270−278.
(24) Aubert, J. H. Note: Thermally removable epoxy adhesives
incorporating thermally reversible diels-alder adducts. J. Adhes. 2003,
79, 609−616.
(25) Luo, X.; Lauber, K. E.; Mather, P. T. A thermally responsive,
rigid, and reversible adhesive. Polymer 2010,51, 1169−1175.
ACS Applied Polymer Materials Article
DOI: 10.1021/acsapm.9b00175
ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
I
(26) Nguyen, M. K.; Huynh, C. T.; Lee, D. S. pH-sensitive and
bioadhesive poly(β-amino ester)−poly(ethylene glycol)−poly(β-
amino ester) triblock copolymer hydrogels with potential for drug
delivery in oral mucosal surfaces. Polymer 2009,50, 5205−5210.
(27) Liou, K.; Khemani, K. C.; Wudl, F. Novel adhesives based on
poly(isocyanates). Macromolecules 1991,24, 2217−2220.
(28) Sudre, G.; Olanier, L.; Tran, Y.; Hourdet, D.; Creton, C.
Reversible adhesion between a hydrogel and a polymer brush. Soft
Matter 2012,8, 8184−8193.
(29) Gilbert, M. D. Electrically disbonding materials. EP 1200252
A4, 2003.
(30) Gilbert, M. D. Electrically disbondable compositions and
related methods. US 7465492, 2008.
(31) Saito, K.; Sakai, A.; Nate, K. Light-sensitive peelable adhesive
tapes and sheets and their manufacture. JP2002212521A, 2002.
(32) Heinzmann, C.; Weder, C.; De Espinosa, L. M. Supramolecular
polymer adhesives: advanced materials inspired by nature. Chem. Soc.
Rev. 2016,45, 342−358.
(33) Yang, L.; Tan, X.; Wang, Z.; Zhang, X. Supramolecular
polymers: historical development, preparation, characterization, and
functions. Chem. Rev. 2015,115, 7196−7239.
(34) De Greef, T. F.; Meijer, E. Materials science: supramolecular
polymers. Nature 2008,453, 171−173.
(35) Wojtecki, R. J.; Meador, M. A.; Rowan, S. J. Using the dynamic
bond to access macroscopically responsive structurally dynamic
polymers. Nat. Mater. 2011,10,14−27.
(36) Burnworth, M.; Tang, L.; Kumpfer, J. R.; Duncan, A. J.; Beyer,
F. L.; Fiore, G. L.; Rowan, S. J.; Weder, C. Optically healable
supramolecular polymers. Nature 2011,472, 334−337.
(37) Cordier, P.; Tournilhac, F.; Soulié
-Ziakovic, C.; Leibler, L. Self-
healing and thermoreversible rubber from supramolecular assembly.
Nature 2008,451, 977−980.
(38) Fiore, G. L.; Rowan, S. J.; Weder, C. Optically healable
polymers. Chem. Soc. Rev. 2013,42, 7278−7288.
(39) Herbst, F.; Döhler, D.; Michael, P.; Binder, W. H. Self healing
polymers via supramolecular forces. Macromol. Rapid Commun. 2013,
34, 203−220.
(40) Sautaux, J.; Montero de Espinosa, L.; Balog, S.; Weder, C.
Multistimuli, multiresponsive fully supramolecular orthogonally
bound polymer networks. Macromolecules 2018,51, 5867−5874.
(41) Kumpfer, J. R.; Rowan, S. J. Thermo-, photo-, and chemo-
responsive shape-memory properties from photo-cross-linked metallo-
supramolecular polymers. J. Am. Chem. Soc. 2011,133, 12866−12874.
(42) Meng, H.; Li, G. A review of stimuli-responsive shape memory
polymer composites. Polymer 2013,54, 2199−2221.
(43) Balkenende, D. W.; Coulibaly, S.; Balog, S.; Simon, Y. C.; Fiore,
G. L.; Weder, C. Mechanochemistry with metallosupramolecular
polymers. J. Am. Chem. Soc. 2014,136, 10493−10498.
(44) Calvino, C.; Neumann, L.; Weder, C.; Schrettl, S. Approaches
to polymeric mechanochromic materials. J. Polym. Sci., Part A: Polym.
Chem. 2017,55, 640−652.
(45) Wietor, J.-L.; Van Beek, D.; Peters, G. W.; Mendes, E.;
Sijbesma, R. P. Effects of branching and crystallization on rheology of
polycaprolactone supramolecular polymers with ureidopyrimidinone
end groups. Macromolecules 2011,44, 1211−1219.
(46) Hentschel, J.; Kushner, A. M.; Ziller, J.; Guan, Z. Self healing
supramolecular block copolymers. Angew. Chem., Int. Ed. 2012,51,
10561−10565.
(47) Van Gemert, G. M.; Peeters, J. W.; Söntjens, S. H.; Janssen, H.
M.; Bosman, A. W. Self healing supramolecular polymers in action.
Macromol. Chem. Phys. 2012,213, 234−242.
(48) Kautz, H.; Van Beek, D.; Sijbesma, R. P.; Meijer, E.
Cooperative end-to-end and lateral hydrogen-bonding motifs in
supramolecular thermoplastic elastomers. Macromolecules 2006,39,
4265−4267.
(49) Heinzmann, C.; Coulibaly, S.; Roulin, A.; Fiore, G. L.; Weder,
C. Light-induced bonding and debonding with supramolecular
adhesives. ACS Appl. Mater. Interfaces 2014,6, 4713−4719.
(50) Elkins, C. L.; Park, T.; McKee, M. G.; Long, T. E. Synthesis and
characterization of poly (2 ethylhexyl methacrylate) copolymers
containing pendant, self complementary multiple hydrogen bonding
sites. J. Polym. Sci., Part A: Polym. Chem. 2005,43, 4618−4631.
(51) Heinzmann, C.; Salz, U.; Moszner, N.; Fiore, G. L.; Weder, C.
Supramolecular cross-links in poly (alkyl methacrylate) copolymers
and their impact on the mechanical and reversible adhesive properties.
ACS Appl. Mater. Interfaces 2015,7, 13395−13404.
(52) Heinzmann, C.; Lamparth, I.; Rist, K.; Moszner, N.; Fiore, G.
L.; Weder, C. Supramolecular Polymer Networks Made by Solvent-
Free Copolymerization of a Liquid 2-Ureido-4 [1 H]-pyrimidinone
Methacrylamide. Macromolecules 2015,48, 8128−8136.
(53) Balkenende, D. W.; Monnier, C. A.; Fiore, G. L.; Weder, C.
Optically responsive supramolecular polymer glasses. Nat. Commun.
2016,7, 10995.
(54) Chabert, F.; Tournilhac, F.; Sajot, N.; Tencé
-Girault, S.;
Leibler, L. Supramolecular polymer for enhancement of adhesion and
processability of hot melt polyamides. Int. J. Adhes. Adhes. 2010,30,
696−705.
(55) Agnaou, R. d.; Capelot, M.; Tencé
-Girault, S.; Tournilhac, F. o.;
Leibler, L. Supramolecular thermoplastic with 0.5 Pa•s melt viscosity.
J. Am. Chem. Soc. 2014,136, 11268−11271.
(56) Hayashi, M.; Tournilhac, F. Thermal stability enhancement of
hydrogen bonded semicrystalline thermoplastics achieved by combi-
nation of aramide chemistry and supramolecular chemistry. Polym.
Chem. 2017,8, 461−471.
(57) Li, A.; Li, K. Pressure-sensitive adhesives based on epoxidized
soybean oil and dicarboxylic acids. ACS Sustainable Chem. Eng. 2014,
2, 2090−2096.
(58) Ahn, B. K.; Kraft, S.; Wang, D.; Sun, X. S. Thermally stable,
transparent, pressure-sensitive adhesives from epoxidized and
dihydroxyl soybean oil. Biomacromolecules 2011,12, 1839−1843.
(59) Song, L.; Wang, Z.; Lamm, M. E.; Yuan, L.; Tang, C.
Supramolecular polymer nanocomposites derived from plant oils and
cellulose nanocrystals. Macromolecules 2017,50, 7475−7483.
(60) Starnes, W. H., Jr.; Kim, S. Organic thiol metal-free stabilizers
and plasticizers for halogen-containing polymers. US 6747081, 2004.
(61) Clegg, W.; Russo, L. Synthesis and structures of alkali metal
complexes of isophthalic acid: the interplay of organic supramolecular
interactions and flexible metal coordination as structure-directing
factors. Cryst. Growth Des. 2009,9, 1158−1163.
(62) Sivakova, S.; Bohnsack, D. A.; Mackay, M. E.; Suwanmala, P.;
Rowan, S. J. Utilization of a combination of weak hydrogen-bonding
interactions and phase segregation to yield highly thermosensitive
supramolecular polymers. J. Am. Chem. Soc. 2005,127, 18202−18211.
(63) Montero de Espinosa, L.; Balog, S.; Weder, C. Isophthalic
acid−pyridine H-bonding: simplicity in the design of mechanically
robust phase-segregated supramolecular polymers. ACS Macro Lett.
2014,3, 540−543.
(64) Yang, J.; Marendaz, J.-L.; Geib, S. J.; Hamilton, A. D. Hydrogen
bonding control of self-assembly: simple isophthalic acid derivatives
form cyclic hexameric aggregates. Tetrahedron Lett. 1994,35, 3665−
3668.
(65) Gole, B.; Shanmugaraju, S.; Bar, A. K.; Mukherjee, P. S.
Supramolecular polymer for explosives sensing: role of H-bonding in
enhancement of sensitivity in the solid state. Chem. Commun. 2011,
47, 10046−10048.
(66) Sapkota, J.; Natterodt, J. C.; Shirole, A.; Foster, E. J.; Weder, C.
Fabrication and properties of polyethylene/cellulose nanocrystal
composites. Macromol. Mater. Eng. 2017,302, 1600300.
(67) Zhao, H.; Kwak, J. H.; Wang, Y.; Franz, J. A.; White, J. M.;
Holladay, J. E. Interactions between cellulose and N-methylmorpho-
line-N-oxide. Carbohydr. Polym. 2007,67,97−103.
(68) Duddu, S. P.; Grant, D. J. The use of thermal analysis in the
assessment of crystal disruption. Thermochim. Acta 1995,248, 131−
145.
(69) Paul, C. W. Hot-melt adhesives. MRS Bull. 2003,28, 440−444.
ACS Applied Polymer Materials Article
DOI: 10.1021/acsapm.9b00175
ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
J
(70) Park, Y.-J.; Joo, H.-S.; Do, H.-S.; Kim, H.-J. Viscoelastic and
adhesion properties of EVA/tackifier/wax ternary blend systems as
hot-melt adhesives. J. Adhes. Sci. Technol. 2006,20, 1561−1571.
(71) Kalish, J. P.; Ramalingam, S.; Wamuo, O.; Vyavahare, O.; Wu,
Y.; Hsu, S. L.; Paul, C. W.; Eodice, A. Role of n-alkane-based additives
in hot melt adhesives. Int. J. Adhes. Adhes. 2014,55,82−88.
(72) Balkenende, D. W.; Olson, R. A.; Balog, S.; Weder, C.; Montero
de Espinosa, L. Epoxy resin-inspired reconfigurable supramolecular
networks. Macromolecules 2016,49, 7877−7885.
(73) Wietor, J.-L.; Dimopoulos, A.; Govaert, L. E.; Van Benthem, R.
A.; De With, G.; Sijbesma, R. P. Preemptive healing through
supramolecular cross-links. Macromolecules 2009,42, 6640−6646.
ACS Applied Polymer Materials Article
DOI: 10.1021/acsapm.9b00175
ACS Appl. Polym. Mater. XXXX, XXX, XXX−XXX
K
