CC BY
26
UDC 541.64
А. B. Glazyrin, M. I. Abdullin, G. E. Zaikov, Kh. S. Abzaldinov
SYNTHESIS AND PROPERTIES OF DICHLOROCYCLOPROPANE DERIVATIVES OF SYNDIOTACTIC 1,2-POLYBUTADIENE
Keywords: ^emical modification, syndiotactic 1,2-polybutadiene, dichlorocyclopropane derivatives, the degree of functionalization,
physico-chemical properties.
Polymeric products containing hem-dichlorocyclopropane units with a degree of functionalization of up to 97% are synthesized via the reaction of syndiotactic 1,2-polybutadiene with dichlorocarbene obtained by the interaction of chloroform with an aqueous solution of sodium hydroxide in the presence of a phase-transfer catalyst. The incorporation of dichlorocyclopropane groups into units of polydiene substantially changes its molecular mass and polydispersity, the solution viscosity, the polymer melt flowability, and the glass-transition temperature and flow temperature of the polymer.
Ключевые слова: химическая модификация, синдиотактический 1,2-полибутадиен, производные дихлорциклопропана,
степень функционализции, физико-химические свойств.
Реакцией синдиотактического 1,2-полибутадиена с дихлоркарбеном, полученным взаимодействием хлороформа с водным раствором гидроксида натрия в присутствии катализатора фазового переноса, синтезированы полимерные продукты, содержащие гем-дихлорциклопропановые звенья со степенью функционализации до 97%. Введение дихлорциклопропановых групп в звенья полидиена существенно изменяет его молекулярную массу и полидисперсность, вязкость раствора, текучесть расплава полимера, температуры стеклования и текучести.
Introduction
The chemical modification of polymers via reactive groups of macromolecules makes it possible to obtain new polymeric products with a wide variety of properties and, thus, to widen the application areas of the modified polymers. Polymers containing unsaturated >C=C< bonds are suitable for modification.
Syndiotactic 1,2-PB (1,2-PB) containing reactive vinyl bonds is a convenient object for chemical modification. The syndiotactic configuration of vinyl units makes it possible to synthesize polymers with a regular arrangement of functional groups and, thus, to obtain products with substantially modified properties relative to those of the initial PB.
The introduction of chlorine atoms into polymer units usually increases the chemical resistance of the asmodified polymers and improves their physico chemical and adhesion properties [1-2]. Earlier, chlorine and brominecontaining polymers were synthesized from syndiotactic 1,2-PB through the electrophilic addition of halogens and HCl to >C=C< double bonds of polydiene in an organic solution [3-5]. It was shown that these polymers show promise as components for adhesive and polymer compositions [6, 7].
A method of chlorine incorporation into 1,2-PB macromolecules that is an alternative to chlorination and hydrochlorination procedures involves the reaction of 1,2-PB with dichlorocarbene generated immediately in the reaction mass during polymer modification. Dichlorocarbene is an active electrophilic agent capable of interacting with carbon-carbon double bonds of polymer chains. The addition of dichlorocarbene to unsaturated macromolecules allows the synthesis of dichlorocyclopropane-containing polymers, which cannot be obtained by other methods. Earlier, the addition of dichlorocarbene to 1,4-PB [8-10], cis- and trans-1,4-polyisoprene [11, 12], and polychloroprene [13] was investigated and the dichlorocyclopropanation
of low-molecular-mass 1,2-PB was examined [9], whereas no data are available on the dichlorocyclopropane derivatives of syndiotactic 1,2-PBThe aim of this study is to investigate the reaction of syndiotactic 1,2-PB with dichlorocarbene and to estimate the effect of functionalization degree on properties of the polymeric products.
Experimental part
The characteristics of the used syndiotactic 1,2-PB were as follows: Mn = 52.6* 103, a polydispersity index of 2.22, a content of 1,2 units of 85% (1,4 units are the remainder), a degree of syndiotacticity of 53%, and a crystallinity of 18%.
The microstructure of modified 1,2-PBs was analyzed via :H and 13C NMR spectroscopy on a Bruker AM-300 spectrometer operating at a frequency of 75.47 MHz in the JMOD and broadband proton decoupling modes. The quantitative 13C NMR measurements were performed with a 10-s delay between pulses. IR spectra were recorded on a Specord 75-JR spectrometer.
The viscosities of polymer solutions in chloroform were measured on an Ubbelohde viscometer at 25±0.1°C. Intrinsic viscosity [n] and Huggins constant Kx were found according to the common procedure [14].
Molecular masses and molecular-mass distributions of polymers were determined on a Waters Alliance TM GPC 2000 System gel permeation chromatograph at 25°C; the flow rate of solvent (toluene) was 1 mL/min. Calculations were performed with the use of the Benoit equation and the constants of the Mark-Kuhn-Houwink equation for polybutadiene [14].
The values of Mw and the size of macromolecules were determined on a Fica-50 photogoniodiffusometer; measurements were conducted at 25°C in chloroform during daylight and at 1 = 546 nm in the angular range 30-150°. The refractive-index
increments of solutions were determined on a Pulfrich refractometer; calculations were performed via the Lange method [15].
The glass-transition temperatures and flow temperatures of the polymers were measured on a thermomechanical unit at a load of 9 kg/mm2 and a heating rate of 3 K/min. The data on the polymer crystallinity were obtained via DSC on a Mettler Toledo DSC-1 calorimeter at a heating rate of 10 K/min. The melt-flow index (MFI) of the polymers was measured on an IIRT-AM instrument at a temperature of 140°C and a load of 49 N (a capillary 8 mm in length and 2.09 mm in diameter).
The weight fractions of chlorine in polymer samples were estimated via combustion according to Schöniger [16]. The degree of functionalization of polydiene, a, was calculated from the content of chlorine in a polymer as described in [3, 6]. Yield B of the polymer with dichlorocyclopropane groups was determined through the formula: B = m/mp x 100%,
where: m is the mass of the synthesized polymer and mp is the calculated amount of the polymer corresponding to the degree of functionalization, a.
1,2-PB was modified with the use of dichlorocarbene generated through the Makosza method [17]. Modification was performed via the interaction of chloroform with a sodium hydroxide aqueous solution in the presence of a phase-transfer catalyst followed by addition of the resulting dichlorocarbene in situ to the double bond of polydiene to give rise to the polymer containing Chem-dichlorocyclopropane unit:
CHCl3 + NaOH cat >
(1)
:CCl2 + NaCl + H2O
__CHCl3 / NaOH
(2)
a b
The synthesis was performed at 55-60°C under intense stirring (a stirrer speed of 500 rpm); to a solution of polymer and catalyst in chloroform, a solution of sodium hydroxide was gradually added for 5-30 min. 1,2-PB solutions in chloroform (3 wt %) and NaOH aqueous solutions (50 wt %) were used. Triethylbenzylammonium chloride (TEBAC) (1% based on the polymer weight) was used as a phase-transfer catalyst. Modification was performed at 1,2-PB : CHCl3 : NaOH = 1 : 14 : 1-6 (mol/mol). Chloroform was a common solvent for the polymer and reagent. After completion of the synthesis, the organic layer was separated and washed with 5% aqueous HCl and water; polymer was precipitated from the organic phase with ethanol and dried in vacuum.
Results and discussion
The effect of reaction time on the content of chlorine in the modified 1,2-PB was studied. It was shown that the maximum degree of polymer functionalization in the presence of TEBAC is achieved within 5-8 h (55-60°C) (Fig. 1). A further increase in the time of reaction insignificantly changes the content of chlorine in the modified polymer.
The rate of dichlorocyclopropanation and the degree of polymer functionalization are affected by the concentration of sodium hydroxide in the reaction mixture. Thus, an increase in NaOH : 1,2-PB from 2 to 6 (mol/mol), all other things being the same, is accompanied by a change in the degree of functionalization from 78-80 to 95-97%, while the reaction time corresponding to the maximum value of a decreases from 8 to 5 h (Fig. 1).
wCl, % 60
Fig. 1 - Effect of reaction time on the content of chlorine in a polymer: T = 55-60°C, [NaOH] = 50 wt %, 1.0 wt % TEBAC at NaOH : 1,2-PB = 2 (1) and 6 (2) (mol/mol)
Variation in the time of synthesis makes it possible to prepare polymeric products based on 1,2-PB with different degrees of functionalization.
As follows from the experimental results, the addition of dichlorocarbene to polydiene double bonds under the conditions of phase-transfer catalysis occurs effectively: It is possible to implement almost complete transformation of olefin bonds into dichlorocyclopropane bonds. Polymeric products containing up to ~50 wt % chlorine were obtained. These values correspond to a functionalization degree of ~97%. The yield of the modified polymers in the reaction of PB with dichlorocarbene was as high as 92-97%.
Modified 1,2-PBs containing up to 35% chlorine are light yellow elastic products, while polymers with higher chlorine contents are solid yellow products.
The presence of dichlorocyclopropane groups in macromolecules of modified syndiotactic 1,2-PB is confirmed by the results of IR and NMR spectroscopy. The IR spectra of the modified polymers display a band at 755.1 cm-1 typical for Cl2C bonds of dichlorocyclopropane units. The 1H NMR spectra of the polymeric product exhibit signals due to cis and trans
30
10
0
Time, h
protons of methylene groups of cyclopropane rings (0.74 and 0.89 ppm).
The 13C NMR spectra of the modified 1,2-PB display not only signals of dichlorocyclopropane units in the backbone, which are similar to the corresponding signals in the 13C NMR spectrum of cyclopropanated 1,4-PB [8], but also signals at 60.83 (s), 27.56 (t), and 33.30 (d) ppm that are due to dichlorocyclopropane units in side chains of macromolecules:
Structural features of syndiotactic 1,2-PB ensure different reactivities of double bonds in 1,2 and 1,4 units of this polymer [18, 19]. An analysis of the 13C NMR spectra of the modified polymers showed that double bonds of 1,4 units are more active in the dichlorocyclopropanation reaction. For example, for the modified polymer with a degree of functionalization of 23%, the ratio between a and b units (scheme 2) is 1 : 2, although the content of 1,4 units in the initial 1,2-PB is 5.6 times lower than that of 1,2 units. A higher activity of double bonds in the polymer backbone with respect to dichlorocarbene should be attributed to their higher electron density related to the inductive effect of alkyl substituents [18, 19].
The incorporation of dichlorocyclopropane groups into macromolecules of 1,2-PB leads to a change in its properties.
The GPC study of molecular masses of the polymers containing dichlorocyclopropane groups shows that, as the degree of functionalization increases, the weight-average molecular mass grows considerably, whereas a change in the number-average molecular mass is insignificant. As a result of modification, the degree of polydispersity of the polymers increases from 2.76 for the initial 1,2-PB to 3.80 for the modified polymer with a degree of functionalization of 97% (Table 1).
The above results correlate with the data of light scattering: An increase in the degree of cyclopropanation of polydiene is accompanied by a marked gain in its weight-average molecular mass (Table 1). For example, the molecular mass of the modified polymer with a degree of functionalization of 84.9% is 1.74 times higher than the Mw of the initial polydiene.
As follows from the experimental results, during modification of 1,2-PB with dichlorocarbene, the molecular mass of the polymeric products does not decrease; that is, the dichlorocyclopropanation reaction is not accompanied by scission of the main chain of the polymer.
It is important that an increase in the degree of functionalization of polymers (along with a gain in their Mw) is accompanied by a significant decrease in the size of the macromolecular coils. This parameter is
characterized by the rms radius of gyration (R2)12 [15] (Table 1). For the polymer with a degree of functionalization of 84.9%, (R2)1/2 is 3.8 times smaller than that of the initial polydiene. The observed decrease in the size of the macromolecular coils may be attributed to a change in the macromolecule conformation as a result of incorporation of polar substituents and deterioration of the thermodynamic affinity of modified macromolecules for the solvent [14].
Table 1 - Effect of degree of functionalization a on the molecular mass and polydispersity of syndiotactic 1,2-PB containing dichlorocyclopropane units
Cl, wt % a, % gel permeation chromatography light scattering
Mw x10"3 Mn x10"3 Mw/ Mn Mw x10"3 (RJ2,
- - 116.1 42.1 2.76 90.8 1007
19.2 37.1 - - - 120.5 497
24.0 46.3 141.2 42.0 3.36 - -
32.1 62.0 145.7 39.2 3.72 148.7 445
44.0 84.9 153.0 40.3 3.80 158.0 268
50.2 97.0 158.6 41.7 3.80 - -
A change in the molecular characteristics of polymeric products that is due to the presence of dichlorocyclopropane units has an effect on the rheological properties of modified polydiene solutions and melts.
The experimental results indicate that solutions of the modified polymers in chloroform have considerably lower viscosities than solutions of the initial polydiene (Table 2). The intrinsic viscosity of a polymer regularly decreases with its degree of functionalization: [n] of the modified polymer with a = 97% is 2.8 times lower than that of the initial 1,2-PB (Table 2). Simultaneously, a decrease in the intrinsic viscosity and a certain gain in Huggins constant Kx of modified polymer solutions are observed (Table 2). This finding may indicate that the thermodynamic affinity of dichlorocyclopropanated 1,2-PB for the solvent (chloroform) worsens [14]. A similar variation in viscosity with the degree of functionalization of polymers was observed for chlorinated and hydrochlorinated derivatives of syndiotactic 1,2-PB [5, 6].
Thus, the incorporation of
dichlorocyclopropane groups into macromolecules of syndiotactic 1,2-PB is accompanied by changes in their conformational state of macromolecules and deterioration of thermodynamic affinity of the modified polymer for the solvent. As a result, the size of macromolecular coils and the intrinsic viscosity of dichlorocyclopropanated polymers decrease.
The rheological study of
dichlorocyclopropanated 1,2-PB melts (140°C, a load of 49 N) demonstrates that the MFI of the polymer regularly decreases as the degree of functionalization of
polydiene grows (Fig. 2); i.e., unlike the observed decline in viscosities of modified polymer solutions, an increase in the viscosities of melts occurs as a result of dichlorocyclopropanation.
Table 2 - Rheological properties of dichlorocyclopropanated derivatives of syndiotactic 1,2-PB (25°C, chloroform)
Cl, wt % a, % fnl, dl/g Kx
- - 1.70 0.22
19.2 37.1 1.23 0.24
24.0 46.3 1.05 0.25
28,9 55.8 0.88 0.27
34.9 67.4 0.76 0.29
44.0 84.9 0.68 0.29
46.8 90.3 0.61 0.32
50.2 97.0 0.59 0.30
A drop in the flowablity of a polymer melt during incorporation of dichlorocyclopropane units into polymer chains can be explained by a gain in the energy of intermolecular interaction related to the presence of polar chlorine atoms.
It should be emphasized that, for chlorinated derivatives of syndiotactic 1,2-PB, the dependence of MFI on the degree of polymer functionalization follows the same pattern [3, 4, 6]. Note that, for dichlorocyclopropanated 1,2-PBs, the MFI is higher than that for the chlorinated polymer with the same degree of functionalization (Fig. 2).
a, %
Fig. 2 - MFIs of (1) dichlorocyclopropane and (2) chlorinated derivatives of syndiotactic 1,2-PB as functions of the degree of functionalization of a polymer, a
It was found that, with an increase in the degree of cyclopropanation of syndiotactic 1,2-PB, its glasstransition temperature increases from -19°C for the initial polymer to +28°C for the modified polydiene containing 46.9% chlorine (a = 90.3%) (Table 3). An increase in Tg must be due to a reduction in the freedom of rotation of macromolecular units and by an increase in the rigidity of polymer chains that result from incorporation of dichlorocyclopropane groups into polydiene macromolecules.
An increase in Tg with the degree of functionalization was observed also for other chlorinated polymers: chlorinated and hydrochlorinated
syndiotactic 1,2-PB [5, 6], chlorinated PE [1] and chlorinated poly(l-butene) [2].
The dependence of flow temperature on the degree of functionalization of 1,2-PB follows a more complex pattern: The minimum value of Tf corresponds to ~36% chlorine in the polymer (Table 3).
Table 3 - Dependences of Tg and Tf of dichlorocyclopropane derivatives of syndiotactic 1,2-PB on the content of chlorine in polymers
Cl, wt % a, % Tg,°C Tf,°C
- - -19 85
3.5 6.8 -14 63
26.9 51.7 9 49
35.7 68.9 13 45
40.5 78.2 19 48
46.8 90.3 28 67
A decrease in Tf is presumably related to deterioration of the regular structure of macromolecules, a decrease in crystallinity, and amorphization of the polymer due to cyclopropanation [2]. This assumption is confirmed by DSC measurements: The thermograms of the modified polydienes containing more than 15 wt % chlorine lack the characteristic peaks in the range 40-100°C that correspond to melting of the crystalline phase [20]. The observed increase in Tf for the modified polymers containing above 40% chlorine (Table 3) must be attributed to strengthening of intermolecular interactions that is due to an increase in the amount of C-Cl polar bonds in macromolecules.
The aforementioned changes in Tf and Tg during modification of syndiotactic 1,2-PB entail narrowing of the temperature range for the rubberlike state of the polymers from 104°C for the initial polydiene to 29°C for the cyclopropanated polymer containing 40.5% chlorine (Table 3).
Conclusions
Thus, our experiments have shown that the dichlorocyclopropane derivatives of syndiotactic 1,2-PB with degrees of functionalization up to 97% can be synthesized via the addition of dichlorocarbene, which is prepared through the interaction of chloroform with an aqueous solution of sodium hydroxide in situ under the conditions of phase-transfer catalysis, at carboncarbon double bonds of the polymer. The modification of syndiotactic 1,2-PB via incorporation of dichlorocyclopropane groups leads to a change in its molecular and physicochemical characteristics: increase in the weight-average molecular mass and decrease in polydispersity, reduction in viscosity of solutions and flowability of melts, increase in the glass-transition temperature, and narrowing of the rubberlike state of the polymer.
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© А. B. Glazyrin - PhD (Engineering Sciences), Associate Professor of Technical Chemistry Department, Bashkir State University, Ufa, Russia, glaab@inbox.ru, M. I. Abdullin - Doctor of Chemistry, Full Professor, Head of Technical Chemistry Department, Bashkir State University, Ufa, Russia, G. E. Zaikov - Doctor of Chemistry, Full Professor of Plastics Technology Department, Kazan National Research Technological University, Kazan, Russia, Kh. S. Abzaldinov - PhD (Chemical Sciences), Associate Professor of Plastics Technology Department, Kazan National Research Technological University, Kazan, Russia.
© А. Б. Глазырин - кандидат технических наук, доцент кафедры Технической химии, Башкирский государственный университет, Уфа, Россия, glaab@inbox.ru, М. И. Абдуллин - доктор химических наук, профессор, заведующий кафедрой Технической химии, Башкирский государственный университет, Уфа, Россия, Г. Е. Заиков - доктор химических наук, профессор кафедры Технологии пластических масс, Казанский национальный исследовательский технологический университет, Х. С. Абзальдинов - кандидат химических наук, доцент кафедры Технологии пластических масс, Казанский национальный исследовательский технологический университет.
