UV-thermal dual cured anti-bacterial thiol-ene networks with superior performance from renewable resources

Article abstract of DOI:10.1016/j.polymer.2016.11.068

Bio-based anti-bacterial cross-linked films with superior properties were prepared via UV-thermal induced thiol-ene “click” reaction of diallyl itaconate (DAI), eugenol allyl ether (EAE) with trimethylolpropane tris (3-mercaptopropionate). DAI and EAE were made from one-step reaction of itaconic acid and eugenol with allyl bromide, respectively. The curing behaviors studied by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC) and gel content measurement illustrated that UV-thermal dual cure technology made the thiol-ene reaction more completely and produced films with higher performance compared with UV cure technology. The investigation of the thermal and mechanical properties of the cross-linked films by DSC, thermogravimetric analysis (TGA) and tensile test indicated that the glass transition temperature, tensile strength and modulus of the films were significantly improved after introducing DAI, and all the films exhibited similar and high thermal stability. Meanwhile, these bio-based polymer films showed excellent efficiency in killing common bacterias, e.g. S.?aureus and E.?coli in the dynamic shake test.

Full text of DOI:10.1016/j.polymer.2016.11.068

Polymer 108 (2017) 215e222
Contents lists available at ScienceDirect
Polymer
journal homepage: www.elsevier.com/locate/polymer
UV-thermal dual cured anti-bacterial thiol-ene networks with
superior performance from renewable resources
Jinyue Dai a , Songqi Ma , Lixia Zhu , Sheng Wang a , Lijing Yang , Zhenlun Song ,
,
b
a
,
*
a
,
b
a
a
a
,
**
a
Xiaoqing Liu
, Jin Zhu
a
Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, Ningbo 315201, PR China
University of Chinese Academy of Sciences, Beijing 100049, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 29 August 2016
Received in revised form
Bio-based anti-bacterial cross-linked films with superior properties were prepared via UV-thermal
induced thiol-ene “click” reaction of diallyl itaconate (DAI), eugenol allyl ether (EAE) with trimethylol-
propane tris (3-mercaptopropionate). DAI and EAE were made from one-step reaction of itaconic acid
and eugenol with allyl bromide, respectively. The curing behaviors studied by Fourier transform infrared
spectroscopy (FTIR), differential scanning calorimetry (DSC) and gel content measurement illustrated
that UV-thermal dual cure technology made the thiol-ene reaction more completely and produced films
with higher performance compared with UV cure technology. The investigation of the thermal and
mechanical properties of the cross-linked films by DSC, thermogravimetric analysis (TGA) and tensile test
indicated that the glass transition temperature, tensile strength and modulus of the films were signifi-
cantly improved after introducing DAI, and all the films exhibited similar and high thermal stability.
Meanwhile, these bio-based polymer films showed excellent efficiency in killing common bacterias, e.g.
S. aureus and E. coli in the dynamic shake test.
18 November 2016
Accepted 26 November 2016
Available online 27 November 2016
Keywords:
Bio-based
Anti-bacterial
Eugenol
Itaconic acid
UV-thermal dual curing
©
2016 Elsevier Ltd. All rights reserved.
1
. Introduction
exhibited good anti-bacterial ability [15]. So far eugenol has been
served as a promising feedstock for the synthesis of bio-based
polymers, such as thermosetting acrylic resins [16e18], benzox-
azines resins [19e22], cyanate ester resins [23], epoxy resins
[24e26] and thiol-ene networks [15,27], etc. Among all the poly-
mers derived from eugenol, the UV-initiated thiol-ene system
seems to be more interesting due to easy availability of eugenol-
based monomers [15] and all the merits of both thiol-ene “click”
reaction and UV-cure technology, including insensitivity to oxygen
and water, short reaction time, and no by-products [28,29].
Compared with traditional addition-type antibacterial agents, the
eugenol-based UV-curing thiol-ene networks have many advan-
tages, such as long action time, environmentally friendly, and good
thermal stability. However, the eugenol-based UV-curing thiol-ene
networks always show poor mechanical and thermal properties
due to the flexible thioether and ether linkages [30].
With continuous consumption of non-renewable fossil re-
sources, the conversion of renewable raw materials to sustainable
fuel or polymeric materials becomes increasing important [1e4].
Up to now, quantities of bio-sourced polymers have been success-
fully developed and commercialized [5e7], and the production of
bioplastics from renewable resources is expected to reach 12
million tons in 2020 [8].
Eugenol is an inexpensive functional aromatic compound,
which can be obtained via pyrolysis [9,10] or depolymerization [11]
of lignin which is the second most abundant natural organic ma-
terials and the only scalable renewable feedstock consisted of ar-
omatic monomers [12]. Another significant advantage of eugenol is
its excellent bactericidal activity against a wide range of common
organisms like E.coli, S. aureus, P.aeruginosaL [13]. Monocytogenes
[
14]. More interesting, polymers synthesized from eugenol also
Itaconic acid, one of the top 12 potential bio-based platform
chemicals selected by the U.S. Department of Energy [31], possesses
two carboxyl groups and one carbon-carbon double bond. By now,
it has been widely used as a monomer for polymer synthesis and
the primary sources for emulsion paints and paper coating latexes
*
Corresponding author.
*
* Corresponding author.
E-mail addresses: masongqi@nimte.ac.cn (S. Ma), liuxq@nimte.ac.cn (X. Liu).
[32e36]. Our previous work has demonstrated that itaconic acid-
http://dx.doi.org/10.1016/j.polymer.2016.11.068
032-3861/© 2016 Elsevier Ltd. All rights reserved.
0

216
J. Dai et al. / Polymer 108 (2017) 215e222
based epoxy resins [37,38] and unsaturated polyesters [39e41]
showed high performance due to its compact and rigid chemical
structure.
Thus, in this paper, itaconic acid was employed to strengthen
the eugenol-based UV-initiated thiol-ene system. Diallyl itaconate
(CDCl
3
) and using tetramethylsilane (TMS) as internal standard at
ꢀ
25 C. The infrared spectrum (FTIR) was measured with NICOLET
6700 FTIR (NICOLET, America) using the KBr pellet method and the
absorbance mode was used. The spectra were recorded from 400 to
4000 cm with a resolution of 4 cm and 16 scans were collected
for each sample. The samples were prepared by dissolving a small
ꢁ1
ꢁ1
(
DAI) and eugenol allyl ether (EAE) were synthesized by one-step
reaction of itaconic acid and eugenol with allyl bromide, and a
series of bio-based networks were prepared from EAE, DAI and
trimethylolpropane tris (3-mercaptopropionate) (Trithiol) via UV-
initiated thiol-ene “click” reaction (Scheme 1). As we know,
another possible reason for the poor properties of eugenol-based
UV-curing thiol-ene materials might be that the complete curing
reaction was difficult to be achieved with sole UV-initiated thiol-
ene reaction [15,42,43] due to the decreasing segmental mobility
along with the reaction time. Therefore, the thermal treatment
after UV-curing (UV-thermal dual cure) was also applied and the
further consumption of remained reactive groups was expected so
as to improve the properties of the thiol-ene system [43]. The
curing kinetics, thermal and mechanical behaviors as well as the
antimicrobial activity of the thiol-ene networks were investigated.
The objective of this work is to develop bio-based anti-bacterial
materials with promoted performance through an environmental
friendly method.
2 2
amount of compound in CH Cl , followed by smearing the solution
onto a KBr crystal plate and evaporating the solvent completely.
Gel content was determined after Soxhlet extraction. Specimens
of about 1 g were cut from bulk resins and extracted with 250 mL of
refluxing acetone using a Soxhlet extractor until the dry weight of
resins did not change (48 h was enough in all of the cases). The
ꢀ
extracted resins were then dried in vacuum oven at 60 C for 24 h.
Gel content was calculated from the weight difference of the dry
samples before and after extraction. The final gel content was taken
as an average of three specimens for accuracy.
Differential scanning calorimetry (DSC) measurements were
performed on a Mettler Toledo Star 1 apparatus in a nitrogen at-
mosphere. The sample weighting about 8e10 mg was heated to
ꢀ
ꢀ
ꢁ1
150 C at a heating rate of 10 C min and held there for 3 min to
ꢀ
eliminate thermal history. Then it was cooled to ꢁ30 C at a cooling
ꢀ
ꢁ1
ꢀ
rate of 100 C min followed by heating again to 150 C at a rate of
ꢀ
ꢁ1
10 C min . The glass transition temperature was obtained from
the peak temperature of the differential curve of the second heating
curve for the samples.
2
. Experimental section
Mechanical properties were carried out using a Universal Me-
chanical Testing Machine (Instron 5569A) with a crosshead speed
2.1. Raw materials
ꢁ
1
of 5 mm min . Before testing, all the samples were conditioned at
ꢀ
25
C for 24 h with the relative humidity of 50%. The tensile
Itaconic acid (IA) was provided by Zhejiang Guoguang
Biochemistry Co., Ltd, Dichloromethane, sodium hydroxide (NaOH),
proteose peptone, dextrose, sodium chloride (NaCl), disodium
properties of each sample were reported as the average of five
measurements.
Thermogravimetric analysis (TGA) was performed using a
Mettler-Toledo TGA/DSC1 Thermogravimetric Analyzer (METTLER
TOLEDO, Switzerland) with high purity nitrogen as purge gas at a
2 4 4
hydrogen phosphate (Na HPO ) and magnesium sulfate (MgSO )
were all purchased from Sinopharm Group Co. Ltd, China., Eugenol,
allyl bromide was obtained from Aladdin Reagent, China. 1-
Hydroxycyclohexyl phenyl ketone (Irgacure184) and trimethylol-
propane tris (3-mercaptopropionate) (Trithiol) were obtained from
JK Chemical Ltd. All chemicals were used as received without
further purification.
ꢁ
1
flow rate of 50 mL min . Approximate 8e10 mg samples were
weighted and put into the aluminum crucible without covers. The
ꢀ
ꢁ1
ꢀ
heating rate is 20 C min with the scanning range from 50 C to
ꢀ
600 C.
Antimicrobial activity of the thiol-ene networks was evaluated
using the dynamic shake flask test method according to the
ASTME2149. The species of microorganism tested were Escherichia
coli ATCC25922 (E.coli, Gram-negative) and Staphylococcus aureus
ATCC6538 (S. aureus, Gram-positive). Bacteria was incubated in
2
.2. Measurements
1H NMR and 13C NMR were examined by an AVANCE III Bruker
NMR spectrometer (Bruker, Switzerland), operating at 400 and
00.6 MHz, respectively. The spectra were recorded by dissolving
the corresponding sample (10 wt/v) in deuterated chloroform
10 mL nutrient medium (containing 10 g/L proteose peptone, 2 g/L
1
dextrose, 5 g/L sodium chloride, and 2.5 g/L disodium hydrogen
Scheme 1. The formation of the EAE-DAI network by UV-thermal dual cure.

J. Dai et al. / Polymer 108 (2017) 215e222
217
Scheme 2. Synthetic route of EAE and DAI.
ꢀ
phosphate) for 18e24 h at 37 C until the exponential growth phase
was reached. then the bacteria-containing medium was centrifuged
at 3000 rpm for 10 min, and after removal of supernatant, the
bacteria cells were washed with sterile phosphate-buffered solu-
tion (PBS) to an optical density of 0.1 A at 600 nm (108 CFU/mL).
Further appropriate dilution using a sterile phosphate buffer gave a
2H, eCH
2
e).
13
C NMR (100.6 MHz, CDCl
3
),
d
(ppm):149.5 (1C, eCHeCHe of
Benzene), 146.4 (1C, eCHeCHe of Benzene), 137.7 (1C, CH
133.6 (1C, CH ]CHe), 133.1 (1C, eCHeCHe of Benzene), 120.4 (1C,
eCHeCHe of Benzene), 117.6 (1C, CH ]CHe), 115.6 (1C, CH
CHe), 113.7 (1C, eCHeCHe of Benzene), 112.3 (1C, eCHeCHe of
Benzene), 69.9 (1C, eOeCH e), 55.8 (1C, eOeCH ), 39.8 (1C,
2
]CHe),
2
2
2
]
5
final concentration of 10 CFU/mL. The cross-linked networks
2
3
(
0.3 g) were placed in flasks containing 20 mL of the bacteria sus-
2
eCH e).
FT-IR (KBr, cm 1): 2935 cmꢁ1 (CeH ofeCH
ꢁ
e), 1510 cm and
ꢁ1
ꢁ1
pensions. The flasks were incubated with continuous shaking at
2
buffer, the bacterial suspensions (0.1 mL) were plated in nutrient
agar. The inoculated plates were incubated at 37 C for 24 h and the
2
ꢀ
ꢁ1
ꢁ1
00 rpm at 37 C for 24 h. After serial dilutions using the phosphate
1420 cm
(C]C of benzene ring), 1638 cm , 995 cm
).
and
ꢁ
1
918 cm (eCH]CH
2
ꢀ
surviving bacterial cells were counted using a colony counter. The
percentage reduction of the microorganisms after contact with the
test specimen (the thiol-ene network) was compared to the num-
ber of bacterial cells surviving after contact with the control.
Equation was used to calculate the percentage reduction of mi-
crobial growth [44].
2.4. Synthesis of diallyl itaconate (DAI)
Diallyl itaconate (DAI) was prepared according to our previous
work [38] with some modification. Into a 250 mL three-necked
round bottom flask equipped with a mechanical stirrer, 13 g
(0.1 mol) of itaconic acid (IA) together with 26.6 g (0.22 mol) of allyl
bromide and 100 mL of acetone were added. The mixture was
N0 ꢁ Nt
ꢀ
immersed in a 65 C oil bath and maintained at this temperature for
Rð%Þ ¼
ꢂ 100
N0
1
8
0 min. Then 8.8 g (0.22 mol) of sodium hydroxide dissolved in
0 mL distilled water was added dropwisely. After being refluxed
for another 8 h, the mixture was cooled to room temperature and
00 mL of dichloromethane was added under vigorous stirring.
where R is the anti-bacterial rate (%), N0 is the mean number of
bacteria on the plates without thiol-ene networks (control sample),
and Nt is the mean number of bacteria on the plates with thiol-ene
networks.
1
Then it was kept stable for 10min and the upper organic layer was
separated off. After removing the residual water in the organic
4
phase by anhydrous MgSO , organic solvents and excess allyl bro-
2
.3. Synthesis of eugenol allyl ether (EAE)
mide were removed by a rotary evaporator. Finally, the target
product diallyl itaconate (DAI) with the weight of 20.4 g was ob-
tained with the yield of 97%. The synthesis route is shown in
Scheme 2.
16.4 g (0.1mol) of eugenol (EG) together with 13.3 g (0.11mol) of
allyl bromide and 100 mL acetone were placed in a 250 mL three-
1H NMR (400 MHz, CDCl
2H, eCH]CH ), 5.72 (s, H, C]CH
(m, 4H, eOeCH e), 3.38 (s, 2H, eCH
C NMR (100.6 MHz, CDCl ), (ppm):169.9 (1C, eCH
165.4 (1C, eCH eCOOe), 133.7 (1C, C]CH ), 131.9 (2C, eCH]CH
128.5 (1C, C]CH ), 117.9 (2C, eCH]CH ), 65.1 (2C, eOeCH
(C, eCH e).
2
FT-IR (KBr, cm ): 2945 cm (CeH ofeCH e), 1736 cm
),
d
(ppm): 6.35 (s, H, C]CH
), 5.28 (m, 4H, eCH]CH
e).
), 5.89 (m,
necked round bottom flask equipped with a mechanical stirrer.
The mixture was immersed in a 65 C oil bath and maintained at
3
2
ꢀ
2
2
2
), 4.64
this temperature for 10 min. Then 4.4 g (0.11mol) of sodium hy-
droxide dissolved in 20 mL distilled water was added dropwisely.
After being refluxed for another 8 h, the mixture was cooled to
room temperature and 100 mL dichloromethane was added under
vigorous stirring. Then it was kept stable for 10min and the upper
organic layer was separated, and the residual water in the organic
2
2
13
3
d
2
eCOOe),
),
2
2
2
2
2
2
e), 37.5
2
ꢁ
1
ꢁ1
ꢁ1
ꢁ1
ꢁ
1
ꢁ1
ꢁ1
phase was dried by anhydrous MgSO
4
. Finally, the target product
(CH2eOeC]O), 1646 cm , 990 cm , 931 cm and 815 cm
(eCH]CH ).
eugenol allyl ether (EAE) with the weight of 19.5 g was obtained
after removing the solvent and unreacted ally bromide by a rotary
evaporator, and the yield was calculated to be 96%. The synthesis
2
2.5. Preparation of the cross-linked networks
route is shown in Scheme 2.
1
H NMR (400 MHz, CDCl
3
),
d
(ppm): 6.72e6.82, (m, 3H, eCH]
), 5.94 (m, H, eCHeCH ),
), 5.08 (m, 2H,
The detailed formulations of different thiol-ene systems are
shown in Table 1. As an example, the preparation of EAE50-DAI50
CHe of Benzene), 6.08 (m, H, eCHeCH
.42 (m, H, eCHeCH ), 5.26 (m, H, eCHeCH
eCHeCH ), 4.59 (m, 2H, eCHeCH
2
2
ꢁ3
5
2
2
system (1 eq SH/C]C) is described here. EAE (1 g, 4.9 ꢂ 10 mol)
2
2
3
), 3.87 (s, 3H, eOeCH ), 3.34 (m,
and Irgacure184 (2 wt% of total mixture) were dissolved in DAI (1 g,

218
J. Dai et al. / Polymer 108 (2017) 215e222
Table 1
Formulations of the thiol-ene networks.
Sample
EAE/DAI (molar ratio)
SH/C]C (molar ratio)
Irgacure184 (wt.%)
EAE100-DAI0
EAE70-DAI30
EAE50-DAI50
EAE30-DAI70
EAE0-DAI100
100/0
71/29
51/49
31/69
0/100
1/1
1/1
1/1
1/1
1/1
2
2
2
2
2
ꢁ
3
ꢁ3
4
.8 ꢂ 10 mol). Trithiol (3.2 g, 8.0 ꢂ 10 mol, molar ratio of eSH to
make a further structure confirmation, the NMR spectrum of EAE
and DAI are shown in Fig. 2, As can be seen, the peaks of protons
and carbons are all in accordance with the characteristic peaks of
C]C is 1:1) was added to the solution. The formulation was
transferred to a stainless steel mould (5 cm (length) ꢂ 5 cm
(
width) ꢂ 0.5 mm (thickness)) and cured for 10 min under UV
irradiation with a high-pressure mercury lamp (500 W) at
66 nm at room temperature. The distance from the lamp to the
3
sample surface is about 15 cm. Then a transparent cross-linked film
ꢀ
was obtained after thermal treatment at 150 C for 20 min.
3
. Results and discussion
3.1. Synthesis and characterization of EAE and DAI
During the synthesis of EAE and DAI, cheaper acid-accepter
NaOH and low toxic acetone were used as the alternatives to
CO and the toxic dimethylformamide used in previous works
15,37], which makes the synthetic process more economic and
relatively environmental-friendly. The chemical structures of EAE
K
2
3
[
1
13
and DAI were determined by FTIR, H NMR and C NMR.
Fig. 1 represents the FTIR spectra of EAE and DAI. For the spec-
ꢁ1
trum of EAE, the peaks at 1510 and 1420 cm
belong to the
characteristic absorption peaks of benzene ring, the peak at
ꢁ
1
2
935 cm is assigned to the CeH stretching vibration of alkane
CH , and the characteristic absorption peaks of the C]CH from
allylate appear at 918, 995, and 1638 cm . Meanwhile, broad peak
2
2
ꢁ
1
ꢁ1
of OeH stretching vibration at around 3400-3500 cm observed
for EG was non-existent for EAE, which is indicative of that the
allyl-etherification completely proceeded. Similarly, for the spec-
trum of DAI, the peak at 2945 cm
stretching of alkane CH , the strong peak at 1736 cm is assigned
to the C]O stretching of ester units, and the peaks at 815, 931, 990,
ꢁ1
is assigned to the CeH
ꢁ1
2
ꢁ
1
and 1646 cm represent characteristic absorption of the C]CH
2
from allylate. At the same time, the absorption peak for eCOOH was
not detected, which confirms a high conversation of IA during the
reaction with allyl bromide. Based on the FTIR analysis, the struc-
tures of EAE and DAI could be confirmed preliminary. In order to
Fig. 1. FTIR spectra of EAE and DAI.
Fig. 2. 1H NMR and 13C NMR spectra of EAE (a, b) and DAI (c, d).

J. Dai et al. / Polymer 108 (2017) 215e222
219
protons and carbons of target compounds (EAE and DAI). These
results demonstrate that the target compounds (EAE and DAI) were
synthesized successfully.
3.2. Curing condition screening by FTIR and DSC
In order to determine the best curing condition, FTIR and DSC
analysis were employed. EAE50-DAI50 system was casted onto the
KBr crystal plate to form thin films with the thickness of about
1
(
00
500 W) at 365 nm for different time. As shown in Fig. 3, the in-
tensity of peak for C]CH and SeH decreased significantly after the
mm before it was exposed to a medium-pressure mercury lamp
2
first 5 min UV curing. After that, the change of the peak standing for
SeH bond is hard to be detected, and further prolonging the curing
time could not completely consume the SeH. It was reported that
the complete curing reaction was difficult to be achieved solely
with UV curing [15,42], and further thermal post-curing was usu-
ally employed to increase the degree of cure [43]. In this work,
differential scanning calorimetry (DSC) was used to determine the
appropriate post-curing temperature for the thiol-ene networks
after UV radiation. Taking EAE50-DAI50 system as an example, the
mixture of DAI and EAE (50/50) were exposed to UV for 10 min at
first, and then sealed into an aluminum crucible for DSC testing. The
sample underwent three cycles of subsequent heating and cooling
Fig. 4. DSC curves during the first, second and third heating scans for the EAE50-DAI50
system.
ꢀ
ꢁ1
scans through DSC (the heating rate is 10 C min ). As could be
seen from Fig. 4, T
from 0.8 to 1.5 C after being heated to 150 C (comparing first and
second heating scans), and further heat treatment did not signifi-
g
of the UV-cured system was increased obviously
ꢀ
ꢀ
cantly affect the T
g
(comparing second and third heating scans).
ꢀ
Based on this result, 150 C was chosen as the thermal post-curing
temperature for all the thiol-ene networks. From Fig. 3, it was noted
that the signal for SeH bond in EAE50-DAI50 system was dis-
appeared completely after 10 min UV curing following by the
ꢀ
thermal treatment at 150 C for 20 min. Therefore, UV radiation for
ꢀ
10 min followed by thermal treatment at 150 C for 20 min was
chosen as the curing condition for all the thiol-ene systems.
3.3. Gel content of the thiol-ene networks
To some extent, the degree of curing reaction could be charac-
terized by the gel content which has a close tie with the properties
of the cross-linked materials. Thus, gel content was measured for all
the cross-linked networks. With reference to Fig. 5, all the UV-
thermal dual cured thiol-ene networks exhibit higher gel content
ranged from 98.8 to 99.8% compared with those of the UV-cured
Fig. 5. Gel content of the thiol-ene networks with or without thermal treatment.
networks without heat treatment (91.5e96.0%).
3.4. Thermal and mechanical properties of the thiol-ene networks
Thermal properties of polymeric material are of critical impor-
tant for its processing and application. DSC measurement was also
employed to determine the glass transition temperature (T ) of all
the cured networks. The DSC heating curves were shown in Fig. 6
and the T data was listed in Table 2. Due to the flexible thioether
linkages [30], the T s of all the thiol-ene networks were much lower
than the room temperature. After the addition of DAI, T of DAI100-
g
g
g
g
ꢀ
EAE0 system was increased from ꢁ2.3e8.5 C for DAI0-EAE100
system. This might be due to the fact that EAI has more unsaturated
double bond in the chemical structure, which led to the increased
cross-link density after more EAI was introduced.
Fig. 7 presents the thermal stability investigation of the different
thiol-ene networks. It can be observed that all the thiol-ene net-
works showed fairly the same thermogravimetric curves with high
thermal stability. All the thiol-ene networks are stable up to around
ꢀ
Fig. 3. FTIR spectra of EAE50-DAI50 system in different curing conditions.
310 C. As could be seen from Table 2, the degradation temperature

220
J. Dai et al. / Polymer 108 (2017) 215e222
Fig. 6. DSC heating curves for the thiol-ene networks.
Fig. 8. Tensile curves for the different the thiol-ene networks.
Table 2
Mechanical and thermal properties of the thiol-ene networks.
a
ꢀ
b
ꢀ
c
sd (MPa)
Ee (MPa)
εf (%)
Sample
T
g
( C)
T
d5% ( C)
R600 (%)
EAE100-DAI0
EAE70-DAI30
EAE50-DAI50
EAE30-DAI70
EAE0-DAI100
ꢁ2.4
0.6
1.5
5.1
8.6
356
350
351
350
348
7.1
7.1
6.3
6.0
5.1
2.1 ± 0.1
1.5 ± 0.1
2.1 ± 0.3
3.0 ± 0.1
4.7 ± 0.6
6.2 ± 0.4
6.8 ± 0.2
8.6 ± 0.5
11.9 ± 0.3
16.9 ± 1.3
33.0 ± 1.2
22.5 ± 2.2
31.5 ± 0.4
29.1 ± 1.1
32.8 ± 2.1
a
Glass transition temperature by DSC.
b
c
d
e
f
The temperature for 5% weight loss by TGA.
The char yield at 600 C by TGA.
Tensile strength.
Young's modulus.
Elongation at break.
ꢀ
behaviors without a yield point. While the elongation at break of all
the thiol-ene networks ranged from 22 to 33%, indicating that the
structure of the thiol-ene networks is very flexible due to the for-
mation of flexible thioether linkages [42,43].
It can be seen the tensile strength and modulus of the thiol-ene
networks (except the EAE100-DAI0 system) were increased with
the increasing DAI content. It is due to the higher density of un-
saturated double bond groups in DAI. The cross-link density of the
thiol-ene networks were obviously increased with the increase of
DAI content, corresponding to the significant improvement in
tensile strength and modulus. More interestingly, a similar trend
was also observed for the elongation at breaking of the thiol-ene
networks. As we know, the higher cross-link density of cross-
linked network always results in the higher strength, modulus
and brittleness [37,47,48]. Nevertheless, for the thiol-ene networks,
with increasing the cross-link density, more flexible thioether
linkages were also formed accordingly, resulting in the increased
elongation at break.
Fig. 7. TGA curves for the thiol-ene networks.
ꢀ
for 5% weight loss (Td5%) and the char yield at 600 C (R600) of the
thiol-ene networks both decreased with the increase of DAI con-
tent. The ester linkage has a tendency to be easily cleaved [45] and
more phenyl groups usually result in a higher char yield [46] under
elevated temperature. Consequently, the decreased Td5% and R600 of
the thiol-ene networks is reasonable because of the increased ester
linkages and the decreased phenyl groups with the increasing
content of DAI.
3.5. Anti-microbial activity of the thiol-ene networks
The antimicrobial activity of the thiol-ene networks was eval-
uated by the dynamic shake method. Before the test, all the films
were rinsed by acetone, ethanol and deionized water and dried in a
ꢀ
vacuum oven at 60 C for 24 h to remove any possible unreacted
monomers and trace solvent. Fig. 9 exhibits the images of E. coli
ATCC29522 and S. aureus ATCC6538 colonies survived on the
nutrient agar plates after contacting with the thiol-ene networks,
and the reduction rate of microorganism was shown in Fig. 10. It
could be seen that the thiol-ene networks showed higher anti-
Fig. 8 shows the typical tensile stress-strain curves of the thiol-
ene networks and their tensile properties are summarized in
Table 2. All of the thiol-ene networks exhibited rigid tensile

J. Dai et al. / Polymer 108 (2017) 215e222
221
Fig. 9. Images of E. coli ATCC29522 (A) and S. aureus ATCC6538 (B) colonies survived on the nutrient agar plates after treatment with control (0), EAE100-DAI0 (1), EAE70-DAI30 (2),
EAE50-DAI50 (3), EAE30-DAI70 (4), EAE0-DAI100 (5) for 24 h.
4. Conclusions
UV-thermal dual curing technology was employed to prepare
the bio-based anti-bacterial networks from eugenol and itaconic
acid. The tensile strength, modulus and glass transition tempera-
ture of the bio-based polymer films were all significantly improved
after the introduction of diallyl itaconate (DAI). Meanwhile, the
thiol-ene networks, especially EAE100-DAI0, showed high anti-
bacterial activity against both E. coli and S. Aureus with the anti-
bacterial rate of 96% and 90%, respectively. And itaconic acid
modified networks even without eugenol segment also exhibited
good efficiency in killing common bacterias, e.g. S. aureus and E. coli.
Combining bio-based eugenol and itaconic acid, together with UV-
initiated thiol-ene click reaction and post thermal treatment
technology, the bio-based anti-bacterial materials with promoted
performance were prepared successfully.
Acknowledgements
The authors are grateful for the financial support from National
Natural Science Foundation of China (Projects NSFC 51473180, NSFC
Fig. 10. Antimicrobial activity of the thiol-ene networks.
51373194), Youth Innovation Promotion Association of the Chinese
Academy of Sciences (2012229).
bacterial efficiency to E. coli colonies compared with S. aureus col-
onies. This phenomenon is caused by the fact that there are distinct
differences between Gram-positive (S. aureus) and Gram-negative
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