Performance of 4,4'-Bis(2,6-di-tert-butylphenol) in stabilization of isoprene rubber and polypropylene

Article abstract of DOI:10.1134/S1070427215050171

The antioxidant performance of a sterically hindered bisphenol antioxidant, 4,4'-bis(2,6-di-tert-butylphenol), in model reactions of accelerated aging of carbon-chain polymers (polypropylene, isoprene rubber) was studied. This antioxidant was examined by differential scanning calorimetry and Wallace plasticity measurements in comparison with known commercial phenolic and amine stabilizers. High performance of 4,4'-bis(2,6-di-tert-butylphenol) as antioxidant was revealed.

Full text of DOI:10.1134/S1070427215050171

ISSN 1070-4272, Russian Journal of Applied Chemistry, 2015, Vol. 88, No. 5, pp. 833−838. © Pleiades Publishing, Ltd., 2015.
Original Russian Text © R.M. Akhmadullin, D.R. Gatiyatullin, L.A. Vasil’ev, A.G. Akhmadullina, N.A. Mukmeneva, E.N. Cherezova, Mingshu Yang, 2015, published
in Zhurnal Prikladnoi Khimii, 2015, Vol. 88, No. 5, pp. 792−797.
MACROMOLECULAR COMPOUNDS
AND POLYMERIC MATERIALS
Performance of 4,4'-Bis(2,6-di-tert-butylphenol)
in Stabilization of Isoprene Rubber and Polypropylene
R. M. Akhmadullina, D. R. Gatiyatullinb, L. A. Vasil’eva, A. G. Akhmadullinaa,
N. A. Mukmenevab, E. N. Cherezovab, and Mingshu Yangc
a IP Akhmadullina A.G., pr. Ibragimova 32a, Kazan, Tatarstan, 420080 Russia
b Kazan National Research University of Technology, ul. Stroitelei 16, Elabuga, Tatarstan, 420015 Russia
c CAS Key Laboratory of Engineering Plastics, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China
e-mail: vas-lev@yandex.ru
Received April 27, 2015
Abstract—The antioxidant performance of a sterically hindered bisphenol antioxidant, 4,4'-bis(2,6-di-tert-butyl-
phenol), in model reactions of accelerated aging of carbon-chain polymers (polypropylene, isoprene rubber) was
studied. This antioxidant was examined by differential scanning calorimetry and Wallace plasticity measurements
in comparison with known commercial phenolic and amine stabilizers. High performance of 4,4'-bis(2,6-di-tert-
butylphenol) as antioxidant was revealed.
DOI: 10.1134/S1070427215050171
The production and consumption of polymeric items
steadily grows. Nevertheless, the demand for polymers is
not always met by their supply, and therefore it becomes
necessary to prolong the operation life of ready items.
The most widely used way to prolong the operation
life of polymeric items is introduction of stabilizers,
antioxidants (AOs).
can be reduced again to the initial BP-5 [8]. This cyclic
process takes place until the stabilizer is completely
exhausted. In the process, BP-5 reacts with peroxy
radicals ROO• [9] (see scheme), and its oxidized form,
DPQ, is a scavenger of alkyl radicals [8, 10].
It is highly probable that specifically these mutual
transformations are responsible for the presence of
compounds exhibiting synergistic AO effect [11] and
ensuring high activity of BP-5 in inhibition of the
thermal oxidation of polymers. This can be proved by the
mechanisms of the inhibiting action of BP-5 and DPQ in
free radical oxidation of carbon-chain polymers, given
in [12]: reaction of alkyl radicals (R•) with quinones and
methylenequinones
Phenolic antioxidants find increasing use in the
practice of polymer stabilization.Among them, bisphenol
(BP) antioxidants exhibiting high performance should
be particularly mentioned [1–3]. 4,4'-Bis(2,6-di-tert-
butylphenol) (BP-5), a BPAO, was synthesized previously
by base oxidative dehydrogenation of hydroquinone with
3,3',5,5'-tetra-tert-butyl-4,4'-diphenoquinone (DPQ).
BP-5 is permitted as an additive to polymers for medical
purpose [5–7]. This fact largely determines the interest in
this stabilizer from the viewpoint of both the development
of efficient methods for its synthesis and the evaluation
of its inhibiting power in aging of polymers of various
structures [8].
R• + InH → RH + In•,
R• + In → •RIn;
reaction of peroxy radicals (ROO•) with sterically
hindered phenols
A significant feature of BP-5 is that, when inhibiting
the oxidation of carbon-chain polymers, it transforms
into 3,3',5,5'-tetra-tert-butyl-4,4'-diphenoquinone, which
ROO• + PhOH → ROOH + PhO•,
ROO• + PhO• → Molecular products,
833

834
AKHMADULLIN et al.
Scheme of mutual transformations of BP-5 and DPQ.
OH
O
HO
O
DPQ
BP-5
+RO•, ROO•/–H•
+O2/–HO2
+R•
+HO2/–O2
O•
O•
RO
HO
+RO•, ROO•/–H•
+O2/–HO2
+R•
+HO2/–O2
O
O
OR
RO
DPQ
ROO• + PhO• → ROOIn,
filtered off and dried. A white powder was obtained,
Тm = 184–185°С. The kinetic curves of the conversion
of DPQ into BP-5 were plotted on the basis of the data
on the light absorption of the reaction solutions of DPQ,
obtained with an Ekros PE5300V spectrophotometer
(λ = 540 nm). The component composition of the reaction
mixture was analyzed with a Khromatek–Kristall 5000
gas chromatograph.
ROO• + PhO• → PhOH + molecular products.
With the aim of characterizing BP-5 more completely
and expanding the prospects for its use, we performed
in this work a comparative study of the stabilizing
performanceofBP-5inisoprenerubberandpolypropylene.
Synchronous evaluation of the stabilizer performance in
a rubber and in a plastic is topical from the viewpoint of
the development of thermoelastoplastic materials.
Study of 4,4′-bis(2,6-di-tert-butylphenol)properties.
The AO performance of the stabilizer in SKI-3 synthetic
rubber was evaluated by the plasticity retention index
(PRI) at thermal aging (130°С, 40 min) in accordance with
ISO 2930:2009 (Sterlitamak Petrochemical Plant). The
stabilizer in the form of a toluene solution was introduced
into SKI-3 polymerizate; the solution was degassed in an
air drier at 75°С. The stabilizer concentration in the rubber
was from 0.05 to 0.3 wt %. Samples of polypropylene
(PP) were submitted by CIBA (China).
EXPERIMENTAL
Synthesis of 4,4′-bis(2,6-di-tert-butylphenol).
An autoclave was charged with 50.0 mL of toluene,
0.0122 mol of DPQ, 0.0022–0.0122 mol of hydroquinone,
and a 0.75 M aqueous NaOH solution. The mixture was
heated to 160°С. The rotation rate of the magnetic stirrer
was 1400 rpm. The reaction mixed decolorized in the
course of the reaction.
TheAO performance of stabilizers in PPwas examined
in the CAS Key Laboratory of Engineering Plastics,
Institute of Chemistry, Chinese Academy of Sciences
(Beijing). Polypropylene samples were prepared either by
introducing AO into a PP melt (Sinopec Yanshan B1101,
melt flow rate 0.5 g min–1) or by introducing it in a two-
worm extruder (Haakepolylab OS Rheodrive 7, length/
After the reaction completion, the reactor was cooled
to 70°С. The reaction mixture consisted of two layers:
the upper toluene layer with the dissolved BP-5 and
the lower aqueous alkaline solution. BP-5 precipitated
from the toluene fraction at room temperature; it was
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 5 2015

PERFORMANCE OF 4,4'-BIS(2,6-DI-tert-BUTYLPHENOL)
835
Table 1. Characteristics of 4,4'-bis(2,6-di-tert-butylphenol)
diameter 25, diameter 16 mm) at a worm rotation rate of
100 rpm. The working temperature of extruder zones was
180, 210, and 210°С. Antioxidants were introduced into
PP in an amount of 0.3 wt %.
Component, parameter
Main substance, %
Value
99.89
After cooling in water, the extrudates were granulated
and dried. The induction periods of oxidation (IPO) were
determined by differential scanning calorimetry (DSC)
using Perkin–Elmer DSC 7 software. The induction period
of oxidation of PP samples was determined in accordance
with ISO 11357-1:2009. Polypropylene samples were kept
for 5 min at 60°С in a nitrogen stream (50 mLmin–1). Then,
the temperature was raised from 60 to 200°С at a rate of
20 deg min–1, and the samples were again kept in a nitro-
gen stream at the same flow rate, 50 mL min–1. After that,
nitrogen was replaced by oxygen (flow rate 50 mL min–1).
The sample oxidation was detected as a sharp increase
in the thermal effect caused by the exothermic oxidation
reaction. The time between the start of feeding oxygen and
the start of heat evolution due to the exothermic process
was considered as IPO of PP.
Alkylphenols, %:
monophenol
2,4-di-tert-butylphenol
0.02
0.04
0.01
unidentified
Volatiles, wt %:
including moisture
0.050
0.048
Ash residue, wt %
Melting point, °C
0.01
184.2‒185.3
Mixed AO Irganox HP2215 (Figs. 1–3, curves 4)
exhibits 6 times lower performance than BP-5 does. It is
known that different phenolic antioxidants compete with
each other under the conditions of oxidant deficiency
The characteristics of BP-5 are given in Table 1. The
stabilizers considered for comparison are presented in
Table 2.
Q, μW
RESULTS AND DISCUSSION
Testing of AO under the conditions of SKI-3 aging
showed that, at concentrations of 0.1–0.3 wt %, BP-5
ensures higher plasticity retention index for rubber than
does Agidol-2. On the other hand, at low temperatures
BP-5 is less effective than S-789 amine antioxidant
(Table 3).
τ, min
Polypropylene
sample
Induction period
of oxidation, min
The induction periods of PP oxidation in the presence
of BP-5 and of commercial AOs are presented in Fig. 1.
Antioxidant
The data obtained show that the stabilizing performance
of BP-5 is 3 times higher than that of Irganox 1098
(Figs. 1–3, curves 3). In Irganox 1098, two 2,4-di-tert-
butylphenyl groups are linked by a linear chain in which
two amide residues are remote from each other.
1
2
3
4
5
6
–

Bisphenol-5





This structure makes Irganox 1098 incapable of
reversible phenol–quinone redox transformations. In
addition, bulkier Irganox 1098 is less mobile; hence, the
probability of collisions of phenol hydroxy groups with
the oxidizing agent decreases.Apparently, bulky tetramer
Irganox 1010 (Figs. 1–3, curves 5) is 3 times less efficient
as AO than BP-5 for the same reasons.
Fig. 1. Induction periods of oxidation (IPO) of PPsamples with
different stabilizers (cАО = 0.3 wt %). (Q) Thermal effect (DSC)
and (τ) time.Antioxidant: (1) none, (2) BP-5, (3) Irganox 1098,
(4) Irganox HP2215, (5) Irganox 1010, and (6) Irganox B215;
the same for Figs. 2 and 3.
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 5 2015

836
Table 2. Characteristics of stabilizers chosen for comparison
Trade name Formula
S-789
AKHMADULLIN et al.
Regulation document
(producer)
H
N
TU 2492-465-05763441–
20040,
OAO Khimprom
C2H5
CH2–CH–(CH3)2–CH3
H
N
OH
OH
Agidol-2
TU 2492-433-05742686-98,
ОАО Sterlitamak
Petrochemical Plant
Irganox 1098
Irganox 1010
CibaCS
O H
H O
N
N
C
C
HO
OH
''
O
HO
C
CH2–CH2–C–O–CH2
Irganox B215
Irganox 1010 33.3%
Irgafos 168 66.7%
''
O
P
Irganox HP2215
Inganox B215 85%
''
Inganox HP-136 15%
O
O
RUSSIAN JOURNAL OF APPLIED CHEMISTRY Vol. 88 No. 5 2015

PERFORMANCE OF 4,4'-BIS(2,6-DI-tert-BUTYLPHENOL)
837
dΔm/dτ, % min–1
m, %
100
5
–5
60
–15
–25
–35
20
–20
300
500
200
300
T, °C
400
T, °C
Fig. 3. DTA curves for PP samples containing different
stabilizers (сАО = 0.3 wt %). (dΔm/dτ) Weight loss rate and
(Т) temperature.
Fig. 2. TG curves for PP samples with different stabilizers
(сАО = 0.3 wt %). (m) Weight and (T) temperature.
[13]. Most probably, the action of polyphenols in Irganox
HP2215 may be determined by competing inhibition.
The relative enhancement of the performance of binary
AO Irganox B215 (Figs. 1–3, curves 6), which consists
of Irganox 1010 and Irgafos 168 in 1 : 2 ratio, indirectly
confirms the above hypothesis. On the other hand, the
AO performance of Irganox B215 is 5 times lower than
that of BP-5.
On the whole, BP-5 is a promising effective anti-
oxidant for a wide range of polymers and their blends.
CONCLUSIONS
(1) BP-5 ensures higher plasticity retention index
of SKI-3 synthetic rubber than does Agidol-2 phenolic
antioxidant and is comparable in performance with S-789
amine antioxidant.
Apparently, the decisive factor of highAO performance
of BP-5 is in situ formation of the phenol–quinone
synergistic mixture.
(2) In polypropylene stabilization, BP-5 considerably
surpasses in performance other antioxidants used in
practice, as judged from the induction period of oxidation.
Thus, BP-5 can be recommended as additive for
It follows from the results of thermogravimetric and
differential thermal analysis (Figs. 2, 3) that introduction
of BP-5 into PP increases the temperatures of its
degradation and weight loss onset (Table 4). This means
that the operation temperature interval of the polymer is
expanded and its operation life is made longer.
Table 4. Degradation temperatures of stabilized polypropylene
samples
T5%
T50%
oC
Tmax
Stabilizer
Table 3. Plasticity retention index of stabilized SKI-3 samples
Plasticity retention index, %
Concentration,
–
247
270
260
262
258
254
299
311
306
316
301
299
307
310
310
323
310
306
wt %
BP-5
Agidol-2
S-789
BP-5
0.05
0.1
0.2
0.3
30
72
86
91
–
97
99
99
99
Irganox 1098
Irganox HP2215
Irganox 1010
Irganox B215
55
63
66
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AKHMADULLIN et al.
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