Synergistic effect of copolymeric resin grafted 1,2-benzisothiazol-3(2H)-one and heterocyclic groups as a marine antifouling coating

Article abstract of DOI:10.1039/d1ra01826d

In order to find a new type of antifouling coating with higher biological activity and more environmental protection, heterocyclic compounds and benzisothiazolinone were introduced into acrylic resin to prepare a new type of antifouling resin. In this stu

Full text of DOI:10.1039/d1ra01826d

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Synergistic effect of copolymeric resin grafted 1,2-
benzisothiazol-3(2H)-one and heterocyclic groups
as a marine antifouling coating†
ab
Cite this: RSC Adv., 2021, 11, 18787
Miao Dong,
and Jianxin Yang
Zheng Liu,b Yuxing Gao,a Xuemei Wang,b Junhua Chenab
ab
*
In order to find a new type of antifouling coating with higher biological activity and more environmental
protection, heterocyclic compounds and benzisothiazolinone were introduced into acrylic resin to
prepare a new type of antifouling resin. In this study, a series of grafted acrylic resins simultaneously
containing benzoisothiazolinone and heterocyclic monomers were prepared by the copolymerization of
an allyl monomer with methyl methacrylate (MMA) and butyl acrylate (BA). Inhibitory activities of the
copolymers against marine fouling organisms were also investigated. Results revealed that the
copolymers exhibit a clear synergistic inhibitory effect on the growth of three seaweeds: Chlorella,
Isochrysis galbana and Chaetoceros curvisetus, respectively, and three bacteria, Staphylococcus aureus,
Vibrio coralliilyticus and Vibrio parahaemolyticus, respectively. In addition, the copolymers exhibited
excellent inhibition against barnacle larvae. Marine field tests indicated that the resins exhibit outstanding
antifouling potency against marine fouling organisms. Moreover, the introduction of the heterocyclic
group led to the significantly enhanced antifouling activities of the resins; the addition of the
heterocyclic unit in copolymers led to better inhibition than that observed in the case of the resin
copolymerized with only the benzoisothiazolinone active monomer.
Received 8th March 2021
Accepted 13th May 2021
DOI: 10.1039/d1ra01826d
rsc.li/rsc-advances
are the widely used antifoulants for preventing and controlling
the marine biofouling.10
Introduction
Conventionally, organotin self-polishing coatings are effec-
tive in control marine biofouling. However, these coatings were
prohibited in 2008 due to their adverse effects on the marine
ecological environment and human health; hence,
environment-friendly antifouling paints are in high
demand.11–13 At present, commercial coatings containing a large
number of cuprous oxide are used, but the release of copper
ions will accumulate in marine organisms and have a negative
impact on the ecological environment. Therefore, self-polishing
antifouling coatings based on zinc polyacrylate, copper poly-
acrylate and polysilyl acrylate have been widely used.14–16 This
type of coating is mainly suitable for ocean going ships, and its
antifouling performance is highly dependent on sailing time
and ship speed. For further improve the antifouling perfor-
mance and environmental protection performance, graed
antifouling functional group antifouling material,17 amphi-
philic polymer-based antifouling material,18 biodegradable
polymer-based antifouling material,19,20 main chain degradable
self-polishing antifouling materials,21,22 low surface energy
antifouling materials,23,24 bionic antifouling materials,25,26 and
nanocomposite antifouling materials27–30 have become current
research hotspots. It should be pointed out that most of the
various technologies are currently in the laboratory research
stage and have excellent anti-pollution effects, but they are still
Biofouling, which is the undesired growth and attachment of
marine organisms on a solid surface of marine articial struc-
tures (i.e., docks, marine pipelines and cages) or hulls, typically
causes serious problems in marine-related industries and
activities.1 For example, large-scale fouling organisms adhered
onto vessels in the ocean increase the weight, reduce travelling
speed and increase energy consumption;2–4 in addition, these
organisms corrode vessels, introduce invasive species and cause
other ecological damage.5–9 A number of antifouling treatment
methods have been developed to prevent the adhesion of
marine fouling organisms; the most efficient method to prevent
marine biofouling is to paint marine coatings on a solid surface;
in this way, antifouling compound molecules (biocides) are
released in a controlled manner to restrain the growth of
adhered organisms. Currently, chemical treatments or biocides
aKey Laboratory of Green Catalysis and Reaction Engineering of Haikou, College of
Science, Hainan University, Haikou 570228, P. R. China. E-mail: dmmc2017@163.
com; yangjxmail@hainanu.edu.cn
bHainan Provincial Fine Chemical Engineering Research Center, Hainan University,
Haikou, 570228, P. R. China
† Electronic supplementary information (ESI) available. See DOI:
10.1039/d1ra01826d
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facing some difficulties in practical application. For example,
the service life, the exudation rate of antifoulant and whether it
is friendly to the environment, etc.
Experimental
Synthesis of BIT monomer
The author is currently focusing on antifouling materials
graed with antifouling functional groups. The key aspect in
the development of environment-friendly antifouling coatings
is the innovation of the polymer resin and antifoulant. Poly-
acrylate is widely used in coatings because of its excellent lm-
forming properties and mechanical properties, fast drying, and
convenient construction. Hence, a coating system based on an
acrylic resin bearing an antifouling agent via copolymerization
is critical to its performance and service life.31–34
Isothiazolinone compounds are a key component in bacte-
ricides, pesticides and medical and health products due to their
strong antibacterial ability, low toxicity and good compatibility
with other additives.35–38 For example, 4,5-dichloro-2-n-octyl-4-
isothiazolin-3-one (DCOIT) has been reported as a green marine
antifoulant,39 and DCOIT derivatives of benzoisothiazolinone also
have been reported to exhibit a strong inhibitory effect against
Escherichia coli, Saccharomyces cerevisiae and Aspergillus niger.40,41
N-Carboxylic acid derivatives of 1,2-benzisothiazol-3(2H)-one (BIT)
exhibit good broad-spectrum antifungal activity against Candida
and Aspergillus.42 This type of antifoulant is graed onto poly-
acrylate, and the release of the antifoulant is carried out through
the chemical method of “hydrolysis and diffusion” to avoid local
antifoulant burst release, which is benecial to improve the utili-
First, allyl alcohol (10 mL), cyanuric chloride (1.85 g, 10 mmol) and
sodium hydrogen carbonate (1.05 g, 12.5 mmol) were sequentially
added in a 50 mL two-necked ask, and the mixture was stirred for
0.5 h in an ice-water bath, followed by stirring at room temperature
for 3 h. Second, the reaction mixture was extracted using ethyl
acetate (40 mL) and washed three times with water. The organic
phase was dried over anhydrous magnesium sulfate and ltered to
afford a colorless transparent ltrate for the next step. In another
ask, BIT (3.02 g, 20 mmol) was added to the above solution; aer
stirring for 1 h, triethylamine (3 mL) was added, and the solution
was stirred at room temperature for another 4 h. The reaction
mixture was ltered, and the ltrate was washed three times with
water. The ester layer was dried over anhydrous magnesium sulfate
and concentrated to obtain monomer BM.
BM: yellow solid powder; 89.8% yield, melting point: 110.5–
1
ꢀ
112.3 C. H NMR (400 MHz, CDCl3), d 7.82 (d, J ¼ 8.4 Hz, 2H,
PhH), 7.74 (d, J ¼ 8.0 Hz, 2H, PhH), 7.51 (t, J ¼ 7.2 Hz, 2H, PhH),
7.37 (t, J ¼ 8.0 Hz, 2H, PhH), 5.85–5.76 (m, H, –CH]), 5.16–5.11
(m, 2H, ]CH2), 4.71 (d, J ¼ 6.0 Hz, 2H, CH2). IR (KBr), v (cmꢁ1):
3058, 2927, 2854, 1587, 1496, 1441, 1325, 967, 925, 738 cmꢁ1
.
Synthesis of heterocyclic monomers
zation rate of antifoulant, thereby increasing the antifouling Heterocyclic monomer compounds were synthesized by the
performance of coatings.
condensation of 2-hydroxyl- or 2-amino-substituted heterocycles
To develop eco-friendly marine antifouling systems with with acryl chloride. The general procedure was as follows: rst,
a good antifouling performance, a series of novel graed a 50 mL two-necked ask was placed in an ice-water bath, followed
copolymers were prepared by the polymerization of alkenyl by the addition of heterocyclic amines or phenols (0.01 mol),
benzoisothiazolinone with an acrylic ester monomer and dichloromethane (20 mL) and triethylamine (1.38 mL). Second,
subsequent modication by alkenyl heterocyclic monomers a mixture of acryloyl chloride (1.09 g, 0.012 mol) and dichloro-
(Scheme 1). In addition, bioactivities of the copolymers were methane (20 mL) was slowly added dropwise, and the mixture was
evaluated, and their practical applications in the marine eld reacted at room temperature for 6–12 h aer the end of addition.
also were investigated for further conrming the antifouling The solution was washed three times with water. The organic phase
performance of the copolymeric coatings.
was dried over anhydrous magnesium sulfate and evaporated under
reduced pressure to afford heterocyclic monomer compounds HM.
2-Acryloxybenzoxazole. 1H NMR (400 MHz, DMSO-d6),
d 8.03–8.00 (m, 1H, PhH),7.50 (dd, J ¼ 17.2, 10.4 Hz, 1H, –CH]),
7.47–7.45 (m, 1H, PhH),7.37–7.31 (m, 2H, PhH), 6.64–6.59 (dd, J
¼ 17.2, 1.2 Hz, 1H, ]CH2(Z)), 6.20–6.17 (dd, J ¼ 10.4, 1.2 Hz,
1H, ]CH2(E)). IR (KBr), v (cmꢁ1): 3056, 1748, 1704, 1623, 1600,
1481, 1251, 1145, 972, 918, 748 cmꢁ1
.
2-Acryloxypyridine. 1H NMR (400 MHz, DMSO-d6), d 8.03–
8.01 (m, 1H, PhH), 7.54–7.47 (dd, J ¼ 17.2, 10.4 Hz, 1H, –CH]),
7.47–7.44 (m, 1H, PhH), 7.37–7.31 (m, 2H, PhH), 6.64–6.59 (dd, J
¼ 17.2, 1.2 Hz, 1H, ]CH2(Z)), 6.20–6.17 (dd, J ¼ 10.4, 1.2 Hz,
1H, ]CH2(E)). IR (KBr), v (cmꢁ1): 3074, 1706, 1641, 1541, 1465,
1215, 1157, 983, 918 cmꢁ1
.
2-Acrylamide-6-chlorobenzothiazole. 1H NMR (400 MHz,
DMSO-d6), d 12.72 (s, H, –NH), 8.18 (d, J ¼ 2.0 Hz, 1H, PhH), 7.78
(d, J ¼ 8.8, Hz, 1H, PhH), 7.49 (dd, J ¼ 8.8, 2.0 Hz, 1H, PhH),
6.64–6.57 (dd, J ¼ 17.2, 10.0 Hz, 1H, –CH]), 6.52–6.47 (dd, J ¼
17.2, 1.6 Hz, 1H, ]CH2(Z)), 6.02–5.99 (dd, J ¼ 10.0, 1.2 Hz, 1H,
]CH2(E)). IR (KBr), v (cmꢁ1): 3452, 3031, 1697, 1623, 1595,
Scheme 1 Synthetic routes of acrylate triazinecopolymers.
18788 | RSC Adv., 2021, 11, 18787–18796
1535, 1442, 1400, 987, 900, 883, 804 cmꢁ1
.
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2-Acrylamide-6-methylbenzothiazole. 1H NMR (400 MHz,
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the plate was placed into a glass cup with fresh seawater and
changed every week. The plate was taken out, rinsed with
deionized water and dried to constant weight at room temper-
ature. The weight loss rate was calculated as follows:
DMSO-d6), d 12.55 (s, H, –NH), 7.81 (s, 1H, PhH), 7.74(d, J ¼
8.8 Hz, 1H, PhH), 7.29 (dd, J ¼ 8.8, Hz, 1H, PhH), 6.60 (dd, J ¼
18.4, 10.0 Hz, 1H, –CH]), 6.47 (dd, J ¼ 18.4, 2.0 Hz, 1H, ]
CH2(Z)), 5.98 (dd, J ¼ 10.0, 2.0 Hz, 1H, ]CH2(E)), 2.44 (s, 3H,
CH3). IR (KBr), v (cmꢁ1): 3434, 3055, 2921, 2854, 1695, 1627,
W0 ꢁ Wt
Mass loss wt% ¼
ꢂ 100%
(1)
W0 ꢁ Wkb
1606, 1552, 1461, 1404, 983, 902 881, 791 cmꢁ1
.
where, W0 is the weight of the initial sample plate, and Wt and
Wkb are the weights of the target sample plate and blank plate
aer the interval time t, respectively. Three independent
experiments were repeated for each sample.
Synthesis of copolymer PBHs
Scheme 1 shows the synthetic pathways of the target copolymer
PBHs comprising BM, MMA, BA and HM monomers. Typically,
MMA, BA, BM, HM and AIBN (0.5–1.0 wt% of total monomers) were
dissolved in a mixture of xylene and n-butanol in a three-necked ask
with a magnetic stirring bar and equipped with a reux condenser.
Contact angle test
Take the copolymer and brush it on a glass slide and dry at
room temperature. Use the SL200KB interfacial tension meter
of Shanghai SUOLUN Company to characterize, test the change
of the contact angle of the ultrapure water on the surface of the
polymer aer hydrolysis. The amount of ultrapure water used is
2 mL each time, and each polymer must be tested in three
different places and averaged.
ꢀ
With the increase in the temperature to 70–85 C, polymerization
was performed under nitrogen for 6–10 h, affording the target
copolymer. The reaction solution was removed at certain intervals for
examining the monomer consumption with reaction time.
Structural measurements
1H NMR spectra (400 MHz) were recorded on a Bruker AVANCE
instrument using CDCl3 or DMSO-d6 as the solvent at room
temperature. Fourier transform infrared (FTIR) spectra of
polymer lms cast onto potassium bromide plates were recor-
ded using a Bruker TENSOR 27 FTIR spectrometer. Gel
permeation chromatography (GPC) curves were recorded on
a United States Waters 1515 apparatus (with THF as the eluent
Algae inhibition measurements
Chlorella, Isochrysis galbana and Chaetoceros curvisetus were
provided by the algae culture group of the Ocean College of
Hainan University. Three different algae were selected for
testing to show the universality of the copolymer's inhibition of
algae. The maximum absorption wavelength of each solution of
marine algae was obtained by scanning the ultraviolet wave-
lengths using a UV-visible spectrophotometer, and the corre-
sponding values of Chlorella, I. galbana and C. curvisetus were
685, 485 and 685 nm, respectively. The concentration of the
algae liquid with different absorbance values was measured by
hemocytometer counting, and each group was measured three
times to obtain an average concentration of the algae solution.
The absorption value of each dilution was measured at the
maximum absorption wavelength. A standard curve was plotted
with the absorption value and marine algae concentration as
the abscissa and ordinate, respectively. Data of the absorbance
and algae liquid concentration were linearly simulated (Fig. 1).
The resin PBH was separately brushed on a surface of a glass
panel (75 mm ꢂ 25 mm ꢂ 1.2 mm), and the commercial acrylic
resin without the BIT component was used as the control group. The
at a ow rate of 1.00 mL minꢁ1 at 35 C). The GPC instrument
ꢀ
was calibrated using polystyrene (PS) standards.
DSC curves were measured on a Q100 SDT thermogravi-
metric analyzer (TA Inc., USA) by placing 10–20 mg of the liquid
polymer sample in an alumina crucible under N2 at a heating
ꢁ1
ꢀ
ꢀ
rate of 10 C min and a heating range of 25–130 C. The Tg
value of the polymer was obtained by DSC characterization.
TGA curves were recorded on a Q600 SDT thermogravimetric
analyzer (TA Inc., USA) by placing 5–10 mg of the liquid polymer
sample in ꢁa1n alumina crucible under N2 at a heating rate of
ꢀ
ꢀ
10 C min and a temperature range of 20–600 C. TGA was
employed to analyze the thermal stability of polymers.
Weight loss measurements
Each copolymer liquid was added dropwise on a slide glass resin panels were naturally dried at room temperature. The algae
surface, followed by naturally drying to constant weight. Next, solution was diluted with the nutrient solution so that the
Fig. 1 Working curves between absorbance and concentration of Chlorella (a), Isochrysis galbana (b) and Chaetocers curvisetus (c).
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absorption value was between 0.05 and 0.1; the resin panel was barnacle larvae were carefully drawn up using a pipette, added into
placed into the algae solution, and the beaker was sealed with the Petri dish and mixed with 30 mL of fresh seawater at room
a semi-permeable membrane. Each of the samples and control temperature. Each Petri dish contained 15 barnacle larvae, and the
group were measured every 24 h, and the absorbance was recorded. survival of barnacle larvae was observed and recorded by a stereo-
In accordance with the absorbance-concentration curve for the algae microscope at 12 h and 24 h. When barnacle larvae greater than
dilution, the corresponding concentration of algae was calculated, 15 s, they were considered to be dead. The death larvae were
and the concentration–time curves of algae were plotted.43,44
removed in time to ensure the accuracy of further experiments.47,48
Each copolymer was tested three times and averaged while using
the blank as the control group.
Antibacterial activity test
Gram-negative bacteria are predominant in seawater, and Vibrio is
a typical marine bacteria. Ocean-going ships dock in the inner bay
area. Generally, both positive and negative bacteria exist in the
inner bay area. S. aureus is a positive bacteria, and it is necessary to
choose S. aureus for antibacterial test. The selection of these three
kinds of bacteria is to show the universality of the copolymer to
inhibit negative bacteria and positive bacteria. S. aureus, V. cor-
alliilyticus and V. parahaemolyticus were provided by the Marine
Drugs Research Laboratory of Hainan University. The antibacterial
property of the target resin was investigated by the absorbance
method. Tryptone soybean broth (TSB) was the culture medium for
S. aureus, and the 2216E liquid culture medium was the culture
media for V. coralliilyticus and V. parahaemolyticus. The resin-
coated cell culture plates were sterilized by ultraviolet light for
2 h before the test. Then, 5 mL of the liquid culture solution and 50
mL of the cultured bacterial solution were separately added to each
well and cultured in an incubator at 37 ꢀC. The absorbance values
of the cells were measured at 600 nm at time intervals of 2 h, 4 h,
6 h, 8 h, 10 hand 12 h, and absorption values of the bacterial
solution in the culture solution were observed.45,46
Marine eld tests
Marine eld tests were performed from August to October in the
South China Sea (110.190E, 20.10N) in China, where the surface
water temperature ranges from 25 to 28 ꢀC. First, low-carbon steel
plates (300 ꢂ 200 ꢂ 3 mm3) were polished twice with sandpaper
(120 mesh) to remove rust, cleaned with pure water and ethanol
and then painted with two layers of acrylic resin. Second, the
copolymer samples were brushed twice on the acrylic resin surface
of the steel panels and marked. Aer the paint dried, and it was
naturally cured in a well-ventilated place, the panels were
immersed into seawater at a depth of 0.5–1.0 m. Meanwhile, blank
samples KB (acrylic resin) were used as the control group. Aer a 1
month interval, the panels were removed from the sea and care-
fully washed with seawater to remove the oating objects and
photographed, followed by immediately placing them back in the
seawater to continue marine eld tests. The antifouling activity
was evaluated according to ASTMD6990-05 (2011).49
Results and discussion
Characterization of copolymers
Barnacle larvae inhibition test
The antifouling resins of copolymers graed with heterocyclic
Barnacles are typical large fouling organisms. It is necessary to test monomers have not been reported in the literature. The
the copolymer for its inhibitory activity. Adult barnacles were molecular weights of the copolymers PBH were ꢃ10 000 (Table
collected near Haikou Bay in Hainan Island. Aer the adult 1). The number-average molecular weights (Mn) ranged from
barnacles were washed with seawater, the elder barnacles were 9858 to 13 226, while the weight-average molecular weights (Mw)
selected and dried in a dark place for 12 h. Then, the barnacles ranged from 10 830 to 13 592, both of which were not quite
were immersed in fresh seawater and exposed to light. As the different. The poly dispersity indexes (PDIs) of the copolymers
phototaxis of barnacle larvae was under sunlight, a large number were between 1.01 and 1.14, indicative of a relatively uniform
of barnacle larvae hatched from adult soon and swam to the light molecular-weight distribution. Each copolymer exhibited
side. First, 1.0 mL of the copolymer was added into each Petri dish, a single glass transition temperature (Tg), suggesting that all of
spread out and dried in air at room temperature. Next, quantitative the PBHs are random copolymers. A melting peak was not
Table 1 Molecular compositions and characterizations of copolymer
Ratio of monomer (%)
Samples
BM/MMA/BA/HM
Mn (g molꢁ1
)
Mw (g molꢁ1
)
PDI
Tg (ꢀC)
PBH1
PBH2
PBH3
PBH4
PBH5
PBH6
PBH7
PBH8
5/47.5/47.5/0
10/45/45/0
15/42.5/42.5/0
20/40/40/0
20/32.5/32.5/15 (R1)
20/32.5/32.5/15 (R2)
20/32.5/32.5/15 (R3)
20/32.5/32.5/15 (R4)
10 658
10 728
10 678
11 357
11 609
10 679
12 077
10 611
11 011
11 110
10 947
11 545
11 772
10 830
12 681
11 390
1.03
1.04
1.03
1.02
1.01
1.01
1.05
1.07
52.36
60.21
55.14
78.34
31.29
54.40
57.80
57.18
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observed in DSC curves, indicative of the amorphous nature of
the copolymers. The successful copolymerization of PBH poly-
mers was conrmed by FTIR and IH NMR (Fig. 2).
Thermal stability analysis of PBHs
Fig. 2c shows the thermal stability analysis of PBHs. With the
increase in the temperature, the weight loss of the polymer was
categorized into two stages. The rst stage occurred at 150–
300 ꢀC, with a small weight loss rate, possibly related to the
decomposition of unreacted small molecular substances. The
second stage occurred at 300–500 ꢀC, with signicant
molecular-weight loss, indicative of the thermal decomposition
of the polymer.
PBH4 was selected as a representative copolymer for compar-
ison with BM to verify whether copolymerization was complete
(Fig. 2a). In the FTIR spectrum of PBH4, a clear absorption peak
was not observed at 3100 to 3000 cmꢁ1 and 995 to 905 cmꢁ1 (green
frame), indicating that the carbon–carbon double bond does not
exist and that the carbon–carbon double bond of each monomer
in the copolymer is completely reacted. The absorption peaks at
1560 and 1595 cmꢁ1 indicate the presence of the benzene ring. The
absorption peak at 759 cmꢁ1 indicates that an ortho-disubstituted
benzene ring is still present. The newly observed absorption peaks
at 1731 and 1680 cmꢁ1 corresponded to the presence of an ester
group, while the absorption peak at 1380 cmꢁ1 corresponded to
the methyl group. Except for the carbon–carbon double bond, the
functional groups of each monomer in the copolymer are present.
Fig. 2b shows the 1H NMR spectrum of the copolymer PBH4. The
copolymer contained a small amount of Ph–H, and multiple sets of
characteristic peaks at d ¼ 7.38–8.27 were observed, corresponding
to the peaks characteristic of H in Ph–H. A group of characteristic
peaks was observed at d ¼ 4.68–4.78, corresponding to the peaks
characteristic of OCH3 in the BM monomer. In the copolymer, C–H
was connected to the ester group in the butyl ester compound, and
the peak corresponding to the methyl ester compound was observed
in the unshielded region of the ether oxygen atom; this peak posi-
tion shied to low eld, and two sets of peaks were observed at d ¼
3.43–4.12, corresponding to the peak characteristic of C–H in
RCOOCH2R and that characteristic of C–H in RCOOCH3. The
copolymer comprised a large amount of C–H, and multiple sets of
characteristic peaks were observed at d ¼ 0.75–1.65, corresponding
to the peaks characteristic of H in CH3 and CH2. The above analysis
conrmed the copolymer PBH4 structure. All of the structural
characterization methods validate that copolymerization is
completed and that each monomer participates in polymerization.
Weight loss rate measurements
The weight loss rate was measured for investigating the
hydrolytic release of the antifoulant in the graed resin
(Fig. 2d). When the plates were immersed in seawater, the mass
of the coatings started to decrease due to the hydrolysis of the
ester bond of the monomers. By the introduction of the
heterocyclic monomer, the loss rate increased, and aer copo-
lymerization with various monomers, the hydrolysis rate of the
resins changed.
In the initial days, the mass loss rate ranged from 0.015 to
0.025 mg cmꢁ2 dꢁ1. Aer 90 days, the mass lost rate tended to
be stable at 0.01–0.015 mg cmꢁ2 dꢁ1, indicative of the sustained
release of the gra coating. In particular, the mass loss rate of
PBH8 was greater than those of other samples, with an average
rate of 0.015 mg cmꢁ2 dꢁ1, and PBH7 exhibited the lowest mass
loss, with an average rate of 0.01 mg cmꢁ2 dꢁ1
.
Contact angle test
Fig. 2e shows the change of the contact angle of the polymer
surface with the immersion time aer the samples with
different monomer contents are immersed in fresh seawater.
The contact angle test can reect the changes in the hydrophi-
licity and hydrophobicity of the surface of the material, and
further reect the changes in the chemical structure of the
1
Fig. 2 (a) FT-IR spectra of BM and copolymer PBH4, (b) H NMR spectrum of copolymer PBH4, (c) trend of thermal stability of polymers, (d)
hydrolysis weight loss of polymers PBH, (e) change of contact angle of polymer PBH after hydrolysis.
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Fig. 3 (a) Inhibition of PBHs on Chlorella, (b) inhibition of PBHs on Isochrysis galbana, (c) inhibition of PBHs on Chaetocers curvisetus, (d)
antibacterial activity of PBHs against Staphylococcus aureus, (e) antibacterial activity of PBHs against Vibrio coralliilyticus, (f) antibacterial activity
of PBHs against Vibrio parahaemolyticus.
surface. At 0 days, the contact angle of the copolymer PBH4 with group. As the cultivation continued, some of the target copoly-
20% by weight of BIT monomer is greater than that of PBH1 mers suppressed the growth of Chlorella to some extent aer 2
with 5% by weight due to the side chain contains hydrophobic days. The compounds polymerized with the monomers BM and
acrylate groups. As the content of side chains increases, the HM clearly exhibited a better inhibitory activity against Chlor-
static water contact angle also increases. It shows that as the ella than that observed for compounds copolymerized only with
content of side chains increases, the content of side chains that the BM monomer, and with the increase in the graed ratio of
migrate to the surface of the sample also increases. Aer BIT, the potency of inhibition increased. Especially, PBH6 and
introducing different heterocyclic monomers into the copol- PBH7, polymerized with 2-acryloxypyridine and 2-acrylamide-6-
ymer, the contact angle of the resin sample decreases with the chlorobenzothiazole, respectively, exhibited signicantly
increase of immersion time. Aer 21 days, the static water improved inhibitory activities against Chlorella, with corre-
contact angle became stable. This is because aer the super- sponding average rates of 92.81% and 92.68%, almost inhibit-
cial acrylate monomer, BM monomer, and heterocyclic mono- ing the growth of Chlorella. PBH5 and PBH8, which were
mer are hydrolyzed, OH or COOH is generated, so that the polymerized with 2-acryloxybenzoxazole and 2-acrylamide-6-
supercial coat of the polymer becomes more hydrophilic and methylbenzothiazole, respectively, exhibited a low inhibitory
the contact angle becomes smaller.
activity with corresponding average rates of 42.17% and
40.64%; these rates are considerably less than those of PBH6
and PBH7.
Inhibition of marine algae growth
The inhibition rate was calculated from the algae absorbance–
concentration working curve. With time and algal concentra-
tion as the horizontal and longitudinal axes, respectively, the
time was set at 1 d, 2 d, 3 d, 4 d, 5 d, 6 d and 7 d. Fig. 3 shows the
inhibition curve of PBHs on the growth of three marine algae
(i.e., Chlorella, I. galbana and C. curvisetus, respectively), and
Table 2 summarizes data on the 7th day.
Table 2 Inhibition rate of copolymer PBHs against the growth of algae
Inhibition rate (7 days)/%
Isochrysis
galbana
Chaetocers
curvisetus
Polymers
Chlorella
From Fig. 3 and Table 2, the absorbance of the algal solution
was linearly related to the concentration. The target copolymers
exhibited certain algal inhibition activities, effectively restrict-
ing the growth of algal cells in the initial stage of passage.
The copolymer PBHs clearly inhibited the growth of Chlorella
(Fig. 3a). At the start of cultivation, Chlorella reproduced slowly
in the solution when immersing the target copolymers, followed
by the favourable inhibition effect compared to the control
PBH1
PBH2
PBH3
PBH4
PBH5
PBH6
PBH7
PBH8
25.77%
26.15%
88.71%
90.24%
42.17%
92.81%
92.68%
40.64%
85.19%
89.06%
90.48%
92.11%
76.25%
98.82%
98.61%
99.43%
39.04%
71.30%
95.24%
96.02%
64.54%
99.93%
99.15%
99.67%
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Compared to the control group, the target copolymers measured to quantify the inhibition potency of the copolymer
exhibited excellent inhibitory activities against I. galbana against bacterial growth. The inhibition rate was calculated
(Fig. 3b). Notable reproduction was not observed in the rst 2 according to the absorbance–concentration working curve.
days, and the algae concentration remained almost unchanged. With the time and algal concentration as the horizontal and
When the seaweed solution was cultured for 7 days, all target longitudinal axes, respectively, the action time was set to 2 h,
copolymers were observed to completely inhibit the growth of I. 4 h, 6 h, 8 h, 10 h and 12 h. Fig. 3 shows the inhibition activity of
galbana. PBH6, PBH7 and PBH8, which were polymerized with PBHs on the growth of S. aureus, V. coralliilyticus and V. para-
2-acryloxypyridine, 2-acrylamide-6-chlorobenzothiazole and 2- haemolyticus, and Table 3 summarizes the values.
acrylamide-6-methylbenzothiazole, respectively, exhibited
The copolymer PBHs clearly inhibited the reproduction of S.
outstanding inhibitory activities against I. galbana; their corre- aureus, and the inhibition rate was linearly related to the BIT
sponding average rates were 98.82%, 98.61% and 99.43%, concentration. Among the copolymers, the resins polymerized
almost inhibiting the growth of I. galbana. On the 1st day, the by the addition of heterocyclic monomers, such as PBH6, PBH7
algae concentrations considerably decreased. However, PBH5 and PBH8, exhibited better antibacterial activities (Fig. 3d).
polymerized with 2-acryloxybenzoxazole exhibited
a
poor
At the beginning of cultivation, S. aureus reproduced slowly
inhibitory activity against I. galbana, with an average rate of and exhibited good inhibition activities compared to the control
76.25%, compared to the other copolymers polymerized with group. With the continuation of cultivation, all target copoly-
the HM monomer.
mers well suppressed the reproduction of S. aureus throughout
Fig. 3c shows the inhibitory activities of the copolymer PBHs the entire experimental period. The compounds polymerized
on the growth of C. curvisetus. All of the BIT polymeric deriva- with the monomers BM and HM clearly exhibited better
tives exhibited a better inhibitory effect than that of the control inhibitory activities, and with the increase in the graed ratio of
group on the reproduction of C. curvisetus. For the cultivation of BIT, the potency of inhibition increased. Especially, PBH6,
the algae on the 1st day, the C. curvisetus concentrations did not PBH7 and PBH8, which were polymerized with 2-acryloxypyr-
signicantly differ between the algae solutions of the polymeric idine, 2-acrylamide-6-chlorobenzothiazole and 2-acrylamide-6-
derivatives.
With the continuation of the culture process, inhibitory improved inhibitory activities against S. aureus; their corre-
activities of the copolymers PBH exhibited notable changes. sponding average rates were 97.82%, 96.83 and 96.24%, almost
methylbenzothiazole, respectively, exhibited signicantly
The resins polymerized with the monomer HM exhibited the inhibiting the growth of S. aureus. PBH5, which was polymer-
best inhibitory performance. Particularly, PBH6, PBH7 and ized with 2-acryloxybenzoxazole, exhibited a low inhibitory
PBH8 exhibited outstanding inhibitory activities against C. activity, with an average rate of 81.19%. Similar to the case of S.
curvisetus, with corresponding average rates of 99.93%, 99.15% aureus, the growth of V. coralliilyticus was efficiently inhibited by
and 99.67%, completely inhibiting the growth of C. curvisetus. the copolymers (Fig. 3e), leading to the marginal reproduction
Among the heterocyclic resins, only PBH5 exhibited a poor and low concentration of V. coralliilyticuson the 1st day. Aer
performance.
the 7 day culture of the bacteria solution, V. coralliilyticus was
The mechanism of inhibiting the growth of algae is: polymer completely blocked by the target copolymers. For instance, the
hydrolysis will produce and release small molecular PBH6, PBH7 and PBH8, which were polymerized with 2-acryl-
compounds. It enters algae cells more easily, destroying the oxypyridine, 2-acrylamide-6-chlorobenzothiazole and 2-
structure and function of organelles. The algae cells gradually acrylamide-6-methylbenzothiazole, respectively, exhibited good
disappear, showing an inhibitory effect on the algae.
inhibitory activities against V. coralliilyticus; their correspond-
ing average rates were 99.08%, 96.01% and 97.24%, resulting in
the complete growth cease.
Inhibition of bacterial growth
Fig. 3f shows the inhibition of the PBHs on the growth of V.
parahaemolyticus. Compared to the control group, the BIT
polymeric derivatives exhibited better inhibitory activity on the
reproduction of V. parahaemolyticus. No considerable difference
in the bacterial concentrations on the 1st day. However,
signicant changes in the inhibitory activities were observed
with the progress of the culture. The resins polymerized with
the monomer HM, such as PBH6, PBH7 and PBH8, exhibited
good performance towards the growth inhibition of V. para-
haemolyticus; the corresponding average rates were 99.03%,
97.42% and 98.39%, respectively. PBH5, with an inhibition rate
of 91.94%, which was slightly less than those of other hetero-
Antibacterial abilities of copolymer PBHs were investigated. The
absorbance of the bacterial solution at different times was
Table 3 Inhibition rate of compounds against bacterial growth
Inhibition rate (12 h)/%
Staphylococcus
aureus
Vibrio
coralliilyticus
Vibrio
parahaemolyticus
Polymers
PBH1
PBH2
PBH3
PBH4
PBH5
PBH6
PBH7
PBH8
77.76%
92.08%
93.47%
95.45%
81.19%
97.82%
96.83%
96.24%
80.06%
87.12%
88.96%
93.87%
92.74%
99.08%
96.01%
97.24%
61.29%
78.06%
93.87%
95.05%
91.94%
99.03%
97.42%
98.39%
cyclic resins, was still
a
good inhibitor against V.
parahaemolyticus.
The mechanism of inhibiting bacterial growth is: polymer
hydrolysis will produce and release small molecules of BIT
compounds. The S–N bond in BIT molecule breaks and forms
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S–S bond with the receptor, which interact with the base on the
biological protein to form a hydrogen bond. The hydrogen bond
has a strong attraction and can rmly adhere to the bacterial
cell, thereby destroying the structure of the DNA, unable to
replicate, and ultimately leading to the death of the bacteria.
Application on antifouling coatings
To further investigate the inhibition potency of these newly
synthesized polymeric PBHs as antifouling coatings, the appli-
cation performance of the copolymers was evaluated in marine
eld tests. Coating samples were painted on the surface of thin
steel sheets and then immersed in seawater near the coast for 3
months, and the marine organisms adhered on the sheet steel
were periodically recorded. For comparison, samples contain-
ing 20% BIT (PBH4–PBH8) were selected for application tests,
and polyacrylate (KB) was selected as the control group for
contrast. Fig. 4c shows the typical images of the tested panels
aer immersion in seawater.
All of the tested coatings comprising the BIT structural unit
exhibited better antibiofouling activity than that of the KB
control group. Aer immersing in seawater for 60 days, a small
amount of seaweeds adhered on the coating surfaces, and rare
large-scale marine organisms, including barnacles and
mussels, adhered on the coatings, suggesting that copolymeric
compounds can be used as outstanding antifouling coatings in
boating and marine industry. On the contrary, the polyacrylate
blank panel exhibited adverse fouling by marine organisms due
to the covering of the surface by mussels and the growth of
barnacles or oysters on the mussels.
Inhibition of barnacle larvae
Fig. 4a shows the death rates of barnacle larvae caused by the
various copolymer PBHs. The inhibitory ability of the copoly-
mers containing BIT was greater than that of the contrast pol-
yacrylic ester, and with the increase in the BIT component, the
survival number of barnacle larvae gradually decreased. Thus,
the introduction of a heterocyclic structure into the compounds
leads to the considerable improvement in the inhibitory
performance of the PBHs against barnacle larvae.
Relative to the control sample, the addition of BIT into the
PBH chemical structures resulted in a higher potency inhibitory
activity. By the introduction of 5% of the BIT component
(PBH1), the inhibition rates of the barnacle larvae increased to
33.3% in 12 h and 55.6% at 24 h. In case of 10% of the BIT
component (PBH2), the inhibition rates of the barnacle larvae
increased to 37.8% in 12 h and 64.4% at 24 h. As the BIT content
reached 20% (PBH4), the inhibition rates of the barnacle larvae
increased to 62.2% in 12 h and 82.2% at 24 h. The presence of
the heterocyclic ring led to the dramatic enhancement in the
polymeric activity. For the copolymer graed with 15% of 2-
acrylamide-6-chlorobenzothiazole (PBH7), the inhibition rates
of the barnacle larvae increased to 71.1% in 12 h and 91.1% at
24 h, while for the copolymer graed with 15% of 2-acrylox-
ypyridine (PBH6),the inhibition rate of the barnacle larvae
increased to 80.0% in 12 h and 100.0% at 24 h.
Aer 90 days marine eld tests, a few of the fouling organ-
isms were observed to adhere on the BIT copolymeric coating
surface. Within the organisms, most were barnacles, and few
mussels were attached. On the other hand, the blank panel
surface was covered by a large amount of barnacles and
mussels.
The introduction of the heterocyclic unit in chemical
compounds signicantly enhanced the antifouling activities of
Fig. 4 (a) Inhibition rates of barnacle larva inhibited by PBHs, (b) statistical density of barnacles on marine field tests, (c) antifouling performance
of the resin immersion in seawater.
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the copolymeric coatings. Although a small number of barna-
cles were still attached on the panel surface, the coatings with
the use of heterocyclic compounds were considerably better in
inhibiting the marine fouling organisms than that observed for
the coatings without the heterocyclic compounds. For PBH6
and PBH7, which were graed by 15% 2-acryloxypyridine or 2-
acrylamide-6-chlorobenzothiazole, respectively, the antifouling
abilities were better than those of non-heterocyclic compounds,
and the average density of fouling organisms on the surface was
less than that of PBH4, revealing that the presence of a hetero-
cyclic unit on the polymer side chain increases the anti-
biofouling efficiencies.
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Conflicts of interest
There are no conicts to declare.
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This research was funded by Scientic Research Project of Sanya
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