Synthesis, Characterization, and Surface Activities of Polymeric Cationic Thiol Surfactants in Aqueous Medium

Article abstract of DOI:10.1002/jsde.12233

A series of cationic polyurethane surfactants [PQ_8-18] were synthesized by the reaction of alkyl bromoacetate (namely: octyl-, decyl-, dodecyl-, tetradecyl-, hexadecyl-, and octadecyl bromoacetate) as quaternizing agents and modified polyurethane contains tertiary amine species. Modified polyurethane was prepared by the reaction of toluene diisocyanate (TDI) and triethanol amine monomercaptoacetate. The chemical structures of the prepared surfactants were confirmed using elemental analysis, Fourier transform infrared spectroscopy (FTIR), and Proton nuclear magnetic resonance (¹H NMR) spectroscopy. The molecular weight measurements of the prepared polymers showed that the segments of each polymer contain average 10 units of the urethane-triethanol amine mercaptoacetate. The surface activities of the prepared surfactants including: surface tension (γ), effectiveness (π_cmc), concentration at micelle formation (CMC), efficiency (Pc₂₀), maximum concentration at the interface (Γ_max), and the average area occupied by each surfactant molecule at the interface at equilibrium (A_min) of surfactants solutions were established at 25°C. The surface tension and the critical micelle concentration values of the prepared surfactants were gradually decreased by the gradual increase of their alkyl chain length. The prepared cationic surfactants showed efficient activity as inhibitors for dissolution of carbon steel in an acidic medium and also as a biocide against the growth of bacteria, fungi, and yeast.

Full text of DOI:10.1002/jsde.12233

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J Surfact Deterg (2018)
DOI 10.1002/jsde.12233
ORIGINAL ARTICLE
Synthesis, Characterization, and Surface Activities of Polymeric
Cationic Thiol Surfactants in Aqueous Medium
Mohamed F. Zaky1 · Ibrahim A. Sabbah2 · Mostafa E. Hendawy2 · Reda S. Abdel Hameed2 ·
Nabel A. Negm1
Received: 4 April 2018 / Revised: 3 September 2018 / Accepted: 24 October 2018
© 2018 AOCS
Abstract A series of cationic polyurethane surfactants
[PQ8-18] were synthesized by the reaction of alkyl bromoa-
cetate (namely: octyl-, decyl-, dodecyl-, tetradecyl-,
hexadecyl-, and octadecyl bromoacetate) as quaternizing
agents and modified polyurethane contains tertiary amine
species. Modified polyurethane was prepared by the reac-
tion of toluene diisocyanate (TDI) and triethanol amine
monomercaptoacetate. The chemical structures of the pre-
pared surfactants were confirmed using elemental analysis,
Fourier transform infrared spectroscopy (FTIR), and Proton
nuclear magnetic resonance (1H NMR) spectroscopy. The
molecular weight measurements of the prepared polymers
showed that the segments of each polymer contain average
10 units of the urethane-triethanol amine mercaptoacetate.
The surface activities of the prepared surfactants including:
surface tension (γ), effectiveness (πcmc), concentration at
micelle formation (CMC), efficiency (Pc20), maximum con-
centration at the interface (Γmax), and the average area
occupied by each surfactant molecule at the interface at
equilibrium (Amin) of surfactants solutions were established
at 25ꢀC. The surface tension and the critical micelle con-
centration values of the prepared surfactants were gradually
decreased by the gradual increase of their alkyl chain
length. The prepared cationic surfactants showed efficient
activity as inhibitors for dissolution of carbon steel in an
acidic medium and also as a biocide against the growth of
bacteria, fungi, and yeast.
Keywords Cationic surfactants ꢁ Micellization ꢁ
Adsorption ꢁ Surface properties ꢁ Polyurethane
J Surfact Deterg (2018).
Introduction
Polyurethanes are an important class of polymers used in a
variety of different applications including furniture, bed-
clothes, chairs, and instrument panels for automobiles, shoes,
thermoinsulation, carpet backings, packaging, and coatings.
The main raw materials for the production of polyurethanes
are polyols based on propylene oxide and diisocyanates.
Bifunctional isocyanates are used to produce long-chain
monolayer polymer systems. Trifunctional isocyanates,
e.g., tris(4-isocyanatophenyl) thiophosphate, are used in pro-
duction of network polyurethanes that have higher mechani-
cal, thermal, and chemical resistance properties. The most
commercial isocyanates are toluene diisocyanate (TDI) and
methylene diphenyl diisocyanate (MDI). Polyether polyols
are used as hydrogen-donating compounds. Chain extenders
and cross linkers are added to the polymerization of polyure-
thane. Chain extenders and cross linkers are low molecular
weight hydroxyl and amine-terminated compounds that play
an important role in the polymer morphology. The type of
chain extender determines flexural, heat, and chemical resis-
tance. The most important chain extenders are ethylene gly-
col, 1,4-butandiol, 1,6-hexandiol, cyclohexane diethanol, and
hydroquinone bis(2-hydroxyethyl) ether. Catalysts of the
polymerization reaction are either amine type or
* Nabel A. Negm
nabelnegm@hotmail.com
1
Petrochemicals Department, Egyptian Petroleum Research
Institute, 1-Ahmed elzommer street-Nasr city, Cairo 11711,
Egypt
2
Chemistry Department, Faculty of Science, Al-Azhar University,
El Nasr Street, BO 11752, Cairo, Egypt
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J Surfact Deterg
organometallic complexes. Amine compounds are triethylene
diamine, dimethyl cyclohexyl amine, and dimethyl ethanol
amine. Organometallic catalysts are dibutylin dilaurate, bis-
muth octanoate, and mercury carboxylate. Polyurethanes
(PUR) are widely used in the fabrication of biomedical
devices or drug delivery systems, due to their excellent physi-
cal properties and good biocompatibility (Akita et al., 2006).
Polyurethane nanoparticles were synthesized using several
techniques such as suspension-polycondensation (Madbouly
and Otaigbe, 2009), interfacial polycondensation combined
to spontaneous emulsification (Mekewi et al., 2017), suspen-
sion polyaddition (Radhakrishnan et al., 2002), and disper-
sion in organic solvent and supercritical carbon dioxide
(Lapprand et al., 2005; Randall and Lee, 2003).
Surface-active agents are chemical compounds character-
ized by lowering the surface tension of water. Because of
their high tendency to decrease the interfacial interaction
between different polar media, surface-active agents are
incorporated in several industrial application as additives,
especially in the polymer production as additives during
emulsion polymerization processes.
acid, and bromoacetic acid were purchased from Sigma-
Aldrich (Berlin, Germany) in a purity of 99.9%. Triethanol
amine, ethyl alcohol, and paraffin oil were purchased from
ADWIC (Egypt) in a purity of 99.8%.
Instrumentation
Elemental analysis: Vario Elementar Analyzer; Fourier
transform infrared spectroscopy (FTIR) spectroscopy: FTIR
spectra were recorded using a Perkin Elmer Genesis Fou-
rier Transformer at 4000–400 (cm−1) applying the potas-
sium bromide compressed thin pellet technique. The
nuclear magnetic resonance spectra were recorded by Var-
ian NMR-300, Mercury 300 MHz spectrometers using
CDCl3 as a solvent and trimethyl silane (TMS) as a refer-
ence to determine the different chemical shifts δ(ppm); sur-
face and interfacial tension measurements were obtained
using a K6-Kruss tensiometer with a platinum ring. Gel
permeation chromatography (GPC) measurements were
performed using a GPC-7890A instrument equipped with a
DB-23 column, 60 mm × 0.25 mm, i.d. of 0.25 μm.
The residues obtained by using conventional small molecu-
lar weight surface-active agents constantly have a negative
impact on the superiority and quality of the polymeric films
formed, and also these residues have antienvironmental influ-
ence as a result of their difficult biodegradation tendency and
reusing ability (Howard, 2002; Tadros, 2005). Consequently,
novel categories of surface-active agents were tailored to
increase the emulsification performance of drugs and medi-
cines and to reduce the environmental pollution impacts (Dong
et al., 2006; Guo et al., 2009; Holmberg et al., 2003).
Polyurethanes displayed an amphiphilic structure (i.e., the
presence of polar head and organic tail), which have a suitable
equilibrium in their lipophilic and lyophilic moieties, and are
of great interest as additives instead of conventional small
molecular weight surface-active agents (Ismail, 1998; Zheng
et al., 2010). The different types of amphiphilic polyurethane
surfactants (cationic, anionic, and nonionic) can be prepared in
simple pathways as the structure of polyurethane can be widely
modified by varying the polyurethane constituents including
the isocyanates, polyols, chain extenders, and blocking agents
(Negm and Mohamed, 2008; Shokry et al., 2015). In the pre-
sent study, cationic polyurethane surfactants were prepared and
characterized and surface activities were measured.
Preparation of Triethanol Amine Monomercaptoacetate
Triethanol amine (0.1 mol) and mercaptoacetic acid
(0.1 mol) were dissolved in xylene (75 mL) in a 250 mL
round flask and p-toluene sulfonic acid (0.1 g) was added as
a dehydrating agent. The completion of the reaction was
monitored by obtaining 0.1 mol of H2O (1.8 mL) (Negm and
Mohamed, 2008). At the end of the reaction, the solvent was
removed by evaporation while p-toluene sulfonic acid was
eliminated from the reaction medium by taking out the esters
obtained by dissolving in diethyl ether. The evaporated sol-
vent was recovered and purified for reuse. The unreacted and
excess reactants were eliminated from the products by succes-
sive sanitization of the crude products to afford triethanol
amine monomercaptoacetate in a yield of 96%.
Preparation of Thiol Polyurethane (P)
Thiol polyurethane polymerization reaction was carried out
in a flat bottom glass reactor (500 mL) equipped with a
mechanical stirrer, a dropping funnel, a thermometer, and a
condenser. Inside the reaction vessel, a mixture of TDI
(0.1 mol) dissolved in methyl ethyl ketone (50 mL),
triethanol amine mercaptoacetate (0.2 mol), and five drops
of triethylene diamine added dropwise over 20 min was
mixed (Shokry et al., 2015). The reaction medium was con-
tinuously mixed at 30ꢀC for 30 min to obtain the prepoly-
mer. The ratio of isocyanates (NCO) to reactive hydroxyl
group (OH) was held constant at 1:2. The prepared polymer
was washed twice using appropriate amounts of methyl
ethyl ketone and dried (yield 92%).
Experimental
Materials
Octanol, decanol, dodecanol, tetradecanol, hexadecanol and
octadecanol, toluene diisocyanate (TDI), mercaptoacetic
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Preparation of Fatty Bromoacetate Esters (Q8-Q18)
Corrosion Measurements
Fatty bromoacetate esters (Q8-Q18) were prepared through
reacting different fatty alcohols (0.1 mol) namely: octanol,
decanol, dodecanol, tetradecanol, hexadecanol, octadecanol
(C8-C18), and bromoacetic acid (0.1 mol) in the presence of
xylene (100 mL) as a solvent and p-toluene sulfonic acid
(0.01 wt.%) as a dehydrating agent under heating and stir-
ring conditions until the expected amount of water
(1.8 mL) is produced. At the end of the reaction, xylene
was stripped off using reduced pressure; p-toluene sulfonic
acid was eliminated by extracting the product from diethyl
ether and the solvent was removed (Negm and Morsy,
2005) to afford the different fatty bromoacetate esters (yield
95–98%).
Corrosion experiments were performed using carbon steel
samples of elemental composition (wt.%): 0.21C, 0.035 Si,
0.025 Mn, 0.082 P, and the remainder is Fe. Carbon steel
samples of 2.5 × 2.0 × 0.6 cm dimensions were scraped
using 320, 500, 800, and 1200 grade emery papers and
washed with acetone and distilled water. After weighing
accurately, the samples were submerged in 250 mL solu-
tion of 1 M H2SO4 containing different concentrations
(50, 100, 200, 400, and 600 ppm) of the tested inhibitors
(PQ8-18) for 14 days. Then, the samples were washed,
dried, and weighed accurately (ASTM G1-72, 1990). The
test was performed for three samples and the weight was
the average of the three specimens. The corrosion rate
(Cr) and the inhibition efficiency (IE %) were calculated
using Eqs. (1) and (2) (Bhupendra et al., 2011):
Preparation of Cationic Thiol Polyurethane Surfactants
(PQ8-18
)
Cr ¼ ΔW=At
ð1Þ
ð2Þ
IE% ¼ ½ðCro – CrÞ=Croꢂx100
Cationic thiol polyurethane surfactants (PQ8-18) were pre-
pared by refluxing equimolar amounts of thiol polyurethane
(P) and octyl, decyl, dodecyl, tetradecyl, hexadecyl, and
octadecyl esters (Q8-Q18) individually in a suitable amount
of dimethyl formamide (DMF) for 20 h. The produced
compounds were filtered off, washed by excess DMF, and
dried under reduced pressure at 50ꢀC to afford yellow to
brown viscous liquids designated as: PQ8, PQ10, PQ12,
PQ14, PQ16, and PQ18 (yield 82–89%) (Negm et al., 2017;
Zaki et al., 2015).
where ΔW is the average weight loss of three parallel car-
bon steel samples, A is the area of the specimen, t is the
immersion time, and Cro and Cr are the Cr without and
with addition of the inhibitor, respectively (Lehr and Said-
man, 2006; Negm and Aiad, 2007).
Antimicrobial Activity Measurements
Antimicrobial activity of the synthesized surfactants was
tested against: Staphylococcus aureus, Escherichia coli,
Pseudomonas aeruginosa, Bacillus subtilis, Desulfomonas
pigra, and Staphylococcus typhimurium. For preparation of
discs and inoculation, 1.0 mL of inocula were added to
50 mL of agar media (40ꢀC) and mixed. The agar was
poured into 120 mm petri dishes and allowed to cool to
room temperature. Wells (6 mm in diameter) were cut into
agar plates using proper sterile tubes and filled up to the
surface of agar with 0.1 mL of the synthesized cationic
Thiol polyurethane surfactants (PQ8-18) dissolved in DMF
(5 mg mL−1). The plates were left on a leveled surface,
incubated for 24 h at 30ꢀC, and then the diameters of the
inhibition zones were read. The inhibition zone formed by
these compounds against the particular test bacterial strain
determined qualitatively the antibacterial activities of the
synthetic compounds. The mean value obtained for three
individual replicates was used to calculate the zone of
growth inhibition of each sample. The antimicrobial activ-
ity was calculated as a mean of three replicates. The tested
compounds were completely compatible with the medium
of agar and no turbidity was observed during the mixing
process (National Committee for Clinical Laboratory Stan-
dards, 1997; Negm et al., 2010a).
Surface Tension Measurements
Surface tension measurements were carried out using a
Kruss-K6 tensiometer with a platinum De-Nouy ring.
Freshly prepared aqueous solutions of the prepared cationic
polyurethane surfactants (PQ8-PQ18) were used at a con-
centration range of 10−7–10−3 M. Apparent surface tension
values were measured at 25ꢀC in triplicate for each sample
within a 2 min interval between the readings and the aver-
age was considered (Negm et al., 2015a). The tensiometer
was calibrated before each measurement using bidistilled
water at 25ꢀC.
Gel Permeation Chromatography
Gel permeation Chromatographic analysis of the prepared
surfactants was performed to determine their molecular
weights using a GPC-7890A instrument equipped with a
DB-23 column, 60 mm × 0.25 mm, i.d. of 0.25 μm, and
water was used as a solvent, while polyethylene glycols of
different molecular weights were used as references
(Azzam et al., 2011).
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Results and Discussion
1736–1738 cm−1 corresponds to carbonyl ester indicating
the ester (Q8-Q18) formation; 1275–1277 cm−1 corresponds
to ether linkages C O C; 2920–2922 cm−1 and
2849–2850 cm1 corresponded to symmetric and asymmet-
ric stretching of C H groups. The characteristic absorption
band of the C Br bond appeared in the range of
663–667 cm−1. Infrared spectroscopy (IR) spectra of the
prepared cationic polyurethane surfactants showed similar
absorption bands to the absorption bands of triethanol
amine mercaptoacetate, thiol polyurethane, and alkyl bro-
moacetate esters. Furthermore, IR spectra showed a disap-
pearance of the absorption band at 660 cm−1 and the
appearance of a new absorption band at 3040 cm−1 corre-
sponding to the C N+ group.
The preparation of polyurethane cationic surfactants is
shown in Scheme 1. The chemical structures of the pre-
pared cationic surfactants and their intermediates were con-
firmed using FTIR spectroscopic analysis. FTIR spectra of
triethanol amine mercaptoacetate showed the following
absorption bands: a broad absorption band centered at
3435 cm−1 corresponds to OH stretching; a weak absorp-
tion band at 2550 cm−1 corresponds to stretching of the
S H group; an absorption band at 2932 cm−1 attributed to
symmetric stretching of C H group; 1018 cm−1 corre-
sponds to the C N stretching group of aliphatic amine, and
an absorption band at 1732 cm−1 corresponds to the C O
ester group.
1
The H NMR spectra of the synthesized cationic surfac-
Thiol polyurethane compound (P) showed the following
absorption bands: 1663 cm−1 corresponds to the C O of
urethane group; 1458 and 1462 cm−1 correspond to the
N H of urethane group; 1508–1510 cm−1 described for
the double bonds in the phenyl moiety (C C) in the TDI
moiety.
tants showed the appearance of signals at: δ = 0.85 ppm (t,
3H, and CH3) assigned to the terminal methyl group;
1.25 ppm (m, nH, CH2) attributed to the methylene groups
of the fatty chains; 2.5 ppm (t, 3H, CH3Ph) assigned to the
methyl group of the TDI moiety; 7.8 ppm, 8.0 ppm, and
8.2 ppm (m, 4H, and phenyl group).
FTIR spectra of alkyl bromoacetate esters (Q8-Q18)
represented the disappearance of the broad band at
3400 cm−1 of alcoholic hydroxyl groups of the reacted
fatty alcohols, the appearance of new absorption bands at:
The elemental analysis of the prepared cationic polyure-
thane surfactants (Table 1) showed the comparable values
of the predicted and obtained ratios of the different ele-
ments in their chemical structure. The molecular weights of
BrCH2COOH
+
CH3(CH2)nCH2OH
CH3
O
O
C
H
N
O
C
OCCH2SH
CH2
OCH2CH2
N
CH2CH2
O
Br CH2
O
CH2(CH2)n CH3 +
CH2
Alkyl bromoacetate
CH2
CH2
N
H
C
O
CH2CH2 N CH2CH2O
OCCH2SH
O
O
m
DMF
reflux
O(CH2)nCH3
O
C
CH3
O
CH2
N+
O
C
H
N
OCCH2SH
CH2
OCH2CH2
CH2CH2
O
CH2
CH2
N+
CH2
N C
O
CH2CH2
CH2CH2O
OCCH2SH
O
H
O
CH2
C
O
O(CH2)nCH3
n=7, 9, 11, 13, 15, and 17.
m= number of repeating units.
m
Scheme 1 Preparation of the cationic polyurethane surfactants
J Surfact Deterg (2018)