Kinetics and structure-activity relationship of dendritic bridged hindered phenol antioxidants to protect styrene against free radical induced peroxidation

Article abstract of DOI:10.1134/S0036024417120056

A series of dendritic poly(amido-amine) (PAMAM) bridged hindered phenols antioxidants were synthesized. The active antioxidant group (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid) was attached to two generations of PAMAM dendrimers, and their structure was verified by nuclear magnetic resonance (NMR) and fourier transform infrared spectra (FT-IR). The antioxidant abilities of the dendritic phenols to inhibit the oxidation of styrene were evaluated and the relationships between the length of core, the generation of dendrimers and the antioxidant activities were established. The reaction kinetics of scavenging peroxyl radicals was followed by oxygen consumption. The inhibition time (t_inh) values showed the dendritic phenols had the ability of scavenging peroxyl radicals, and that the antioxidant ability increased with the increasing length of the core and the generation. The kinetic analysis demonstrated that dendritic phenols could slow the rate of styrene peroxidation induced by AIBN, as shown by the number of trapping ROO· (n), and this role was in accordance with that of the t_inh values.

Full text of DOI:10.1134/S0036024417120056

ISSN 0036-0244, Russian Journal of Physical Chemistry A, 2017, Vol. 91, No. 12, pp. 2350–2360. © Pleiades Publishing, Ltd., 2017.
CHEMICAL KINETICS
AND CATALYSIS
Kinetics and Structure-Activity Relationship of Dendritic Bridged
Hindered Phenol Antioxidants to Protect Styrene against Free
1
Radical Induced Peroxidation
Cui-Qin Li*, Su-Yue Guo, Jun Wang, Wei-Guang Shi, Zhi-Qiu Zhang, and Peng-Xiang Wang
Provincial Key Laboratory of Oil and Gas Chemical Technology, College of Chemistry and Chemical Engineering, Northeast
Petroleum University, Daqing, Heilongjiang, 163318 China
*
e-mail: dqpilicuiqin@126.com
Received October 18, 2016
Abstract—A series of dendritic poly(amido-amine) (PAMAM) bridged hindered phenols antioxidants were
synthesized. The active antioxidant group (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid) was
attached to two generations of PAMAM dendrimers, and their structure was verified by nuclear magnetic res-
onance (NMR) and fourier transform infrared spectra (FT-IR). The antioxidant abilities of the dendritic
phenols to inhibit the oxidation of styrene were evaluated and the relationships between the length of core,
the generation of dendrimers and the antioxidant activities were established. The reaction kinetics of scaveng-
ing peroxyl radicals was followed by oxygen consumption. The inhibition time (t ) values showed the den-
inh
dritic phenols had the ability of scavenging peroxyl radicals, and that the antioxidant ability increased with
the increasing length of the core and the generation. The kinetic analysis demonstrated that dendritic phenols
could slow the rate of styrene peroxidation induced by AIBN, as shown by the number of trapping ROO· (n),
and this role was in accordance with that of the t values.
inh
Keywords: dendritic phenol, generation, antioxidant ability, kinetic parameter
DOI: 10.1134/S0036024417120056
INTRODUCTION
2-picrylhydrazyl (DPPH) radical assay. The results
showed that polymers bearing 3,5-di-tert-butyl-4-
hydroxyphenyl-propionate, as side chain, exhibited a
higher radical scavenging ability than the polymers
bearing 3,5-di-tert-butyl-4-hydroxy-benzoate as side
chain. Shi et al. [9] synthesized a functionalization of
multiwalled carbon nanotubes (MWCNTs) with anti-
oxidant ability by grafting the antioxidant group onto
the surface of MWCNTs. The resulting antioxidant
activity showed that not only the free radical scaveng-
ing ability of functional MWCNTs but also the disper-
sion and antioxidant efficiency the antioxidants in the
polyethylene matrix are increased.
Polymer materials, which are commonly hydrocar-
bon polymers, have a broad range of applications in
food packaging, pipeline, and medical equipment due
to their excellent mechanical properties, low cost, and
superior processability [1–3]. However, polymer
materials are susceptible to oxidative degradation
during processing or in the presence of light, heat,
oxygen, and chemical agents [4]. As a consequence
free radicals, produced by oxidation, could lead to a
loss of performance. Therefore, hindered phenol anti-
oxidant is an essential additive, due to the presence of
a hydroxyl substituent and aromatic structure, which
inhibits oxidation by a hydrogen atom competing with
Dendrimer, with its uniform and well-defined size
the polymer in the formation of peroxy radicals [5, 6]. and shape, has attracted great interest. Dendrimer has
Several synthetic approaches of hindered phenol anti- a large number of surface groups which can be easily
oxidants have been developed to improve the antioxi- tailored to achieve various objects [10]. For their
dant properties. These include the grafting of phenolic unique architecture and macromolecular characteris-
antioxidants onto the polymer backbone or nanopar- tics, dendrimers have become one of the research
ticles to increase the molecular weight of phenolic hotspots in areas such as inorganic chemistry, organic
antioxidants [7]. Xue et al. [8] synthesized several nor- chemistry, polymer chemistry, coordination chemis-
bornene derivatives by attaching sterically hindered try and bioscience, especially in synthesis, drug deliv-
phenol to norbornene, and the antioxidant activity of ery, biotechnology, nanotechnology, detection and
the hindered phenol was investigated by 1,1-diphenyl- catalyst [11]. Surface functional dendrimers have been
synthesised and their applications have become the
primary focus. Malgas et al. [12] synthesised first-gen-
1
The article is published in the original.
2350

KINETICS AND STRUCTURE-ACTIVITY RELATIONSHIP
2351
eration and second-generation multinuclear nickel dendritic poly(amidoamine) (2.0G PAMAM) with
complexes based polypropyleneimine dendrimers, different lengths of the core were also synthesized in
and the use of the corresponding Ni complexes for our laboratory [18]. The structures of the 1.0G and
catalysis were evaluated in the oligomerization of eth- 2.0G dendritic PAMAM bridged hindered phenols
1
ylene. The oligomerization results showed these den- were characterized by H NMR (NOVA400 MHz
dritic catalysts exhibited catalysis activity, and that the spectrometer) and FT-IR (TENSOR27).
second-generation dendritic catalyst showed higher
activity than that of the first-generation catalyst.
Syntheses of Dendritic PAMAM Bridged Hindered
Zarghami et al. [13] successfully synthesized inte-
Phenol Antioxidants
grated biosorbents for heavy metals, by grafting differ-
ent generation PAMAM dendrimers to chitosan, and
Syntheses of 1.0G dendritic PAMAM bridged hin-
2+
their reactive Pb removal potential was evaluated.
The results showed that the products with higher gen-
erations of dendrimer, have more adsorption capaci-
ties than those of products with lower generations of
dendrimer and chitosan alone. Phenolic units were
attached to 4-aminomethylbenzylamine to form an
antioxidant and the ability of the dendritic antioxidant
to scavenge DPPH is higher than that of some natural
antioxidants [14]. Li et al. [15] synthesized two den-
dritic antioxidants by grafting 3-(3,5-di-tert-butyl-4-
hydroxyphenyl)propionic acid to dendritic PAMAM
with ammonia as core, and evaluated their antioxidant
activity in polyolefins. The results showed that the
antioxidant activity of dendritic antioxidants was bet-
ter than that of antioxidant 3114 and antioxidant 1010
in polyolefin. Later, Li et al. [16] synthesized two den-
dritic antioxidants by grafting 3-(3,5-di-tert-butyl-4-
hydroxy-phenyl)-propionic acid to dendritic
dered phenol antioxidants. 1.0G PAMAM (0.003 mol)
and anhydrous potassium carbonate (0.024 mol) were
dissolved in 20 mL of distilled water at room tempera-
ture. A solution of 3,5-propionyl chloride (0.030 mol)
in 60 mL toluene was added slowly to the solution of
1.0G PAMAM at 0°C. The mixture was heated slowly
to 25°C and was reacted for 24 h at 25°C. The mixture
was cooled to 5°C and left for 5 h, then filtered under
vacuum pressure. The crude solid was recrystallized
twice from benzene-chloroform to obtain a series of
1
.0G dendritic PAMAM bridged hindered phenol
antioxidants (C2-1.0G dendritic phenol, C4-1.0G
dendritic phenol, C6-1.0G dendritic phenol, and C8-
1.0G dendritic phenol).
–1
C2-1.0G dendritic phenols. IR spectrum, ν, cm :
3
633(Ar–OH), 3289(N–H), 3089(=CH from ben-
zene ring), 2955(–CH or –CH ), 1650(C=O),
2
3
1
PAMAM with ethanediamine as core, and evaluated 1233(–C(CH )); НNMR spectrum, δ, ppm: 7.30 (s,
3
their antioxidant activity using the DPPH assay. The 8H, –CONH–), 7.05 (d, 8H, Ar–H), 5.07 (s, 4H,
results showed that the scavenging capacities of den- Ar–OH), 4.10–4.19 (m, 16H, CH –CONH–), 3.31–
2
dritic hindered phenols were superior to antioxidant
3
.37 (s, 8H, Ar–CH –CH –), 2.53–2.58(s, 8H, Ar–
2 2
1
010 and antioxidant 1098 at the same phenol
CH –CH –), 2.61–2.68 (t, 16H, –CONH –CH ),
2
2
2
hydroxyl groups.
2.15–2.27 (m, 4H, N–CH –CH –N), 1.45 (s, 72H,
2 2
The aim of this work is to synthesize a series of den- ‒C(CH ) ).
3
3
dritic antioxidants by changing the length of the core
and the generation of dendritic PAMAM. The influ-
ences of the concentration of phenol hydroxyl, struc-
ture and the generation of PAMAM on the antioxidant
–1
C4-1.0G dendritic phenols. IR spectrum, ν, cm :
3
632(Ar–OH), 3289(N–H), 3091(=CH from ben-
zene ring), 2958(–CH or –CH ), 1652(C=O), 1233
2
3
1
activities by inhibiting styrene oxidation induced by (‒C(CH )); НNMR spectrum, δ, ppm: 7.28 (s, 8H,
3
azodiisobutyronitrile (AIBN) were also examined. –CONH–), 6.99 (d, 8H, Ar–H), 5.08 (s, 4H, Ar–
The synthetic route and the names of these dendritic OH), 4.11–4.17 (m, 16H, CH –CONH–), 3.29–3.32
2
PAMAM bridged hindered phenol antioxidants are (s, 8H, Ar–CH –CH –), 2.54-2.58 (s, 8H, Ar–
2
2
shown in Schemes 1 and 2.
CH –CH –), 2.59–2.65 (t, 16H, –CONH–CH ),
2
2
2
2
.18–2.25 (m, 4H, N–CH –CH –CH –CH –N),
2 2 2 2
.89–1.96 (s, 4H, N–CH –CH –CH –CH –N),
1
2 2 2 2
EXPERIMENTAL
1.46 (s, 72H, –C(CH ) ).
3 3
Materials
–1
C6-1.0G dendritic phenols. IR spectrum, ν, cm :
Chloroform, benzene, toluene, styrene, potassium
carbonate and azodiisobutyronitrile (AIBN) pur-
chased from Tianjin Kemiou Chemical Reagent
Development Center (China), were of an analytical
reagent grade and used directly. 3-(3,5-Di-tert-butyl-
3
634(Ar–OH), 3293(N–H), 3095(=CH from ben-
zene ring), 2955(–CH or –CH ), 1655(C=O),
2
3
1
1
8
233(–C(CH )); НNMR spectrum, δ, ppm: 7.26 (s,
3
H, –CONH–), 6.95 (d, 8H, Ar–H), 5.05 (s, 4H,
Ar–OH), 4.12–4.18 (m, 16H, CH –CONH–), 3.26–
2
4
-hydroxyphenyl)-propionyl chloride(3,5-propionyl
3
.33 (s, 8H, Ar–CH –CH –), 2.51-2.54 (s, 8H, Ar–
chloride) was synthesized in our laboratory [17].
A series of the first-generation dendritic poly(amido-
2 2
CH –CH –), 2.56–2.61 (t, 16H, –CONH–CH ),
2
2
2
amine) (1.0G PAMAM) and the second-generation 2.15–2.21 (m, 4H, N–CH
–(CH –CH ) –CH –N),
2 2 2 2
2
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 91 No. 12 2017

2352
CUI-QIN LI et al.
H N
2
NH2
NH
HN
O
O
N
N
4HO
CH CH COCl
2
2
n
O
O
NH
HN
H N
2
NH2
n = 1, 2, 3, 4
HO
OH
O
HN
NH
O
O
O
O
O
NH
NH
HN
HN
Cat: K2CO3
Solv: Benzene
Temp: RT
N
N
n
O
HN
NH
O
HO
OH
Scheme 1. Synthetic routes of a series of 1.0G dendritic PAMAM bridged hindered phenol antioxidants.
1
.94–2.08 (s, 8H, N–CH – (CH – CH ) –CH –N), CH –CH –), 2.55–2.59 (t, 16H, –CONH–CH ),
2 2 2 2 2 2 2 2
1
.42 (s, 72H, –C(CH ) ).
2.11–2.17 (m, 4H, N–CH –(CH –CH ) –CH –N),
3
3
2
2
2 3
2
–1
1.92–2.09 (s, 12H, N–CH
–(CH
2
2
–CH
2
) –CH –
3 2
C8-1.0G dendritic phenols. IR spectrum, ν, cm :
N), 1.40 (s, 72H, –C(CH ) ).
3
633(Ar–OH), 3330(N–H), 3095(=CH from ben-
3 3
zene ring), 2955(–CH or –CH ), 1648(C=O),
2
3
Syntheses of 2.0G dendritic PAMAM bridged hin-
dered phenol antioxidants. 2.0G PAMAM (0.002 mol)
and anhydrous potassium carbonate (0.0075 mol)
were dissolved in 20 mL of distilled water at room tem-
1
1
234(–C(CH )); НNMR spectrum, δ, ppm: 7.22 (s,
3
8
H, –CONH–), 6.93 (d, 8H, Ar–H), 5.03 (s, 4H,
Ar–OH), 4.10–4.13 (m, 16H, CH –CONH–), 3.28–
2
3.32 (s, 8H, Ar–CH –CH –), 2.49–2.52 (s, 8H, Ar– perature. The solution of 3,5-propionyl chloride
2
2
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KINETICS AND STRUCTURE-ACTIVITY RELATIONSHIP
2353
2
H N
NH
2
NH
HN
O
O
N
N
2
H N
NH
2
NH
HN
HN
NH
O
O
O
O
+
8 HO
2 2
CH CH COCl
N
N
n
O
O
NH
O
HN
NH
2
2
H N
O
NH
HN
N
N
O
O
NH
HN
2
H N
NH
2
n = 1, 2, 3, 4
HO
OH
O
HN
NH
O
NH
NH
O
N
O
O
O
N
HN
NH
HO
NH
NH
OH
NH
NH
O
O
O
NH
NH
O
O
O
Cat: K2CO3
Solv: Benzene
Temp: RT
N
N
n
O
O
HO
NH
NH
OH
HN
NH
O
N
O
N
O
O
NH
NH
O
HN
NH
O
HO
OH
Scheme 2. Synthetic routes of a series of 2.0G dendritic PAMAM bridged hindered phenol antioxidants.
(
0.040 mol) in 60 mL toluene was added slowly to the The mixture was cooled to 5°C and left for 5 h, then
solution of 1.0G PAMAM at 0°C. The mixture was filtered under vacuum pressure. The crude solid was
heated slowly to 25°C and was reacted for 24 h at 25°C. recrystallised twice from benzene-chloroform to
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 91 No. 12 2017

2354
CUI-QIN LI et al.
obtain a series of 2.0G dendritic PAMAM bridged
hindered phenol antioxidants (C2-2.0G dendritic
phenol, C4-2.0G dendritic phenol, C6-2.0G den-
dritic phenol, and C8-2.0G dendritic phenol).
Styrene Protection Against AIBN-Induced Oxidation
by Dendritic PAMAM Bridged Hindered
Phenol Antioxidants
The experiment of AIBN-induced oxidation of sty-
rene was performed as described in the literature with
a little modification. Briefly, styrene toluene solution
and AIBN toluene solution were put into a stainless
steel autoclave that had been charged with dry nitro-
–1
C2-2.0G dendritic phenols. IR spectrum, ν, cm :
3
632(Ar–OH), 3296(N–H), 3089(=CH from ben-
zene ring), 2952(–CH or –CH ), 1652(C=O),
2
3
1
1
2
233(–C(CH )), НNMR spectrum, δ, ppm: 7.23 (s, gen three times and then purged by oxygen. The result-
3
0H, –CONH–), 6.97 (d, 16H, Ar–H), 5.05 (d, 8H, ing mixture was then stirred for 10 min at 50°C. Den-
dritic phenol solution was injected into the autoclave
and the exhausted oxygen was measured in the reac-
tion process. Every experiment was repeated at least
three times and the final result was the average values
from the three independent measurements.
Ar–OH), 4.11 (m, 40H, –CH –CONH–), 3.28–3.32
2
(
s, 8H, Ar–CH –CH –), 2.49–2.52 (s, 8H, Ar–
2 2
CH –CH –), 2.56–2.60 (t, 40H, –CONH–CH ),
2
2
2
2
.52–2.63 (s, 8H, –CH –tert–N–), 2.16–2.29 (m,
2
4H, N–CH –CH –N), 1.42 (s, 144H, –C(CH ) ).
2
2
3 3
–
1
C4-2.0G dendritic phenols. IR spectrum, ν, cm :
RESULTS AND DISCUSSION
3
632(Ar–OH), 3288(N–H), 3087(=CH from ben-
zene ring), 2953(–CH or –CH ), 1651(C=O),
233(–C(CH )), НNMR spectrum, δ, ppm: 7.30 (s,
Deduction of AIBN-Induced Peroxidation Based
on the Oxygen Consumption Determination
2
3
1
1
3
The hydrogen atom from the phenolic antioxidants
can trap peroxyl radicals to form more stable macro-
molecular radicals, which couple rapidly with the per-
oxyl radical to form the non-radical compound. The
peroxidation would then effectively be inhibited. In
order to study the reaction rate and mechanism of the
2
0H, –CONH–), 6.95 (d, 16H, Ar–H), 5.02 (d, 8H,
Ar–OH), 4.10 (m, 40H, –CH –CONH–), 3.35 (s,
2
8
H, Ar–CH –CH –), 2.33–2.50 (s, 8H, Ar–CH –
2 2 2
CH –), 2.54–2.61 (t, 40H, –CONH–CH ), 2.54–
2
2
2
.63 (s, 8H, –CH –tert–N–), 2.18–2.29 (m, 4H, N–
2
CH –CH –CH –CH –N), 1.89–1.96 (s, 4H, N– chemical reaction process, it is necessary to explore
2
2
2
2
the chemical reaction kinetics. One of the more
important parameters of evaluating phenolic antioxi-
CH –CH –CH –CH –N), 1.41 (s, 144H, ‒C(CH ) ).
2
2
2
2
3 3
–1
C6-2.0G dendritic phenols. IR spectrum, ν, cm : dants abilities is the rate constant for its reaction with
peroxyl radicals. In the experiment the values were
obtained by studying the thermally initiated autoxida-
tion of styrene, in the absence and presence of the
antioxidant.
3
630(Ar–OH), 3286(N–H), 3089(=CH from ben-
zene ring), 2952(–CH or –CH ), 1645(C=O),
2
3
1
1
234(–C(CH )), НNMR spectrum, δ, ppm: 7.25 (s,
3
2
0H, –CONH–), 6.98 (d, 16H, Ar–H), 5.04 (d, 8H,
The process of peroxidation of styrene by AIBN
can be represented by the following equations [19],
where k , k , and k are rate constants for decomposi-
Ar–OH), 4.10 (m, 40H, –CH –CONH–), 3.28–3.30
2
(s, 8H, Ar–CH –CH –), 2.47–2.52 (s, 8H, Ar–
2 2
d
p
t
CH –CH –), 2.57–2.60 (t, 40H, –CONH–CH ),
2
2
2
tion of the initiator, for chain propagation (the value is
2.54–2.63 (s, 8H, –CH –tert–N–), 2.16–2.29 (m,
–1 –1
2
238 M
s
at 50°C) and for chain termination,
4
H, N–CH –(CH –CH ) –CH –N), 1.89–1.95 (s, respectively.
2
2
2 2
2
8H, N–CH –(CH –CH ) –CH –N), 1.41 (s, 144H,
2 2 2 2 2
Initiation:
R−N=N−R ⎯ → 2R + N ,
–
C(CH ) ).
3 3
k
d
•
(1)
(2)
–1
2
C8-2.0G dendritic phenols. IR spectrum, ν, cm :
632(Ar–OH), 3288(N–H), 3089(=CH from ben-
zene ring), 2952(–CH or –CH ), 1647(C=O),
3
•
•
R + O → ROO ,
2
2
3
1
•
1
233(–C(CH )), НNMR spectrum, δ, ppm: 7.23 (s,
3
ROO + Ph−CH=CH2
(3)
2
0H, –CONH–), 6.97 (d, 16H, Ar–H), 5.03 (d, 8H,
•
→
ROOH + Ph−CH=CH .
Ar–OH), 4.11 (m, 40H, –CH –CONH–), 3.27–3.32
2
(
s, 8H, Ar–CH –CH –), 2.49–2.52 (s, 8H, Ar–
Propagation:
2 2
CH –CH –), 2.56–2.63 (t, 40H, –CONH–CH ),
2
2
2
•
fast
•
Ph−CH=CH + O ⎯ ⎯→ Ph−CH COO ,
(4)
(5)
2
4
.52–2.60 (s, 8H, –CH –tert–N–), 2.16–2.24 (m,
2
2
2
H, N–CH –(CH –CH ) –CH –N), 1.88–1.96 (s,
2
2
2 3
2
•
Ph−CH COO + Ph−CH=CH
2
2
1
2H, N–CH –(CH –CH ) –CH –N), 1.37 (s,
44H, –C(CH ) ).
2 2 2 3 2
•
kp
1
⎯ → Ph−CH COOH + Ph−CH=CH.
3
3
2
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2355
(a)
(b)
3
3
2
120
120
2
C
1
80
80
1
40
40
B
t/s
0
A
0
t
inh
0
1000 2000 3000 4000 5000
0
1000 2000 3000 4000 5000
(c)
(d)
3
2
1
3
1
20
120
80
40
0
2
8
0
1
4
0
0
0
1000 2000 3000 4000 5000
0
1000 2000 3000 4000 5000
Fig. 1. Oxygen consumption curve of styrene protection against AIBN-induced oxidation by 1.0G dendritic bridged hindered
phenol antioxidants; (a) C2-1.0G dendritic phenol, (b) C4-1.0G dendritic phenol, (c) C6-1.0G dendritic phenol, (d) C8-1.0G
dendritic phenol; concentrations of antioxidant: (1) 8.77, (2) 4.38, (3) 0.88 μM.
Termination:
where k , [LH], and [AH] represent the susceptibility
inh
of the peroxy radical to capture the hydrogen atom
from antioxidants, and the concentrations of styrene
and dendritic phenol, respectively [20]. The stoichio-
metric factor from equation:
•
2
Ph−CH COO
2
(6)
kt
⎯
→ Ph−CH COOOOCCH −Ph.
2
2
In the presence of dendritic PAMAM bridged hin-
dered phenol antioxidants, the peroxyl radicals can be
n = (Ritinh)/[AH],
(10)
trapped rapidly and the peroxidation would be inhib- where n refers to the number of peroxy free radicals
ited. The process is showed in equations:
trapped by every antioxidant molecule, t stands for
inh
the inhibition period of the dendritic phenol in the ini-
•
•
2
Ph−CH COO + AH → Ph−CH COOH + A ,(7) tiation of AIBN-induced oxidation of styrene. This
2
2
can be measured by the cross-point from the tangent
•
•
2
Ph−CH CO + A → Ph−CH COOA.
(8) lines for the inhibition and oxidation periods in Fig. 1a
2
2
[
21]. The inhibition rate, can also be expressed by
In this paper, the oxygen consumption was mea-
equation:
sured in styrene protection against AIBN-induced
oxidation by dendritic phenol antioxidants at different
concentrations of antioxidant, and the reaction kinet-
ics in the process were studied by the oxygen con-
sumption at different reaction time (Figs. 1 and 2).
−d O dt = Rinh = k LH t k
[
2]
[
]
(
)
.
(11)
p
inh inh
The free radical is supplied by the decomposition of
AIBN at 50°C, where the generation rate of free radi-
cal, R , can be expressed by equation:
g
The inhibition rate (R ) of a series of dendritic phe-
nol antioxidants during the inhibition period can be
obtained from the figures and be expressed by equation:
inh
−
6
R = R = 2.64 ×10 [AIBN].
(12)
g
i
After consumption of all the antioxidant at point B,
−
d[O ]/dt = R = k R [LH]/(nk [AH]),
(9) the oxygen consumption rate increased and changed
2
inh
p
i
inh
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CUI-QIN LI et al.
(a)
(b)
3
3
120
120
2
2
8
0
0
0
80
1
1
4
40
0
0
1000 2000 3000 4000 5000
0
1000 2000 3000 4000 5000
(c)
(d)
3
120
3
120
2
2
8
0
0
0
1
80
40
0
1
4
0
1000 2000 3000 4000 5000
0
1000 2000 3000 4000 5000
Fig. 2. Oxygen consumption curve of styrene protection against AIBN-induced oxidation by 2.0G dendritic bridged hindered
phenol antioxidants; (a) C2-2.0G dendritic phenol, (b) C4-2.0G dendritic phenol, (c) C6-2.0G dendritic phenol, (d) C8-2.0G
dendritic phenol; (1–3) see Fig. 1.
obviously with the increasing concentration of the dendritic phenol antioxidants at different concentra-
phenol hydroxyl. Based on the steady-state kinetic tions are shown in Tables 1 and 2. With increasing con-
treatment, the reaction rate in the period of propaga- centration of dendritic phenol antioxidants, the amount
tion, R , can be expressed by equation:
of oxygen consumption decreased while the t values
p
inh
increased. The results suggested that dendritic phenol
antioxidants played a role in inhibiting oxidation during
the styrene polymerization process.
0
.5
0.5
R = −d[O ]/dt = (k /(2k ) )R [LH],
(13)
p
2
p
t
i
0
.5
where k /(2k ) is referred to the oxidizability of the
p
t
substrate, representing the susceptibility of styrene to
undergo peroxidation [22]. The kinetic chain length,
kcl, that defines the number of chain propagation by
each initiating radical in the periods of inhibition
By comparing tinh with the corresponding value in
Fig. 3, it is shown that the tinh value of dendritic phe-
nols not only increased with the increase of the length
of core but also with the generation of PAMAM. This
was because the chance of dendritic phenols coming
(14) into contact with the long chain alkyl radical produced
during the polymerization, increased with the increas-
(
kcl ) and propagation (kcl ), are shown in equations:
inh
p
kclinh = Rinh /Ri ,
kcl = R /R .
(15)
p
p
i
ing length of core. For the different generation den-
Therefore, the kinetic detail of a free radical related reac- dritic phenols, the tinh value of the C8-1.0G phenol
tion can be described by n, k , oxidizability, and kcl.
was 2614 s, while that of the C8-2.0G phenol was
inh
3
290 s. The possible reason was that dendritic phenol
antioxidants are an inter-molecular complex phenolic
amine antioxidant, and terriary amines could donate
electron-pair to terminate free radicals, except for the
Antioxidant Ability of Dendritic PAMAM Bridged
Hindered Phenol Antioxidants
It can be seen from Figs. 1 and 2 that dendritic phe- hydroxyl group in the molecular. When the concentra-
nol antioxidants were well-behaved antioxidants which tion of phenolic hydroxyl of 1.0G and 2.0G dendritic
showed inhibition periods. The inhibition periods of phenols is the same, the concentration of N atom of
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KINETICS AND STRUCTURE-ACTIVITY RELATIONSHIP
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Table 1. Parameters of inhibition of AIBN-induced peroxidation of styrene by 1.0G dendritic PAMAM bridged hindered
phenol antioxidants
R × 10 , Rinh × 108,
8
kinh × 10-5,
–3
p
0.5
Antioxidants
c, μM
tinh, s
k /(2k ) /10
kclp
kclinh
p
t
M s–1
M s–1
M–1 s–1
C2-1.0G
dendritic
phenol
0.88
34.11
29.52
26.42
34.11
29.35
27.91
34.11
30.06
27.16
32.57
29.48
26.29
27.71
18.05
12.77
27.75
20.90
14.88
28.65
21.35
15.03
28.88
21.85
15.53
2010
2092
2170
2064
2142
2217
2112
2210
2351
2312
2496
2614
0.17
0.15
0.13
0.17
0.15
0.14
0.17
0.15
0.14
0.16
0.15
0.13
3.27
4.89
6.69
3.17
4.07
5.52
3.01
3.86
5.15
2.73
3.34
4.49
5.38
4.66
4.17
5.38
4.63
4.40
5.38
4.74
4.28
5.13
4.65
4.15
4.37
2.84
2.01
4.38
3.29
2.35
4.52
3.37
2.38
4.55
3.45
2.45
4
8
.38
.77
C4-1.0G
dendritic
phenol
0.88
4
8
.38
.77
C6-1.0G
dendritic
phenol
0.88
4
8
.38
.77
C8-1.0G
dendritic
phenol
0.88
4.38
8.77
R = R = 2.64 × 10–6[AIBN] s–1 = 6.34 × 10–8 M s–1 when the concentration of AIBN was 2.4 mM. [LH] = 0.765 mol/L.
i
g
Table 2. Parameters of inhibition of AIBN-induced peroxidation of styrene by 2.0 G dendritic PAMAM bridged hindered
phenol antioxidants
R × 10 , Rinh × 108,
8
kinh × 10-5,
–3
p
0.5
Antioxidants
c, μM
tinh, s
k /(2k ) /10
kclp
kclinh
p
t
M s–1
M s–1
M–1 s–1
C2-2.0G
phenol
0.44
41.23
40.89
40.56
41.72
39.35
38.54
42.98
42.35
41.67
40.46
40.22
39.67
17.37
13.33
9.13
2801
2855
2930
2875
2955
3012
2947
3023
3132
3069
3123
3290
0.21
0.21
0.21
0.21
0.20
0.20
0.22
0.21
0.21
0.20
0.21
0.21
3.74
4.80
6.80
3.70
4.89
6.97
3.98
5.02
7.07
4.07
5.56
7.20
6.50
6.45
6.39
6.58
6.21
6.08
6.78
6.68
6.57
6.38
6.34
6.26
2.74
2.10
1.44
2.69
1.99
1.37
2.45
1.89
1.61
3.09
2.13
1.54
2
.19
.39
0.44
.19
.39
0.44
.19
.39
0.44
.19
.39
4
C4-2.0G
phenol
17.09
12.59
8.67
2
4
C6-2.0G
phenol
15.54
11.98
8.22
2
4
C8-2.0G
phenol
14.57
10.49
7.69
2
4
R = R = 2.64 × 10–6[AIBN] s–1 = 6.34 × 10–8 M s–1 when the concentration of AIBN was 2.4 mM. [LH] = 0.765 mol/L.
i
g
2
.0G dendritic phenols are higher than that of 1.0G of antioxidant concentration, reduced oxygen con-
hindered phenols. Therefore, 2.0G dendritic phenols sumption rate (R ), kinetic chain length (kcl ) and
inh
inh
0.5
–2
had higher antioxidant ability for protecting styrene
against AIBN-induced oxidation.
oxidizability (k /(2k ) /10 ), demonstrating that the
p
t
styrene was protected more markedly by dendritic
phenol antioxidants [23]. This was because the
hydroxyl groups of dendritic phenol antioxidants can
be hydrogen-abstracted, by either the initiating radical
or the propagating radical, and therefore decreasing
the peroxidation rate of styrene (Eq. (7)).
Reaction Kinetics of Dendritic PAMAM Bridged
Hindered Phenol Antioxidants
Kinetics parameters of dendritic phenol antioxi-
dants to protect styrene against free radical induced
Above all, the kinetic discussion on a free radical
peroxidation are shown in Tables 1 and 2. The increase related reaction is based on knowing Ri. The relation-
RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 91 No. 12 2017

2358
CUI-QIN LI et al.
We suggest the possible hypotheses to explain the
1
.0G
.0G
4
3
2
1
000
000
000
000
anti-radical efficiencies of 1.0G dendritic phenol anti-
oxidants. After donating hydroxyl atom, 1.0G den-
dritic phenol radical species could form peroxy radical
molecules combined with alkyl radicals as showed in
Fig. 4. The same reaction mechanism appeared for
2
2.0G dendritic phenol antioxidants.
Structure-Activity Relationship of Dendritic PAMAM
Bridged Hindered Phenol Antioxidants
0
C2-phenol C4-phenol C6-phenol C8-phenol
The thermodynamics parameter, n, just indicates
an aspect of antioxidant ability, and the authentic
reaction behavior should be expressed by an inhibition
rate constant (k ). The k of adding 2.0G dendritic
Fig. 3. Inhibition period (tinh) of a series of dendritic
bridged hindered phenols.
inh
inh
phenol antioxidants was much higher than that of add-
ship between tinh and [AH] should be established, ing 1.0G dendritic phenol antioxidants. This demon-
where the slope, n/R , can be obtained from Eq. (10). strated 2.0G dendritic phenol antioxidants played the
i
The equation of tinh ~ [AH] is listed in Table 3. The n more effective role in suppressing radical propagation.
values of dendritic phenol antioxidants all increased This role was in accordance with those of n value and
with increasing of the length of core, and the n values
tinh value. This mean the antioxidant ability of den-
of 2.0G dendritic phenol antioxidants were higher dritic phenol antioxidants were affected by the gener-
than those of 1.0G dendritic phenol antioxidants. This ation, and increased with an increase of the generation
was in accordance with that of t values. As for den- of antioxidants. The possible reason is that the inner
inh
dritic phenol antioxidants, a much higher n value space of dendritic phenols molecule increased with an
implies that it appears to be a strong antioxidant. increase in the generation and could accommodate
However, the n value of dendritic phenols was less more peroxy radicals to react with tertiary amine
than the number of hydroxyl groups in the molecular. groups. Surprisingly, the kinh of adding 2.0G dendritic
This implies that the dendritic phenols could effec-
tively trap the peroxy free radicals, (Eq. (7)), but the
dendritic phenol radical formed might be subject to
side reactions that diminishes the effectiveness of the
reaction. See Eq. (8) [24].
phenols increased with increasing of the concentra-
tion, and the kinh of adding 1.0G dendritic phenols
decreased. This was because the kinh value is related to
not only the tinh value but also the Rinh value, as
Eq. (11) shows.
Table 3. The equation of t , s = ac+b (c is concentration
inh
of antioxidant, μM, and a = n/R ) and the stoichiometric
CONCLUSIONS
i
factor, n, of hindered phenol antioxidants in protecting sty-
rene against AIBN-induced oxidation
A number of hindered phenol active group have
been covalently grafted onto the first-generation and
second-generation dendritic PAMAM by the conden-
sation reaction of the amidation. The antioxidant abil-
ities were assessed by inhibiting AIBN induced oxida-
tion of styrene. Based on the test results, the scaveng-
ing ability of the dendritic phenol antioxidants on the
peroxy free radicals increased, through both increas-
ing the concentration of hydroxyl groups, and also on
increasing the length of the core for the same number
of hydroxyl groups. Furthermore, compared with the
r2
Antioxidant
a
b
n
C2-1.0G dendritic phenol
C4-1.0G dendritic phenol
C6-1.0G dendritic phenol
C8-1.0G dendritic phenol
C2-2.0G dendritic phenol
C4-2.0G dendritic phenol
C6-2.0G dendritic phenol
C8-2.0G dendritic phenol
15.2 1996.1 0.99 0.96
19.3 2050.7 0.98 1.21
30.3 2082.3 0.98 1.92
37.8 2297.2 0.92 2.39
32.9 2781.6 0.94 2.08
34.3 2867.6 0.99 2.17
46.9 2924.1 0.99 2.97
56.8 3027.7 0.99 3.60
1
.0G dendritic phenols, 2.0G dendritic phenols anti-
oxidants exhibited higher tinh values and n values and
were more efficient in preventing styrene from AIBN-
induced oxidation. This was due to more secondary
amine groups and tertiary amine groups. A series of
R = R = 6.34 × 10–8 M s–1, thus, n = coefficient × 6.34 × 10–8 M s–1
.
g
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RUSSIAN JOURNAL OF PHYSICAL CHEMISTRY A Vol. 91 No. 12 2017

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CUI-QIN LI et al.
4
. S. Beißmann, M. Reisinger, K. Grabmayer, G. Wall-
7
6
5
4
3
2
1
0
ner, D. Nitsche, and W. Buchberger, Polym. Degrad.
1
.0G
Stab. 110, 509 (2014).
2
.0G
5
6
7
8
. E. Foldes and J. Lohmeijer, Polym. Degrad. Stab. 66,
31 (1999).
. A. Ritter, E. Michel, M. Schmid, and S. Affolter,
Polym. Test. 24, 498 (2005).
. X. F. Wang, B. B Wang, L. Song, P. Y. Wen, G. Tang,
and Y. Hu, Polym. Degrad. Stab. 98, 1945 (2013).
. B. Y. Xue, K. Ogata, and A. Toyota, Polym. Degrad.
Stab. 93, 347 (2008).
9. X. M. Shi, J. D. Wang, B. B, Jiang, and Y. R. Yang,
Polym. 54, 1167 (2013).
10. J. B. Wolinsky and M. W. Grinstaff, Adv. Drug Deliv.
C2-phenol C4-phenol C6-phenol C8-phenol
Rev. 60, 1037 (2008).
1
1. H. F. Chow, T. K. K. Mong, M. F. Nongrum, and
Fig. 5. Relationship between the inhibition rate constant
and the different dendritic phenols.
C. W. Wan, Tetrahedron 54, 8543 (1998).
12. R. Malgas, S. F. Mapolie, S. O. Ojwach, G. S. Smith,
and J. Darkwa, Catal. Commun. 9, 1612 (2008).
1
3. Z. Zarghami, A. Akbari, A. M. Latifi, and M. A. Amani,
PAMAM dendrimers with phenol ending groups are
expected to have many applications. Other properties
of these hindered phenols will be studied in our further
work.
Bioresour. Technol. 205, 230 (2016).
14. C. Y. Lee, A. Sharma, J. E. Cheong, and J. L. Nelson,
Bioorg. Med. Chem. Lett. 19, 6326 (2009).
15. C. Q. Li, J. Wang, M. M. Ning, and H. P. Zhang,
J. Appl. Polym. Sci. 124, 4127 (2012).
1
6. C. Q. Li, Y. J. Wei, W. G. Shi, J. Wang, and B. H. Wang,
ACKNOWLEDGMENTS
Prog. React. Kinet. Mech. 40, 279 (2015).
1
7. J. Wang, H. P. Zhang, C. Q. Li, H. J. Yang, and
This work was supported by the financial founda-
tion of National Nature Science Foundation of China
X. H. Di, Fine Chem. Intermed. 37, 61 (2007).
18. J. Wang, C. Q. Li, H. J. Qu, F. L. Hu, and Y. Yang, Pet.
(
no. 51303020). We are grateful to State Key Lab of
Sci. Technol. 28, 883 (2010).
Inorganic Synthesis and Preparative Chemistry, Jilin
University for the characterization work.
19. Z. S. Jia, B. Zhou, L. Yang, L. M. Wu, and Z. L. Liu,
J. Chem. Soc. Perkin Trans. 2, 911 (1998).
2
0. D. Huang, B. Ou, and R. L. Prior, J. Agric. Food
Chem. 53, 1841 (2005).
REFERENCES
2
1. M. A. Freyaldenhoven, P. A. Lehman, T. J. Franz,
R. V. Lioyd, and V. M. Samokyszyn, Chem. Res. Toxi-
col. 11, 102 (1998).
1
2
3
. T. Andersson, M. H. Holmgren, T. Nielsen, and
B. Wesslén, J. Appl. Polym. Sci. 95, 583 (2004).
2
2. L. R. C. Barclay and K. U. Ingold. J. Am. Chem. Soc.
03, 6478 (1981).
3. Z. Q. Liu, J. Phys. Chem. A 110, 6372 (2006).
. A. E. Zaikin, S. Y. Sofina, and O. V. Stoyanov, Polym.
Sci. 4, 209 (2011).
1
2
. P. A. Gunatillake, and R. Adhikari, Biosynth. Polym. 24. Z. Q. Liu, L. P. Ma, B. Zhou, L. Yang, and Z. L. Liu,
Med. Appl. 33 (2016). Chem. Phys. Lipids 106, 53 (2000).
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