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AZERBAIJAN CHEMICAL JOURNAL № 3 2019
ISSN 2522-1841 (Online) ISSN 0005-2531 (Print)
UDC 532.783
NMR STUDY OF THE OXIDATIVE CHLOROPHOSPHORYLATION OF STYRENE-BUTADIENE RUBBER
N.A.Efendiyeva, A.M.Maharramov, A.A.Azizov, A.Y.Melikova, I.A.Bunyad-zadeh, R.M.Alosmanov
Baku State University
i_buniatzade@mail.ru
Received 12.03.2019
The reaction of oxidative chlorophosphorylation of styrene-butadiene rubber was studied by 1H, 13C, and 31P NMR method. Investigations of functionalized styrene-butadiene rubber were carried out using low phosphorus containing samples selected from reaction medium at regular intervals. The obtained results have been discussed in detail, and make it possible to interpret the mechanism of the reaction and the structure of the polymer obtained.
Keywords: oxidative chlorophosphorylation, styrene-butadiene rubber, NMR measurements. https://doi.org/10.32737/0005-2531-2019-3-20-24 Introduction
Oxidative chlorophosphorylation is one way to synthesize phosphorus-containing organic compounds and polymers [1-11]. In spite of the fact that publications addressing the synthesis of phosphorus-containing compounds have presented extensive information on different low-molecular-weight compounds and have studied the mechanism of the reaction and the chemical structure of the products obtained [16] studies of polymers of the polyolefin type (polyethylene, polypropylene, polyvinyl acetate etc.) and contain information relating mainly to the properties of the polymers obtained [7-11]. Our team for the first time have been investigated the oxidative chlorophosphorylation of diene polymers on example of butadiene rubber (BR) [12, 13]. It was confirmed that during the oxidative chlorophosphorylation of BR by the action of PCl3 in the presence of oxygen, functionally active groups with P-Cl bonds are introduced into the polymer matrix, as in the case of polyolefin polymers. But unlike of polyole-fines during the modification reaction of the BR
occurs cross-linking process between macromo-lecular chains. On the other hand it is known that the oxidative chlorophosphorylation of polystyrene proceeds mainly with the destruction of the polymer backbone [2]. So it would be interesting to study the oxidative chlorophos-phorylation of styrene-butadiene rubber (SBR) which is the copolymer of butadiene and styrene.
In this work we have studied the oxidative chlorophosphorylation of styrene-butadiene rubber using NMR spectroscopy. It should be noted that these researches have also a practical value. So, preparation of phosphorus-containing polymers on the basis of one of the most widely produced elastomers - SBR - seems to be very promising.
Experimental part
Materials and their purification
SBR was purchased from Voronezh Synthetic Rubber Manufactory (Russia). Its mac-romolecular structure is shown in Figure 1.
1 2 I I 1 2 3 4. 11
CH2 - CH ^ -j CH2— CH = CH— CH2 f-„ -f CH2 —
C
H = CH9
3
1,2-butadiene
1,4-butadiene Fig.1. Macromolecular structures of the SBR
styrene
4
6
To prepare the initial SBR for the experiments, the latter was dissolved in CCl4 with subsequent precipitation in CH3OH for removing the different kinds of impurity. CCl4 and PCl3 were purified by distillation, and oxygen was dried by passing it through concentrated H2SO4.
Methods
Preparation of samples (oxidative chlo-rophosphorylation reaction of SBR)
A 2% solution of SBR in CCU was prepared. After that PCl3 was added to the reaction mixture in weight ratio of 1:5 (SBR:PCl3) and the reaction system was purged with oxygen at a rate 7 L/h. Reaction started at 22±20C and due to exothermic character the temperature increased up to 55-600C. After 1 h polymer as a result of crosslinking reaction precipitated, i.e. occurs heterogenization in the reaction medium. The total duration of reaction - 8 h. Low phosphorus containing samples were sequentially selected from reaction medium during the oxidative chlo-rophosphorylation(ChP) of SBR at regular intervals (25 and 50 min) that were identified as ChP-SBR-1 and ChP-SBR-2, respectively.
Nuclear Magnetic Resonance spectroscopy analysis
The samples were characterized by Nuclear Magnetic Resonance (NMR) spectroscopy using a Bruker AV300 spectrometer (1H 300 MHz, 13C 75 MHz and 31P 12.4 MHz). The spectrometer was connected to an HP computer. The 1H NMR spectrum was obtained with pulses of 7.3 p,s width (20 0C), with a pulse delay of 3 s; 2% (by mass) solutions of the reaction products in CCl4 were used. The 13C NMR
113
spectrum was taken with H ( C) suppression, with a pulse width of 9 p,s (20 C), a pulse delay of 1 s, and CCl4 as the solvent (external reference D2O). The chemical shift was calculated on the basis of the external (CH3)4Si DEPT signal obtained using the standard DEPT program (Bruker).
Results and discussion
The NMR investigations of modified
1 1 ^
SBR was preceded by 1H, C NMR analysis of the structure of initial polymer.
The 1H NMR spectra of SBR and of ChP-SBR samples are shown in Figure 2.
1 r
7.0
so
7.5
6.5
6.0
5.5
5.0 4.5
4.0
3.5
3.0
2.5
Fig. 2 (a). 1H spectrum of SBR.
10
Fig. 2 (b). 1H spectrum of ChP-SBR-1.
20
ppm
1.5
ppm
12
" 11 11
10
ppm
Fig. 2 (c). 1H spectrum of ChP-SBR-2.
As seen from Figure 2 (a), in initial SBR signals corresponding to aliphatic protons (~2 ppm) as well as to aromatic protons (~7.5 ppm) can be found. The multiple signals in the 4.85.5 region relate to unsaturated functionalities (-CH=CH2, -CH=CH-). In comparison with initial polymer the noticeable changes can be observed in 1H spectrums of ChP-SBR-1 and
modification of vinyl bonds in the butadiene part of the polymer is carried out with high speed. This can be explained by absence of any steric hindrance for the addition reaction. The modified macromolecule conformation contributes to the screening of styrene fragments and makes it more stable for external influence. Thus, some broadening of absorption bands in ChP-SBR-2 samples in 4.0-4.8 and 6.8-8 ppm 6.8-8 ppm region and new signals in 4.0-4.8
region. The appearance of new signals in ChP-SBR-1 and ChP-SBR-2 samples can be referred to >CH-Cl (~4.1 and ~4.5 ppm) and >CH-O (~4.8 ppm) groups. It should be noted that the
ppm suggested the primary modification in the butadiene part of the polymer.
13
In Figure 3 NMR C spectrum of initial (2a) and ChP-SBR (2b) have been presented.
200
180
160
140
120
100
80
—I— 60
40
20
ppm
Fig. 3 (a). C-spectrum of SBR
As seen from Figure 3 (a, b), some signal intensity decrease and some broadening of the band are observed not only in aliphatic part of spectrums. The 25-45 ppm region corresponding to the C1 and C2 carbons in vinyl or styrene groups and the C1 and C4 carbons in the cis and trans units. The 125-132 ppm region corresponding to the C3 and C4 carbons in vinyl units; C2 and C3 in cis and trans units; C3 ,C8 in styrene units, that correlated with data presented in [14]. Signal at 78-80 ppm refers to the solvent. The broadening observed in the NMR
13
13C spectrum indicates that the molecular mobility of the polymer chains is reduced after chlorophosphorylation. This is mainly due to the fact that the resonance line width is related to the segmental polymer motion. If the molecule is free to move in any direction, then the spectrum line width is narrow. On the other hand, if the motion is restricted, then the line width increases. In terms of rubber chloro-hposphorylation processes, it seems to be consistent with the formation of extra cross-links restricting the motion of molecules, since the chains lose their ability to move as individual
polymer chains. The nature of spectrum confirmed that in double bonds region synthesized compounds are more flexible and homogeneous [15]. The 13C-NMR spectrum of Ch SBR (Figure 3b), along with signals related to styrene and butadiene units, showed new characteristic signals assigned to phosphonyldichloride (>CH-POCl2, 38-42 ppm), phosphoryldichlo-ride (>CH-O-POCl2, -78 ppm) and >CHCl groups (57-60 ppm).
The 31P NMR spectrum of Ch-SBR (Figure 4) confirmed the presence of >CH-O-POCl2 group (7.5-7.8 ppm) in sample. Thus, the analysis of the spectra, no changes were found in the styrene units of the ChP-SBR, which can be interpreted as follows. At the initial stage of oxidative chlorophosphorylation reaction, due to sterically more accessibility and high percentage the butadiene units can be easily subject to modification. As a result, the conformation will be changed and the macromole-cules take a relatively curved shape. This contributes to the preservation of the styrene unit in an unmodified form.
Fig. 4. P-spectrum of ChP-SBR-1
Conclusions
ChP-SBR-1 and ChP-SBR-2 samples of chlorophosphorylated SBR have been investi-
1 i a
gated using 1H, 13 C, P - NMR measurements. It has been established that despite of the presence of styrene units in macromolecules of SBR chemical modification of the polymer proceeds similarly to butadiene rubber. This is explained by the fact that the reaction begins in the butadiene unit of the SBR and is accompanied by conformational changes in the macromolecules.
References
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phorus(III) chloride of the surface of polyethylene on its thermo-oxidative resistance. VINITI Database RAS. 2002. 374-V.
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15. Arantes T.M., Leao K.V., Tavares M.B., Ferreira A.G., Longo E., Emerson R., Camargo E.R. NMR study of styrene-butadiene rubber (SBR) and TiO2 nanocomposites. Polymer Testing. 2009. V. 28. P. 490-494.
BUTADIEN-STIROL KAUCUKUNUN OKSIDLO§MO XLORFOSFORLA§MA NMR METODU
iLO TODQiQi
N.A.Ofandiyeva, A.M.M3h3rramov, A.O.Ozizov, A.Y.Malikova, i.A.Bünyadzada, R.M.Alosmanov
Butadien-stirol kaugukunun oksidla§ma xlorfosforlaijma reaksiyasi 13C, va 31P NMR metodu ila tadqiq olunmu§dur. Tadqiqatlar ügün reaksiya mühitindan müayyan zaman fasilalari ila götürülmüij va tarkibinda az miqdarda fosfor olan funksiyala§dinlmi§ butadien-stirol kauguku nümunalarindan istifada edilmi§dir. Alinmi§ naticalar atrafli analiz olun-mu§dur. Natica reaksiyanin mexanizminin interpretasiyasi alinmi§ polimerin qurulu§u müayyanla§dirilmi§dir.
Agar sözlzr: oksidh§m3 xlorfosforla§ma, butadien-stirol kauguku, NMR metodu ila tadqiqi.
ИССЛЕДОВАНИЕ МЕТОДОМ ЯМР ОКИСЛИТЕЛЬНОГО ХЛОРФОСФОРИЛИРОВАНИЯ
БУТАДИЕН-СТИРОЛЬНОГО КАУЧУКА
Н.А.Эфендиева, А.М.Магеррамов, А.А.Азизов, А.Я.Меликова, И.А.Буният-заде, Р.М.Алосманов
Методом 1И, 13С, и Р ЯМР исследовано окислительное хлорфосфорилирования бутадиен-стирольного каучука. Исследование проводилось с использованием образцов функционализированного бутадиен-стирольного каучука с низким содержанием фосфора, которые отбирались из реакционной среды через определенные промежутки времени. Полученные результаты детально проанализированы, что позволило интерпретировать механизм реакции и структуру получения полимера.
Ключевые слова: окислительное хлорфосфорилирование, бутадиен-стирольный каучук, метод ЯМР.
