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Polymerization of 4-vinylpyridine on polyphosphate macromolecules in aqueous solution
2704
A. N. GVOZDETSKII e$ a/.
5. L. TRELOAR, Fizika uprugosti kauchuka (The Physics Literature Publishing House, 1953 (Russian translation) 6. V. N. TSVETKOV, V. Ye. ESKIN and S. Ya. FRENKEL', t v o r a k h (Structure of Macromolecules in Solution). Izd. 7. W. KUHN, R. PASTERNAK a n d H. KUHN, Helv. chim.
of R u b b e r Elasticity). Foreign S t r u k t u r a makromolekul v" ras" N a u k a " , 1964 acta 30: 1705, 1947
POLYMERIZATION OF 4-VINYLPYRIDINE ON POLYPHOSPHATE MACROMOLECULES IN AQUEOUS SOLUTION* A . N . GVOZDETSKII, V. O. K I M , V. I . SMETAlgYUK, V. A . KABAI~OV
and V. A.KARor~ (dec.) A. V. Topchiev I n s t i t u t e of Petrochemical Synthesis, U.S.S.R. A c a d e m y of Sciences
(Received 29 January 1970)
THERE has been a number of recent papers on polymerization of certain monomers in the presence of a macromolecular matrix [1-4]. An example of this is the polymerization of 4-vinylpyridine (4-VP) on carbon-chain polyanions (polyacrylate, polyethylenesulphonate, polystyrenesulphonate, polymethaerylate) [4-8]. The products consist of complexes of the polyanions (the matrix) and the macro-cations formed. The high strength of these cations, due to cooperative interaction between the oppositely charged components, hinders separation of the new polymer from the original matrix. In order to overcome this difficulty we have chosen as the matrix easily hydrolysable polyphosphate macromolecules (PP). This material is convenient also because by varying the conditions of preparation it is possible to obtain polyphosphates with different, chosen degrees of polymerization. The present paper describes a study of polymerization of 4-VP in aqueous solution in the presence of polyphosphates, and of some properties of the polymer formed. EXPERIMENTAL
4-Vinylpyridine (4-VP) supplied b y Lowson Ltd. (Gt. Britain), was purified b y redistfllation in vacuo (b.p. 64.5°]15 ram, n~° 1.5497). I m m e d i a t e l y before each experiment the redistil]ed monomer was again evaporat~d a n d recondensed under high vacuum (10 -~1 0 - ' ram). The synthe~ of polyphosphates with known number-average degrees of polymerization (/~,) was carried out in a specially designed, quartz-glass apparatus, in which it is possible to m a i n t a i n a constant water-vapour pressure over a molten phosphate for a long time * Vysokomo]. soyed. AIS: No. 11, 2409-2416, 1971.
Polymerization of 4-vinylpyridine
2705
(equilibrium is established in a b o u t 24 hr). I t is known [9] t h a t the number-average degree of polymerization o£ P P ' s prepared from a dihydrophosphate b y the reaction nNaH2PO4"2H,O -~H (NaPO3),OH + (3n-- 1) H20
(z)
is dependent on the temperature of the molten phosphate and on the pressure of water v a p o u r ever it.
F i e . 1. A p p a r a t u s for syntheses of polyphosphates. A small q u a n t i t y of water was placed in the lower p a r t 1 of the a p p a r a t u s (Fig. 1) and a weighed q u a n t i t y of sodium dihydrophosphate in the p l a t i n u m crucible 2, supported in the holder 3. The a p p a r a t u s was evacuated through t h e side-arm 4 a n d scaled b y rotating t h e ground-glass joint 5. The temperature of the lower p a r t of the a p p a r a t u s was thermostatically controlled a t the t e m p e r a t u r e corresponding to the desired equilibrium waterv a p o u r pressure over the liquid water. The upper p a r t of the a p p a r a t u s is provided with an electric heater 6. The sleeve 7 contains a thermocouple for measurement a n d automatic control of the temperature. After continuous application of heat for 24 hr the joint 5 is disconnected a n d the crucible containing the molten product is quickly placed in a large copper block for cooling. The products were colourless, transparent, polymeric glasses. The number-average degree of polymerization of the P P was determined b y end-group analysis b y potentiometric back-titration. F o r kinetic measurements we used the spectrophotometric m e t h o d described in reference [8].
~k. N. ~VOZDETSKII 8~ aS.
2706
q, ! 30 20 D----
I0 i
i
i
0"8
L
I
i
t.O -log[PP) 20 JO 0.8 0"8 Time, rain FIO. 2. Determination of the order of reaction with respect to PP (~, = 100). Total initial concentration of monomer (4-VP)=0.184 mole/].; pH0 =5"57; 25°: a--kinetic curves for polyphosphate concentrations of : 0.093 (1); 0.140 (2); 0.186 (3); 0.280 g-equiv/]. (4); b--log-log graph of the dependence of the initial reaction rate on concentration of PP.
I0
Vpo/K . I0 -0
-[og[(dq/dt)o'No]
q, % #0
tO
t'8 Cl
b
#
30
8 2 .1"2
ZO
o
!
iO E8 I
I
2O O~ Time, rain
O.8 0"8 I'0 -log [Me]
3
5
7
gpH
FIG. 4
Fro. 3
FIG. 3. Determination of the order of reaction with respect to monomer. [PP]=0.184 g-equiv/].; pH0=5-56; 20° (i~=100) • a--initial monomer concentration: 0.094 (1); 0"140 (2); 0"186 (3); 0-270 mole/]. (4); b--log-log graph of the dependence of initial polymerization rate on monomer concentration. FIG. 4. Dependence on pH of the initial rate of polymerization of 4-VP in the presence of a p p (/5 =100). Total monomer concentration [4-VP] =0.172 mole/].; [PP] =200 g-equivft., 25°. RESULTS AND DISCUSSION
P o l y m e r i z a t i o n kinetics. I t is seen f r o m Fig. 2 t h a t t h e initial r a t e o f polym e r i z a t i o n o f 4-VP is i n d e p e n d e n t o f t h e c o n c e n t r a t i o n o f t h e p o l y p h o s p h a t e (zero order w i t h respect to p o l y p h o s p h a t e ) . W e n e x t studied t h e d e p e n d e n c e o f t h e initial p o l y m e r i z a t i o n r a t e on m o n o m e r concentration at constant p i t and polyphosphate concentration (~n~100).
Polymerization of 4-vinylpyridino
2707
T he concentration of 4-VP was varied between 0-094 and 0.270 mole/1. The results are presented in Fig. 3a. I t is seen from Fig. 3b t h a t the reaction is of the second order with respect to monomer.
toj[Cdq/dt)o%1 ao !
I'¢
- [(dq/dVo'Mol
q,%
1"8
a
/,~ 2
2o
1"0
1 fO
tO 0"~ 1
i
Io 20 T/me, rain
0"6
I
i
P
1"0
0.6
- fMJo
I
O'8
1
f.O
-log [M]o
Fio. 5
FIG. 6
Fio. 5. Polymerization of 4-VP in the presence of monomeric phosphate ions. Phosphate concentration 0.200 g-ion/l.; pho=5"56, 25°: a---kinetic curves for initial monomer concentrations of: 0.100 (•); 0.125 (2); 0.150 mole/1. (3); b--log-log graph of the dependence of initial polymerization rate on monomer concentration (mole/1.); 25°. FIG. 6. Graph for determining the order of reaction of polymerization of 4-VP on shorter matrices. [PP] =0.192 g-equiv/1.; pH0 =5.56; 25°; Pn =33.
Figure 4 shows the dependence of the rate of polymerization on the p H of the solution at constant concentrations of monomer and polyphosphate. The curve has a sharp m a x i m u m at pH-=5-6, which is equal to pKa of 4-VP. The kinetic results are described satisfactorily b y the equation
[H+]
(II)
V,o-=K x [M]0* ([H+]_t_ka)~ where vp0 is the initial rate, K a constant for a given monomer and matrix, [M]0 the total concentration of p r o t o n a t e d and u n p r o t o n a t e d monomer at zero time, ka the dissociation constant of the p r o t o n a t e d monomer and [H +] the hydrogen ion concentration. The continuous line in Fig. 4 is the curve of the dependence of the initial rate of polymerization on the p H of the solution, calculated from this equation. The " m a t r i x effect" of a polyphosphate on polymerization of 4-VP is confirmed by comparison of the above kinetic relationships with the kinetics of polymcri-
2708
Ao I~T. GVOZDETS]~II •t al.
zation of 4-VP in solutions containing an equivalent amount of monomeric phosphate ions instead of a polyphosphate. Figure 5 shows the kinetic curves and a graph for finding the order of reaction with respect to monomer, which in this instance is three. Polymerization of 4 - V P on shorter matrices. The kinetics of polymerization could be altered by passing to a sh,rter matrix. Figure 6 shows a log-log graph of the dependence of the initial polymerization rate on monomer concentration at a constant p H and a constant concentration of PP-33. Here the order of reaction with respect to monomer is 1.8, i.e. close to the order found in the presence of PP-100. Thus for manifestation of the matrix effect, due to adsorption of the reacting monomer molecules and growing chains on the polyanion, it is sufficient
a
d
e
i
i
2000
1600
f
1200
i
800
v, cm -/
Fxo. 7. I n f r a r e d spectra: a - - p r o d u c t of polymerization of 4-VP on polyphosphate matrices; b - - m o d e l complex; c - - p o l y m e r separated from the m a t r i x in the presence of a large quant i t y of triethylamine; d - - t h e same without addition of triethylamine; e - - r a d i c a l poly-4-VP.
for the average length of the latter to be about thirty units. ~A transition to the kinetics characteristic of polymerization in the presence of low-molecular anions (third order reaction with respect to mono~ner) would be expected with matrices of lower degrees of polymerization. Isolation of polymerization products. Some time after the commencement of polymerization of 4-VP in the presence of P P ' s a precipitate is deposited.
Polymerization of 4-vinylpyTidino
2709
This is a salt complex of the two component chains (of the newly formed polymer and the PP). It is evident from the infrared spectra in Fig. 7 that all the units of the reaction product are charged. Similar infrared spectra in the 2000-700 cm -1 region are obtained for the products obtained by mixing ordinary, "radical" poly-4-VP with PP's. The spectra of both complexes (Fig. 7, curves a and b) contain a band at 1640 cm -1, assigned to the charged pyridinium nucleus. A partially charged polymer usually gives two absorption bands, at 1640 and 1600 cm -1. The latter corresponds to the unprotonated pyridine nucleus. It is absent from the spectra of both complexes. X-ray analysis reveals, however, a substantial difference between the structures of the polymerization product and the model complex. The polymer growing on the matrix forms a regular, crystallizable poly-sol with it (lattice spacings 4.30 and 3.38 A). The poly-sol that precipitates when ordinary, "radical" poly-4VP is mixed with a polyphosphate is amorphous like the polyphosphate. As was mentioned above, the P - - O bonds forming the linear polyphosphate chain are easily hydrolysed. This should permit separation of the polymeric complex by decomposition of the macromoleeules of the matrix. Separation of the polymer from the polyphosphate does not in fact involve any fundamental difficulties. A model complex obtained by mixing solutions of radical poly-4-VP (Pn----10,000) and PP-150 in equimolar proportions is easily broken down by boiling it for several hours in very dilute hydrochloric acid (about 0.01 N). After quantitative neutralization of the acid hydrolysate, poly-4-VP precipitates. Elementary analysis shows that it is pure and its infrared spectrum is identical with the spectrum of the original 4-VP. The polyphosphate chain of the complex formed by polymerization of 4-VP on a polyphosphate is also easily hydrolysed under the same conditions. This is shown by the fact that the hydrolysate gives with the molybdate reagent, the yellow precipitate characteristic of monomeric phosphate ions. When the hydrolysate is treated with caustic alkali solution a polymer separates, the infrared spectrum of which contains a strong band in the 1600 cm -1 region, characteristic of the uncharged pyridine nucleus. The polymer separated in a strongly alkaline medium darkens rapidly however. To exclude the oxidizing effect of atmospheric oxygen all operations associated with polymerization, hydrolysis of the polyphosphate and isolation of the polymer, were subsequently carried out in a specially designed, totally enclosed glass apparatus. Dissolved air was removed from all the solutions by freezing under high vacuum. When the hydrolysate is neutralized in this apparatus with a large excess of ammonia a colourless polymer was obtained. This gave an infrared spectrum that contains a band at 1640 cm -1 as well as the peak at 1600 cm-L When this product was treated with caustic alkali however, and also when the polymer was isolated from the hydrolysate with caustic alkali without access of air, a 4iscoloured product was always obtained. These facts are not in accord with the previously stated assumption that
2710
A. N. GVOZDETSKIIeta/.
the structure of the complex is a continuous sequence of the type ~H2--CH--CHz~CH~
(111) H
H
I o-
P~,
because, as was stated above, when a model complex from radical poly-4-VP and a PP is treated similarly completely deprotonated poly-4-VP is obtained, completely free from charged pyridinium nuclei, the infrared spectrum of which does not contain a band at 1640 cm -1 and which is not discoloured by the alkali. It is well known that when alkylated pyridine nuclei are treated with alkali they undergo extensive chemical changes, involving ring opening and the appearance of colour. It must be assumed therefore that the polymer obtained by alkaline treatment of the product of matrix polymerization contains fragments of the type +//
(IV)
giving rise to absorption in the 1640 cm -1 region. A possible way in which these fragments arise in the chain is as follows. According to the scheme proposed in reference [4], initiation of polymerization consists in addition of the anion X to the protonated monomer, to form the zwitter-ion
CH--X~H,--~N+--H,
(V)
which then undergoes polymerization. This produces compounds with terminal ~ CHPy--CH2X groups, having a high alkylating ability. As long as the poly-4VP is attached to the polyphosphate matrix alkylation of the pyridine nuclei cannot occur, but during isolation of the polymer, after breakdown of the matrix, by addition of alkali, when the pH of the medium is increased and the polymer coagulates, alkylation of unprotonated pyridine nuclei occurs. Therefore the polymer isolated as described above contains Mkylated units. I f this suggestion is correct it would be expected that if a large quantity of a sufficiently easily alkylatable tertiary amine were added to the system during isolation of the polymer, the competition would result in reduction of the proportion of alkylated units in the poly-4-VP molecule. It was found in fact that the content of alkylated units in a polymer isolated from the hydrolysate by the action of a large excess of triethylamine, was considerably less than in a sample of the polymer isolated in a parallel experiment without addition of
Polymerization of 4-vinylpyridine
2711
triethylamine (Fig. 7, curves c and d). The first product was only slightly discoloured after prolonged boiling in a medium of pH about 12.* For study of the properties of the polymer formed on the matrix it is not expedient to a t t e m p t to isolate it by the action of alkaline reagents, because the secondary reactions t h a t then occur cause change in the structure of the polymer. Therefore for subsequent study the product of matrix polymerization was isolated in the form of polyphosphate, perchlorate or picrate complex salts having poor solubility in water. To prepare the perchlorate complex the polyphosphate complex and excess P P were precipitated from the reaction mixture by addition of methanol. The precipitate was washed repeatedly with methanol to remove monomer, then with water to remove the excess polyphosphate. The residue was hydrolysed in aqueous acid solution. A one and a half times excess of perchloric acid was added to the hydrolysate and the precipitated perchlorate of the polymer was washed several times with water, acidified with HC1Oa, to remove inorganic salts (test with molybdate reagent for absence of phosphate ions). The product was then washed several times with alcohol and dried i n vacuo. The pelleted product was subjected to X-ray analysis, which showed t h a t the perchlorate complex possesses well defined crystallinity (lattice spacings 5.06, 4-31, 3.78 and 3.38 A). The perchlorate of ordinary, radical poly-4VP, prepared in the same way, is amorphous. The perchlorate is more highly crystalline t h a n the complex with the PP. I f the hydrolysate is boiled for a long time in air before separation of the perchlorate complex an uncrystallizable perchlorate is obtained, probably as a result of disturbance of the regularity of the polymer. The number-average degree of polymerization of the polymer, which is determined by the method of gel-chromatography, was about twenty. The absence of low-molecular organic impurities from the samples was proved by gel-chromatography, t For this we used a cylindrical glass column of diameter 12 mm and length 500 ram, packed with the swollen, hydrophilic gel Sephadex G-15, through which a 0.1 ~ solution of potassium bromide, acidified with hydrochloric acid to p H = 3 , was pumped continuously at a constant rate (100 ml/hr). After passage of the solution through the column it was passed directly through a quartz through-flow cell of length 10 m m and volume 0.5 ml, placed in the sample beam of a CF-dDR (Optica Milano) double-beam spectrophotometer. The ab* After the experiments described above [10] and the present paper had been completed a paper was published giving the results of NMR analysis [11]. This showed that the product of matrix polymerization before alkaline treatment is not poly-4-VP but the isomeric polycation of regular structure, poly-l,4-pyridiniumethylene (ionene), containing the fragments {IV). The kinetics and mechanism taking this into account, and also the way in which normal 4-VP appears in the product of alkaline treatment, is discussed in detail in reference [12]. ¢ The authors express their gratitude to M. A. ~¢Iartynovufor assistance in this part of the work.
2712
A. N. GVOZDETSKII et a~.
sorption of light by the solution passing through the cell was continuously recorded on a moving chart. Test samples of a 0.1 ~/o solution of the material being studied (0.05-0.15 ml) were introduced into the column by means of a special device. Figure 8 shows gel-chromatograms of the perchlorate of poly-4-VP (curve a), the pure monomer (curve b) and specially prepared mixtures of the polymer I ......
0.8
I
bI
• xk. j
ZO
. . . . -.--" -
/ /c r~
ZS Time, m/n
\\
/d.. \,
\ ~.~..~
30
FIG. 8. Gel-chromatograms. a---perehlorate of polymer prepared b y m a t r i x polymerization; b---4-VP monomer; c--artificially prepared perchlorate complex containing 1 ~ of monomer; d - - t h e same with 3 ~ of monomer. D is the optical density a t 2 =260 mp.
perchlorate and the monomer, containing 1~/o (curve c) and 30/o (curve d) of the latter. It is seen that the given perchlorate complex does not contain significant amounts of low-molecular organic substances. Thus polymerization of 4-VP on polyphosphate anions results in formation of regular chains. The reaction product is an ordered complex made up from a chemically and structurally complementary polyanion and polycation. CONCLUSIONS
(1) A study has been made of the polymerization of 4-vinylpyridine in aqueous solution in the presence of polyphosphate maeromolecules of different lengths. (2) It is shown that during the course of polymerization an ordered, crystalline complex is formed, made up from the chemically and structurally complementary polymer chains. (3) The product of matrix polymerization, which forms with perchloric acid a highly crystalline complex salt with low solubility in water, has been separated from the polyphosphate complex by hydrolysis of the matrix.
Polymerization of oligomers in a shear-stress field
2713
(4) The product of matrix polymerization is unstable in an alkaline medium, undergoing secondary reactions resulting in a change in structure and disturbance of the regularity of the polymer molecules. Transldted by E. O. PHILLIPS REFERENCES 1. H. K ~ M M E R E R and A. JUNG, Makromolek. Chem. 101: 284, 1967 2. V. V. VLASOV, L. G. TOKAREVA, D. Ya. IVASHIN, B. L. TSETLIN and M. V. SHARLYGIN, Dokl. Akad. N a u k SSSR 161: 857, 1965 3. M. IMOTO, K. T~IKEMOTO a n d K. OSHIMA, Makromolek. Chem. 104: 244, 1967 4. V. A. KARANOV, K. V. ALIEV, T. I. PATRIKEYEVA, O. V. KARGINA and V. A. KARGIN, International Symposium on Macromolecular Chemistry, p. 129, Prague, 1965 5. V. A. KARGIN, V. A. KABANOV and O. V. KARGINA, Dokl. Akad. N a u k SSSR 161: 1131, 1965 6. O. V. KARGINA, M. V. UL'YANOVA, V. A. KABANOV and V. A. KARGIN, Vysokomol. soyed. A9: 340, 1967 (Translated in P o l y m e r Sei. U.S.S.R. 9: 2, 380, 1967) 7. O. V. KARGINA, V. A. KARANOV and V. A. KARGIN, International S y m p o s i u m on Macromolecular Chemistry, Brussels, 1967 8. V. A. KABANOV, V. A. PETROVSKAYA and V. A. KARGIN, Vysokomol. soyed. A1O: 925, 1968 (Translated in P o l y m e r Sci. U.S.S.R. 1O: 4, 1077, 1968) 9. E. TILO, K h i m i y a i tekhnol, polimerov, Nos. 7-8, 73, 1960 10. A. N. GVOZDETSgH~ Dissertation, 1969 11. J. C. SALAMON, B. SNIDER and W. L. FITCH, Polymer Preprints 2: 625, 1970 12. V. A. KABANOV, O. V. KARGINA a n d V. A. PETROVSKAYA, Vysokomol. soy~d. A I 3 : 348, 1971 (Translated in Polymer Sci. U.S.S.R. 13: 2, 394, 1971)
POLYMERIZATION OF OLIGOMERS IN A SHEAR-STRESS FIELD* Y u . S. LITATOV a n d L. M. SUSHKO Institute of the Chemistry of Maeromoleeular Compounds, Ukr. S.S.R. A c a d e m y of Sciences
(Received 27 March 1970)
IN recent years, in the study of polymerizable oligomers, much attention has been given to the question of preliminary ordering of the oligomer molecules before polymerization to a three-dimensional network. It has been shown in a number of papers [1, 2] that previous ordering of the oligomer molecules, brought about in different ways, results in the production of polymers with a new combination of properties. For example Lipatov and his collaborators [3, 4] showed, by the example of anionic polymerization of oligoester-aerylates, that the possible * Vysokomol. soyed. A13: 1~o. 11, 2417-2421, 1971.
A. N. GVOZDETSKII e$ a/.
5. L. TRELOAR, Fizika uprugosti kauchuka (The Physics Literature Publishing House, 1953 (Russian translation) 6. V. N. TSVETKOV, V. Ye. ESKIN and S. Ya. FRENKEL', t v o r a k h (Structure of Macromolecules in Solution). Izd. 7. W. KUHN, R. PASTERNAK a n d H. KUHN, Helv. chim.
of R u b b e r Elasticity). Foreign S t r u k t u r a makromolekul v" ras" N a u k a " , 1964 acta 30: 1705, 1947
POLYMERIZATION OF 4-VINYLPYRIDINE ON POLYPHOSPHATE MACROMOLECULES IN AQUEOUS SOLUTION* A . N . GVOZDETSKII, V. O. K I M , V. I . SMETAlgYUK, V. A . KABAI~OV
and V. A.KARor~ (dec.) A. V. Topchiev I n s t i t u t e of Petrochemical Synthesis, U.S.S.R. A c a d e m y of Sciences
(Received 29 January 1970)
THERE has been a number of recent papers on polymerization of certain monomers in the presence of a macromolecular matrix [1-4]. An example of this is the polymerization of 4-vinylpyridine (4-VP) on carbon-chain polyanions (polyacrylate, polyethylenesulphonate, polystyrenesulphonate, polymethaerylate) [4-8]. The products consist of complexes of the polyanions (the matrix) and the macro-cations formed. The high strength of these cations, due to cooperative interaction between the oppositely charged components, hinders separation of the new polymer from the original matrix. In order to overcome this difficulty we have chosen as the matrix easily hydrolysable polyphosphate macromolecules (PP). This material is convenient also because by varying the conditions of preparation it is possible to obtain polyphosphates with different, chosen degrees of polymerization. The present paper describes a study of polymerization of 4-VP in aqueous solution in the presence of polyphosphates, and of some properties of the polymer formed. EXPERIMENTAL
4-Vinylpyridine (4-VP) supplied b y Lowson Ltd. (Gt. Britain), was purified b y redistfllation in vacuo (b.p. 64.5°]15 ram, n~° 1.5497). I m m e d i a t e l y before each experiment the redistil]ed monomer was again evaporat~d a n d recondensed under high vacuum (10 -~1 0 - ' ram). The synthe~ of polyphosphates with known number-average degrees of polymerization (/~,) was carried out in a specially designed, quartz-glass apparatus, in which it is possible to m a i n t a i n a constant water-vapour pressure over a molten phosphate for a long time * Vysokomo]. soyed. AIS: No. 11, 2409-2416, 1971.
Polymerization of 4-vinylpyridine
2705
(equilibrium is established in a b o u t 24 hr). I t is known [9] t h a t the number-average degree of polymerization o£ P P ' s prepared from a dihydrophosphate b y the reaction nNaH2PO4"2H,O -~H (NaPO3),OH + (3n-- 1) H20
(z)
is dependent on the temperature of the molten phosphate and on the pressure of water v a p o u r ever it.
F i e . 1. A p p a r a t u s for syntheses of polyphosphates. A small q u a n t i t y of water was placed in the lower p a r t 1 of the a p p a r a t u s (Fig. 1) and a weighed q u a n t i t y of sodium dihydrophosphate in the p l a t i n u m crucible 2, supported in the holder 3. The a p p a r a t u s was evacuated through t h e side-arm 4 a n d scaled b y rotating t h e ground-glass joint 5. The temperature of the lower p a r t of the a p p a r a t u s was thermostatically controlled a t the t e m p e r a t u r e corresponding to the desired equilibrium waterv a p o u r pressure over the liquid water. The upper p a r t of the a p p a r a t u s is provided with an electric heater 6. The sleeve 7 contains a thermocouple for measurement a n d automatic control of the temperature. After continuous application of heat for 24 hr the joint 5 is disconnected a n d the crucible containing the molten product is quickly placed in a large copper block for cooling. The products were colourless, transparent, polymeric glasses. The number-average degree of polymerization of the P P was determined b y end-group analysis b y potentiometric back-titration. F o r kinetic measurements we used the spectrophotometric m e t h o d described in reference [8].
~k. N. ~VOZDETSKII 8~ aS.
2706
q, ! 30 20 D----
I0 i
i
i
0"8
L
I
i
t.O -log[PP) 20 JO 0.8 0"8 Time, rain FIO. 2. Determination of the order of reaction with respect to PP (~, = 100). Total initial concentration of monomer (4-VP)=0.184 mole/].; pH0 =5"57; 25°: a--kinetic curves for polyphosphate concentrations of : 0.093 (1); 0.140 (2); 0.186 (3); 0.280 g-equiv/]. (4); b--log-log graph of the dependence of the initial reaction rate on concentration of PP.
I0
Vpo/K . I0 -0
-[og[(dq/dt)o'No]
q, % #0
tO
t'8 Cl
b
#
30
8 2 .1"2
ZO
o
!
iO E8 I
I
2O O~ Time, rain
O.8 0"8 I'0 -log [Me]
3
5
7
gpH
FIG. 4
Fro. 3
FIG. 3. Determination of the order of reaction with respect to monomer. [PP]=0.184 g-equiv/].; pH0=5-56; 20° (i~=100) • a--initial monomer concentration: 0.094 (1); 0"140 (2); 0"186 (3); 0-270 mole/]. (4); b--log-log graph of the dependence of initial polymerization rate on monomer concentration. FIG. 4. Dependence on pH of the initial rate of polymerization of 4-VP in the presence of a p p (/5 =100). Total monomer concentration [4-VP] =0.172 mole/].; [PP] =200 g-equivft., 25°. RESULTS AND DISCUSSION
P o l y m e r i z a t i o n kinetics. I t is seen f r o m Fig. 2 t h a t t h e initial r a t e o f polym e r i z a t i o n o f 4-VP is i n d e p e n d e n t o f t h e c o n c e n t r a t i o n o f t h e p o l y p h o s p h a t e (zero order w i t h respect to p o l y p h o s p h a t e ) . W e n e x t studied t h e d e p e n d e n c e o f t h e initial p o l y m e r i z a t i o n r a t e on m o n o m e r concentration at constant p i t and polyphosphate concentration (~n~100).
Polymerization of 4-vinylpyridino
2707
T he concentration of 4-VP was varied between 0-094 and 0.270 mole/1. The results are presented in Fig. 3a. I t is seen from Fig. 3b t h a t the reaction is of the second order with respect to monomer.
toj[Cdq/dt)o%1 ao !
I'¢
- [(dq/dVo'Mol
q,%
1"8
a
/,~ 2
2o
1"0
1 fO
tO 0"~ 1
i
Io 20 T/me, rain
0"6
I
i
P
1"0
0.6
- fMJo
I
O'8
1
f.O
-log [M]o
Fio. 5
FIG. 6
Fio. 5. Polymerization of 4-VP in the presence of monomeric phosphate ions. Phosphate concentration 0.200 g-ion/l.; pho=5"56, 25°: a---kinetic curves for initial monomer concentrations of: 0.100 (•); 0.125 (2); 0.150 mole/1. (3); b--log-log graph of the dependence of initial polymerization rate on monomer concentration (mole/1.); 25°. FIG. 6. Graph for determining the order of reaction of polymerization of 4-VP on shorter matrices. [PP] =0.192 g-equiv/1.; pH0 =5.56; 25°; Pn =33.
Figure 4 shows the dependence of the rate of polymerization on the p H of the solution at constant concentrations of monomer and polyphosphate. The curve has a sharp m a x i m u m at pH-=5-6, which is equal to pKa of 4-VP. The kinetic results are described satisfactorily b y the equation
[H+]
(II)
V,o-=K x [M]0* ([H+]_t_ka)~ where vp0 is the initial rate, K a constant for a given monomer and matrix, [M]0 the total concentration of p r o t o n a t e d and u n p r o t o n a t e d monomer at zero time, ka the dissociation constant of the p r o t o n a t e d monomer and [H +] the hydrogen ion concentration. The continuous line in Fig. 4 is the curve of the dependence of the initial rate of polymerization on the p H of the solution, calculated from this equation. The " m a t r i x effect" of a polyphosphate on polymerization of 4-VP is confirmed by comparison of the above kinetic relationships with the kinetics of polymcri-
2708
Ao I~T. GVOZDETS]~II •t al.
zation of 4-VP in solutions containing an equivalent amount of monomeric phosphate ions instead of a polyphosphate. Figure 5 shows the kinetic curves and a graph for finding the order of reaction with respect to monomer, which in this instance is three. Polymerization of 4 - V P on shorter matrices. The kinetics of polymerization could be altered by passing to a sh,rter matrix. Figure 6 shows a log-log graph of the dependence of the initial polymerization rate on monomer concentration at a constant p H and a constant concentration of PP-33. Here the order of reaction with respect to monomer is 1.8, i.e. close to the order found in the presence of PP-100. Thus for manifestation of the matrix effect, due to adsorption of the reacting monomer molecules and growing chains on the polyanion, it is sufficient
a
d
e
i
i
2000
1600
f
1200
i
800
v, cm -/
Fxo. 7. I n f r a r e d spectra: a - - p r o d u c t of polymerization of 4-VP on polyphosphate matrices; b - - m o d e l complex; c - - p o l y m e r separated from the m a t r i x in the presence of a large quant i t y of triethylamine; d - - t h e same without addition of triethylamine; e - - r a d i c a l poly-4-VP.
for the average length of the latter to be about thirty units. ~A transition to the kinetics characteristic of polymerization in the presence of low-molecular anions (third order reaction with respect to mono~ner) would be expected with matrices of lower degrees of polymerization. Isolation of polymerization products. Some time after the commencement of polymerization of 4-VP in the presence of P P ' s a precipitate is deposited.
Polymerization of 4-vinylpyTidino
2709
This is a salt complex of the two component chains (of the newly formed polymer and the PP). It is evident from the infrared spectra in Fig. 7 that all the units of the reaction product are charged. Similar infrared spectra in the 2000-700 cm -1 region are obtained for the products obtained by mixing ordinary, "radical" poly-4-VP with PP's. The spectra of both complexes (Fig. 7, curves a and b) contain a band at 1640 cm -1, assigned to the charged pyridinium nucleus. A partially charged polymer usually gives two absorption bands, at 1640 and 1600 cm -1. The latter corresponds to the unprotonated pyridine nucleus. It is absent from the spectra of both complexes. X-ray analysis reveals, however, a substantial difference between the structures of the polymerization product and the model complex. The polymer growing on the matrix forms a regular, crystallizable poly-sol with it (lattice spacings 4.30 and 3.38 A). The poly-sol that precipitates when ordinary, "radical" poly-4VP is mixed with a polyphosphate is amorphous like the polyphosphate. As was mentioned above, the P - - O bonds forming the linear polyphosphate chain are easily hydrolysed. This should permit separation of the polymeric complex by decomposition of the macromoleeules of the matrix. Separation of the polymer from the polyphosphate does not in fact involve any fundamental difficulties. A model complex obtained by mixing solutions of radical poly-4-VP (Pn----10,000) and PP-150 in equimolar proportions is easily broken down by boiling it for several hours in very dilute hydrochloric acid (about 0.01 N). After quantitative neutralization of the acid hydrolysate, poly-4-VP precipitates. Elementary analysis shows that it is pure and its infrared spectrum is identical with the spectrum of the original 4-VP. The polyphosphate chain of the complex formed by polymerization of 4-VP on a polyphosphate is also easily hydrolysed under the same conditions. This is shown by the fact that the hydrolysate gives with the molybdate reagent, the yellow precipitate characteristic of monomeric phosphate ions. When the hydrolysate is treated with caustic alkali solution a polymer separates, the infrared spectrum of which contains a strong band in the 1600 cm -1 region, characteristic of the uncharged pyridine nucleus. The polymer separated in a strongly alkaline medium darkens rapidly however. To exclude the oxidizing effect of atmospheric oxygen all operations associated with polymerization, hydrolysis of the polyphosphate and isolation of the polymer, were subsequently carried out in a specially designed, totally enclosed glass apparatus. Dissolved air was removed from all the solutions by freezing under high vacuum. When the hydrolysate is neutralized in this apparatus with a large excess of ammonia a colourless polymer was obtained. This gave an infrared spectrum that contains a band at 1640 cm -1 as well as the peak at 1600 cm-L When this product was treated with caustic alkali however, and also when the polymer was isolated from the hydrolysate with caustic alkali without access of air, a 4iscoloured product was always obtained. These facts are not in accord with the previously stated assumption that
2710
A. N. GVOZDETSKIIeta/.
the structure of the complex is a continuous sequence of the type ~H2--CH--CHz~CH~
(111) H
H
I o-
P~,
because, as was stated above, when a model complex from radical poly-4-VP and a PP is treated similarly completely deprotonated poly-4-VP is obtained, completely free from charged pyridinium nuclei, the infrared spectrum of which does not contain a band at 1640 cm -1 and which is not discoloured by the alkali. It is well known that when alkylated pyridine nuclei are treated with alkali they undergo extensive chemical changes, involving ring opening and the appearance of colour. It must be assumed therefore that the polymer obtained by alkaline treatment of the product of matrix polymerization contains fragments of the type +//
(IV)
giving rise to absorption in the 1640 cm -1 region. A possible way in which these fragments arise in the chain is as follows. According to the scheme proposed in reference [4], initiation of polymerization consists in addition of the anion X to the protonated monomer, to form the zwitter-ion
CH--X~H,--~N+--H,
(V)
which then undergoes polymerization. This produces compounds with terminal ~ CHPy--CH2X groups, having a high alkylating ability. As long as the poly-4VP is attached to the polyphosphate matrix alkylation of the pyridine nuclei cannot occur, but during isolation of the polymer, after breakdown of the matrix, by addition of alkali, when the pH of the medium is increased and the polymer coagulates, alkylation of unprotonated pyridine nuclei occurs. Therefore the polymer isolated as described above contains Mkylated units. I f this suggestion is correct it would be expected that if a large quantity of a sufficiently easily alkylatable tertiary amine were added to the system during isolation of the polymer, the competition would result in reduction of the proportion of alkylated units in the poly-4-VP molecule. It was found in fact that the content of alkylated units in a polymer isolated from the hydrolysate by the action of a large excess of triethylamine, was considerably less than in a sample of the polymer isolated in a parallel experiment without addition of
Polymerization of 4-vinylpyridine
2711
triethylamine (Fig. 7, curves c and d). The first product was only slightly discoloured after prolonged boiling in a medium of pH about 12.* For study of the properties of the polymer formed on the matrix it is not expedient to a t t e m p t to isolate it by the action of alkaline reagents, because the secondary reactions t h a t then occur cause change in the structure of the polymer. Therefore for subsequent study the product of matrix polymerization was isolated in the form of polyphosphate, perchlorate or picrate complex salts having poor solubility in water. To prepare the perchlorate complex the polyphosphate complex and excess P P were precipitated from the reaction mixture by addition of methanol. The precipitate was washed repeatedly with methanol to remove monomer, then with water to remove the excess polyphosphate. The residue was hydrolysed in aqueous acid solution. A one and a half times excess of perchloric acid was added to the hydrolysate and the precipitated perchlorate of the polymer was washed several times with water, acidified with HC1Oa, to remove inorganic salts (test with molybdate reagent for absence of phosphate ions). The product was then washed several times with alcohol and dried i n vacuo. The pelleted product was subjected to X-ray analysis, which showed t h a t the perchlorate complex possesses well defined crystallinity (lattice spacings 5.06, 4-31, 3.78 and 3.38 A). The perchlorate of ordinary, radical poly-4VP, prepared in the same way, is amorphous. The perchlorate is more highly crystalline t h a n the complex with the PP. I f the hydrolysate is boiled for a long time in air before separation of the perchlorate complex an uncrystallizable perchlorate is obtained, probably as a result of disturbance of the regularity of the polymer. The number-average degree of polymerization of the polymer, which is determined by the method of gel-chromatography, was about twenty. The absence of low-molecular organic impurities from the samples was proved by gel-chromatography, t For this we used a cylindrical glass column of diameter 12 mm and length 500 ram, packed with the swollen, hydrophilic gel Sephadex G-15, through which a 0.1 ~ solution of potassium bromide, acidified with hydrochloric acid to p H = 3 , was pumped continuously at a constant rate (100 ml/hr). After passage of the solution through the column it was passed directly through a quartz through-flow cell of length 10 m m and volume 0.5 ml, placed in the sample beam of a CF-dDR (Optica Milano) double-beam spectrophotometer. The ab* After the experiments described above [10] and the present paper had been completed a paper was published giving the results of NMR analysis [11]. This showed that the product of matrix polymerization before alkaline treatment is not poly-4-VP but the isomeric polycation of regular structure, poly-l,4-pyridiniumethylene (ionene), containing the fragments {IV). The kinetics and mechanism taking this into account, and also the way in which normal 4-VP appears in the product of alkaline treatment, is discussed in detail in reference [12]. ¢ The authors express their gratitude to M. A. ~¢Iartynovufor assistance in this part of the work.
2712
A. N. GVOZDETSKII et a~.
sorption of light by the solution passing through the cell was continuously recorded on a moving chart. Test samples of a 0.1 ~/o solution of the material being studied (0.05-0.15 ml) were introduced into the column by means of a special device. Figure 8 shows gel-chromatograms of the perchlorate of poly-4-VP (curve a), the pure monomer (curve b) and specially prepared mixtures of the polymer I ......
0.8
I
bI
• xk. j
ZO
. . . . -.--" -
/ /c r~
ZS Time, m/n
\\
/d.. \,
\ ~.~..~
30
FIG. 8. Gel-chromatograms. a---perehlorate of polymer prepared b y m a t r i x polymerization; b---4-VP monomer; c--artificially prepared perchlorate complex containing 1 ~ of monomer; d - - t h e same with 3 ~ of monomer. D is the optical density a t 2 =260 mp.
perchlorate and the monomer, containing 1~/o (curve c) and 30/o (curve d) of the latter. It is seen that the given perchlorate complex does not contain significant amounts of low-molecular organic substances. Thus polymerization of 4-VP on polyphosphate anions results in formation of regular chains. The reaction product is an ordered complex made up from a chemically and structurally complementary polyanion and polycation. CONCLUSIONS
(1) A study has been made of the polymerization of 4-vinylpyridine in aqueous solution in the presence of polyphosphate maeromolecules of different lengths. (2) It is shown that during the course of polymerization an ordered, crystalline complex is formed, made up from the chemically and structurally complementary polymer chains. (3) The product of matrix polymerization, which forms with perchloric acid a highly crystalline complex salt with low solubility in water, has been separated from the polyphosphate complex by hydrolysis of the matrix.
Polymerization of oligomers in a shear-stress field
2713
(4) The product of matrix polymerization is unstable in an alkaline medium, undergoing secondary reactions resulting in a change in structure and disturbance of the regularity of the polymer molecules. Transldted by E. O. PHILLIPS REFERENCES 1. H. K ~ M M E R E R and A. JUNG, Makromolek. Chem. 101: 284, 1967 2. V. V. VLASOV, L. G. TOKAREVA, D. Ya. IVASHIN, B. L. TSETLIN and M. V. SHARLYGIN, Dokl. Akad. N a u k SSSR 161: 857, 1965 3. M. IMOTO, K. T~IKEMOTO a n d K. OSHIMA, Makromolek. Chem. 104: 244, 1967 4. V. A. KARANOV, K. V. ALIEV, T. I. PATRIKEYEVA, O. V. KARGINA and V. A. KARGIN, International Symposium on Macromolecular Chemistry, p. 129, Prague, 1965 5. V. A. KARGIN, V. A. KABANOV and O. V. KARGINA, Dokl. Akad. N a u k SSSR 161: 1131, 1965 6. O. V. KARGINA, M. V. UL'YANOVA, V. A. KABANOV and V. A. KARGIN, Vysokomol. soyed. A9: 340, 1967 (Translated in P o l y m e r Sei. U.S.S.R. 9: 2, 380, 1967) 7. O. V. KARGINA, V. A. KARANOV and V. A. KARGIN, International S y m p o s i u m on Macromolecular Chemistry, Brussels, 1967 8. V. A. KABANOV, V. A. PETROVSKAYA and V. A. KARGIN, Vysokomol. soyed. A1O: 925, 1968 (Translated in P o l y m e r Sci. U.S.S.R. 1O: 4, 1077, 1968) 9. E. TILO, K h i m i y a i tekhnol, polimerov, Nos. 7-8, 73, 1960 10. A. N. GVOZDETSgH~ Dissertation, 1969 11. J. C. SALAMON, B. SNIDER and W. L. FITCH, Polymer Preprints 2: 625, 1970 12. V. A. KABANOV, O. V. KARGINA a n d V. A. PETROVSKAYA, Vysokomol. soy~d. A I 3 : 348, 1971 (Translated in Polymer Sci. U.S.S.R. 13: 2, 394, 1971)
POLYMERIZATION OF OLIGOMERS IN A SHEAR-STRESS FIELD* Y u . S. LITATOV a n d L. M. SUSHKO Institute of the Chemistry of Maeromoleeular Compounds, Ukr. S.S.R. A c a d e m y of Sciences
(Received 27 March 1970)
IN recent years, in the study of polymerizable oligomers, much attention has been given to the question of preliminary ordering of the oligomer molecules before polymerization to a three-dimensional network. It has been shown in a number of papers [1, 2] that previous ordering of the oligomer molecules, brought about in different ways, results in the production of polymers with a new combination of properties. For example Lipatov and his collaborators [3, 4] showed, by the example of anionic polymerization of oligoester-aerylates, that the possible * Vysokomol. soyed. A13: 1~o. 11, 2417-2421, 1971.