Synthesis and applications of quaternized highly branched polyacrylamide as a novel multi-site polymeric phase transfer catalyst

Article abstract of DOI:10.1007/s13738-012-0214-0

In current study, quaternized highly branched polyacrylamide (HBAA) was synthesized and used as an efficient multi-site polymeric phase transfer catalyst in nucleophilic substitution reactions and also in synthesis of α, β-unsaturated nitriles from reaction of acetonitrile and carbonyl compounds. The quaternized HBAA was synthesized via two steps. First, HBAA was synthesized via self-condensing vinyl polymerization of acrylamide at appropriate molar ratio of monomer to diperiodatocuprate(III). In the second step, 3-acrylamidopropyl trimethylammonium iodide was polymerized on peripheral area of the HBAA in the presence of diperiodatocuprate(III) solution again. The thermal behavior of HBAA and that of the quaternized HBAA were studied by DSC and TGA analysis. This phase transfer catalyst was easily recovered after reaction and reused several times without any loss of activity.

Full text of DOI:10.1007/s13738-012-0214-0

J IRAN CHEM SOC (2013) 10:791–797
DOI 10.1007/s13738-012-0214-0
ORIGINAL PAPER
Synthesis and applications of quaternized highly branched
polyacrylamide as a novel multi-site polymeric phase
transfer catalyst
•
Hossein Mahdavi Mehdi Amirsadeghi
Received: 29 August 2012 / Accepted: 27 December 2012 / Published online: 22 January 2013
Ó Iranian Chemical Society 2013
Abstract In current study, quaternized highly branched
polyacrylamide (HBAA) was synthesized and used as an
efficient multi-site polymeric phase transfer catalyst in
nucleophilic substitution reactions and also in synthesis of
a, b-unsaturated nitriles from reaction of acetonitrile and
carbonyl compounds. The quaternized HBAA was syn-
thesized via two steps. First, HBAA was synthesized via
self-condensing vinyl polymerization of acrylamide at
appropriate molar ratio of monomer to diperiodatocup-
rate(III). In the second step, 3-acrylamidopropyl trimethy-
lammonium iodide was polymerized on peripheral area of
the HBAA in the presence of diperiodatocuprate(III)
solution again. The thermal behavior of HBAA and that of
the quaternized HBAA were studied by DSC and TGA
analysis. This phase transfer catalyst was easily recovered
after reaction and reused several times without any loss of
activity.
scientific and industrial important applications such as
viscosity modifiers, drug delivery systems, efficient support
of catalysts and scaffolds [3–6].
Generally, there are three main strategies for synthesis
of highly branched polymers involving: (1) Step-growth
polycondensation of ABX and/or A2 ? B3 monomers, (2)
Self-condensing vinyl polymerization (SCVP) of AB*
monomers, and (3) Multi-branching ring-opening poly-
merization of latent ABX monomers [7–9].
Self-condensing vinyl polymerization of AB* monomers
was proposed by Frechet in 1995 [10]. ‘‘A’’ denotes a vinyl
group and ‘‘B*’’ represents a functional group that can
initiate group A into propagating site A*. The feature of
this approach is that the vinyl group A can undergo self-
polymerization, and hence, this method is called SCVP.
According to this idea, Matyjaszewski [11] prepared hy-
perbranched polystyrene through one-pot atom transfer
radical polymerization using p-(chloromethyl) styrene.
This approach has also been applied in the other living
polymerizations, i.e., cationic [12, 13], ATRP [14], nitr-
oxide mediated radical polymerization [15], GTP [16], and
ring-opening polymerization [17].
Keywords Highly branched polymers ꢀ Self-condensing
vinyl polymerization ꢀ Phase transfer catalyst ꢀ
a, b-Unsaturated nitrile
Xi in 1999 [18] reported a smart method for preparation of
highly branched polyacrylamide (HBAA), which was carried
out in the presence of basic solution of potassium diperioda-
tocuprate. This method was a subclass of SCVP in which
double bond of acrylamide is as A moiety and its nitrogen
radicals that is generated via oxidation of amide group by
potassium diperiodatocuprate play role of B* moiety. The
benefit of this method is that acrylamide used solely and no
previous preparation of AB* monomer was needed.
Among variety of phase transfer catalysts (PTC), qua-
ternary ammonium and phosphonium salts have more
application because of their appropriate activity and also low
cost.
Introduction
Hyperbranched and highly branched polymers are a special
type of dendrimers and have common similarity such as
high degree of branching and high functional group density
on the surface [1, 2]. In recent years, highly branched
polymers have received much attention owing to their
H. Mahdavi (&) ꢀ M. Amirsadeghi
School of Chemistry, College of Science,
University of Tehran, P.O. Box 14155-6455, Tehran, Iran
e-mail: hmahdavi@khayam.ut.ac.ir
123

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J IRAN CHEM SOC (2013) 10:791–797
Synthesis of 3-acrylamidopropyl trimethylammonium
iodide
Recently, many studies have been reported on attempts
to develop multi-site phase transfer catalysts (MPTCs)
containing more than one catalytic active site in a molecule
[19–23]. This type of MPTCs offers the potential of pro-
viding greater PTC activity and accelerating the particular
synthetic transformation even under mild conditions.
One important salient feature for employing MPTC for
any chemical reaction is that the concentration of MPTCs
required to conduct the reaction are relatively low com-
pared to soluble single-site PTCs.
In a 100 ml flask, N,N-DMAPAA (1.56 g, 0.01 mol) was
dissolved in dichloromethane (20 ml) and kept in an ice
bath. An excess amount of iodomethane (5 ml, 0.08 mol)
dissolved in dichloromethane (10 ml) was added drop wise
to the flack content. The mixture was stirred for 2 h at 0 °C
and then 4 h at ambient temperature. After that, the
dichloromethane was evaporated and the viscose brown
liquid of 3-acrylamidopropyl trimethylammonium iodide
was obtained in 92 % yield (2.75 g). The FT-IR spectra of
3-acrylamidopropyl trimethylammonium iodide showed
peaks at 2,930, 1,665, 1,613, 1,560, 1,480, 1,430, 1,373,
Herein, we report the synthesis and applications of
quaternized HBAA as an efficient and novel multi-site
polymeric phase transfer catalyst.
1,256, 1,054 and 990 cm-1
.
Experimental
Synthesis of highly branched acrylamide
Materials
Highly branched acrylamide (HBPAA) was synthesized
according to Xi procedure with some modification [18].
Typical procedure: 2.0 g acrylamide (28 mmol) and
100 ml potassium diperiodatocuprate solution (0.056 mol)
were added to a 250 ml flask. The polymerization was
carried out for 48 h at 40 °C under nitrogen atmosphere.
Then, the reaction component was filtered and pH of the
polymer solution was adjusted to 6–7 by addition of HCl
solution (10 %), and that precipitated byproduct was fil-
tered out. The remaining filtrate was concentrated and
poured into methanol. The resulting polymer was filtered
and washed with methanol (three times) and then dried
under vacuum at 50 °C for 2 days (yield 90 %).
Acrylamide was purchased from Merck and recrystallized
from methanol. N,N-dimethylaminopropyl acrylamide
(DMAPAA) and potassium periodate were purchased from
Aldrich. Other reagents were purchased from Merck and
used as received without further purifications. In order to
obtain reaction yields, gas chromatography was used and
recorded on a shimadzu GC14-A.
H-NMR spectra
IR spectra were run on a perkin-Elmer-IR-157.G spectro-
photometer. TGA spectra were obtained by TGA-Q-50-
V6.3 build 189. DSC measurements were made on a TA
DSC Q100 V9.0 (New Castle, DE, USA) equipped with
thermal analysis data acquisition software. The rate of
heating was 5 °C/min.
Synthesis of quaternized highly branched
polyacrylamide
50 ml potassium diperiodatocuprate solution and 0.5 g
HBAA were added to a 150 ml flask equipped with
nitrogen inlet and outlet, and were stirred under nitrogen
atmosphere at 40 °C. Thereafter, an aqueous solution of
3-acrylamidopropyl trimethylammonium iodide (1.0 g in
5 ml of DW) was added to the reaction mixture through
drooping funnel in 30 min. The polymerization was
carried out at 40 °C for 48 h. In the next step, the pH of
reaction mixture was adjusted to 7 by adding HCl. The
precipitate was filtered, and the filtrate was concentrated
and then poured to methanol. The precipitated polymer
was filtered and washed with methanol and dried under
vacuum at 60 °C. The yield of reaction was 62 %. The
amount of iodide ion present in the quaternized HBAA
was determined by Volhard’s method and found to be
2.4 mmol/g.
Synthesis of potassium diperiodatocuprate solution
The potassium diperiodatocuprate solution was prepared
according to reported procedure [24]. Typical procedure
was as the following: CuSO4ꢀ5H2O (3.54 g, 14 mmol),
KIO4 (6.82 g, 30 mmol), K2S2O8 (2.20 g, 8 mmol) and
KOH (9.00 g, 160 mmol) were added to 200 ml of
deionized water (DW). The mixture was refluxed for
40 min. After cooling to room temperature, the mixture
was filtered through sintered glass and the filtrate was
diluted to 250 ml with DW. The concentration of copper
(III) in aqueous solution was determined by iodometric
titration and also gravimetrically by the thiocyanate
method. The final concentration of Cu (III) was titrated as
0.056 mol/L and the concentration of KOH as 0.55 mol/L.
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793
Application of quaternized highly branched
polyacrylamide as the phase transfer catalyst
in biphasic reactions
Results and discussion
Diperiodatocuprate (III) is an efficient radical initiator that
can generate radical on substance containing mono or di-
substituted amine, amide or hydroxyl group [25–28]. The
mechanism of initiation involves an one-electron transfer
oxidation process. For example, the amide group can be
converted to an amidyl radical in the presence of Cu(III). In
this reaction, one electron of the nitrogen atom is taken by
Cu(III) to form a cation radical. Then, the cation radical
loses a proton in alkaline medium and produce amidyl
radical, which is capable to initiate a radical polymeriza-
tion (Scheme 1).
Nucleophilic substitution on benzyl chloride
Typical procedure: 0.01 mol of nucleophilic salt (M?X-)
was added to a 25 ml flask contained 10 ml distillated
water. 0.12 ml benzyl chloride (1 mmol) dissolved in 3 ml
toluene was added to flask and stirred at room temperature.
0.01 g of quaternized HBAA was added to reaction vessel
and reaction was carried out at 70 °C. After appropriate
time, a sample of reaction was taken from organic layer
and after drying by sodium sulfate, the yield of reaction
was determined by GC.
Xi et al. [18] demonstrated that HBAA could be syn-
thesized via SCVP method using appropriate molar ratio of
monomer to diperiodatocuprate(III) solution. They showed
that by increasing amount of Cu(III), degree of branching
increased and structure of polymer became more similar to
highly branched polymers. Since only acrylamide mono-
mer was used in this method for the synthesis of HBAA,
the obtained highly branched polymer had a numerous
amide groups on its surface.
Condensation of acetonitrile with ketones
Typical procedure: 0.5 g of powdered KOH, 10 ml dry
acetonitrile and 0.02 g quaternized HBAA were added to a
25 ml flask and stirred at room temperature. Thereafter,
1 mmol of ketone was added to the reaction mixture and
refluxed at 83 °C for appropriate time. After that, a sample
of reaction was taken from organic layer and the yield of
reaction was determined by GC.
In this research after preparation and purification of
HBAA via mentioned procedure, it was resolved again and
reacted with fresh solution of Cu(III) in the presence of
3-acrylamidopropyl trimethylammonium iodide as the
functional monomer. It is envisaged in this approach that
some of peripheral amide groups of HBAA react with
Cu(III) complexes and generate corresponding radical
species which are then able to initiate radical polymeriza-
tion with appropriate monomer. Therefore, it is reasonable
to expect that the final functional system have HBAA in its
core and grafted poly (3-acrylamidopropyl trimethylam-
monium iodide) on its peripheral section (Scheme 2).
The resulting quaternized copolymer was characterized
at first by IR spectroscopy. The IR spectrum showed peaks
Selected spectral data
Cyclohexenylacetonitrile: bp 50 °C (0.5 torr) [lit [31]: bp
1
82–84 °C (3–4 torr)]; H-NMR (CCl4): d 1.25–2.0 (m, 4
H), 1.25–2.0 (m, 2 H), 2.0–2.8 (m, 4 H), 3.3 (s, 1H); IR
(neat) 2,252 (w) cm-1.; 2,2-Diphenylacrylonitrile: Color-
less oil: bp 128–131 °C (0.2 torr) [lit. mp 47–48 °C; bp
1
160–200 °C (1.5 torr) H-MR (CCl4) d 5.69 (s, 1 H), 7.4
(d, 10 H); IR (neat) 2,218 (s) cm-1.; (E)- and (Z)-2-Methyl-
2-phenylacrylonitrile pale yellow oil [E/Z ca. 4.0 (NMR)]:
1
bp 78 °C (0.2 torr) [lit. bp 120–129 °C (2 torr)]; H-NMR
(CCl4) E isomer, d 2.5 (d, 3 H), 5.7 (m, 1 H), 7.55 (s, 5 H);
1H-NMR (CCl4) Z isomer, d 2.3 (d, 3 H), 5.45 (m, 1 H),
7.55 (s, 5 H); IR(neat) 2,221 (s) cm-1.; 2-(9H-fluoren-9-
ylidene)acetonitrile: yellow solid, mp 109–110 °C (lit. 30
O
O
Cu(III)
OH-
1)
2)
Y
NH2
Y
NH2
Y= R, Ar
1
mp 109–111 °C). H-NMR(CCl4) d 5.98 (s, 1 H), 7.2–7.7,
8.2–8.35 (m, 8 H); IR (CCl4) 2,205 (s) cm-1
.
O
O
Y
NH
Recycling of catalyst
Y
NH2
In order to recover the catalyst at the end of reaction, the
organic phase was separated and concentrated under
reduced pressure. Then, the concentrated mixture was
added to methanol (100 ml) as a non-solvent. The precip-
itated polymer was filtrated and washed three times by
methanol (20 ml) and dried under vacuum at 50 °C.
O
R
O
R
n
+
3)
Y
NH
HN
m
Scheme 1 The mechanism of intiation process
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J IRAN CHEM SOC (2013) 10:791–797
CONH2
CONH2
CONH2
3.29 ppm (0.68), methylene groups attached to quaternary
nitrogen at 3.07 ppm (3.41) and methyen groups attached
to nitrogen at 3.1 ppm (1.36).
CONH2
CONH
CONH2
H2NOC
H2NOC
HNOC
H2NOC
Cu(III)
HBPAA
HBPAA
H2NOC
H2NOC
H2NOC
CONH2
CONH
H2NOHC
To study the thermal behavior of samples, DSC mea-
surements were carried out. Figure 1 represents the DSC
thermograms of HBPAA and quaternized HBPAA. The
thermal glass transition peak and the onset thermal glass
transition of the two samples were 8.52, 13.66 and 11.02,
14.01 °C, respectively. By increasing the quaternary
ammonium sites, change in the characteristic temperatures
in DSC was clearly observed in Fig. 1b in comparison to
Fig. 1a. Obviously, increasing Tg for quaternized HBPAA
was attributed to introducing of quaternary ammonium
sites.
CONH2
H2NOC
CONH2
H2NOC
CONH2
CONH2
O
+
N
-
I
N
H
+
-
CONHCH2CH2N(CH2)3
I
CONH2
HNOC
H2NOC
CONH (CH2-CH)n
+
-
CONHCH2CH2N(CH2)3
I
CONH2
HBPAA
H2NOC
H2NOC
CONH
(CH2-CH)n
CONHCH2CH2N(CH2)3
+
-
I
The thermal degradation behavior of samples was
measured. The thermo-gravimetric (TG) curves of HBPAA
and quaternized HBPAA were plotted in Fig. 2. As
observed, two samples exhibited one-step degradations but
with different residual weight percent. The onset decom-
position temperature (Ton), the temperature at 20 % weight
loss (T20), final decomposition temperature (Tf) and final
weight loss percent (% WLf) of the samples are listed in
Table 1. The difference of Ton of the two samples was
related to higher water content of quaternized HBPAA
CONH2
CONH2
NHOC
(CH2-CH)n
CONHCH2CH2N(CH2)3
+
-
I
Core-shell type quaternized polyacrylamide
Scheme 2 The synthesis steps of quaternized highly branched
polyacrylamide
at 3,400 cm-1 (N–H amide), 1,655 cm-1 (C = O amide),
1,544 cm-1 and 1,408 cm-1. The capacity of quaternized
copolymer was quantitatively estimated by Volhard [29]
method and was found to be 2.4 mmol/g.
H-NMR spectra of quaternized HBAA in D2O shows
methylene group at 2.17 ppm (1.66), methyn groups at
Fig. 1 DSC curves of a HBPAA and b quaternized HBPAA
Fig. 2 TG curves of a HBPAA and b quaternized HBPAA
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J IRAN CHEM SOC (2013) 10:791–797
795
Table 1 TG results of samples
Table 2 Substitution reactions of benzyl chloride with a variety of
nucleophiles
Sample
Ton (oC)
T
20(oC)
Tf(oC)
WLf(%)
Entry Nucleophile Product
Time Yield
(min) (%)
HBPAA
124
90
355
405
590
590
57.88
49.47
Quaternized HBPAA
O
1
OAc
CN-
40
95
O
Nu
Cl
CN
2
3
4
5
30
30
30
40
100
100
100
90
Cl-
+
Nu
+
N3
Scheme 3 Substitution reaction of benzyl chloride
-
N3
because of its quaternary ammonium salts. In addition, all
the three other parameters obviously showed that quat-
ernized HBPAA have higher thermal stability than HBPAA
because of its additional salt structure.
SCN
SCN-
NO2
-
NO2
Applications of quaternized HBPAA in biphasic
reaction
At first, the activity of the quaternized HBPAA as a phase
transfer catalyst was studied for the substitution reactions
Reaction condition: benzyl chloride 1 mmol in 1 ml toluene, Nu
0.01 mol in 5 ml H2O, HBAA-APTMAI 0.02 g, T = 70 °C
of benzyl chloride with
(Scheme 3; Table 2).
a variety of nucleophiles
These substitutions satisfactorily proceeded in excellent
yields without detectable side reactions in the presence of
quaternized HBPAA as a phase transfer catalyst at 70 °C.
As reported before in the literature for other catalyst, in
these nucleophilic reactions, there was no reaction pro-
ceeding or taking place in very low yield in the absence of
the quaternized HBPAA [30]. Furthermore, in comparison
to numerous reported results about same nucleophilic
reaction in the presence of phase transfer catalyst [31], the
quaternized HBPAA has higher reactivity. A reasonable
description of this higher reactivity is that the quaternized
HBPAA has multiple quaternary catalytic site because of it
highly branched structure.
spontaneously dehydrated to afford the a, b-unsaturated
nitrile under reaction condition (Scheme 4).
Finally, in all of these applications workup of the
reaction was easy and the polymer was removed from the
reaction mixture via simple precipitation by adding to
methanol and/or filtration. Interestingly, it was also
observed that this recycled quaternized HBPAA after
several times recycling (at least five times) could be used
without any loss in their efficiency in the mentioned
reactions.
1)
2)
Q+ I-
Q+ OH-(org) +
K+ I-
- (aq) +
K+OH
Q+ OH-
(org)
In continuation of applications, the quaternized HBPAA
was used in a standard condensation reaction. For instance,
the synthesis of a, b-unsaturated nitriles from reaction of
acetonitrile and carbonyl compounds was selected as
model reaction [32]. The condensation reaction of aceto-
nitrile with various carbonyl compounds were carried out
in the presence of the quaternized HBPAA as a phase
transfer catalyst at 70 °C (Table 3). In this reaction,
cynamoethide ion was generated via deprotonation of
acetonitrile by KOH in the presence of the PTC. Then,
cynamoethide ion was added to carbonyl group of
ketones, and b-hydroxynitrile intermediate prepared that
Q+ CH C
Q+
N
(org)
+
+
H2O
H3C
C
N
O
O
CH2CN
R2
Q+ CH C
N
+
3)
R1
R2
R2
N
Q+
O
CH2CN
4)
Q+ OH-
+
R2
R2
R1
R2
Scheme 4 Phase transfer catalysis mechanism in synthesis of a,
b-unsaturated nitriles
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J IRAN CHEM SOC (2013) 10:791–797
Table 3 Synthesis of
a, b-unsaturated nitriles
Time
(min)
Yield
(%)
Reported
Entry
1
Substrate
Product
Yield(%)[32]
CN
72
O
60
95
O
CN
60
2
3
45
90
O
CN
CH3
50
20
80
CH3
15
76
O
CN
4
100
Reaction condition: KOH
(0.5 g), dry acetonitrile (10 ml),
HBAA-PTMAI (0.02 g), ketone
(5 mmol)
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Conclusion
In conclusion, we have demonstrated a very effective
method for the synthesis of quaternized HBAA. The
quaternized HBAA was synthesized via two steps. First,
HBAA was synthesized via SCVP of acrylamide using
appropriate molar ratio of monomer to diperiodatocup-
rate(III). In the second step, 3- acrylamidopropyl trime-
thylammonium iodide was polymerized on peripheral
area of the HBAA in the presence of diperiodatocup-
rate(III) solution again. This multi-site polymeric phase
transfer catalyst was used effectively in nucleophilic
substitution reactions and also in the synthesis of a, b-
unsaturated nitriles from reaction of acetonitrile and
carbonyl compounds. This phase transfer catalyst was
easily recovered and reused several times without any
loss of activity.
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Acknowledgments We are thankful to Research Council of the
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