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Anionic oligomerization of dimethyl itaconate
European Polymer Journal. Vo[. 12, pp. 563 to 569. Pergamon Press 1976. Printed in Great Britain.
A N I O N I C O L I G O M E R I Z A T I O N O F DIMETHYL ITACONATE ARYEH BACHRACH, YOEL TSUR and ALBERT ZILKHA Department of Organic Chemistry, The Hebrew University of Jerusalem, Israel
(Received 25 September 1975) Abstraet--Methanolic solutions of alkali metal and magnesium methoxides were used as initiators for the oligomerization of dimethyl itaconate in methanol, DMF and DMSO. The yield of oligomers was higher in the aprotic solvents. The oligomeric mixtures contained a preponderance of trimer, the structure of which was elucidated by mass spectrometry as a cyclohexane derivative. The oligomers contained no methoxyl end-groups, and initiation is postulated to be an acid-base reaction, in which the allylic hydrogen c~- to the carbonyl is abstracted. This belief was supported by the fact that the use of sodium naphthalene and triethylamine as initiators gave the same oligomers. The trimer was tested as a plasticizer.
INTRODUCTION
Free radical polymerizations of allylic monomers have shown significant differences from those of vinyl monomers [1-5]. The allylic polymerizations were slower [5], and the molecular weights of the polymers were much lower [-4] due to chain transfer to the acidic allylic hydrogens. For the same reason, attempts to polymerize allylic monomers by anionic catalysts were unsuccessful [6-8]. In the present work we studied the anionic oligomerization of allylic monomers, using dimethyl itaconate (DMI) as a typical example. It has a double bond susceptible to attack by nucleophiles due to electron withdrawal by the ester groups, making it suitable for anionic polymerization. Furthermore, oligomers of D M I may be of interest as plasticizers. It was reported [6-8] that D M I did not undergo polymerization under basic conditions. In the presence of C 2 H s O - / C z H s O H the monomer isomerized to dimethyl citraconate (DMC) and mesaconate (DMM) and ethoxide was added to the double bond [%13]. COOCH3
We studied the oligomerization in the presence of solutions of magnesium and alkali metal methoxides in methanol as well as in dipolar aprotic solvents. Sodium naphthalene in the absence of a proton donor was also used as initiator. RESULTS AND DISCUSSION
It has been shown that methyl methacrylate [14, 15] and rnethacrylonitrile [16-18] undergo oligomerization in the presence of C H 3 0 - / C H 3 O H , the degree of oligomerization depending on the molar ratio of (monomer)/(methanol). We investigated the same system of C H 3 0 - / C H 3 O H for the oligomerization of DMI. Methanolic potassium methoxide was reacted with D M I at room temperature. The reaction was allowed to proceed for 1 day, and the products were separated by vacuum distillation (Table 1). Gas chromatography was utilized to identify the products. The first fraction (23~o of the total) was found to contain 17.5~o DMI together with the isomerization
CH300C
[ C~C--CH2COOCH3
COOCH 3
\c /
=
CH 3 DMI
CH 3
COOCH 3
\ C ~ c/
c/ \
CH300C ~
H DMC
\ H DMM
Table 1. Products of oligomerization by KOCH 3 in methanol* Fraction no.
Boiling pt. (°/1 mm)
Yield (~)
C (~o)
H (~o)
OCH 3 (~)
l 2 3 4 5
90 110-130 160-180 220-240 Undistillable
23 53 14 7 3
52.95 50.23 53.17 53.03
6.29 7.42 6.37 6.12 --
38.5 49.2 39.08 38.36 --
nD
1.4375 t.4405 1.4703 1.4820
* Experimental conditions: methanolic KOCHa (3.8 N, 3.2ml, 0.38mole/I) was added to DMI (0.158 mole, 5 mole/l), total methanol (6.6 ml). reaction time 24 hr at room temperature. 563
564
ARYEH BACHRACH, YOEL TSUR and ALBERT ZILKHA
Table 2. Products of oligomerization by KOCH3 in DMSO* Fraction no.
Boiling pt. (°/1 mm)
Yield (%)
C (%)
1 2 3
160 220-240 Undistillable
13 69 18
53.37 53.36 .
H (%) 6.48 6.25 . .
OCH 3
(%)
no
37.90 38.10 .
1.469 1.477
* Experimental conditions: methanolic KOCH 3 (4.6N, 0.47 ml, 0.0143mole/l) was added to DMI (0.316 mole, 2.1 mole/l) in DMSO (100ml), reaction time 24hr at room temperature. Table 3. Products of oligomerization by sodium naphthalene* Fraction no.
Boiling pt. (°/1 mm)
Yield (%)
C (%)
1 2 3
180-200 220-230 Undistillable
25 64 12
53.78 53.17 .
H (%) 6.51 5.77 . .
OCH 3
(%)
no
38.36 39.40 .
1.471 1.486
* Experimental conditions: sodium naphthalene in THF (1.9 N, 5.1 rnl, 0.121 mole/l) was added to DMI (0.158mole, 1.9 mole/l) in DMSO (50ml); reaction time 2 hr at room temperature. products DMM (48.8%) and DMC (33.7%). The second and main fraction (53%) was that of the addition product of methoxide to DMI, (n = 1), identified by i.r. and NMR. The third fraction (14%) was that of a dimer, without initiator fragments as shown by mass spectra (parent peak 316); the fourth fraction (7%) was that of a trimer (parent peak, m/e 474). The molecular weights of the oligomers were also confirmed by Rast's method [19]. The index of refraction increased with increasing the molecular weight of the oligomer fraction. In the oligomerization of methacrylonitrile and methyl methacrylate, it was shown that the DP of the oligomers increased on increasing the dielectric constant of the reaction medium 1-15,17]. Therefore we investigated the oligomerization using KOCH3/ CH3OH in DMSO which has a high dielectric constant (E = 46.4 [20]) and good solvation for cations. The results (Table 2) indicate that the oligomer fraction greatly increased. Gas chromatography study of the reaction showed that the monomer disappeared completely in 5 min. The reaction was allowed to proceed for 24 hr at room temperature. No material having n = 1 was detected. The first fraction (13%) consisted of the dimer, second one (69%) of a trimer and the third (18%) of higher boiling oligomers, which could not be distilled. Mass spectra of this fraction showed a peak at m/e = 632 which is the parent peak of a tetramer. In the oligomerization of methyl methacrylate by CH30-/CH3OH, it was found [15] that the product of addition of methoxide to the double bond suffered a reversible reaction. To find out whether the corresponding product with DMI suffered such a reaction n = 1 (20 mmole) was treated in DMF (20 ml) with methanolic potassium methoxide, (0.35mmole KOCH3 and 2.5 mmole methanol) but no change was detected in the concentration of the material having n = 1 even after 2 days. To increase further the yield of higher ologimers, the reaction was carried out in the absence of meth-
anol, which serves as chain stopper. The initiator was sodium naphthalene and the polymerization was carried out in DMSO. The results (Table 3) indicate that here too the predominant oligomer fraction was that of the trimer and not higher. This trimer was identical with that obtained in the oligomerization with methoxide. The effect of the type of the metal counterion of the methoxide on the oligomerization was studied in methanol and in DMF using the alkoxides of Li, Na, K and Mg. In methanol, it can be seen (Table 4) that, while with K-methoxide oligomerization occurred, there was no oligomerization with Li-methoxide and the main product had n = 1, obtained in 88% yield. With Mg-methoxide, only isomerization occurred. However different results were obtained for reaction in DMF. Even with Mg-methoxide, oligomers were obtained (Table 5) although the molecular weight of the oligomer mixture was much lower than that of the mixture obtained with the alkali metals, each of which gave the same order of molecular Table 4. Products of oligomerization by methoxide in methanol---effect of the counterion
Counterion
DMI + DMM + DMC (%)
n= 1 (%)
Dimer (%)
Trimer (%)
K* Lit Mg;~
23 11 100
53 88 --
14 ---
7 ---
* Methanolic KOCH3 (0.38mole/l) was added to DMI (5 mole/l); reaction time 24 hr at room temperature. ? Methanolic LiOCH 3 (0.09 mole/l) was added to DMI (0.9 mole/D; reaction time 5 hr at room temperature. :~Methanolic Mg(OCH3)2, (0.22 mole/l) was added to DMI (2.2mole/l); reaction time 24 hr at room temperature.
Anionic oligomerization of dimethyl itaconate
565
Table 5. Products of oligomerization by methoxides in DMF--effect of the counterion* DMI + DMC + DMM
ion Na K Li Mg
n= 1 (~o)
Dimer (~o)
Trimer (~)
Higher oligomers o/ (~o)
Mol wtt
%
25 21 19 18
65 68 70 11
8 ll 9 6
437 471 494 240
1.479 1.478 1.482 1.458
----. . . . 48 15
* Experimental conditions: methanolic methoxide (0.014mole/I) was added to DMI (0.0633 mole, 1.04 mole/l) in DMF (50 ml); [methanol] = 0.116 mole/1 ; reaction time 5 hr at 10°. t Average tool. wt. of crude reaction product after removing the DMF. weights. The major product obtained with the alkali metals was the trimer, but higher oligomers were also formed. The effect of the [monomer]/[initiator] ratio on the oligomerization was studied in D M F (Table 6) at constant methanol concentration. The time for complete disappearance of the monomer increased with increasing [monomer]/[initiator] ratio. At very low initiator concentrations, [monomer]/[initiator] > 75, isomerization of the monomer occurred but no oligomerization. No methanol was consumed during the reaction, and indicated by the fact that no product of n = 1 was formed. As seen, the oligomerization reaction is accompanied by isomerization of the monomer. To test this further in a system where the chances for oligomerization are small, D M I was heated in methanol in the presence of triethylamine. The isomer ratios obtained were D M I : D M C : D M M 12.3: 25.4: 62.3, respectively, i.e. the main fraction was that of the more stable t r a n s isomer. These results may be compare d with those reported for the base-catalysed isomerization of DMI, where D M M was also found as the major product [9, 10]. Since D M I undergoes base-catalysed isomerization to D M M and D M C , it was necessary to verify the extent of the participation of these isomers in the oli-
COOCH 3 CH2~
COOCH~
I
C - - ~..ICOOCH~ ~
~,H2 -
r
C~
CI)
(111
gomerization. Experiments were carried out in which D M M or D M C (34.0 mmole) were reacted with methanolic potassium methoxide (3.4mmole KOCH3, 10 mmole methanol) in D M S O (20 ml) at room temTable 6. Effect of the monomer/initiator (M/I) ratio on the time of disappearance of monomer* M/I Time (min)
10 5
25 l0
perature for 26hr. No oligomers were formed and only traces of D M I were detected. This latter fact is in accordance with the fact that the equilibrium between the isomers is not in favour of DMI. This leads to a low concentration of DMI, which in turn is unfavourable for oligomerization. The major product formed in the oligomerization was the trimer, having a molecular peak at m/e = 474 (exactly three times that of the monomer) in the mass spectrum. This fact, together with the facts that the elemental analysis is identical with that of the monomer and the i.r. spectrum lacks an absorption at 1100 cm-1 for an ether linkage, indicates that the mechanism of the oligomerization does not involve addition of the methoxide initiator to the double bond as the initiation step. The fact that the same trimer was obtained in the sodium naphthalene catalysed reaction also points out that initiation of the oligomerization does not proceed through addition of the methoxide to the double bond of DMI. In support of this conclusion, no dimethyl methoxymethyl succinate, n = 1, was detected in the reaction mixture during oligomerization in DMSO. Since methoxide does not add to the vinyl double bond, initiation of the oligomerization must proceed through abstraction of the acidic allylic hydrogen by the base (whether methoxide or sodium naphthalene) forming a stabilized carbanion:
50 45
75 180
100 t
* Experimental conditions: the required amount of methanolic KOCH3 was added to DM! (2.1 mole/l) in DMF (50 ml), total methanol (1.6 mole/l); temperature 10°. t Only isomerization occurred.
O-W,OOCH 3 -
i L
i
OO¢~s
-7
!L ° ....
Carbanion (II), being a terminal one and less sterically hindered, is expected to be the dominant reacting species. This acid-base reaction is favoured since methoxide is more of a base than a nucleophile [21, 22]. To confirm that the initiation is an acid base reaction, we used triethylamine as initiator, since it is known to react only as a base and does not add to double bonds. If initiation occurs only through addition of the initiator to the double bond, then triethylamine will not lead to oligomerization. The reaction was carried in D M S O at l(X)-120 °, and oligomers were actually formed in high yield (Table 7). Here also the trimer was the major product.
566
ARYEH BACHRACH,YOEL TSUR and ALBERTZILKHA
Table 7. Products of oligomerization by triethylamine in DMSO* Fraction no.
Boiling pt. (°/1 mm)
Yield (~)
1 2 3
160-180 240 Undistillable
18 62 19
C (~) 53.37 53.49 . .
H (~)
OCH 3
(~o)
no
6.31 6.22 .
39.51 39.4 .
1.471 1.486
* Experimental conditions: triethylamine (0.014mole, 0.33mole/I) was added to DMI (0.06 mole, 1.42 mole/l); reaction time 2 hr at 110°. In methanol, addition of methoxide to the double bond of DMI did occur yielding product with n = 1. However the main reaction is actually base-catalysed isomerization, which is also an acid-base reaction [ i i ] . But since the formation of the product having n = 1 is not reversible, high yields of it could be obtained. Propagation through carbanion (II) will lead to a dimer (III), having a double bond, as was found.
COOCH3
~.l 2 -
C~
growing anion on an ester group, third in the chain, leading to a cyclic ketone [24], i.r. absorption at 1712 c m - 1 [26], with elimination of methanol. In the corresponding DMI polymerization, this is not a significant reaction, since the trimer obtained gave a negative test for ketone with 2,4-dinitrophenyl hydrazine, and no carbonyl absorption besides that of the ester at 1745 cm- 1 was found.
COOCH3
CHCOOCH3
+
Since propagation was found to proceed only to a relatively small extent after the formation of the trimer, then there must be a dominating reaction leading to termination at this stage. Both the dimer and tetramer fractions were found by test with potassium permanganate and i.r. spectra to contain C=C unsaturation. However, the permanganate test as well as spectroscopic studies did not show the presence of an unsaturated double bond in the trimer. Therefore this termination must be a cyclization involving the terminal double bond, which might be addition of the growing carbanion to the double bond. This reaction can proceed through a pseudo six-membered ring as follows:
H-- C--COOCH~ CH3CO0 ~ C O O a ' 1 3
j
GH2---- CCH2COOCH3
CO0~l z
CH2COOCH 3
OJO
Concerning the above cyclization, a question arises why addition of the carbanion to the terminal double bond occurs although this bond is the same as that in D M M and DMC which were found to be unreactive towards oligomerization, unlike DMI. This may be explained by the fact that, contrary to the reaction with DMM, cyclization is an intramolecular reaction and as such is expected to be much faster than an intermolecular process due to "local concentration" [27] by several orders of magnitude. The conformation of the trimer can be shown to be a chair conformation with only one 1,3-di-axial interaction. Its molecular weight and elemental analysis CHzCOOCHz
+ H :b
COOCH 3
c ~
3 (tVl
=
CH3COOCH2
•
d
(iv) COOCH3
This cyclization may also explain the great preference for formation of the trimer over the higher oligomers. In the corresponding anionic polymerization of methyl methacrylate, it was also found [23-25] that there was a strong tendency for trimerization of the monomer through formation of a pseudo cyclohexane ring. In the polymerization of methyl methacrylate, internal cyclization occurred through attack of the
are in accordance with what was found. Physical analyses support the structure; i.r. (crn -z 925-1005 and 1000-1055 (cyclohexane) [28], 1350 (stretching of O II C----OCH3), 1015(stretching of methyl ester), 1745(carbonyl of ester); NMR (6) 1.9(CH2 at position a) shown in structure (IV), 2.2-2.6(CH2 groups at positions b,c) (the peaks were not sharp because of axial-
Anionic oligomerization of dimethyl itaconate equatorial flip), 2.4(CH 2 groups at position d) 3.69 (CH30 groups, e) (the peaks were not sharp because of small magnetic differences between the three CH 2 groups, and also the six methyl ester groups). In the mass spectrum of (IV), the important m/e values were: 474(M, molecular peak), 442(Mm CH3OH), 410(M--2CH3OH), 378(M--3CH3OH), 443, 412, 381, 350, 319 (equivalent to splitting off of one or several methoxyl groups), 31(OCH3), 32(CH3OH), 415(M--COOCH3), 59(COOCH3), 252(main peak). The main peak at 252 is due to three McLafferty rearrangements involving the hydrogens, 7- to the carbonyl double bond, leading to a trisubstituted benzene. The relative stability of the aromatic compound explains why m/e = 252 is the main peak.
O~ 3
o/4 H ~ , , . ~ 1 ~ CH,
J AA ~ - ~ 3
3
--
the following 4 fragmentation patterns will be observed; R R
-~.
H" R'
R
R:
t..
+
\H
R~
C5" R(
R'
R
R'
R
R'
R
R'
R
/"
R
"R
Table 8. Effect of the trimer on the plasticization of PVC* PVC + D.O.P. + trimer
Colorless Light yellow 77 min 55 rain 1325
1875
460 67
280 84
m/e 112
R
R.>
m/e 28
Rt
role 3-/'2
R
RI R/ m/e 2 9 0
m/e I10 R' =
CHzCOOCH 3
25,2
This substituted benzene undergoes further fragmentation to m/e = 221 (252~OCH3) and m/e = 193 (221~CO or 252---COOCH3). The fact that the fragmentation produces as the parent peak the substituted benzene supports the cyclohexane ring structure for (IV). From a study of the fragmentation, it can be shown that the structure of the trimer (IV) is that of a l,l,3,3,4,4-hexasubstituted cyclohexane and not of the symmetrical 1,1,3,3,5,5-hexasubstituted derivative. The corresponding 1,1,2,2,3,3-hexasubstituted derivative cannot undergo three McLafferty rearrangements, so that no benzene derivative can be formed. It may be noted that, if (IV) undergoes 1 McLafferty rearrangement, cyclohexene derivatives will be formed, which in the mass spectrograph can undergo retro Diels-Alder reaction. Since there are 4 possible modes in which this rearrangement can occur, then
PVC+ D.O.P.
R
m/e 288
R = COOCH3
m/e
Eli m/e 290
m/e IlO
R
OH3O /
R
Jl
R
co2c~
C
Color Heating time at 180' until decomposition Tensile strength (p.s.i.) Ultimate clongation(!'/,; Shore hardness A
567
* PVC sheet plasticized with 45~o dioctyl phthalate (D,O.P.) was compared with sheet plasticized with 22.5~/o D.O.P. and 22.5°;; trimer.
the ratio between the m/e values 290:112:372 will be 2:1:1, as was found. With the 1,1,3,3,5,5-hexasubstituted derivative the ratio between these m/e values should have been 1:1:1, since it is symmetrical.
Effect of solvent and the counterion It was seen that in methanol the reaction led mostly to the formation of isomerization products and to addition of methoxide to the double bond forming product with n = 1 (Table 1); in aprotic solvents (Table 2), the yield of the oligomers was much higher. This difference may on the one hand be due to the fact that oligomerization, being a nucleophilic addition to C----C double bonds, is expected to be much faster in aprotic solvents of high dielectric constant, than in protic ones, since reaction rates involving hydrogen-solvated nucleophiles are very slow compared to those involving non-solvated ones [29-31]. On the other hand, in both cases anions of DMI, DMM and DMC are present. In the protic solvent, there are more chances for protonation and formation of the respective isomeric esters, while in the aprotic solvent the anions that did not undergo protonation can isomerize easily to the DMM or DMC anions (II), which as was seen, initiate the oligomerization. It may be noted that there is a great difference in the acidity of the allylic hydrogen in the three isomeric esters, and only in DMI this hydrogen is also ~- to carbonyl and so is easily abstracted by base, so that in methanol the chances are that any DMM or DMC esters formed from the DMI will participate much less in the oligomerization. As regards the effect of the metal counterion of the methoxide on the reaction, it was seen that while in methanol Li behaved differently from Na and K, in DMSO and DMF all the alkali metals showed the same behavior. It is known that organo-lithium
568
ARYEH BACHRACH,YOEL TSUR and ALBERTZILKHA Table 9. Plasticization of epoxy resin with trimer*
Epoxy + DETA (g)
Trimer added (g)
5 5 3 3
-1 1 2
Appearance of resin Hard, brittle Hard, flexible Soft, flexible Flexible
Tensile strengtht (p.s.i.)
Elongation (%)
Heat distortion temp.~
Rockwell hardness
6130 4850 3000 1700
0.5 12.5 52 78
115 108 92 88
118 92 80 47
* Epoxy resin, ERL-2795 (Bakelite) (100 parts) was mixed with diethylene triamine (DETA) (11 parts). ~ Measured on an Instron instrument. ,+ Measured on a Heat Distortion Apparatus G. V. Planer. bonds are more covalent than those of Na and K and are more highly associated. Aprotic solvents of high dielectric constant and high degree of solvation lead to total dissociation of the alkali methoxide and that is why similar results were obtained with all the alkali metals in D M S O and D M F . Magnesium methoxide, due to its lower ionic character than the alkali metals, showed different behaviour. Use o f the trimer as a plasticizer for P V C
The physical properties of PVC plasticized with 45% dioctyl phthalate were compared with those of PVC plasticized with 22.5% dioctyl phthalate and 22.5% of the trimer. It can be seen (Table 8) that the trimer can be used as a plasticizer extender in combination with dioctyl phthalate. It contributes to increasing the tensile strength, decrease of per cent elongation and increase of the hardness of the PVC. The temperature resistance was lower than with dioctyl phthalate alone. The trimer was also tested as a plasticizer for PVC emulsion. An emulsion of PVC, used for coatings and as a mould release containing 35% solids, was mixed with 15% wt/wt of the trimer. The emulsion was added to a silicone rubber mould and the solvents were dried. The PVC from the emulsion had a tensile strength of 700 psi and 300% ultimate elongation while with the addition of the trimer the tensile strength was 600 psi and the ultimate elongation 450%. The trimer was also tested as a plasticizer for epoxy resins. The system used was Bakelite ERL-2795 and diethylene triamine as hardener. It can be seen (Table 9) that addition of the trimer led to lowering of the tensile strength and the hardness of the polymer, accompanied by an increase in the per cent elongation. The heat distortion of the polymer also decreased. The plasticized resins were tested for resistance to solvents using methylethyl ketone, chloroform, D M F , benzene and cyclohexane. After immersion for 3 weeks no trimer was extracted and there was no visible change. It can be that there was interaction of the ester groups of the trimer with the amine groups, securing more the plasticizer to the resin. EXPERIMENTAL
Materials
Dimethyl itaconate (DMI) m.p. 38 ° (Fluka) was used. Methanol was dried over magnesium. Dimethyl sulphoxide
(DMSO) was dried by azeotropic distillation with benzene, and fractionally distilled in vacuo. Dimethyl formamide, (DMF) absolute (Merck) was used. Tetrahydrofuran was dried over sodium and benzophenone. NMR spectra were taken on Varian HA-100 and T-60 spectrometers and mass spectra on an Atlas MAT CH-4 instrument. Oligomerization procedure
The reactions were carried out in three-necked flasks fitted with a mechanical stirrer, thermometer, and an opening fitted with a self-sealing rubber cap through which the reagents were added by syringe. The flask was dried by flaming in vacuo. All the reactions were carried out under nitrogen. Catalyst was added to the DMI; when the reaction was complete, acetic acid was added to neutralize the reaction mixture which was then diluted with chloroform and extracted several times with water. The chloroform was dried over magnesium sulphate, and distilled off. The products of the reaction were separated by fractional distillation. Oligomerization by sodium naphthalene
To a solution of DMI (25 g) in DMSO (50 ml) sodium naphthalene in THF (1.94 N, 5.1 ml) was added with stirring. After 2 hr at room temperature, the mixture was neutralized with acetic acid, diluted with chloroform and extracted with water. The chloroform was driven off and the residue was steam distilled to remove any naphthalene. The oligomer mixture was fractionally distilled in vacuo. Gas chromatography
Gas chromatography was used to monitor quantitatively for the monomer, for the product with n = 1, and for the isomeric esters, DMM and DMC. It was not possible to monitor the trimer because of its high boiling point. The analysis was carried out using a Packard 7400 Gas Chromatograph. The column was packed with butane diol succinate 5% and H3PO 4 4~o on C.W./H.M.D.S. 60/80. Injector and detector temperatures were 150°, and the column was held at 110 °.
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Weissberger), p. 208. lnterscience, New York {1954). 20. J. J. Lindberg and J. Kenttamaa, Acta chem. fl, nn. B33, 104 (1960). 21. S. Boileau and P. Sigwalt, Makromolek, Chem. 171, 11 (1973). 22. D. M. Simons and J. J. Verbanc, J. Polym. Sci. 44, 303 (1960). 23. D. L. Glusker, R. A. Gullucio and R. A. Evans. J. Am. chem. Soc. 86, 187 (1964). 24. S. Bywater, Fortschr. HochpolymForsch. 4, 66 (1965). 25. D. M. Wiles and S. Bywater, Polymer 3, 175 (1962). 26. W. Goode, d. Polym. Sci. 47, 75 (1960). 27. W. P. Jencks, Catalysis in Chemistry and El~zymolo~ly, p. 8. McGraw-Hill, New York (1969). 28. L. W. Morrison, J. chem. Soc. 1614 (1951). 29. A. J. Parker, Quart. Rev. 16, 163 (1962). 30. B. A. Felt, J. Sinnreich and A. Zilkha, J. or~j. Chem. 28, 3245 (1963). 31. B. A. Felt, J. Sinnreich and A. Zilkha. J. orq. Chem. 32, 2570 (1967).
A N I O N I C O L I G O M E R I Z A T I O N O F DIMETHYL ITACONATE ARYEH BACHRACH, YOEL TSUR and ALBERT ZILKHA Department of Organic Chemistry, The Hebrew University of Jerusalem, Israel
(Received 25 September 1975) Abstraet--Methanolic solutions of alkali metal and magnesium methoxides were used as initiators for the oligomerization of dimethyl itaconate in methanol, DMF and DMSO. The yield of oligomers was higher in the aprotic solvents. The oligomeric mixtures contained a preponderance of trimer, the structure of which was elucidated by mass spectrometry as a cyclohexane derivative. The oligomers contained no methoxyl end-groups, and initiation is postulated to be an acid-base reaction, in which the allylic hydrogen c~- to the carbonyl is abstracted. This belief was supported by the fact that the use of sodium naphthalene and triethylamine as initiators gave the same oligomers. The trimer was tested as a plasticizer.
INTRODUCTION
Free radical polymerizations of allylic monomers have shown significant differences from those of vinyl monomers [1-5]. The allylic polymerizations were slower [5], and the molecular weights of the polymers were much lower [-4] due to chain transfer to the acidic allylic hydrogens. For the same reason, attempts to polymerize allylic monomers by anionic catalysts were unsuccessful [6-8]. In the present work we studied the anionic oligomerization of allylic monomers, using dimethyl itaconate (DMI) as a typical example. It has a double bond susceptible to attack by nucleophiles due to electron withdrawal by the ester groups, making it suitable for anionic polymerization. Furthermore, oligomers of D M I may be of interest as plasticizers. It was reported [6-8] that D M I did not undergo polymerization under basic conditions. In the presence of C 2 H s O - / C z H s O H the monomer isomerized to dimethyl citraconate (DMC) and mesaconate (DMM) and ethoxide was added to the double bond [%13]. COOCH3
We studied the oligomerization in the presence of solutions of magnesium and alkali metal methoxides in methanol as well as in dipolar aprotic solvents. Sodium naphthalene in the absence of a proton donor was also used as initiator. RESULTS AND DISCUSSION
It has been shown that methyl methacrylate [14, 15] and rnethacrylonitrile [16-18] undergo oligomerization in the presence of C H 3 0 - / C H 3 O H , the degree of oligomerization depending on the molar ratio of (monomer)/(methanol). We investigated the same system of C H 3 0 - / C H 3 O H for the oligomerization of DMI. Methanolic potassium methoxide was reacted with D M I at room temperature. The reaction was allowed to proceed for 1 day, and the products were separated by vacuum distillation (Table 1). Gas chromatography was utilized to identify the products. The first fraction (23~o of the total) was found to contain 17.5~o DMI together with the isomerization
CH300C
[ C~C--CH2COOCH3
COOCH 3
\c /
=
CH 3 DMI
CH 3
COOCH 3
\ C ~ c/
c/ \
CH300C ~
H DMC
\ H DMM
Table 1. Products of oligomerization by KOCH 3 in methanol* Fraction no.
Boiling pt. (°/1 mm)
Yield (~)
C (~o)
H (~o)
OCH 3 (~)
l 2 3 4 5
90 110-130 160-180 220-240 Undistillable
23 53 14 7 3
52.95 50.23 53.17 53.03
6.29 7.42 6.37 6.12 --
38.5 49.2 39.08 38.36 --
nD
1.4375 t.4405 1.4703 1.4820
* Experimental conditions: methanolic KOCHa (3.8 N, 3.2ml, 0.38mole/I) was added to DMI (0.158 mole, 5 mole/l), total methanol (6.6 ml). reaction time 24 hr at room temperature. 563
564
ARYEH BACHRACH, YOEL TSUR and ALBERT ZILKHA
Table 2. Products of oligomerization by KOCH3 in DMSO* Fraction no.
Boiling pt. (°/1 mm)
Yield (%)
C (%)
1 2 3
160 220-240 Undistillable
13 69 18
53.37 53.36 .
H (%) 6.48 6.25 . .
OCH 3
(%)
no
37.90 38.10 .
1.469 1.477
* Experimental conditions: methanolic KOCH 3 (4.6N, 0.47 ml, 0.0143mole/l) was added to DMI (0.316 mole, 2.1 mole/l) in DMSO (100ml), reaction time 24hr at room temperature. Table 3. Products of oligomerization by sodium naphthalene* Fraction no.
Boiling pt. (°/1 mm)
Yield (%)
C (%)
1 2 3
180-200 220-230 Undistillable
25 64 12
53.78 53.17 .
H (%) 6.51 5.77 . .
OCH 3
(%)
no
38.36 39.40 .
1.471 1.486
* Experimental conditions: sodium naphthalene in THF (1.9 N, 5.1 rnl, 0.121 mole/l) was added to DMI (0.158mole, 1.9 mole/l) in DMSO (50ml); reaction time 2 hr at room temperature. products DMM (48.8%) and DMC (33.7%). The second and main fraction (53%) was that of the addition product of methoxide to DMI, (n = 1), identified by i.r. and NMR. The third fraction (14%) was that of a dimer, without initiator fragments as shown by mass spectra (parent peak 316); the fourth fraction (7%) was that of a trimer (parent peak, m/e 474). The molecular weights of the oligomers were also confirmed by Rast's method [19]. The index of refraction increased with increasing the molecular weight of the oligomer fraction. In the oligomerization of methacrylonitrile and methyl methacrylate, it was shown that the DP of the oligomers increased on increasing the dielectric constant of the reaction medium 1-15,17]. Therefore we investigated the oligomerization using KOCH3/ CH3OH in DMSO which has a high dielectric constant (E = 46.4 [20]) and good solvation for cations. The results (Table 2) indicate that the oligomer fraction greatly increased. Gas chromatography study of the reaction showed that the monomer disappeared completely in 5 min. The reaction was allowed to proceed for 24 hr at room temperature. No material having n = 1 was detected. The first fraction (13%) consisted of the dimer, second one (69%) of a trimer and the third (18%) of higher boiling oligomers, which could not be distilled. Mass spectra of this fraction showed a peak at m/e = 632 which is the parent peak of a tetramer. In the oligomerization of methyl methacrylate by CH30-/CH3OH, it was found [15] that the product of addition of methoxide to the double bond suffered a reversible reaction. To find out whether the corresponding product with DMI suffered such a reaction n = 1 (20 mmole) was treated in DMF (20 ml) with methanolic potassium methoxide, (0.35mmole KOCH3 and 2.5 mmole methanol) but no change was detected in the concentration of the material having n = 1 even after 2 days. To increase further the yield of higher ologimers, the reaction was carried out in the absence of meth-
anol, which serves as chain stopper. The initiator was sodium naphthalene and the polymerization was carried out in DMSO. The results (Table 3) indicate that here too the predominant oligomer fraction was that of the trimer and not higher. This trimer was identical with that obtained in the oligomerization with methoxide. The effect of the type of the metal counterion of the methoxide on the oligomerization was studied in methanol and in DMF using the alkoxides of Li, Na, K and Mg. In methanol, it can be seen (Table 4) that, while with K-methoxide oligomerization occurred, there was no oligomerization with Li-methoxide and the main product had n = 1, obtained in 88% yield. With Mg-methoxide, only isomerization occurred. However different results were obtained for reaction in DMF. Even with Mg-methoxide, oligomers were obtained (Table 5) although the molecular weight of the oligomer mixture was much lower than that of the mixture obtained with the alkali metals, each of which gave the same order of molecular Table 4. Products of oligomerization by methoxide in methanol---effect of the counterion
Counterion
DMI + DMM + DMC (%)
n= 1 (%)
Dimer (%)
Trimer (%)
K* Lit Mg;~
23 11 100
53 88 --
14 ---
7 ---
* Methanolic KOCH3 (0.38mole/l) was added to DMI (5 mole/l); reaction time 24 hr at room temperature. ? Methanolic LiOCH 3 (0.09 mole/l) was added to DMI (0.9 mole/D; reaction time 5 hr at room temperature. :~Methanolic Mg(OCH3)2, (0.22 mole/l) was added to DMI (2.2mole/l); reaction time 24 hr at room temperature.
Anionic oligomerization of dimethyl itaconate
565
Table 5. Products of oligomerization by methoxides in DMF--effect of the counterion* DMI + DMC + DMM
ion Na K Li Mg
n= 1 (~o)
Dimer (~o)
Trimer (~)
Higher oligomers o/ (~o)
Mol wtt
%
25 21 19 18
65 68 70 11
8 ll 9 6
437 471 494 240
1.479 1.478 1.482 1.458
----. . . . 48 15
* Experimental conditions: methanolic methoxide (0.014mole/I) was added to DMI (0.0633 mole, 1.04 mole/l) in DMF (50 ml); [methanol] = 0.116 mole/1 ; reaction time 5 hr at 10°. t Average tool. wt. of crude reaction product after removing the DMF. weights. The major product obtained with the alkali metals was the trimer, but higher oligomers were also formed. The effect of the [monomer]/[initiator] ratio on the oligomerization was studied in D M F (Table 6) at constant methanol concentration. The time for complete disappearance of the monomer increased with increasing [monomer]/[initiator] ratio. At very low initiator concentrations, [monomer]/[initiator] > 75, isomerization of the monomer occurred but no oligomerization. No methanol was consumed during the reaction, and indicated by the fact that no product of n = 1 was formed. As seen, the oligomerization reaction is accompanied by isomerization of the monomer. To test this further in a system where the chances for oligomerization are small, D M I was heated in methanol in the presence of triethylamine. The isomer ratios obtained were D M I : D M C : D M M 12.3: 25.4: 62.3, respectively, i.e. the main fraction was that of the more stable t r a n s isomer. These results may be compare d with those reported for the base-catalysed isomerization of DMI, where D M M was also found as the major product [9, 10]. Since D M I undergoes base-catalysed isomerization to D M M and D M C , it was necessary to verify the extent of the participation of these isomers in the oli-
COOCH 3 CH2~
COOCH~
I
C - - ~..ICOOCH~ ~
~,H2 -
r
C~
CI)
(111
gomerization. Experiments were carried out in which D M M or D M C (34.0 mmole) were reacted with methanolic potassium methoxide (3.4mmole KOCH3, 10 mmole methanol) in D M S O (20 ml) at room temTable 6. Effect of the monomer/initiator (M/I) ratio on the time of disappearance of monomer* M/I Time (min)
10 5
25 l0
perature for 26hr. No oligomers were formed and only traces of D M I were detected. This latter fact is in accordance with the fact that the equilibrium between the isomers is not in favour of DMI. This leads to a low concentration of DMI, which in turn is unfavourable for oligomerization. The major product formed in the oligomerization was the trimer, having a molecular peak at m/e = 474 (exactly three times that of the monomer) in the mass spectrum. This fact, together with the facts that the elemental analysis is identical with that of the monomer and the i.r. spectrum lacks an absorption at 1100 cm-1 for an ether linkage, indicates that the mechanism of the oligomerization does not involve addition of the methoxide initiator to the double bond as the initiation step. The fact that the same trimer was obtained in the sodium naphthalene catalysed reaction also points out that initiation of the oligomerization does not proceed through addition of the methoxide to the double bond of DMI. In support of this conclusion, no dimethyl methoxymethyl succinate, n = 1, was detected in the reaction mixture during oligomerization in DMSO. Since methoxide does not add to the vinyl double bond, initiation of the oligomerization must proceed through abstraction of the acidic allylic hydrogen by the base (whether methoxide or sodium naphthalene) forming a stabilized carbanion:
50 45
75 180
100 t
* Experimental conditions: the required amount of methanolic KOCH3 was added to DM! (2.1 mole/l) in DMF (50 ml), total methanol (1.6 mole/l); temperature 10°. t Only isomerization occurred.
O-W,OOCH 3 -
i L
i
OO¢~s
-7
!L ° ....
Carbanion (II), being a terminal one and less sterically hindered, is expected to be the dominant reacting species. This acid-base reaction is favoured since methoxide is more of a base than a nucleophile [21, 22]. To confirm that the initiation is an acid base reaction, we used triethylamine as initiator, since it is known to react only as a base and does not add to double bonds. If initiation occurs only through addition of the initiator to the double bond, then triethylamine will not lead to oligomerization. The reaction was carried in D M S O at l(X)-120 °, and oligomers were actually formed in high yield (Table 7). Here also the trimer was the major product.
566
ARYEH BACHRACH,YOEL TSUR and ALBERTZILKHA
Table 7. Products of oligomerization by triethylamine in DMSO* Fraction no.
Boiling pt. (°/1 mm)
Yield (~)
1 2 3
160-180 240 Undistillable
18 62 19
C (~) 53.37 53.49 . .
H (~)
OCH 3
(~o)
no
6.31 6.22 .
39.51 39.4 .
1.471 1.486
* Experimental conditions: triethylamine (0.014mole, 0.33mole/I) was added to DMI (0.06 mole, 1.42 mole/l); reaction time 2 hr at 110°. In methanol, addition of methoxide to the double bond of DMI did occur yielding product with n = 1. However the main reaction is actually base-catalysed isomerization, which is also an acid-base reaction [ i i ] . But since the formation of the product having n = 1 is not reversible, high yields of it could be obtained. Propagation through carbanion (II) will lead to a dimer (III), having a double bond, as was found.
COOCH3
~.l 2 -
C~
growing anion on an ester group, third in the chain, leading to a cyclic ketone [24], i.r. absorption at 1712 c m - 1 [26], with elimination of methanol. In the corresponding DMI polymerization, this is not a significant reaction, since the trimer obtained gave a negative test for ketone with 2,4-dinitrophenyl hydrazine, and no carbonyl absorption besides that of the ester at 1745 cm- 1 was found.
COOCH3
CHCOOCH3
+
Since propagation was found to proceed only to a relatively small extent after the formation of the trimer, then there must be a dominating reaction leading to termination at this stage. Both the dimer and tetramer fractions were found by test with potassium permanganate and i.r. spectra to contain C=C unsaturation. However, the permanganate test as well as spectroscopic studies did not show the presence of an unsaturated double bond in the trimer. Therefore this termination must be a cyclization involving the terminal double bond, which might be addition of the growing carbanion to the double bond. This reaction can proceed through a pseudo six-membered ring as follows:
H-- C--COOCH~ CH3CO0 ~ C O O a ' 1 3
j
GH2---- CCH2COOCH3
CO0~l z
CH2COOCH 3
OJO
Concerning the above cyclization, a question arises why addition of the carbanion to the terminal double bond occurs although this bond is the same as that in D M M and DMC which were found to be unreactive towards oligomerization, unlike DMI. This may be explained by the fact that, contrary to the reaction with DMM, cyclization is an intramolecular reaction and as such is expected to be much faster than an intermolecular process due to "local concentration" [27] by several orders of magnitude. The conformation of the trimer can be shown to be a chair conformation with only one 1,3-di-axial interaction. Its molecular weight and elemental analysis CHzCOOCHz
+ H :b
COOCH 3
c ~
3 (tVl
=
CH3COOCH2
•
d
(iv) COOCH3
This cyclization may also explain the great preference for formation of the trimer over the higher oligomers. In the corresponding anionic polymerization of methyl methacrylate, it was also found [23-25] that there was a strong tendency for trimerization of the monomer through formation of a pseudo cyclohexane ring. In the polymerization of methyl methacrylate, internal cyclization occurred through attack of the
are in accordance with what was found. Physical analyses support the structure; i.r. (crn -z 925-1005 and 1000-1055 (cyclohexane) [28], 1350 (stretching of O II C----OCH3), 1015(stretching of methyl ester), 1745(carbonyl of ester); NMR (6) 1.9(CH2 at position a) shown in structure (IV), 2.2-2.6(CH2 groups at positions b,c) (the peaks were not sharp because of axial-
Anionic oligomerization of dimethyl itaconate equatorial flip), 2.4(CH 2 groups at position d) 3.69 (CH30 groups, e) (the peaks were not sharp because of small magnetic differences between the three CH 2 groups, and also the six methyl ester groups). In the mass spectrum of (IV), the important m/e values were: 474(M, molecular peak), 442(Mm CH3OH), 410(M--2CH3OH), 378(M--3CH3OH), 443, 412, 381, 350, 319 (equivalent to splitting off of one or several methoxyl groups), 31(OCH3), 32(CH3OH), 415(M--COOCH3), 59(COOCH3), 252(main peak). The main peak at 252 is due to three McLafferty rearrangements involving the hydrogens, 7- to the carbonyl double bond, leading to a trisubstituted benzene. The relative stability of the aromatic compound explains why m/e = 252 is the main peak.
O~ 3
o/4 H ~ , , . ~ 1 ~ CH,
J AA ~ - ~ 3
3
--
the following 4 fragmentation patterns will be observed; R R
-~.
H" R'
R
R:
t..
+
\H
R~
C5" R(
R'
R
R'
R
R'
R
R'
R
/"
R
"R
Table 8. Effect of the trimer on the plasticization of PVC* PVC + D.O.P. + trimer
Colorless Light yellow 77 min 55 rain 1325
1875
460 67
280 84
m/e 112
R
R.>
m/e 28
Rt
role 3-/'2
R
RI R/ m/e 2 9 0
m/e I10 R' =
CHzCOOCH 3
25,2
This substituted benzene undergoes further fragmentation to m/e = 221 (252~OCH3) and m/e = 193 (221~CO or 252---COOCH3). The fact that the fragmentation produces as the parent peak the substituted benzene supports the cyclohexane ring structure for (IV). From a study of the fragmentation, it can be shown that the structure of the trimer (IV) is that of a l,l,3,3,4,4-hexasubstituted cyclohexane and not of the symmetrical 1,1,3,3,5,5-hexasubstituted derivative. The corresponding 1,1,2,2,3,3-hexasubstituted derivative cannot undergo three McLafferty rearrangements, so that no benzene derivative can be formed. It may be noted that, if (IV) undergoes 1 McLafferty rearrangement, cyclohexene derivatives will be formed, which in the mass spectrograph can undergo retro Diels-Alder reaction. Since there are 4 possible modes in which this rearrangement can occur, then
PVC+ D.O.P.
R
m/e 288
R = COOCH3
m/e
Eli m/e 290
m/e IlO
R
OH3O /
R
Jl
R
co2c~
C
Color Heating time at 180' until decomposition Tensile strength (p.s.i.) Ultimate clongation(!'/,; Shore hardness A
567
* PVC sheet plasticized with 45~o dioctyl phthalate (D,O.P.) was compared with sheet plasticized with 22.5~/o D.O.P. and 22.5°;; trimer.
the ratio between the m/e values 290:112:372 will be 2:1:1, as was found. With the 1,1,3,3,5,5-hexasubstituted derivative the ratio between these m/e values should have been 1:1:1, since it is symmetrical.
Effect of solvent and the counterion It was seen that in methanol the reaction led mostly to the formation of isomerization products and to addition of methoxide to the double bond forming product with n = 1 (Table 1); in aprotic solvents (Table 2), the yield of the oligomers was much higher. This difference may on the one hand be due to the fact that oligomerization, being a nucleophilic addition to C----C double bonds, is expected to be much faster in aprotic solvents of high dielectric constant, than in protic ones, since reaction rates involving hydrogen-solvated nucleophiles are very slow compared to those involving non-solvated ones [29-31]. On the other hand, in both cases anions of DMI, DMM and DMC are present. In the protic solvent, there are more chances for protonation and formation of the respective isomeric esters, while in the aprotic solvent the anions that did not undergo protonation can isomerize easily to the DMM or DMC anions (II), which as was seen, initiate the oligomerization. It may be noted that there is a great difference in the acidity of the allylic hydrogen in the three isomeric esters, and only in DMI this hydrogen is also ~- to carbonyl and so is easily abstracted by base, so that in methanol the chances are that any DMM or DMC esters formed from the DMI will participate much less in the oligomerization. As regards the effect of the metal counterion of the methoxide on the reaction, it was seen that while in methanol Li behaved differently from Na and K, in DMSO and DMF all the alkali metals showed the same behavior. It is known that organo-lithium
568
ARYEH BACHRACH,YOEL TSUR and ALBERTZILKHA Table 9. Plasticization of epoxy resin with trimer*
Epoxy + DETA (g)
Trimer added (g)
5 5 3 3
-1 1 2
Appearance of resin Hard, brittle Hard, flexible Soft, flexible Flexible
Tensile strengtht (p.s.i.)
Elongation (%)
Heat distortion temp.~
Rockwell hardness
6130 4850 3000 1700
0.5 12.5 52 78
115 108 92 88
118 92 80 47
* Epoxy resin, ERL-2795 (Bakelite) (100 parts) was mixed with diethylene triamine (DETA) (11 parts). ~ Measured on an Instron instrument. ,+ Measured on a Heat Distortion Apparatus G. V. Planer. bonds are more covalent than those of Na and K and are more highly associated. Aprotic solvents of high dielectric constant and high degree of solvation lead to total dissociation of the alkali methoxide and that is why similar results were obtained with all the alkali metals in D M S O and D M F . Magnesium methoxide, due to its lower ionic character than the alkali metals, showed different behaviour. Use o f the trimer as a plasticizer for P V C
The physical properties of PVC plasticized with 45% dioctyl phthalate were compared with those of PVC plasticized with 22.5% dioctyl phthalate and 22.5% of the trimer. It can be seen (Table 8) that the trimer can be used as a plasticizer extender in combination with dioctyl phthalate. It contributes to increasing the tensile strength, decrease of per cent elongation and increase of the hardness of the PVC. The temperature resistance was lower than with dioctyl phthalate alone. The trimer was also tested as a plasticizer for PVC emulsion. An emulsion of PVC, used for coatings and as a mould release containing 35% solids, was mixed with 15% wt/wt of the trimer. The emulsion was added to a silicone rubber mould and the solvents were dried. The PVC from the emulsion had a tensile strength of 700 psi and 300% ultimate elongation while with the addition of the trimer the tensile strength was 600 psi and the ultimate elongation 450%. The trimer was also tested as a plasticizer for epoxy resins. The system used was Bakelite ERL-2795 and diethylene triamine as hardener. It can be seen (Table 9) that addition of the trimer led to lowering of the tensile strength and the hardness of the polymer, accompanied by an increase in the per cent elongation. The heat distortion of the polymer also decreased. The plasticized resins were tested for resistance to solvents using methylethyl ketone, chloroform, D M F , benzene and cyclohexane. After immersion for 3 weeks no trimer was extracted and there was no visible change. It can be that there was interaction of the ester groups of the trimer with the amine groups, securing more the plasticizer to the resin. EXPERIMENTAL
Materials
Dimethyl itaconate (DMI) m.p. 38 ° (Fluka) was used. Methanol was dried over magnesium. Dimethyl sulphoxide
(DMSO) was dried by azeotropic distillation with benzene, and fractionally distilled in vacuo. Dimethyl formamide, (DMF) absolute (Merck) was used. Tetrahydrofuran was dried over sodium and benzophenone. NMR spectra were taken on Varian HA-100 and T-60 spectrometers and mass spectra on an Atlas MAT CH-4 instrument. Oligomerization procedure
The reactions were carried out in three-necked flasks fitted with a mechanical stirrer, thermometer, and an opening fitted with a self-sealing rubber cap through which the reagents were added by syringe. The flask was dried by flaming in vacuo. All the reactions were carried out under nitrogen. Catalyst was added to the DMI; when the reaction was complete, acetic acid was added to neutralize the reaction mixture which was then diluted with chloroform and extracted several times with water. The chloroform was dried over magnesium sulphate, and distilled off. The products of the reaction were separated by fractional distillation. Oligomerization by sodium naphthalene
To a solution of DMI (25 g) in DMSO (50 ml) sodium naphthalene in THF (1.94 N, 5.1 ml) was added with stirring. After 2 hr at room temperature, the mixture was neutralized with acetic acid, diluted with chloroform and extracted with water. The chloroform was driven off and the residue was steam distilled to remove any naphthalene. The oligomer mixture was fractionally distilled in vacuo. Gas chromatography
Gas chromatography was used to monitor quantitatively for the monomer, for the product with n = 1, and for the isomeric esters, DMM and DMC. It was not possible to monitor the trimer because of its high boiling point. The analysis was carried out using a Packard 7400 Gas Chromatograph. The column was packed with butane diol succinate 5% and H3PO 4 4~o on C.W./H.M.D.S. 60/80. Injector and detector temperatures were 150°, and the column was held at 110 °.
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