Novel multifunctional hybrid diallyl ether monomer via azide alkyne click reaction as crosslinking agent in protective coatings

Article abstract of DOI:10.1016/j.polymer.2015.02.017

Functionalized hybrid monomers with crosslinking ability can provide advantages over the other monomers due to the flexibility of using it with any vinylic family of monomers. Azide alkyne click reaction is a convenient way of introducing triazole moieties into a molecule and opens up the possibility to add more functionality by suitable design of azide and alkyne compounds. In the present study, we report synthesis and use of new azide click linker containing allyl ether functionality, (3-(2-azidoethoxy) prop-1-ene) as a first example in the click reaction with a siloxane functionalized dialkyne to make a novel triazole, siloxane functionalized diallyl ether (TSDE) monomer. Chemical structure of the as synthesized TSDE, azide click linker and other compounds were characterized by FT-IR, ¹H NMR, ¹³C NMR, and ESI-MS techniques. Hybrid coatings of TSDE with methyl methacrylate (MMA) were evaluated for chemical structure, morphology, wettability, tensile and thermal properties by FTIR, XRD, SEM, UTM, WCA, DSC & TGA. Experimental results from EPS and fog tests indicate significant enhancements in the anticorrosion and antibacterial performance of the as synthesized new Poly (MMA-co-TSDE) hybrid coatings in comparison to PMMA.

Full text of DOI:10.1016/j.polymer.2015.02.017

Accepted Manuscript
Novel multifunctional hybrid diallyl ether monomer via azide alkyne click reaction as
crosslinking agent in protective coatings
Kesavarao Sykam, Shailaja Donempudi
PII:
S0032-3861(15)00168-8
10.1016/j.polymer.2015.02.017
JPOL 17630
DOI:
Reference:
To appear in: Polymer
Received Date: 9 October 2014
Revised Date: 14 January 2015
Accepted Date: 11 February 2015
Please cite this article as: Sykam K, Donempudi S, Novel multifunctional hybrid diallyl ether monomer
via azide alkyne click reaction as crosslinking agent in protective coatings, Polymer (2015), doi: 10.1016/
j.polymer.2015.02.017.
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ACCEPTED MANUSCRIPT
Graphical Abstract
Schematic representation

ACCEPTED MANUSCRIPT
Novel multifunctional hybrid diallyl ether monomer via azide
alkyne click reaction as crosslinking agent in protective coatings
Kesavarao Sykam, Shailaja Donempudi*
Polymers & Functional Materials Division, Indian Institute of Chemical Technology, Hyderabad 500007, India.
*Corresponding author: Email: sdonempudi@iict.res.in
Abstract: Functionalized hybrid monomers with crosslinking ability can provide advantages over the other monomers due to
the flexibility of using it with any vinylic family of monomers. Azide alkyne click reaction is a convenient way of introducing
triazole moieties into a molecule and opens up the possibility to add more functionality by suitable design of azide and alkyne
compounds. In the present study, we report synthesis and use of new azide click linker containing allyl ether functionality, (3-(2-
azidoethoxy) prop-1-ene)as a first example in the click reaction with a siloxane functionalized dialkyne to make a novel triazole,
siloxane functionalized diallyl ether (TSDE) monomer. Chemical structure of the as synthesized TSDE, azide click linker and
1
other compounds were characterized by FT-IR, H NMR, 13C NMR, and ESI-MS techniques. Hybrid coatings of TSDE with
methyl methacrylate (MMA) were evaluated for chemical structure, morphology, wettability, tensile and thermal properties by
FTIR, XRD, SEM, UTM, WCA, DSC &TGA. Experimental results from EPS and fog tests indicate significant enhancements in
the anticorrosion and antibacterial performance of the as synthesized new Poly (MMA-co-TSDE) hybrid coatings in comparison
to PMMA.
Keywords: click chemistry, crosslinking, hybrid coatings
Introduction
The ubiquitous demand for multifunctional, high performance coatings are best met by organic inorganic hybrids that can offer
synergistic benefits of both. Hybrid properties in a coating are generally obtained by sol gel method which allows incorporation
of organic polymers into an inorganic network. Incorporation of siloxane network into such compounds will play a vital role in
enhancing protection to metal substrates by improving barrier properties of coatings and decreasing the scope of permeability of
aggressive species (O2, H+) to the substrate. In general, such hybrid films are known to present hydrophobic character up to 90○
WCA for a well crosslinked (Si-O-Si) film forming a compact network. However, these films may suffer from hydrolysis (Si-
OH) when exposed to air or aqueous medium causing reduction in the WCA1. Moreover, incorporation of higher concentrations
of siloxane in the films makes them brittle and tends to develop cracks, thereby compromising corrosion resistance2. It is also
known from literature that materials consisting of hetero atoms like N, O, S, P and aromatic nucleus provide better corrosion
resistant properties to coatings3.Crosslinking of coating resins is of immense practical importance as it enhances the performance
of the coating. Therefore, design of a new hybrid monomer with crosslinking ability that can insert siloxane groups in to the
network of the polymer by covalent bonding with the monomers and can offer flexibility for use with any chosen monomers in
low volumes and provide significant enhancement in the performance of protective coatings. Key element in designing new
functional polymer materials is the accessibility of starting material and ease of functionalization which can be achieved by
adopting synthetic organic chemistry concepts4.Among them, copper catalysed azide alkyne “click” reaction5 (CuAAC) is widely
used for synthesizing 1,2,3-triazole based compounds which are extensively used as functional materials in the field of corrosion
resistant coatings 6,10,11,anti-fouling coatings 7, biodegradable 8, antimicrobial10,11and biomedical applications.9
In the present study, we report the use of this click reaction to synthesize a unique hybrid diallyl ether monomer functionalized
with triazole and inorganic siloxane groups designated as TSDE, a first example of hybrid crosslinkable monomer. We also
report synthesis of allyl ether containing azide12and used it as a click linker for the first time. The diallyl ether monomer (TSDE)
is shown in Fig. 1 with both triazole nucleus and siloxane moiety in a single structure. Here the molecule was designed to
incorporate both organic (triazole) and inorganic (siloxane) groups in the monomer such that combined benefits of improving
adhesion to the substrate and enhancing hydrophobicity on surface respectively could be achieved when used in protective
coatings applications. Literature reveals that admixtures of allyl containing compounds with vinyl monomers present promising
applications due to improved physical and electric properties.13Crosslinked alkyl acrylates with allyl ethers of pentaeryhtritol,
sucrose, and trimethylolpropane are reported to be safe for use in cosmetics.14Allyl ether maleate functional hyperbranched ester
resins were synthesized by Johansonn et al. to study their curing performance and film properties.15Cross-linking of dendrimers
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with allyl ether end-groups using the ring-closing metathesis to develop new dendrimer architectures16and found that in the
presence of a catalyst analogous hyperbranched systems can be polyallylated to give nearly complete cross-linking17. The
difference in reactivity between allyl acrylate and diallyl ether was reported by Busfield et al stating that in case of allyl acrylates,
products were formed by H-abstraction as well as addition of both allyl and acryloyl double bonds whereas for allyl ethers it was
H-abstractionalone18. However, it was reported that at lower compositions of < 10 mol %, these diallyl compounds show similar
reactivity to that of methyl methacrylate homopoymer. The crosslinking efficiency of the as synthesized hybrid TSDE was
investigated by copolymerizing with MMA and their performance as hybrid coatings was evaluated by subjecting them to
anticorrosion and antibacterial study in comparison to the unmodified PMMA coatings. Crosslinking ability of TSDE with
vinylic monomers and choice of its content in the resin opens up an alternative and easy method of making hybrid resins useful in
high performance protective coatings.
Fig.1 Multifunctionality in hybrid TSDE structure
Experimental section
Materials
Sodium azide (99% extra pure), calcium hydride (93%), allyl bromide (99% stabilized), propargyl bromide (80 Wt% solution in
toluene) and tetrahydrofuran (99.5% extra dry over molecular sieves stabilized), were purchased from Acros organics, Belgeum.
Sodium hydride (57-63% oil dispersion powder) and (3-Aminopropyl) triethoxysilane (98%) were purchased from Alfa Aesar,
Massachusetts, USA. Copper(I)iodide 98%, 2-chloro ethanol 98% were purchased from Avra Chemicals, Hyderabad, India. Dry
n-pentane, dichloromethane and diethyl ether were purchased from Finar chemicals Ltd, Mumbai, India. Methyl methacrylate
and benzoyl peroxide were purchased from Aldrich chemicals. Benzoyl peroxide was recrystallized before use and remaining all
above chemicals were used without further purification.
Measurements
The FT-IR spectra of synthesized molecules and polymers were recorded on Thermo Nicolet Nexus 670 spectrometer. 1H NMR
and 13C NMR of the synthesized samples were done with BRUKER-300 MHz spectroscopy by taking CDCl3 as solvent and
tetramethylsilane (TMS) as reference at room temperature. The Electro spray Ionization – Mass Spectroscopy (ESI-MS) analysis
was done on Waters Micromass Quattro micro, API instrument. The morphology of hybrid free films was characterized by
Scanning Electron Microscopy (SEM) using JEOL JSM-6550F. The Thermo Gravimetric Analysis (TGA) was conducted for
synthesized cross-linker based PMMA films with temperature ramp rate at 10oC per minute under continuous Nitrogen
atmosphere by TGA Q500 Universal TA instrument (UK) and Differential Scanning Calorimetry(DSC) was carried out with
DSC Q100 Universal TA instrument (UK). Tensile properties of the films (5x1 cm2) with a thickness of 100 microns were tested
on a Universal Testing Machine (EPS) of TSDE loaded PMMA coated mild steel panels with 2×2 cm2 were subjected to test the
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corrosion resistance by Tafel method in 3.5% NaCl solution with IM6ex (ZAHNER Elektrik, Germany). The contact angle
studies of coating free films were carried out with KRUSS contact angle measuring system G10, Germany. The gel content,
crosslink density, νc,s and the average molecular weight between cross-links, Mc , for the free films of Poly (MMA-co-TSDE)
(TSDE = 2.5%, 5%, 7.5% and 10% ) were determined by soaking a sample of 0.1g in chloroform for 2 days. The swollen
polymer was separated from the dissolved portion by filtration and then dried. From the weights of both swollen and dry gel,
weight fraction of the non-dissolved part i.e., gel content; ν
c,s and Mc were calculated based on Flory’s equation 1 19
ꢃ
ꢀꢁ ꢂ ꢄ
ꢅ,ꢆ
ꢏ
ꢇꢁ,ꢈ =ꢉꢊln(1-Vr) + Vr+ χꢋꢍꢌꢎ/V1(ꢋꢐ ꢉ ꢍVr)
…..(2)
ꢌ
ꢑ
Here, ρ is the density of the polymer (PMMA=1.18 g/cm3 @ 25 ○C), Vr in eq (2) is the volume fraction of polymer in the swollen
gel, and χ is the polymer-solvent interaction parameter (0.345; calculated from solubility parameter values20. V1 is the molar
volume of the solvent (80.7cm/mol), and is the number of functional groups on a crosslinked point(4). Solvent swelling data
can give absolute values for crosslink density. However, this calculation stands only as an approximation as it assumes that the
polymerization goes to completion, which is not always the case.
Synthetic procedures
Synthesis of (N-(prop-2-ynyl)-N-(3-(triethoxysilyl) propyl) prop-2-yn-1-amine) (Compound-1)
APTES (13.28g, 60 mmol) was dissolved in 200ml of dry THF in a round bottom flask. To this calcium hydride (12.6g,
300mmol, 5 eq.) and of propargyl bromide (15.70g, 120mmol, 2 eq.) were added. The mixture was stirred for 12 hours at room
temperature under nitrogen atmosphere. To the resulting mixture, 200 ml of dry n-pentane solvent was added. The residual
calcium hydride was then removed by vacuum filtration and the n-pentane solvent was removed under vacuum to get the final
product as viscous orange coloured liquid (85% yield). The schematic representation of the reaction was shown in Scheme 1.
1
IR (neat, cm-1): 3300 (≡C-H Str), 1108-1080 ( Si-O Str); H NMR (300 MHz, CDCl3): δ (ppm) 0.61(t, 2H), 1.23(t, 9H), 1.59(q,
2H), 2.21(t, 2H), 2.53(t, 2H), 3.44(d, 4H), 3.82(q, 6H); 13C NMR (75 MHz, CDCl3):δ (ppm) 7.83, 18.27, 20.79, 42.07, 55.87,
58.32, 72.73, 78.91; ESI-MS m/z calculated for C15H27NSiO3 is 297, found (M+H) peak 298.
Synthesis of 2-azido ethanol (Compound 2)
In a round bottom flask, 2-chloro ethanol (10g, 0.124mol, 1 eq.) and sodium azide (20.153g, 0.31, 2.5 eq.) were dissolved in
100ml of deionised water. The reaction mixture was refluxed for 24 hours with continuous stirring. To the resulting mixture, 25 g
of sodium sulphate was added and stirred for another 20 minutes. The mixture was filtered and the product in the filtrate was
extracted using dichloromethane (3×50 ml). After evaporating the solvent the product 2-azidoethanol was obtained as a
colourless liquid with 90 % yield. (Scheme 1)
IR (neat, cm-1): 3382(O-H Str), 2937,2881(C-H Str), 2100(N3Str); 1H NMR (300 MHz, CDCl3): δ (ppm) 3.2 ( s, 1H), 3.44 ( t,
2H), 3.77 ( t, 2H); 13C NMR (75 MHz, CDCl3):δ (ppm) 52.92, 60.74 ; ESI-MS m/z calculated for C2H5ON3 is 87.08 found
(M+H) peak 88.
Synthesis of 3-(2-azidoethoxy) prop-1-ene (Compound-3)
2-azidoethanol (7.5g, 0.08mol, 1eq) in 10 ml dry THF was added to the solution of the Sodium hydride (4.17g, 0.17mol, 2 eq.) in
35ml of dry THF at 0oC. After the complete addition, 50 ml of diethyl ether solvent was added. The reaction mixture was stirred
for 30 minutes under nitrogen atmosphere. To the reaction mixture, allyl bromide (12.5g, 0.1 mol, 1.2 eq.) was added drop wise
and the stirred for overnight at room temperature. The reaction mixture was cooled to 0oC and 50 ml deionised water was added
to quench the reaction. The diethyl ether layer was separated and the aqueous layer was washed with 25ml diethyl ether for three
times. The combined diethyl ether layers were dried over sodium sulphate. After filtration, the final product was obtained by
removing the solvent under reduced pressure. The product was acquired as a pale yellow viscous liquid with 80 % of yield.
(Scheme 1)
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IR (neat, cm-1): 3050(=C-H Str), 1630(C=C Str), 2100(N3 Str) ;1H NMR (300 MHz, CDCl3): δ (ppm) 3.39(t, 2H), 3.62(t, 2H),
4.04(d, 2H), 5.2(d, 1H), 5.32(d, 1H), 5.91(m, 1H); 13C NMR (75 MHz, CDCl3): δ (ppm) 50.4, 68.5, 72.3, 134, 117.02; ESI-MS
m/z calculated for C5H9ON3 is 127, found (M+H) 128.
Synthesis of triazole siloxane based multifunctional cross-linker (TSDE):
The above synthesized compounds 1 and 3 were taken in 1:2 ratios and dissolved in dry THF solvent. To the resulting mixture 5
mol% of Copper iodide was added portion wise. The mixture was stirred for 24 hours under nitrogen atmosphere. The reaction
was monitored by using FT-IR spectroscopy. The reaction was stopped when the azide stretching peak around 2100 cm-1 was
disappeared. Finally, the product was collected after evaporating the solvent as a viscous green liquid with nearly 100% yield.
(Scheme 1)
IR (neat, cm-1): 3100(Triazole C-H Str), 1630( =C-H Str), 1450(Triazole C=C Str) 1080-1103( Si-O Str); 1H NMR (300 MHz,
CDCl3):δ (ppm) 0.60(t, 2H), 1.22(t, 9H), 1.67(m, 2H), 2.49(t, 2H), 3.76(m,4H), 3.80( m,10H), 3.97(d, 4H), 4.54(t, 4H),
5.19(m,2H), 5.8(m, 2H), 7.72(s, 1H); 13C NMR (75 MHz, CDCl3):δ (ppm) 14.2, 18.5, 23.2, 50.02, 56.5, 57.6, 58.4, 63, 73.5,
144.8, 118.2, 124.9, 134.6; ESI-MS m/z calculated for C25H45N7SiO5 is 551, found (M+H) 552 .
Scheme 1 Synthetic steps involved in synthesis of TSDE.
Step-1
NH2
O
O
Br
O
N
Si
Si
O
O
O
CaH2
1
APTES
Step-2
NaN3
Br
O
OH
HO
N3
N3
Cl
NaH
3
2
2-chloroethanol
Step-3
N
N
N
O
O
N
O
N
Si
Cu(I)
R.T
O
O
N
Si
N3
O
O
O
O
N
N
3
1
TSDE Cross linker
Synthesis of poly (MMA-co-TSDE)
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Copolymerization of TSDE crosslinker with vinylic monomers (methyl methacrylate) was examined under free radical
polymerization conditions. The monomers MMA and TSDE were copolymerized in presence of benzoyl peroxide initiator. For
this initially, MMA and TSDE (0, 2.5, 5, 7.5 and 10 wt% with respect to MMA) monomers were taken in dry THF along with
BPO initiator (1 wt% with respect to monomers)and the mixture was stabilized for 30 mins with agitation under nitrogen
atmosphere at room temperature. The temperature was then raised to 80○C and the reaction was continued for 10-15 hours until a
viscous liquid was obtained (Scheme 2).Coatings of Poly methyl methacrylate (PMMA) and TSDE crosslinked PMMA named as
TSDE-2.5, TSDE-5, TSDE-7.5, TSDE-10 were prepared by manually driven applicator to test the effect of TSDE crosslinking
and its content on the performance of Poly(MMA-co-TSDE) hybrid coatings in comparison to PMMA homopolymer.
Scheme 2 Synthesis of poly (MMA-co-TSDE).
N
N
N
N
O
O
BPO
O
O
N
Si
THF, 80oC
O
O
O
N
N
MMA
TSDE
poly(MMA-co-TSDE)
o
Si
=TSDE
Where
o
=PMMA
o
Results and discussions
1H NMR, 13C NMR and ESI-MS analysis
The formation of chemical structures of compound-1, 2-azidoethanol, compound-3 and TSDE cross-linker was confirmed by 1H
1
NMR, 13C NMR and ESI-MS spectroscopic techniques. The H NMR, 13C NMR spectras of various compounds were shown in
Fig. 2,3. And the ESI-MS spectra were shown in Fig. 4. The formation of compound-1 was confirmed by the occurrence of a
1
doublet at δ 3.44 (CH2-C≡CH) and triplet at δ 2.21 (CH2-C≡CH) in H NMR spectra; the presence of peaks at δ 42.07 (CH2-
C≡CH), δ 72.73 (CH2-C≡CH) and δ78.91 (CH2-C≡CH) in 13C NMR spectra corresponding to propargyl group. The formation of
1
2-azidoethanol was confirmed by the presence of a triplet at δ 3.44 (CH2-N3) in H NMR spectra and a sharp peak at δ 52.92
(CH2-N3) in 13C NMR spectra. The compound-3 was confirmed by the presence of two doublets at δ 5.2 (CH2-CH=CH2), δ 5.32
(CH2-CH=CH2), a multiplet at δ 5.91(CH2-CH=CH2) and a doublet at δ 4.04 (CH2-CH=CH2) in 1H NMR spectra; the presence of
δ 72.3 (CH2-CH=CH2), δ117 (CH2-CH=CH2) and δ134 (CH2-CH=CH2) in 13C NMR spectra corresponding to allyl group. The
occurrence of click reaction between compound-1 and 3 was confirmed by the presence of new peaks at δ 7.72 (triazole C-H) in
1H NMR and at δ 124.9 (triazole C-H) in 13C NMR spectra of TSDE cross-linker.
From ESI-MS analysis the formation of compound-1, 2-azidoethanol, compound-3 and TSDE cross-linker was supported by the
presence of a (M+H) peaks at m/z 298, 88, 128 and 552 respectively.
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Fig. 2 1H NMR spectra of (a) 2-azido ethanol, (b) 3-(2-azidoethoxy) prop-1-ene, (c) (N-(prop-2-ynyl)-N-(3-(triethoxysilyl)
propyl) prop-2-yn-1-amine), (d) TSDE.
Fig.
(triethoxysilyl)propyl)prop-2-yn-1-amine), (d)TSDE.
3
13C NMR spectra of (a) 2-azido ethanol, (b) 3-(2-azidoethoxy) prop-1-ene, (c) (N-(prop-2-ynyl)-N-(3-
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Fig.
4
ESI-MS analysis of (a) 2-azido ethanol, (b) 3-(2-azidoethoxy)prop-1-ene, (c) (N-(prop-2-ynyl)-N-(3-
(triethoxysilyl)propyl)prop-2-yn-1-amine), (d) TSDE.
XRD studies
The synthesized poly (MMA-co-TSDE) free films such as PMMA,TSDE-2.5, TSDE-5, TSDE-7.5, TSDE-10were examined for
the crystalline behaviour by using X-ray diffraction technique. It is observed that a broad peak present in between 10 and 20 on 2
theta-scale in all the samples (Fig.7). Initially, upon addition of 2.5% of TSDE cross-linker, the crystallinity of the sample was
decreased but with increase in the TSDE percentage, the crystalline nature of the polymeric film gradually increases and which is
credited to the high cross-linking ability of siloxane groups.
Morphology
The micrographs reported in (Fig.5) shows a clear difference between the crosslinked and linear PMMA films. Appearance of
lighter regions representing the inorganic moieties was noticed to be proportional to the degree of crosslinking. PMMA-siloxane
hybrid films made by sol gel method tend to develop cracks causing discontinuities in the film due to brittle nature of the film on
crosslinking. Here, the images present a perfect hybrid film with no macroscopic phase separation. Formation of uniformly
networked structure can be attributed to the covalent bonding between TSDE and MMA during polymerization.
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Fig.5 SEM images of PMMA and Poly (MMA-co-TSDE) free films.
Thermal analysis
The thermal stability of the synthesized poly (MMA-co-TSDE) free films along with pure PMMA was evaluated using Thermo
gravimetric analysis studies. (Fig.6). The onset decomposition temperature (TON), maximum degradation temperature (Td max),
10%, 30%, 50% weight loss temperatures and percentage of weight remained at 400oC of all the samples were tabulated in the
(Table 1). The thermal stability of the polymeric films gradually increases with the loading of TSDE cross-linker percentage. For
instance, the maximum decomposition temperature and the percent weight remaining at 400oC for PMMA, TSDE-2.5, TSDE-5,
TSDE-7.5, TSDE-10 are 373oC, 391oC, 412oC, 414oC and 416oC; 2.9, 15.1, 41.5, 44.9 and 45.9 respectively. It is known from
the literature that the PMMA shows three step thermal degradation 21. From DTG analysis, it is observed that all the polymeric
samples are showing a three step degradation profile. However, the maximum decomposition temperature (Td max) is increased
with the loading of TSDE cross-linker. For instance the Td max of PMMA, TSDE-2.5, TSDE-5, TSDE-7.5, TSDE-10are 373.85,
391.03, 412.39, 414.75 and 416.74 respectively. A similar type of result is obtained from DSC analysis (Fig.7). The glass
transition temperature (Tg) of the polymeric films was improved with the loading of TSDE cross-linker. For instance the Tg of
PMMA, TSDE-2.5, TSDE-5, TSDE-7.5, TSDE-10 are 80.04oC, 88.14oC, 92.29oC, 94.21oC and 94.32oC respectively. The overall
improvement in the thermal stability and glass transition temperature of the polymeric films is credited to the presence of highly
thermally stable 1,2,3-triazole and siloxane units on TSDE cross-linker.
Fig.6 (a) TGA and (b) DTG profiles of PMMA and Poly (MMA-co-TSDE) films
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Fig. 7.DSC scans and XRD patterns of PMMA and Poly (MMA-co-TSDE) films.
Table 1 Thermal stability and glass transition temperatures of PMMA and Poly (MMA-co-TSDE) free films.
Sample code
TON (OC)
Tdmax(OC) Td 10%(OC)
Td 50%(OC)
%Weight
Tg (OC)
remains at 400 OC
PMMA
288.07
290.90
299.26
302.37
309.79
373.85
391.03
412.39
414.75
416.74
165.62
178.63
219.70
225.91
233.07
333.45
374.64
390.02
394.37
394.51
2.912
15.05
41.53
45.93
45.89
80.04
88.14
92.29
94.21
94.32
TSDE-2.5
TSDE-5
TSDE-7.5
TSDE-10
Crosslink density
Table 2 summarizes the cross linking characteristics of Poly (MMA-co-TSDE) samples by swelling method.The results display
gel content enhancement leading to increased crosslink densities and lower number of monomer units between the cross links
with higher TSDE contents and a more significant change was noticed for TSDE-10 sample. Because, the 10% TSDE loaded
PMMA would be less capable of swelling to the same magnitude as others due to the drastic decrease in the number of elastically
active chains comparatively. Generally, increasing degree of crosslinking is always associated with a decrease in Mc leading to
lower chain flexibility that results in enhanced glass transition temperatures 22. The results of Tg from DSC measurements as
expected are also in support of the observation.
Table 2 Characteristics of Poly (MMA-co-TSDE) samples from the swelling data using Flory’s equation.
Sample
Code
Weight of
swollen gel
(W2)g
Weight of
dry gel
(W1)g
Gel content
W2/W1x100
(Wt %)
Equilibrium
swelling
S=(W2-W1/W1)
Vr
Mc
1/(1+S)3
(mol/cm3)
(g/mol)
TSDE-2.5 0.067
TSDE-5. 0.083
TSDE-7.5 0.095
TSDE-10 0.119
0.015
0.026
0.032
0.060
15
26
32
60
3.47
2.19
1.97
0.98
0.01
0.03
0.04
0.13
9.31x10-7
6.23x10-6
1.04x10-5
3.74x10-3
1.27×106
1.89×105
1.13×105
3.15×102
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Tensile properties
The tensile strength and elongation at break values for PMMA and TSDE cross linked PMMA samples are presented in Table 3
and represented in Fig. 10. It is a well-known feature that average molar mass between cross links, Mc, affects the tensile
properties of the films. Therefore, as Mc decreases, crosslink densities of the polymer increase resulting in higher tensile strength
due to greater maximum stress values and lower elongation at break.
Table 3. Tensile properties of PMMA and Poly(MMA-co-TSDE) free films.
Sample code
Max. stress
(N/mm2)
Elongation at break
(%)
PMMA
TSDE-2.5
TSDE-5
TSDE-7.5
TSDE-10
16.19
17.06
18.96
20.52
24.32
5.06
3.81
3.36
3.12
3.00
Water contact angle results
The as prepared polymer hybrids were coated onto glass substrates for water contact angle measurements. Drop shape analyses of
the obtained TSDE incorporated hybrid reveal an outstanding hydrophobic property with increase in the amount to cross linker. It
is inferred that the silica backbone of the cross-linker forms a network making highly dense siloxane linkages leading to an
enhancement in hydrophobicity. It is observed that pristine PMMA had a contact angle of 62o±2oand following the addition of
TSDE the angle boosted to 101o±2ofor TSDE-10. The water contact angles of TSDE-2.5, TSDE-5, TSDE-7.5are 73o,86o and
91o±2orespectively (Fig. 8).
Fig. 8 Water contact angle results for plain PMMA and Poly (MMA-co-TSDE) free films.
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Electrochemical Polarization Studies (EPS) and Fog tests
The corrosion of metal substrates is a major problem observed all over the world and most of the available coating formulations
suffer from leaching of oxygen, moisture and ions. Incorporation of inorganic moieties and heterocyclic groups into the coating
formulations is a dependable choice to address this problem. In the present work, all the synthesized polymeric films are tested
for the anticorrosive properties by potentiodynamic polarization studies and salt spray fog tests 23
.
Corrosion protection of metal by application of the as synthesized PMMA and the Poly (MMA-co-TSDE) coatings has been
evaluated by Tafel method.The values of E corr, I corr, polarization resistance (Ω), and corrosion rate (mm/year) are given in Table
4. A typical Tafel plot is shown in Fig. 9.Poly (MMA-co-TSDE) films reduced the corrosion currents drastically indicating
improvement in corrosion resistance in comparison to PMMA. TSDE-10 displayed better corrosion resistance with least
corrosion current (I corr) value and a significant shift of the corrosion potential (Ecorr) to positive value. A gradual decrease in
corrosion rate was noticed with increase in the degree of TSDE crosslinking of PMMA indicating its better corrosion resistance
behaviour comparatively. Thus, it is understood that coatings with TSDE provide enhanced corrosion protection and the results
comply very well with the findings from salt spray fog tests. These results support the hydrophobic nature of TSDE that repels
moisture/corrosive media from being absorbed on the surface, preventing the underlying metal from corrosion attack as also
evidenced by the contact angle (wettability) measurements.
The corrosion test for the coatings was performed through fog test. (Fig. 9). Each coating was cast on a thoroughly cleaned mild
steel panel (3×5 cm) with acetone, ethanol and de ionized water so as to remove trace impurities, surface oils, and dust
particulates. The coatings were spin coated onto these panels with a thickness around 100 microns and left for drying at room
temperature for 24 hours. Following this the dried panels were placed in a salt spray chamber. The fog of 5% NaCl solution was
continuously sprayed on the coated panels for about 250 hours. The coatings were monitored at regular intervals to estimate the
corrosion rate. It was observed that with increase in percentage of TSDE in the coating there was a substantial increase in
corrosion resistance. TSDE-10comparatively was found to give maximum corrosion resistance up to 250 hours salt spray while
PMMA had shown 90% corrosion within 120 hours. This clearly indicates that the performance of the cross-linked coatings was
proportional to the crosslinked percentage of TSDE. Thus, the presence of triazole and siloxane functionalities in TSDE in the
25
coating has fulfilled their role by offering improved adhesion to the metal substrate 24 and protective barrier properties at the
film surface simultaneously.
Fig. 9 Fog test results and Polarization curves on Tafel plot for PMMA and Poly (MMA-co-TSDE) coatings on mild steel panels.
a) PMMA, b) TSDE-2.5 c) TSDE-5 d) TSDE-7.5 e) TSDE-10.
Table 4.Corrosion parameters obtained from Electrochemical Impedance Spectroscopy studies for PMMA and TSDE crosslinked
PMMA films coated on mild steel.
Sample code
E corr
(mV)
I corr
(A)
Polarization
resistance(Ω)
Corrosion rate
(mm/year).
PMMA
TSDE-2.5
-601.820
-656.650
2.29 µA
44.29 nA
27.6690 kΩ
1.07840 MΩ
2.6677×10-2
5.1473×10-4
TSDE-5
-254.290
-46.2340
1.65500
1.11 nA
0.50 nA
0.24 nA
42.5920 MΩ
98.7670 MΩ
97.3630 MΩ
1.2907×10-5
5.8682×10-6
2.7996×10-6
TSDE-7.5
TSDE-10
11

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Antibacterial results
The antibacterial activities were measured based on the formation of inhibition zone loss of bacterial growth beneath and
surroundings of the films placed on Luria Bertani agar medium. The colonies of various bacteria were grown on CzapekDox
medium. (Fig.10). The CzapekDox plates consist of bacterial cultures, and the embedded films were incubated for 4−5 days at
ambient temperatures of 28 ± 4 °C; loss of bacterial moss surrounds beneath the film was monitored. In the present work,
Staphylococcus aureus and Klebsiella pneumonia were used as gram positive and gram negative bacterial stains. The embedded
TSDE loaded PMMA polymeric films were showing excellent resistance towards the bacteria compared to the pristine PMMA.
This resistance towards various bacteria can be attributed mostly to the presence of 1,2,3-triazole units in the crosslinked polymer
in comparison to the similar effect contributed by the presence of catalytic amounts of Cu (1.6wt%) with respect to TSDE that
may be considered almost negligible.
Fig. 10 Antibacterial activity and Tensile properties of PMMA and Poly (MMA-co-TSDE) free films.
Conclusions
In summary, we have reported the use of azide alkyne “click” reaction to make a multifunctional hybrid diallyl ether
crosslinker compound (TSDE) with siloxane and triazole functionalities in a single structure. The as synthesized new
azide click linker opens up the possibility to design a wide class of azides with other functionalities that can be used to
react with the terminal dialkynes on the sol gel synthesized siloxane compound resulting in a multifunctional hybrid
crosslinker. This new method opens up the scope for synthesis of such class of monomers with appropriately
functionalized azide click linkers that can be useful in making variety of hybrid coatings. A comparative study of the
properties like thermal, wettability, corrosion and bacterial resistance of Poly (MMA-co-TSDE) versus PMMA
homopolymer have proved the enhanced performance of the hybrid coatings with a low < 10% TSDE. Hence, the role
of TSDE crosslinker in the coating has successfully proved the advantages of such designed monomers with hybrid
functionalities that help form homogeneous and compact films useful in the field of protective coatings.
Acknowledgements
Mr. Kesavarao Sykam would like to express his gratitude to University Grants Commission (UGC) for the fellowship
and the authors thank CSIR-XII Five year plan programme INTELCOAT-0114 for financial support.
12

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Highlights of the work
‹
A multifunctional hybrid diallyl ether monomer (TSDE) useful as crosslinking agent in polymer
synthesis was synthesized using azide alkyne click chemistry as first example.
‹
‹
A new allyl ether functional azide was synthesized and used as click linker for the first time.
TDSE could be used to copolymerize with any vinylic family of monomers to make hybrid coatings
with synergistic benefits from organic triazoles and inorganic siloxane functionalities.
Siloxane groups here get incorporated into the polymer network by covalent bonding with the
monomers to form a more compact film unlike the ones prepared by sol gel method.
Copolymers of Poly (MMA-co-TSDE) result in enhanced barrier, corrosion resistance and anti-
bacterial protection properties to the films in comparison to PMMA.
‹
‹
‹
This new method opens up the scope for synthesis of such class of monomers with appropriately
functionalized azide click linkers that can be useful in making variety of hybrid coatings.

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Supporting Information.
Novel multifunctional hybrid diallyl ether monomer via azide
alkyne click reaction as crosslinking agent in protective coatings
Kesavarao Sykam, Shailaja Donempudi*
Polymers & Functional Materials Division, Indian Institute of Chemical Technology, Hyderabad 500007, India.
*Corresponding author: Email: sdonempudi@iict.res.in
FT-IR analysis
In the present work, FT-IR analysis was performed to verify the formation of various steps involved in the development of poly
(MMA-co-TSDE) free films such as synthesis of (N-(prop-2-ynyl)-N-(3-(triethoxysilyl)propyl)prop-2-yn-1-amine) (compound-
1), 2-azidoethanol (Compound 2), Synthesis of 3-(2-azidoethoxy)prop-1-ene (Compound-3), TSDE cross-linker and the poly
(MMA-co-TSDE) polymers.(Fig.1,2)
The formation of compound-1 can be confirmed by the disappearance of broad peak of N-H str at 3400 cm-1 and the formation of
new sharp peak at 3300 cm-1 (≡C-H Str). The strong peak in the range of 1108-1080cm-1 corresponds to Si-O stretching. The
formation of 2-azidoethanol from 2-chloroethanol was confirmed by the presence of new peak at 2100 cm-1 corresponding to
azide (-N3) group. Compound-3 formation was confirmed by presence of two stretching frequencies related to the alkene
functional group such as the peak at 3050 cm-1 (=C-H str) and the peak at 1630 cm-1 (C=C str). The click reaction between
compound-1 and 3 for the formation of TSDE cross-linker is confirmed by the disappearance of alkyne and azide stretching
frequencies around 3300 cm-1 and 2100 cm-1 respectively and the formation of new peaks related to the 1,2,3-triazole unit such as
a low intense peak at 3100 cm-1 (triazole C-H) and a sharp peak at 1450 cm-1 (triazole C=C str). Finally, the formation of poly
(MMA-co-TSDE) polymers were confirmed by the disappearance of peaks corresponding to alkene functional group at1648 cm-1
and the presence of stretching peaks at 1722cm-1 (C=O str), 1150-1250cm-1 (C-O-C str). 1170-1160cm-1, 1085cm-1,970-940cm-1
relates to stretching frequencies of Si-O-CH2CH3 present in TSDE based PMMA.

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a
b
N3Str
N3Str
C=C str
=C-H str
%T
c
≡C-H Str
d
triazoleC-H str
triazoleC=C str
4000.0
3600
3200
2800
2400
2000
1800
cm-1
1600
1400
1200
1000
800
600
450.0
Fig. 1 FT-IR spectra of a) 2-azido ethanol b) 3-(2-azidoethoxy) prop-1-ene c) (N-(prop-2-ynyl)-N-(3-(triethoxysilyl)propyl)prop-
2-yn-1-amine) d) TSDE
a
b
c
%T
d
e
4000.0
3600
3200
2800
2400
2000
1800
cm-1
1600
1400
1200
1000
800
650.0
Fig. 2 FT-IR spectra of a)TSDE-10 b) TSDE-7.5 c) TSDE-5 d) TSDE-2.5 e) PMMA.