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Application of the nuclear magnetic resonance to study of the kinetics of synthesis of polyester plasticizers
S t u d y of the kinetics of synthesis of polyester plasticizers
21
12. B. A. ROZENBERG, Ye. B. LYUDVIG, N. V. DESYATOVA, A. R. GANTMAKHER and S. S. iWEI~VEDEV, Vysokomol. soyed. 7: 1010, 1965 (Translated in P o l y m e r Sci. U.S.S.R. 7: 6, 1116, 1965) 13. J. JAMASHITA, M. OKADA and lYl. KASAHARA, Makromolec. Chem. 117: 256, 1968 14. Q. OLAH, Friedel-Crafts and R e l a t e d Reactions. I General Aspects, New Y o r k - L o n d o n , 1963 15. V. V. IVANOV, O. A. PLECHOVA, R. D. SABIROVA, L. V. KOMPANIETS, T. I. PROK O F ' E V A and N. S. YENIKOLOPYAN, I I I konferentziya p c khimii i fizike poliatsetalei (Third Conference on the Chemistry and Physics of Polyacetals). Frunze, 1971
APPLICATION OF THE NUCLEAR MAGNETIC RESONANCE TO STUDY OF THE KINETICS OF SYNTHESIS OF POLYESTER PLASTICIZERS* V. G. GORBVNOVA, YA. G. UR~A~, T. S. KnRA~OVA, L. K. KADYROVA, R. S. BARSHT~I~ and I. YA. SLO~I~ Plastics Research Institute
(Received 12 April 1971) AT T~E present time polyester plasticizers are being more and more widely used in the plastics industry [1-3]. One of the methods of synthesis of polyester plasticizers is by transesterification of dialkyl esters of dicarboxylie acids with glycols [4-6]. The kinetics of transesterification have been studied by many authors, b u t most of the papers discuss the transesterification of dimethyl terephthalate with glycols. It is shown in references [7-9] that the transesterification of dimethyl terephthalate with ethylene glycol (EG), with the latter considerably in excess, exhibits the relationships of a reaction of the first order. It seemed of interest to investigate the kinetics of transesterification of dialkyl esters of dicarboxylic acids with these in excess, which is a necessary condition for the production of polyester plasticizers, i.e. polyesters with alkoxyl groups at the ends of the chains. The present paper describes a study of the kinetics of transesterification of dibutyl adipate (DBA) with glycols, in production of polyester plasticizers of the general formula C4HgOOC(CH2)4CO(OROOC(CH~)aCO)8OCaH9 where R is the radical of the glycol. * Vysokomol. soyed. A15: No. 1, 20-26, 1973.
V. G. GORBU~OVAe$ a l .
22
EXPERIMENTAL In this kinetic study of the synthesis of polyester plasticizcrs the molar ratio of DB~to the glycol was 1 : 0.75. The glycols used were the alkylene glycols ethylene glycol (EG), 1,4-butanediol (1,4-BD0), 1,5.pent~nediol (PDO) and 1,6-hexanediol (HDO), the oxyalkylene glycols diethylene glycol (DEG) and tricthylcne glycol (TEG), and the isoalkylene glycols propylcne glycol (PG) and 1,3-butanediol (1,3.BDO). The purity of the glycols was 97-99~/o and of the DBA 97-98~/~. In addition chemically pure grade zinc acetate and grade A activated carbon were used. Transesterification was carried out in a three-necked flask, provided with a Dean and Stark separator and a condenser. The reaction was conducted at 140-200° in the presence of zinc acetate and activated carbon. The butanol (BA) eliminated in the course of the reac. tion was collected in the Dean and Stark separator. The degree of reaction, P = a t l a , was monitored by means of the quantity of butanol distilled off in known periods of time (a is the calculated quantity of butanol (g) for the complete process and a t the quantity distilled off after a given time). The composition of the reaction mixture during the course of transesterification of DBA with ethylene glycol was studied by the ~lYIR method. The fi~t sample was taken for analysis after the reaction mixture had attained a constant temperature (the degree of reaction at ¢his point was 2 - 5 ~ , depending on the temperature). The NMR spectra of 30-50~ solutions of the test samples in carbon tetrachloride were recorded in a high-resolution TsLA spectrometer [10] at 70-80 ° and a frequency of 60 MHz. Hexamcthyldisiloxane was used as the internal standard. The area of the signals was detmrmined by the weighing method. The results obtained are the average of several measurements.
DISCUSSION F i g u r e 1 shows t h e v a r i a t i o n in the degree of p o l y c o n d e n s a t i o n w i t h t i m e in transesterification of D B A w i t h the a b o v e glycols. T h e linear v a r i a t i o n of I / ( 1 - - P ) w i t h t i m e shows t h a t this is a r e a c t i o n of t h e first order. This transest~rification
__L
#
1-P
3
3
2
1
L
O
z/O
80
120 160 Time , rain
8
i
t,
,
2OO
Fro. l. Kinetics of transesterification of DBA with glycols at 170°: / - - E G ; 2--1,4-BDO; 3--PDO; 4--I~DO; 5--DEG; 6--TEG; 7--PG; 8--1,3-BDO. is a n e x a m p l e o f a nucleophilic s u b s t i t u t i o n reaction, where t h e glycol is t h e nueleophilic reagent. C o n s e q u e n t l y t h e g r e a t e r t h e nucleophilic t e n d e n c y of t h e glycol (other conditions being equal) t h e higher will be t h e r e a c t i o n rate.
Study of the kinetics of synthesis of polyester plasticizers
23
I t is known t h a t the nucleophilic tendency of glycols is directly related to their structure [11]. I n the alkylene glycol series the glycols become more nucleophilie and the transesterification rate increases as the number of methylene groups, which can donate electrons (exhibit a positive/-effect), increases. The highest rate is found in transesterification of DBA with hexanedio]. The ether linkage in the oxyalkylene glycols (DEG and TEG), which has a negative/-effect, makes the glycols less nucleophilic. The rate of transesterification with the oxyalkylene glycols is lower t h a n with alkylene glycols of corresponding length,
2
J I
I
I
/-/
3
2
I
I 8, ,p.,o.m.
FIG. 2. High-resolution NMR spectra of solutions in C014 of the reaction mixture after 30 (1) and 240 rain (9) from the beginning of traa~esterifieation of DBA with ethylene glycol at 170°. for example DEG and PDO. The isoalkylene glycols PG and 1,3-BD0, which have a secondary hydroxyl group, transesterify with DBA considerably more slowly t h a n the normal alkylene glycols. The methyl group of the iso-glycols creates steric hindrance to the transesterification reaction. Our results are in agreement with those of reference [12] and are not in accord with the conclusions of Griehl and Schnock [7], who considered t h a t the rate of transesterification is dependent on the nature of the acid and is independent of the nature of the glycol. The energy of activation for these reactions under our conditions is not dependent on the nature of the glycol, the value being 24~-1.1 kcal/mole, indicating t h a t the mechanism of the transesterification process is the same in each case. The pre-exponential factors (which are respectively 440 (EG), 810 (1,4-BDO), 877 (PDO), 1172 (HDO), 298 (I)EG), 297 (TEG), 208 (PG) and 571 (1,3-BDO)) vary with the type of glycol used. Since the pre-exponential factor is dependent on the structure of the reactant molecules, the
24
V . G . GOI~BU~TOVAet 02.
distance between the atoms in the molecule, the mutual orientation of the molecules etc., it m a y be supposed that in transesterification of DBA with the oxyalkylene glycols and PG favourable orientation of the reacting molecules is more difficult than in transesterification with alkylene glycols. The NMR method was used for study of the mechanism of transesterification in the present work, because other methods of investigation of the kinetic parameters (from the acid value or the quantity of alcohol distilled off) do not provide the possibility of finding the composition of the reaction mixture in individual stages of the reaction. One of the main advantages of the high-resolution NMR method in comparison with other physical and chemical methods of study of the kinetics of polycondensation is the possibility of stepwise determination of the disappearance of the reactants. The kinetic study was carried out on the example of transesterification of DBA with ethylene glycol. The spectra of solutions ot the reaction mixture after 30 and 240 min from the time of taking of the first sample, are shown in Fig. 2. The following signals can be seen in the spectra: the triplet signal of the terminal methyl groups of butyl alcohol (BA_) at ~ 0 . 9 2 p.p.m., the signal of methylene protons in --CH 2 --CHa--CHa-- fragments at ~ 1 . 5 8 p.p.m. (the protons of adipic acid (A/k) and BA) and the signal of the protons of methylene groups next to carbonyl, --CH~--C(O)--, at ~----2.2 p.p.m. (protons of AA). The region of the spectrum containing the signals of protons of EG is of greatest interest. I n the system being studied three types of EG molecules can be present, namely 1) unreacted or "free" EG, the methylene protons of which give a signal at ~----3.53 p.p.m. (the signal of the OH protons of EG can also be seen in the recording at ~ 3 . 2 p.p.m.); 2) EG at the ends of a chain ("terminal"), --C(O)--OCH2--Ctt~OH, the methylene protons next to the hydroxyl group giving a signal in the region of ~-----3.6 p.p.m., and those next to the ester linkage giving a signal at ~-~4.0 p.p.m. (the signal of the corresponding protons of BA are superimposed on this), and 3) EG within the chain ("combined"), --C(O)--OCH2CH~.OC(O)--, which gives a singlet signal at ~ - 4 . 1 5 p.p.m. From the ratio of the areas of the signals at ~=3.53 p.p.m. (Sa) and ~ - 4 . 1 5 p.p.m. (Sg) the quantity of free (x) and combined (y) EG in the reaction mixture can be found at any given moment, and twice the area of the signal in the region of ~--~3.6 p.p.m. (2Se) is proportional to the content of terminal EG. Sa Sg 2Se x : Sa+2S~+Sg Y = Sa+2S~+Sg z Sa--]-2Se+Sg ,
,
°
Figure 3 shows the variation in the amounts of free, combined and terminal EG during the course of transesterification of DBA by ethylene glycol at 160 °. I t is seen that as the reaction proceeds the proportion of free EG falls, the proportion of combined EG increases and that of terminal EG first increases, passes through a maximum and then decreases. The form of the kinetic curve of the variation in the proportion of terminal EG is typical of the curve of the accumula-
Study of the kinetics of synthesis of polyester plasticizers
25
tion and consumption of an intermediate product in a system. Figure 3 also contains a curve of the variation in the concentration of OH groups (W) in the reaction system. W was found as the sum of the relative amount of free EG and half the relative amount of terminal EG Z
W=x+~ . By regarding W as a measure of the extent to which the reaction is incomplete, the order of the reaction can be determined. A,°/ 80
x
ffw
50 -
°r~
×
Q
u
A
~2
o
~0
3
20
o
~
o
o
z I
50
/x
&
zx
/x
~ l
120
I
180
,,, ~ I I
I
Z4zO d00 Time, rain
I
I
J50
30
I
I
I
9g
I
I
150
Time, m/n
FIG. 3
'FIG. 4
FIG. 3. Variation of the proportion of free (1), combined (2) and terminal (3) EG, and the concentration of OH groups (A) (g), during transesterification of DBA with ethylene glycol at
160 ° .
FIG. 4. Kinetics of transesterification of DBA with ethylene glycol at 180°, from NMR measurements. I t is seen from Fig. 4 t h a t the transesterification process is shown by the IqMR method to be a reaction of the second order. This is in agreement with the kinetic result obtained above from measurement of the q u a n t i t y of BA eliminated. The variation in the number-average molecular weight (2~/n) of the polyester formed, can also be followed by means of the NMR spectra. The transesterification reaction produces a poly(ethylene glycol adipate) with butoxyl groups at the ends of the chain. I t was shown in reference [13] t h a t for polyesters of this type ~/n can be determined from the ratio of the area of the signals in the NM_R spectrum to the area of the signal of the terminal OH 3 groups. The chains formed in the transesterification process can, however, have both butoxyl and hydroxyl end groups, as is shown by the presence in the 2qMR spectrum of the signal of terminal EG. This alters the increase in ff~rn. Let us denote the terminal butoxyl groups by A and the terminal hydroxyl groups by B. I t is assumed t h a t there is no free BA in the system. Then the fraction of ends of type A is given b y
n.= 2/~,s,,,+,s'~'
(1)
26
V. G. GolmuNovA ~ aL
and of type B b y nr=l--nA,
(2)
where S , is the area of the signal of terminal methyl groups of BA and Se is the area of the signal of terminal EG, at 5 = 3 . 6 p.p.m.
K
5SO
,/y
50g
/~
.
2
-, 60
180 Time, rain
JOg
FIG. 5. Variation in molecular weight during transes¢erification at 160° (1), 170° (2) and 180 ° (s). The number of terminal protons
Num=6nx + 2n~
(3)
and the area of the signals, which is proportional to Nurm, is 1
S,~.._,-,==S~+~ Se.
(4)
The area of signal c (Fig. 2) is The area of signal b is S b = 4 (~-1-1)--1-8~,A.
(6)
From equations (4)-(6) it is seen that
-x-2
A --i
)ldn= 1 7 2 ~ + 2 5 8 n x + 2 3 4 n B .
(7) (8) (9)
The calculated values of ~/~ are shown in Fig. 5. I t is seen that the molecular weight at the same reaction time increases as the reaction temperature is increased.
Study of the kinetics of synthesis of polyester plasticizers
27
On the basis of the above results on the variation in the amounts of free, combined and terminal EG, some idea of the composition of the reaction mixture in separate stages of transesterification can be obtained. In transesterification of DBA with ethylene glycol the following products can be formed I-IgC40--A H HOCH2CH20~A----H
I
II
H~C,0--(A)~--CO(CH2),COOCdH9
Ill
HgCdO--(A)~--H
IV
HgCd0--(A)~--CO(CtL.)~COOCdH9,
V
where A-~--(OC(CH~)dCOOCH~CH20)--. It is seen from Fig. 3 that 15 rain after the time that the first sample was taken the system contains EG~e~35~/o, E G m ~ 4 7 ~ / o and EG~mb~180/o. Bearing in mind that at that moment a large proportion of hydroxyl groups is present, it may be concluded that the first test sample contains predominantly products I - H I . After 30 and 60 rain from the start of the reaction the fractions of EG~m and EG~ombincrease, while the fraction of EG~e is halved, which suggests the accumulation of product IV in the reaction mixture. After 90 rain the quantity of EGtem in the system remains unchanged, while that of EGae , decreases and that of EGcomb increases by the same amount. This indicates reaction between hydroxyl-containing components and DBA, with predominant formation of products I I I and V. The quantity of hydroxyl-containing components is replenished however by reaction of free EG with oligomers and DBA. In the period from 90 to 240 min the content of EGfr~ varies only slightly, while EGcomb increases and EG~r m decreases, indicating further increase in molecular weight (Fig. 5), mainly by reaction between oligomers already formed, and between oligomers and DBA. CONCLUSIONS
(1) It is shown that the synthesis of polyester plastieizers by transesterification of dibutyl phthalate with glycols, with a molar excess of the former, is a reaction of the second order. The transesterification reaction rate is dependent on the composition and structure of the glycol. (2) The transesterification of dibutyl phthalate with ethylene glycol has been studied by the high-resolution NMR method. It is shown that by means of the NMR method it is possible to follow the variation of the concentration in the reaction system of three types of ethylene glycol molecules, namely "free" (unreacted), "terminal" (at the ends of a chain) and "combined" (in the middle
28
V . V . Ko~s~A~ et at.
of a chain). A method has been developed and used for determination of the number-average molecular weight of the polyesters with terminal butoxyl and hydroxyl end groups, formed during the course of the reaction. Translated by E. O. P~LI~PS
REFERENCES 1. K. ZOHI{EI{ and A. M.EI{Z, Kunststoffe 47: 102, 1957 2. J. R. DARBY and J. R. SEARS, Encyclopedia of Polymer Science and Tectmology 10: 228, 1968 3. l{. S. BARSHTEIN, Plast. massy, No. 8, 19, 1971 4. U.S. Pat. 2695279, 1954 5. F r e n c h Pat. 1110857, 1956 6. R. S. BARSHTEIN and P. Z. LI, Plast. massy, No. 9, 30, 1967 7. W. GRIEHL and G. SCH~0CK, Faserforch. und Textilteclm. 8: 408, 1957 8. R. S. MURAMOVA and I. A. SHARAPOVA, Khim. volokna, No. 1, 19, 1963 9. F. M. MEDVEDEVA, Dissertation, 1970 10. A. N. LYUBIMOV, 1. Z. BELITSKII, I. Ya. SLONIM, A. F. VARENIK and V. I. FEDOROV, Zavod. lab. 32: 1163, 1966 11. T. I. TEMNIKOVA, Kurs teoreticheskikh osnov organicheskoi khimii (Course in the Theoretical Principles of Organic Chemistry). Goskhimizdat, 1969 12. T A N G AO-CH'ING, ~ KU0-TSUI, HSU CH'UAN-P'I a n d IAU CHIN-P'O, Sei. Record (Peking) 3: 16, 1959 13. Ya. G. URMAN, T. S. K ~ O V A , V. G. GORBUNOVA, l{. S. BARSHTEIN and I. Ya. SLONIM, Vysokomol. soyed. A12: 160, 1970 (Translated in Polymer Sci. U.S.S.R. 12: 1, 183, 1970)
SYNTHESIS AND PROPERTIES OF POLYPHENYLENES OBTAINED BY POLYCYCLOTRIMERIZATION OF DIETHYNYLBENZENE* V. V. KORSHAK, V. A. SERGEY~V, V. K. SHIT~OV and V. G. DA~ILOV I n s t i t u t e of Hetero-organic Compounds, U.S.S.R. A c a d e m y of Sciences
(Received 12 April 1971) POLYMERS containing aromatic rings in the chain have high softening points and high thermal stability in an inert atmosphere a n d in air [1]. Among such polymers those of the t y p e of polyphenylene, with a chain constructed only of benzene rings, are of special interest. Of these the polymer with the highest working t e m p e r a t u r e and greatest thermal stability is poly-p-phenylene, which does not melt or degrade up to temperatures in the region of 500 ° [2-4]. Various methods of preparing polymers of the polyphenylene t y p e have been described. As examples mention m a y be made of the synthesis of polyphenylenes from dihalobenzenes * Vysokomol. soyed. A15: No. 1, 27-34, 1973.
21
12. B. A. ROZENBERG, Ye. B. LYUDVIG, N. V. DESYATOVA, A. R. GANTMAKHER and S. S. iWEI~VEDEV, Vysokomol. soyed. 7: 1010, 1965 (Translated in P o l y m e r Sci. U.S.S.R. 7: 6, 1116, 1965) 13. J. JAMASHITA, M. OKADA and lYl. KASAHARA, Makromolec. Chem. 117: 256, 1968 14. Q. OLAH, Friedel-Crafts and R e l a t e d Reactions. I General Aspects, New Y o r k - L o n d o n , 1963 15. V. V. IVANOV, O. A. PLECHOVA, R. D. SABIROVA, L. V. KOMPANIETS, T. I. PROK O F ' E V A and N. S. YENIKOLOPYAN, I I I konferentziya p c khimii i fizike poliatsetalei (Third Conference on the Chemistry and Physics of Polyacetals). Frunze, 1971
APPLICATION OF THE NUCLEAR MAGNETIC RESONANCE TO STUDY OF THE KINETICS OF SYNTHESIS OF POLYESTER PLASTICIZERS* V. G. GORBVNOVA, YA. G. UR~A~, T. S. KnRA~OVA, L. K. KADYROVA, R. S. BARSHT~I~ and I. YA. SLO~I~ Plastics Research Institute
(Received 12 April 1971) AT T~E present time polyester plasticizers are being more and more widely used in the plastics industry [1-3]. One of the methods of synthesis of polyester plasticizers is by transesterification of dialkyl esters of dicarboxylie acids with glycols [4-6]. The kinetics of transesterification have been studied by many authors, b u t most of the papers discuss the transesterification of dimethyl terephthalate with glycols. It is shown in references [7-9] that the transesterification of dimethyl terephthalate with ethylene glycol (EG), with the latter considerably in excess, exhibits the relationships of a reaction of the first order. It seemed of interest to investigate the kinetics of transesterification of dialkyl esters of dicarboxylic acids with these in excess, which is a necessary condition for the production of polyester plasticizers, i.e. polyesters with alkoxyl groups at the ends of the chains. The present paper describes a study of the kinetics of transesterification of dibutyl adipate (DBA) with glycols, in production of polyester plasticizers of the general formula C4HgOOC(CH2)4CO(OROOC(CH~)aCO)8OCaH9 where R is the radical of the glycol. * Vysokomol. soyed. A15: No. 1, 20-26, 1973.
V. G. GORBU~OVAe$ a l .
22
EXPERIMENTAL In this kinetic study of the synthesis of polyester plasticizcrs the molar ratio of DB~to the glycol was 1 : 0.75. The glycols used were the alkylene glycols ethylene glycol (EG), 1,4-butanediol (1,4-BD0), 1,5.pent~nediol (PDO) and 1,6-hexanediol (HDO), the oxyalkylene glycols diethylene glycol (DEG) and tricthylcne glycol (TEG), and the isoalkylene glycols propylcne glycol (PG) and 1,3-butanediol (1,3.BDO). The purity of the glycols was 97-99~/o and of the DBA 97-98~/~. In addition chemically pure grade zinc acetate and grade A activated carbon were used. Transesterification was carried out in a three-necked flask, provided with a Dean and Stark separator and a condenser. The reaction was conducted at 140-200° in the presence of zinc acetate and activated carbon. The butanol (BA) eliminated in the course of the reac. tion was collected in the Dean and Stark separator. The degree of reaction, P = a t l a , was monitored by means of the quantity of butanol distilled off in known periods of time (a is the calculated quantity of butanol (g) for the complete process and a t the quantity distilled off after a given time). The composition of the reaction mixture during the course of transesterification of DBA with ethylene glycol was studied by the ~lYIR method. The fi~t sample was taken for analysis after the reaction mixture had attained a constant temperature (the degree of reaction at ¢his point was 2 - 5 ~ , depending on the temperature). The NMR spectra of 30-50~ solutions of the test samples in carbon tetrachloride were recorded in a high-resolution TsLA spectrometer [10] at 70-80 ° and a frequency of 60 MHz. Hexamcthyldisiloxane was used as the internal standard. The area of the signals was detmrmined by the weighing method. The results obtained are the average of several measurements.
DISCUSSION F i g u r e 1 shows t h e v a r i a t i o n in the degree of p o l y c o n d e n s a t i o n w i t h t i m e in transesterification of D B A w i t h the a b o v e glycols. T h e linear v a r i a t i o n of I / ( 1 - - P ) w i t h t i m e shows t h a t this is a r e a c t i o n of t h e first order. This transest~rification
__L
#
1-P
3
3
2
1
L
O
z/O
80
120 160 Time , rain
8
i
t,
,
2OO
Fro. l. Kinetics of transesterification of DBA with glycols at 170°: / - - E G ; 2--1,4-BDO; 3--PDO; 4--I~DO; 5--DEG; 6--TEG; 7--PG; 8--1,3-BDO. is a n e x a m p l e o f a nucleophilic s u b s t i t u t i o n reaction, where t h e glycol is t h e nueleophilic reagent. C o n s e q u e n t l y t h e g r e a t e r t h e nucleophilic t e n d e n c y of t h e glycol (other conditions being equal) t h e higher will be t h e r e a c t i o n rate.
Study of the kinetics of synthesis of polyester plasticizers
23
I t is known t h a t the nucleophilic tendency of glycols is directly related to their structure [11]. I n the alkylene glycol series the glycols become more nucleophilie and the transesterification rate increases as the number of methylene groups, which can donate electrons (exhibit a positive/-effect), increases. The highest rate is found in transesterification of DBA with hexanedio]. The ether linkage in the oxyalkylene glycols (DEG and TEG), which has a negative/-effect, makes the glycols less nucleophilic. The rate of transesterification with the oxyalkylene glycols is lower t h a n with alkylene glycols of corresponding length,
2
J I
I
I
/-/
3
2
I
I 8, ,p.,o.m.
FIG. 2. High-resolution NMR spectra of solutions in C014 of the reaction mixture after 30 (1) and 240 rain (9) from the beginning of traa~esterifieation of DBA with ethylene glycol at 170°. for example DEG and PDO. The isoalkylene glycols PG and 1,3-BD0, which have a secondary hydroxyl group, transesterify with DBA considerably more slowly t h a n the normal alkylene glycols. The methyl group of the iso-glycols creates steric hindrance to the transesterification reaction. Our results are in agreement with those of reference [12] and are not in accord with the conclusions of Griehl and Schnock [7], who considered t h a t the rate of transesterification is dependent on the nature of the acid and is independent of the nature of the glycol. The energy of activation for these reactions under our conditions is not dependent on the nature of the glycol, the value being 24~-1.1 kcal/mole, indicating t h a t the mechanism of the transesterification process is the same in each case. The pre-exponential factors (which are respectively 440 (EG), 810 (1,4-BDO), 877 (PDO), 1172 (HDO), 298 (I)EG), 297 (TEG), 208 (PG) and 571 (1,3-BDO)) vary with the type of glycol used. Since the pre-exponential factor is dependent on the structure of the reactant molecules, the
24
V . G . GOI~BU~TOVAet 02.
distance between the atoms in the molecule, the mutual orientation of the molecules etc., it m a y be supposed that in transesterification of DBA with the oxyalkylene glycols and PG favourable orientation of the reacting molecules is more difficult than in transesterification with alkylene glycols. The NMR method was used for study of the mechanism of transesterification in the present work, because other methods of investigation of the kinetic parameters (from the acid value or the quantity of alcohol distilled off) do not provide the possibility of finding the composition of the reaction mixture in individual stages of the reaction. One of the main advantages of the high-resolution NMR method in comparison with other physical and chemical methods of study of the kinetics of polycondensation is the possibility of stepwise determination of the disappearance of the reactants. The kinetic study was carried out on the example of transesterification of DBA with ethylene glycol. The spectra of solutions ot the reaction mixture after 30 and 240 min from the time of taking of the first sample, are shown in Fig. 2. The following signals can be seen in the spectra: the triplet signal of the terminal methyl groups of butyl alcohol (BA_) at ~ 0 . 9 2 p.p.m., the signal of methylene protons in --CH 2 --CHa--CHa-- fragments at ~ 1 . 5 8 p.p.m. (the protons of adipic acid (A/k) and BA) and the signal of the protons of methylene groups next to carbonyl, --CH~--C(O)--, at ~----2.2 p.p.m. (protons of AA). The region of the spectrum containing the signals of protons of EG is of greatest interest. I n the system being studied three types of EG molecules can be present, namely 1) unreacted or "free" EG, the methylene protons of which give a signal at ~----3.53 p.p.m. (the signal of the OH protons of EG can also be seen in the recording at ~ 3 . 2 p.p.m.); 2) EG at the ends of a chain ("terminal"), --C(O)--OCH2--Ctt~OH, the methylene protons next to the hydroxyl group giving a signal in the region of ~-----3.6 p.p.m., and those next to the ester linkage giving a signal at ~-~4.0 p.p.m. (the signal of the corresponding protons of BA are superimposed on this), and 3) EG within the chain ("combined"), --C(O)--OCH2CH~.OC(O)--, which gives a singlet signal at ~ - 4 . 1 5 p.p.m. From the ratio of the areas of the signals at ~=3.53 p.p.m. (Sa) and ~ - 4 . 1 5 p.p.m. (Sg) the quantity of free (x) and combined (y) EG in the reaction mixture can be found at any given moment, and twice the area of the signal in the region of ~--~3.6 p.p.m. (2Se) is proportional to the content of terminal EG. Sa Sg 2Se x : Sa+2S~+Sg Y = Sa+2S~+Sg z Sa--]-2Se+Sg ,
,
°
Figure 3 shows the variation in the amounts of free, combined and terminal EG during the course of transesterification of DBA by ethylene glycol at 160 °. I t is seen that as the reaction proceeds the proportion of free EG falls, the proportion of combined EG increases and that of terminal EG first increases, passes through a maximum and then decreases. The form of the kinetic curve of the variation in the proportion of terminal EG is typical of the curve of the accumula-
Study of the kinetics of synthesis of polyester plasticizers
25
tion and consumption of an intermediate product in a system. Figure 3 also contains a curve of the variation in the concentration of OH groups (W) in the reaction system. W was found as the sum of the relative amount of free EG and half the relative amount of terminal EG Z
W=x+~ . By regarding W as a measure of the extent to which the reaction is incomplete, the order of the reaction can be determined. A,°/ 80
x
ffw
50 -
°r~
×
Q
u
A
~2
o
~0
3
20
o
~
o
o
z I
50
/x
&
zx
/x
~ l
120
I
180
,,, ~ I I
I
Z4zO d00 Time, rain
I
I
J50
30
I
I
I
9g
I
I
150
Time, m/n
FIG. 3
'FIG. 4
FIG. 3. Variation of the proportion of free (1), combined (2) and terminal (3) EG, and the concentration of OH groups (A) (g), during transesterification of DBA with ethylene glycol at
160 ° .
FIG. 4. Kinetics of transesterification of DBA with ethylene glycol at 180°, from NMR measurements. I t is seen from Fig. 4 t h a t the transesterification process is shown by the IqMR method to be a reaction of the second order. This is in agreement with the kinetic result obtained above from measurement of the q u a n t i t y of BA eliminated. The variation in the number-average molecular weight (2~/n) of the polyester formed, can also be followed by means of the NMR spectra. The transesterification reaction produces a poly(ethylene glycol adipate) with butoxyl groups at the ends of the chain. I t was shown in reference [13] t h a t for polyesters of this type ~/n can be determined from the ratio of the area of the signals in the NM_R spectrum to the area of the signal of the terminal OH 3 groups. The chains formed in the transesterification process can, however, have both butoxyl and hydroxyl end groups, as is shown by the presence in the 2qMR spectrum of the signal of terminal EG. This alters the increase in ff~rn. Let us denote the terminal butoxyl groups by A and the terminal hydroxyl groups by B. I t is assumed t h a t there is no free BA in the system. Then the fraction of ends of type A is given b y
n.= 2/~,s,,,+,s'~'
(1)
26
V. G. GolmuNovA ~ aL
and of type B b y nr=l--nA,
(2)
where S , is the area of the signal of terminal methyl groups of BA and Se is the area of the signal of terminal EG, at 5 = 3 . 6 p.p.m.
K
5SO
,/y
50g
/~
.
2
-, 60
180 Time, rain
JOg
FIG. 5. Variation in molecular weight during transes¢erification at 160° (1), 170° (2) and 180 ° (s). The number of terminal protons
Num=6nx + 2n~
(3)
and the area of the signals, which is proportional to Nurm, is 1
S,~.._,-,==S~+~ Se.
(4)
The area of signal c (Fig. 2) is The area of signal b is S b = 4 (~-1-1)--1-8~,A.
(6)
From equations (4)-(6) it is seen that
-x-2
A --i
)ldn= 1 7 2 ~ + 2 5 8 n x + 2 3 4 n B .
(7) (8) (9)
The calculated values of ~/~ are shown in Fig. 5. I t is seen that the molecular weight at the same reaction time increases as the reaction temperature is increased.
Study of the kinetics of synthesis of polyester plasticizers
27
On the basis of the above results on the variation in the amounts of free, combined and terminal EG, some idea of the composition of the reaction mixture in separate stages of transesterification can be obtained. In transesterification of DBA with ethylene glycol the following products can be formed I-IgC40--A H HOCH2CH20~A----H
I
II
H~C,0--(A)~--CO(CH2),COOCdH9
Ill
HgCdO--(A)~--H
IV
HgCd0--(A)~--CO(CtL.)~COOCdH9,
V
where A-~--(OC(CH~)dCOOCH~CH20)--. It is seen from Fig. 3 that 15 rain after the time that the first sample was taken the system contains EG~e~35~/o, E G m ~ 4 7 ~ / o and EG~mb~180/o. Bearing in mind that at that moment a large proportion of hydroxyl groups is present, it may be concluded that the first test sample contains predominantly products I - H I . After 30 and 60 rain from the start of the reaction the fractions of EG~m and EG~ombincrease, while the fraction of EG~e is halved, which suggests the accumulation of product IV in the reaction mixture. After 90 rain the quantity of EGtem in the system remains unchanged, while that of EGae , decreases and that of EGcomb increases by the same amount. This indicates reaction between hydroxyl-containing components and DBA, with predominant formation of products I I I and V. The quantity of hydroxyl-containing components is replenished however by reaction of free EG with oligomers and DBA. In the period from 90 to 240 min the content of EGfr~ varies only slightly, while EGcomb increases and EG~r m decreases, indicating further increase in molecular weight (Fig. 5), mainly by reaction between oligomers already formed, and between oligomers and DBA. CONCLUSIONS
(1) It is shown that the synthesis of polyester plastieizers by transesterification of dibutyl phthalate with glycols, with a molar excess of the former, is a reaction of the second order. The transesterification reaction rate is dependent on the composition and structure of the glycol. (2) The transesterification of dibutyl phthalate with ethylene glycol has been studied by the high-resolution NMR method. It is shown that by means of the NMR method it is possible to follow the variation of the concentration in the reaction system of three types of ethylene glycol molecules, namely "free" (unreacted), "terminal" (at the ends of a chain) and "combined" (in the middle
28
V . V . Ko~s~A~ et at.
of a chain). A method has been developed and used for determination of the number-average molecular weight of the polyesters with terminal butoxyl and hydroxyl end groups, formed during the course of the reaction. Translated by E. O. P~LI~PS
REFERENCES 1. K. ZOHI{EI{ and A. M.EI{Z, Kunststoffe 47: 102, 1957 2. J. R. DARBY and J. R. SEARS, Encyclopedia of Polymer Science and Tectmology 10: 228, 1968 3. l{. S. BARSHTEIN, Plast. massy, No. 8, 19, 1971 4. U.S. Pat. 2695279, 1954 5. F r e n c h Pat. 1110857, 1956 6. R. S. BARSHTEIN and P. Z. LI, Plast. massy, No. 9, 30, 1967 7. W. GRIEHL and G. SCH~0CK, Faserforch. und Textilteclm. 8: 408, 1957 8. R. S. MURAMOVA and I. A. SHARAPOVA, Khim. volokna, No. 1, 19, 1963 9. F. M. MEDVEDEVA, Dissertation, 1970 10. A. N. LYUBIMOV, 1. Z. BELITSKII, I. Ya. SLONIM, A. F. VARENIK and V. I. FEDOROV, Zavod. lab. 32: 1163, 1966 11. T. I. TEMNIKOVA, Kurs teoreticheskikh osnov organicheskoi khimii (Course in the Theoretical Principles of Organic Chemistry). Goskhimizdat, 1969 12. T A N G AO-CH'ING, ~ KU0-TSUI, HSU CH'UAN-P'I a n d IAU CHIN-P'O, Sei. Record (Peking) 3: 16, 1959 13. Ya. G. URMAN, T. S. K ~ O V A , V. G. GORBUNOVA, l{. S. BARSHTEIN and I. Ya. SLONIM, Vysokomol. soyed. A12: 160, 1970 (Translated in Polymer Sci. U.S.S.R. 12: 1, 183, 1970)
SYNTHESIS AND PROPERTIES OF POLYPHENYLENES OBTAINED BY POLYCYCLOTRIMERIZATION OF DIETHYNYLBENZENE* V. V. KORSHAK, V. A. SERGEY~V, V. K. SHIT~OV and V. G. DA~ILOV I n s t i t u t e of Hetero-organic Compounds, U.S.S.R. A c a d e m y of Sciences
(Received 12 April 1971) POLYMERS containing aromatic rings in the chain have high softening points and high thermal stability in an inert atmosphere a n d in air [1]. Among such polymers those of the t y p e of polyphenylene, with a chain constructed only of benzene rings, are of special interest. Of these the polymer with the highest working t e m p e r a t u r e and greatest thermal stability is poly-p-phenylene, which does not melt or degrade up to temperatures in the region of 500 ° [2-4]. Various methods of preparing polymers of the polyphenylene t y p e have been described. As examples mention m a y be made of the synthesis of polyphenylenes from dihalobenzenes * Vysokomol. soyed. A15: No. 1, 27-34, 1973.