Pressure-sensitive adhesive utilizing molecular interactions between thymine and adenine

Article abstract of DOI:10.1002/pola.27977

A simple pressure-sensitive adhesion (PSA) system incorporating noncovalent interaction between thymine and adenine is presented. A copolymer having thymine moieties is combined with a low-molecular-weight bifunctional adenine cross-linker. Molecular inte

Full text of DOI:10.1002/pola.27977

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
Pressure-Sensitive Adhesive Utilizing Molecular Interactions Between
Thymine and Adenine
Nobuhiro Ishikawa, Masahiro Furutani, Koji Arimitsu
Department of Pure and Applied Chemistry, Tokyo University of Science, 2641 Yamazaki, Noda, Chiba 278-8510, Japan
Correspondence to: K. Arimitsu (E-mail: arimitsu@rs.noda.tus.ac.jp)
Received 25 September 2015; accepted 28 October 2015; published online 22 November 2015
DOI: 10.1002/pola.27977
ABSTRACT: A simple pressure-sensitive adhesion (PSA) system
incorporating noncovalent interaction between thymine and
adenine is presented. A copolymer having thymine moieties is
combined with a low-molecular-weight bifunctional adenine
cross-linker. Molecular interactions caused by multiple hydro-
gen bonds between the thymine and adenine units are eval-
uated by FT-IR spectral measurement. Mechanical properties of
the PSA are examined by stress–strain curves and dynamic
mechanical analysis. As the number of adenine cross-linkers
increases, Young’s modulus increases from 0.24 to 3.0 MPa,
and the glass transition temperature increases. Furthermore, it
is found that the PSAs have adequate adhesive property from
their shear strength test. Heat treatment at 80 8C is effective for
reinforcement because of interchange of the hydrogen bonds.
C
V
2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym.
Chem. 2016, 54, 1332–1338
KEYWORDS: adenine; hydrogen bond; molecular interaction;
pressure-sensitive adhesive; thymine
none (Upy)16–22 or 2,6-bis(10-methylbenzimidazolyl)pyridine
(Mebip)21,23 moieties were designed.
INTRODUCTION Pressure-sensitive adhesive (PSA) is one of
the viscoelastic materials1 that have been used in many
applications, such as automobiles,1–4 electronics,5–7 and med-
icines.8–10 PSAs are classified into acryl-based, rubber-based,
and silicone-based adhesives.1 Among them, acryl-based
PSAs are used mainly in industrial fields because there are
many kinds of abundant acrylic monomers to design PSAs
according to their applications.
PSAs utilizing noncovalent interactions have recently been
reported where reversible polymer networks are formed.
Weder et al. reported adhesive materials consisting of poly-
mers having Upy or Mebip moieties, where multiple hydro-
gen or co-ordination bonds are formed between the
moieties.21,24 Zimmerman et al. reported adhesive materials
utilizing noncovalent interactions between nucleobase analog
units.25 Long et al. designed acrylic copolymers having thy-
mine or adenine units, and applied their mixtures as adhe-
sives.26 The thymine–adenine interaction is very common in
DNA chemistry, and the nucleobase unit is available for
chemical modifications where vinyl,27–31 methacryl,32,33 and
acryl26 groups are readily introduced. However, the adhesive
system that Long et al. reported consisted of two kinds of
high-molecular-weight copolymers, which is often accompa-
nied by difficulty in mixing them, leading to poor control of
the macroscopic adhesive properties. In our previous work,
we reported adhesive materials where a high-molecular-
weight copolymer having thymine units at its side chains is
combined with a low-molecular-weight cross-linker having
two adenine units, as shown in Scheme 1.34 It is expected
that these thymine and adenine compounds will mix
Macroscopic properties of these PSAs, such as adhesive and
creep properties, are based on the microscopic states of
polymers in bulk as well as on the interface. For example,
the molecular weights of polymers and degree of entangle-
ment between them are important factors in determining
properties of the materials. The cross-linking state is also
important, and there are various kinds of cross-linkers for
PSAs. Multifunctional epoxy and isocyanate compounds are
generally used as cross-linkers in industrial acryl-based
PSAs, and they form irreversible covalent bonds.11,12 On the
other hand, it has been reported that chemical units for non-
covalent interactions were incorporated into a soft material
to change the properties of the bulk by temporal cross-link-
ing.13–15 These units were introduced at side chains or ter-
mini of main chains to form reversible polymer networks.
Copolymers and telechelic polymers having ureidopyrimidi-
Additional Supporting Information may be found in the online version of this article.
C
V
2015 Wiley Periodicals, Inc.
1332
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 1332–1338

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
SCHEME 1 Schematic representation of molecular interaction of thymine copolymer 1 and adenine cross-linker 2. [Color figure
can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
homogeneously, and it would be easy to control the adhesive
properties of the mixtures.35 In this study, thymine copoly-
mers 1 having three different molecular weights were syn-
thesized, and PSA materials consisting of each thymine
copolymer and various amounts of the bifunctional adenine
cross-linker 2 were prepared. Thymine–adenine interaction
of the PSA materials was examined, and macroscopic adhe-
sive properties of such materials were investigated by tensile
test, dynamic mechanical analysis (DMA), and shear strength
test to examine the influences of molecular weight and/or
glass transition temperature of 1.
extraction was performed with dichloromethane. The oil
layer was dried over MgSO4. Column chromatography was
performed on silica gel with chloroform/methanol (20/1, v/
v) to give the product in 66% yield. 1H-NMR (500 MHz,
CDCl3) 1.51–1.68 (m, 4H, –CH2–), 1.71 (s, 3H, –CH3), 2.66 (t,
2H, J 5 6.0 Hz, –CH2–), 3.83 (t, 2H, J 5 5.2 Hz, –CH2–), 3.97–
4.13 (m, 4H, –CH2–), 5.91 (d, 1H, J 5 6.8 Hz, –CH@CH2), 6.14
(dd, 1H, J1 5 15 Hz, J2 5 10 Hz, –CH@CH2), 11.23 (br, 1H, –
NH–).
Synthesis of P(BA-co-Tac) 1
Copolymer 1 was synthesized using free-radical polymeriza-
tion with butyl acrylate (BA) and Tac. A typical synthesis
method is described below. BA (32 g, 249.7 mmol) and Tac
(9.0 g, 27.7 mmol) were dissolved in toluene (46 mL). After
N2 bubbling for 30 min, azobisisobutyronitrile (AIBN,
0.042 g, 0.26 mmol) in toluene (2 mL) was added at 55 8C.
The solution was stirred at 65 8C for 10 h. The reaction mix-
ture was dissolved again in methanol/water (1/1, v/v), and
reprecipitation was performed with hexane as a poor sol-
vent. The resulting viscous liquid was dried in vacuo at room
temperature for 24 h to give 1 in 83% yield. The mole ratio
of BA/Tac units was found to be 91/9, estimated using 1H-
NMR. The molecular weight (Mw) and polydispersity index
(Mw/Mn) were 1.50 3 105 and 3.00, respectively.
EXPERIMENTAL
Materials and Equipment
Chemical reagents were purchased from Tokyo Chemical
Industry Co., Ltd. (Tokyo, Japan) and Wako Pure Chemical
Industries, Ltd. (Osaka, Japan). They were used without fur-
ther purification.
1H- and 13C-NMR were performed using a JEOL ECP-500 and
AL-300. FT-IR measurements were performed using a JASCO
FT-IR-600 and a METTLER TOREDO HS82. Differential scan-
ning calorimetry (DSC) measurements were performed using
a HITACHI DSC7000X. Fast atom bombardment mass spec-
trometry (FAB–MS) was performed using a JEOL MS700 in
positive ion mode. Gel permeation chromatography (GPC)
was performed using a TOSOH HLC-8320GPC with polysty-
rene standards. Measurement of dynamic elastic modulus
was performed using an Anton Paar MCR 300. Shear
strength tests were conducted using a Shimadzu AG-Xplus.
Synthesis of Adenine Cross-Linker 2
Isophorone diisocyanate (1.0 g, 4.5 mmol) in benzene
(20 mL) was dropped into 2-hydroxyethyl acrylate (1.15 g,
9.9 mmol), di-n-butyltin dilaurate (1 drop), and BHT (0.12 g,
0.54 mmol) in benzene (20 mL) at 70 8C. The mixture was
stirred at 70 8C for 6 h. After removing solvent, the residue
was purified using column chromatography on silica gel with
ethyl acetate/hexane (1/2, v/v) to give 2-(((5-((2-
(aryloyloxy)carbonyl)amino)21,3,3-trimethylcyclohexyl)me-
thyl)carbamoyl)oxyethyl acrylate (intermediate, 20) in 75%
yield as a viscous liquid. 1H-NMR (300 MHz, CDCl3): 0.89–
1.78 (m, 15H, –CH2–, –CH3), 2.92 (d, 2H, J 5 6 Hz, –CH2–),
3.87 (br, 1H, –CH<), 4.29–4.34 (m, 8H, –CH2–), 4.62 (br, 1H,
–NH–), 4.88 (br, 1H, –NH–), 5.87 (d, 2H, J 5 9 Hz, –CH@CH2),
Synthesis and Measurement
Synthesis of Thymine Acrylate Monomer (4-(((3-Thymine-
1-yl)propanoyl)oxy)butyl Acrylate (Tac)
Thymine (2.0 g, 15.6 mmol), triethylamine (0.04 g, 0.4
mmol), and dibutylhydroxytoluene (BHT, 0.06 g, 0.27 mmol)
were mixed in DMF (40 mL) at room temperature for 1 h.
1,4-Bis(acryloyloxy)butane (6.28 g, 31.7 mmol) was added to
the suspension, and the mixture was stirred at room temper-
ature for 24 h. After adding dichloromethane and water,
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 1332–1338
1333

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
set on a Mettler Toledo hot-stage HS-82, and FT-IR measure-
ments were carried out.
Measurement of Stress–Strain Curves
Each sample (ca 200 lm thick) was prepared by integrating
several thin PSA sheets. Samples were treated in an auto-
clave (at 80 8C for 20 min) to remove unnecessary air bub-
bles. The measurement area was 1 3 1 cm. Young’s modulus
was calculated from the modulus deformation region of the
obtained stress–strain curve.
Measurements of DMA
Each sample (ca 700 lm thick) was prepared by integrating
several thin PSA sheets. Samples were treated in an auto-
clave (at 80 8C for 20 min) to remove unnecessary air bub-
bles. Storage modulus (G0) and loss tangent (tan d) were
measured. Setting temperatures for measurements of tem-
perature dispersion were from 260 to 140 8C, and the mea-
surement frequency was 1 Hz.
SCHEME 2 Synthesis of copolymer 1. [Color figure can be
viewed in the online issue, which is available at wileyonlineli-
brary.com.]
6.15 (dd, 1H, J1 5 18 Hz, J2 5 12 Hz, –CH@CH2), 6.45 (d,
J 5 18 Hz, –CH@CH2).
Adenine (3.76 g, 27.4 mmol), BHT (0.12 g, 0.54 mmol), and
K2CO3 (0.12 g, 0.92 mmol) were mixed in DMSO (35 mL),
and the suspension was stirred at 50 8C for 1 h. Intermediate
20 (6.22 g, 13.7 mmol) in DMSO (5 mL) was added to the
suspension, and the mixture was stirred at 50 8C for another
6 h. After adding dichloromethane and water, extraction was
performed with dichloromethane. The organic layer was
evaporated, and the residue was dissolved again in THF, fol-
lowed by drying over MgSO4. Column chromatography was
performed on silica gel with chloroform/methanol (20/1, v/
v) to give 2 in 55% yield as a white solid. 1H-NMR (500
MHz, CDCl3): 0.86–2.13 (m, 17H, –CH2–, –CH3), 2.88–2.99
(m, 4H, –CH2–), 3.76 (br, 1H, –CH<), 4.18–4.51 (m, 8H, –O–
CH2–), 4.33–4.49 (t, 4H, J 5 6 Hz, –NH–CH2–), 5.26 (br, 1H, –
NH–C@O), 5.50 (br, 1H, –NH–C@O), 6.17 (br, 4H, –NH2), 7.93
(s, 2H, –N@CH–NH–), 8.33 (s, 2H, –N@CH–NH–).
Measurements of Shear Strength
A PSA sheet sample cut to a size of 2.5 3 2.5 cm was stuck
on an SUS test piece, and sanded with another SUS test
piece. After 72 h, the sanded sample was set to the device
and measured at 23 8C. Measurement speed was 50 mm/
min. Measurements were also performed on other sanded
samples which were treated with an autoclave (80 8C, 5 kg,
20 min) before the measurement.
RESULTS AND DISCUSSION
Synthesis of Pressure-Sensitive Adhesive Copolymers,
Poly(BA-co-Tac), Poly(Butyl Acrylate) (pBA), and
Poly(Butyl acrylate-co-Acrylic Acid) (pBA-co-AA, AA10)
Synthesis of Tac has already been reported in the litera-
ture.26 BA is available and usually used as a monomer of
PSAs, and its polymer has very low Tg. Acrylic copolymer
bearing thymine units (1) was synthesized with free-radical
polymerization using AIBN as initiator (Scheme 2). Copoly-
mers having various kinds of molecular weights were
obtained in high yields, and their molecular weights were
controlled by the amount of AIBN and reaction temperature.
Results on the synthesis of poly(BA-co-Tac) are shown in
Table 1. As blank polymers, poly(butyl acrylate) (pBA) and
FT-IR Measurement of PSA Sheets
Copolymer 1 (0.2 g) and cross-linking reagent 2 (100 mol %
of adenine moieties of 2 relative to thymine units of 1)
were dissolved in chloroform (2 mL). The solution was
spin-coated on a silicon wafer (3000 rpm, 30 s) and pre-
baked at 80 8C for 1 min to give thin films. The sample was
TABLE 1 Results on Synthesis of Copolymers
Copolymer ratioa (m:n)
Mw 3 105
Mw/Mn
Tg (8C)
b
b
c
Sample name
Sub monomer (M)
Tac9-1.5
Tac9-2.4
Tac9-3.4
Tac19-0.7
pBA
Tac
91:9
1.50
2.36
3.39
0.69
4.72
2.17
3.00
4.99
4.51
3.17
3.99
2.87
241.1
240.0
238.6
222.9
253.3
244.9
Tac
91:9
Tac
91:9
Tac
81:19
100:0
90:10
BA only
AA10
Acrylic acid (AA)
a
c
Calculated from 1H NMR.
Calculated from DSC.
b
Determined by gel permeation chromatography calibrated by standard
polystyrene samples.
1334
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 1332–1338

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
SCHEME 3 Synthesis of adenine cross-linker 2. [Color figure
can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
pBA-co-AA (AA10) were also synthesized under similar reac-
tion conditions. The results of the syntheses are shown in
Table 1. Copolymerizing ratios were estimated by 1H-NMR
spectral measurements. The ratios almost corresponded to
the monomer feed, as was mentioned in the literature.26
From the results of GPC, values of Mw/Mn were relatively
high. These polymerizations were carried out under N2 flow
conditions, and the viscosity of the polymerization system
increased remarkably in the latter half of the polymerization.
Therefore, it is considered that dispersion of the molecular
weight was increased by the gel effect.36,37 From DSC meas-
urements, all these copolymers have Tg sufficiently below
room temperature, which is required for polymers working
as PSAs1.
FIGURE 1 Temperature dependence of absorbances in FT-IR
spectra of a thin film of 1 (Tac9-1.5: 91 mol % BA and 9 mol %
Tac, Mw 5 1.5 3 105) containing 100 mol % of adenine moieties
of 2 (toward thymine units of 1). [Color figure can be viewed in
the online issue, which is available at wileyonlinelibrary.com.]
copolymer 1 at room temperature (see Supporting Informa-
tion). This also indicates the thymine–adenine intermolecular
interaction between 1 and 2.
Mechanical Property of PSA Samples Using 1 and 2
From the results of FT-IR spectral measurements, interaction
between 1 and 2 was confirmed. Such molecular interaction
would cause a characteristic change of the bulk. To evaluate
Synthesis of Adenine Cross-Linker (2)
A symmetric cross-linker having two adenine units was syn-
thesized in our previous work.34 However, the product has
poor solubility in general organic solvents. Thus, we
designed and synthesized an asymmetric adenine cross-
linker that has an isophorone skeleton. Cross-linker 2 was
synthesized in two reaction steps, as shown in Scheme 3,
and 2 has good solubility in general organic solvents.
Interaction Copolymers Having Thymine Units with
Adenine Cross-Linker
Generally, there is a temperature dependence in noncovalent
intermolecular interactions. To monitor such dependency, FT-
IR spectral measurements were performed with thin films of
1 (Tac9-1.5: 91 mol % BA and 9 mol % Tac, Mw 5 1.5 3
105) containing 100 mol % of adenine moieties of 2 (Fig. 1).
With increase in temperature, the peak intensity was
decreased at 1670 cm21 that is assigned to C@O bond of
thymine unit in the hydrogen bonding. On the other hand,
two broaden peaks appeared at 1634 and 1587 cm21 for
hydrogen bonding-free N–H bonds of thymine and adenine
units. These results indicate dissociation of the intermolecu-
lar interaction between these two units.26 Moreover, a peak
shift to the lower wave number region was observed on the
C@O bond of thymine units, by adding cross-linker 2 toward
FIGURE 2 Stress–strain curves of PSA samples of 1 (Tac9-3.4:
BA 91 mol % and Tac 9 mol %, Mw 5 3.4 3 105) containing 30–
100 mol % of adenine moieties of 2 (toward thymine units of
1). [Color figure can be viewed in the online issue, which is
available at wileyonlinelibrary.com.]
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 1332–1338
1335

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
and 12.7 (100 mol %), while the sample was not broken and
extended to the measurement limit in the case of 30 mol %
of adenine moieties of 2. These results indicate that hydro-
gen bonding between thymine and adenine units contributes
strongly to the mechanical properties of the PSA samples.24
Similar stress–strain curves were also recorded with samples
of copolymers of different molecular weights. Young’s moduli
from stress–strain curves are shown in Figure 3. A signifi-
cant effect of addition of 2 was observed with Tac9-3.4 sam-
ples (BA 91 mol % and Tac 9 mol %, Mw 5 3.4 3 105),
where Young’s modulus was increased from 0.24 to 3.0 MPa.
On the other hand, almost zero Young’s modulus was
obtained with AA10, which does not have such an
interaction.
Appropriate extension property and breaking strength are
required for PSA materials ensuring desirable stress-
relaxation characteristics. In the case of 100 mol % of ade-
nine moieties of 2, PSA sheet showed high Young’s moduli,
which are also not suitable for such material. On the other
hand, in the cases of 30 and 60 mol %, PSA sheets had mod-
erate extension property and tensile stress. With the compo-
sition in the latter cases, they could work as a hot-melt-type
adhesive due to their reversible cross-linking with heating.
FIGURE 3 Young’s modulus of PSA samples of 1 containing
30–100 mol % of adenine moieties of 2 (toward thymine units
of 1). Tac9-1.5, Tac9-2.4, and Tac9-3.4 are BA 91 mol % and
Tac 9 mol %, and Mw are 1.5 3 105, 2.4 3 105, and 3.4 3 105,
respectively. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com.]
bulk properties of PSA films of 1 containing various amounts
of 2, stress–strain curves were recorded.
Viscoelastic Property of PSA Samples Using 1 and 2
To evaluate the viscoelastic properties, DMA measurements
in a shearing mode were carried out with co-polymer 1
(Tac9-3.4: BA 91 mol % and Tac 9 mol %) and cross-linker
2. Storage modulus (G0) and loss tangent (tan d) are both
important parameters. Results on these values are shown in
Figure 4. All samples have a rubbery plateau, and G0 was
shifted to the high-temperature region by adding 2 [Fig.
4(a)]. In comparison with G0 values at 20 8C between sam-
ples, the G0 value rose from 2.40 3 105 to 1.95 3 106 Pa.
Furthermore, the peak top of tan d was shifted to the high-
temperature region by adding cross-linker 2 [Fig. 4(b)].
These results indicate that the glass transition temperature
(Tg) is increased by cross-linker 2 in a matrix of 1 because
Stress–strain curves of samples (Tac9-3.4 series: BA 91 and
9 mol %, Mw 5 3.4 3 105) are shown in Figure 2. Addition
of adenine cross-linker 2 to thymine copolymer 1 greatly
influenced their stress–strain curves and Young’s moduli.
Samples without 2 could not be prepared because of their
low viscosity. In the case of 30 mol % of adenine moieties of
2, the stress–strain curve showed a low Young’s modulus,
like uncross-linked polymers. This is because molecular
interaction between 1 and 2 is not reflected in the mechani-
cal property. On the other hand, the moduli changed dramat-
ically on increasing the amount of 2. The values of strain at
break point were 42.8 (60 mol % of adenine moieties of 2)
FIGURE 4 DMA traces of a mixture of copolymer 1 (Tac9-3.4: BA 91 mol % and Tac 9 mol %), Mw 5 3.4 3 105) and adenine cross-
linker 2. (a) Storage modulus G0, (b) loss tangent (tan d). Adenine moieties of 2 in copolymer 1 is 0 mol % (green line), 50 mol %
(blue line), and 100 mol % (red line). [Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com.]
1336
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 1332–1338

JOURNAL OF
POLYMER SCIENCE
WWW.POLYMERCHEMISTRY.ORG
ARTICLE
FIGURE 5 Shear strength of PSA samples of 1 ((a) Tac9-1.5, (b) Tac9-2.4, and (c) Tac9-3.4) containing 0–100 mol % of adenine moi-
eties of 2, or control samples (pBA, AA10). Blue (left) side of each column: after 72 h without heating; red (right) side of each col-
umn: after heating in an autoclave (80 8C, 5 kg, 20 min). [Color figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com.]
of hydrogen bonding between them.26,38 Similar results were
also obtained for other samples of 1 having different molecu-
lar weights.
Considering the above, another shear strength test was car-
ried out after treatment of samples in an autoclave (80 8C,
5 kg, 20 min), to obtain better adhesive properties. The
results are shown in Figure 5 (red, right side of each
column).
It is necessary for Tg of PSA polymers to be suppressed
below room temperature, because PSA polymers are
required to adapt to the surface of adherend. It is known
that a desirable G0 value in use is below 106 Pa from Dahl-
quist’s criterion.39 In the case of 50 mol % of adenine moi-
eties of 2, the requirement is satisfied adequately. In the
case of 100 mol % (one-to-one interaction), G0 is nearly 106
Pa or more, which could not be suitable for PSA.
The reason why high shear strength is obtained after the
autoclave treatment is that the wettability of PSA polymers
toward adherend is improved. It is indicated that the inter-
molecular interaction is dissociated by the autoclave treat-
ment where the material behaves as fluidity. At room
temperature, the noncovalent cross-linking points are recon-
structed, leading to the strong adhesive property.
Shear Strength Test
CONCLUSIONS
To examine the adhesive properties of mixtures of thymine
copolymer 1 and adenine cross-linker 2, a shear strength
test was carried out. The PSA sheet sample with thickness of
ca 10 lm was cut to a size of 25 3 25 mm. A cut sample
was sandwiched between stainless steel test pieces. After
72 h, the shear strength test was carried out at 23 8C. The
results are shown in Figure 5. In the absence of adenine
cross-linker 2, the shear strength was almost equal to that of
AA10. On the other hand, the strength was greatly increased
by adding 2, and a significant improvement was observed
with 15 mol % of adenine moieties of 2. However, the
strength was greatly decreased when 30 mol % of adenine
moieties of 2 was added to Tac9-2.4 (BA 91 mol % and Tac
9 mol %, Mw 5 2.4 3 105), resulting in a technical problem
where the sample was stuck with adherent. On the other
hand, with more than 60 mol %, the adhesive strength
tended to decrease. The reason would be that the wettability
of PSA sheets fell by excess molecular interaction between 1
and 2. In fact, the G0 value was dramatically increased by
addition of 100 mol % of adenine moieties of 2 where the
tan d maximum was shifted to higher than 23 8C, as shown
in Figure 4.
Introducing interaction units of thymine and adenine to an
acrylic PSA system significantly improved the adhesive prop-
erties. We have synthesized both acrylic copolymers bearing
thymine units and a low-molecular-weight cross-linker hav-
ing two adenine units. The former had low Tg values, which
is appropriate for PSAs. Molecular interaction of copolymer
1 and adenine cross-linker 2 was confirmed by FT-IR spec-
tral measurements. Furthermore, the degree of interaction
was controlled by the amount of additive 2, which dramati-
cally changed the mechanical properties of these PSA sam-
ples. The storage modulus and loss tangent values were also
shifted to the high-temperature region by the molecular
interaction. Finally, the shear strength test showed a unique
result, leading to development of smart adhesive materials.
REFERENCES AND NOTES
1 C. Creton. MRS Bull. 2003, 28, 434–439.
2 K. Y. Bae, D. H. Lim, J. W. Park, H. J. Kim, M. Rafailovich, J.
Sokolov. J. Adhes. Sci. Technol. 2012, 26, 361–379.
WWW.MATERIALSVIEWS.COM
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 1332–1338
1337

JOURNAL OF
POLYMER SCIENCE
ARTICLE
WWW.POLYMERCHEMISTRY.ORG
ꢀ
3 Z. Czech, A. Kowalczyk, J. Kabatc, J. Swiderska. Eur. Polym.
J. 2012, 48, 1446–1454.
22 K. Yamauchi, J. R. Lizotte, T. E. Long. Macromolecules 2003,
36, 1083–1088.
4 S. W. Lee, J. W. Park, Y. E. Kwon, S. Kim, H. J. Kim, E. A.
Kim, H. S. Woo, J. Swiderska. Int. J. Adhes. Adhes. 2012, 38,
5–10.
23 S. Sivakova, D. A. Bohnsack, M. E. Mackay, P. Suwanmala,
S. J. Rowan. J. Am. Chem. Soc. 2005, 127, 18202–18211.
24 C. Heinzmann, U. Salz, N. Moszner, G. L. Fiore, C. Weder.
ACS Appl. Mater. Interfaces 2015, 7, 13395–13404.
5 K. Y. Bae, D. H. Lim, J. W. Park, H. J. Kim, H. M. Jeong, A.
Takemura. Polym. Eng. Sci. 2013, 53, 1968–1978.
25 Y. Zhang, C. A. Anderson, S. C. Zimmerman. Org. Lett.
2013, 15, 3506–3509.
6 C. M. Ryu, B. Pang, H. I. Kim, H. J. Kim, J. W. Park, S. W.
Lee, K. M. Kim. Int. J. Adhes. Adhes. 2013, 40, 197–201.
26 S. Cheng, M. Zhang, N. Dixit, R. B. Moore, T. E. Long. Mac-
romolecules 2012, 45, 805–812.
7 C. T. Murray, R. L. Rudman, M. B. Sabade, A. V. Pocius. MRS
Bull. 2003, 28, 449–454.
€
27 J. F. Lutz, S. Pfeifer, M. Chanana, A. F. Thunemann, R.
8 I. Webster. Int. J. Adhes. Adhes. 1997, 17, 69–73.
Bienert. Langmuir 2006, 22, 7411–7415.
28 J. Pitha. Polymer 1977, 18, 425–430.
9 Z. Czech, K. Wilpiszewska, B. Tyliszczak, X. Jiang, Y. Bai, L.
Shao. Int. J. Adhes. Adhes. 2013, 44, 195–199.
€
29 J. F. Lutz, A. F. Thunemann, R. Nehring. J. Polym. Sci. Part
10 S. Venkatraman, R. Gale. Biomaterials 1998, 19, 1119–1136.
11 Z. Czech. Polym. Int. 2003, 52, 347–357.
A Polym. Chem. 2005, 43, 4805–4818.
30 H. Kaye. Macromolecules 1971, 4, 147–152.
31 J. Pitha, P. P. Ts’o. J. Org. Chem. 1968, 33, 1341–1344.
12 Z. Czech, A. Butwin, U. Głuch, J. Kabatc. J. Appl. Polym.
Sci. 2011, 123, 118–123.
32 Y. Kang, A. Lu, A. Ellington, M. C. Jewett, R. K. O’Reilly.
ACS Macro Lett. 2013, 2, 581–586.
13 R. J. Wojtecki, M. A. Meador, S. J. Rowan. Nat. Mater. 2011,
10, 14–27.
33 H. J. Spijker, A. J. Dirks, J. C. M. van Hest. J. Polym. Sci.
Part A Polym. Chem. 2006, 44, 4242–4250.
14 P. Cordier, F. Tournilhac, C. Soulie-Ziakovic, L. Leibler.
Nature 2008, 451, 977–980.
34 N. Ishikawa, M. Furutani, K. Arimitsu. ACS Macro Lett. 2015,
4, 741–744.
15 M. Hayashi, A. Noro, Y. Matsushita. J. Polym. Sci. Part B
Polym. Phys. 2014, 52, 755–764.
35 Feldstein et al. prepared PSA hydrogels consisting of
poly(N-vinylcaprolactam) and ethylene glycol oligomers, and
controlled their adhesive properties by temperature and water
content; see M. M. Feldstein, K. A. Bovaldinova, E. V.
Bermesheva, A. P. Moscalets, E. E. Dormidontova, V. Y.
Grinberg, A. R. Khokhlov, Macromolecules 2014, 47, 5759–
5767.
16 R. P. Sijbesma, F. H. Beijer, L. Brunsveld, B. J. Folmer, J. H.
Hirschberg, R. F. Lange, J. K. Lowe, E. W. Meijer. Science 1997,
278, 1601–1604.
17 H. Kautz, D. J. M. van Beek, R. P. Sijbesma, E. W. Meijer.
Macromolecules 2006, 39, 4265–4267.
18 P. Y. W. Dankers, M. C. Harmsen, L. A. Brouwer, M. J. A.
Van Luyn, E. W. Meijer. Nat. Mater. 2005, 4, 568–574.
36 S. K. Soh, D. C. Sundberg. J. Polym. Sci. Polym. Chem. Ed.
1982, 20, 1299–1313.
19 A. Faghihnejad, K. E. Feldman, J. Yu, M. V. Tirrell, J. N.
Israelachvili, C. J. Hawker, E. J. Kramer, H. Zeng. Adv. Funct.
Mater. 2014, 24, 2322–2333.
37 S. K. Soh, D. C. Sundberg. J. Polym. Sci. Polym. Chem. Ed.
1982, 20, 1315–1329.
38 C. L. Lewis, K. Stewart, M. Anthamatten. Maclomolecules
2014, 47, 729–740.
20 C. L. Elkins, T. Park, M. G. McKee, T. E. Long. J. Polym. Sci.
Part A Polym. Chem. 2005, 43, 4618–4631.
21 C. Heinzmann, S. Coulibaly, A. Roulin, G. L. Fiore, C. Weder.
ACS Appl. Mater. Interfaces 2014, 6, 4713–4719.
39 C. A. Dahlquist, In Adhesion: Fundamentals and Practice;
McLaren & Sons, London, 1966, p 143.
1338
JOURNAL OF POLYMER SCIENCE, PART A: POLYMER CHEMISTRY 2016, 54, 1332–1338