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Preparation of block copolymers using oligoperoxide initiators containing peroxide groups of different heat stabilities
PREPARATION OF BLOCK COPOLYMERS USING OLIGOPEROXIDE INITIATORS CONTAINING PEROXIDE GROUPS OF DIFFERENT HEAT STABILITIES* Yu. L. ZHEREBIN,S. S. IVAI~CHEVand N. M. DOMAR~.VA Scientific Industrial Association "Plastpolymer"
(Received 21 August 1972) The prospects were indicated of using diacyl oligoperoxide initiators with peroxide groups of variable heat stabilities for the synthesis of poly(styrene-block-methylmethacrylate) and poly(butadiene-block-styrene) with high ( ~ 83 %) yields. Optimum process conditions were found. I t was found possible to regulate the composition of block copolymers, prepare block copolymers with frequently alternating blocks of both monomers. A s t u d y of composition heterogeneity of poly(styrene-block-methylmethacrylate) b y light scattering, refractometry and osmometry enabled us to establish t h a t it increases with an increase in the proportion of " a c t i v e " polystyrene during block copolymerization and with a reduction in the molecular weight of the latter. Pm~A~ON of block copolymers b y radical polymerization involves in every case the polymerization of one of the monomers using initiating systems to enable a polymer to be obtained which contains peroxide groups ("active" prepolymer) and polymerization of a second monomer initiated b y the prepolymer obtained. Pol3rfunctional peroxide compounds of different structures appeared to be the most suitable for obtaining "active" prepolymers with initiating systems [1-4]. I t has been pointed out [1] t h a t the yield of the block copolymer depends on the content of "inactive" polymer in the prepolymer, of which the gravimetric proportion ~ m a y be determined b y the ratio
~=(1-~)/(p-~),
(1)
where ~ is the average proportion of undecomposed peroxide groups of the polyfunetionM initiator during polymerization; p is the number of peroxide groups in the initiator; ~ is the average number of peroxide groups remaining in the prepolymer macromoleeule. I t is easy to see t h a t the efficiency of block copolymerization can be easily regulated b y changing t h e / 9 - - f u n c t i o n a l i t y of the initiator used. I f when using diperoxide compounds (/9=2) the gravimetric proportion of the "inactive" polymer reaches 25%, for oligoperoxide with /9~10 it is less t h a n 1%. This is the significant advantage of oligoperoxide compounds proposed b y Tsvetkov [1] for preparing block eopolymers. However, the initiators indicated have shortcomings owing to the equivalence of peroxide groups in the peroxide molecule. Values of ~ and !c are proportional to the time of polymerization, which does not always enable us to reach high degrees of conversion with the retention of requisite values of a n d ~. I n addition, peroxide groups are contained in the polymer maeromolecule as blocks, which also reduces the efficiency of bloek-copolymerization. This explains the experimental fact t h a t even in the case of sufficiently high functionality of the initiator (/9----10-20) the * Vysokomol. soyed. A16: No. 4, 893-901, 1974. 1033
1034
Yu. L. ZKERERINet ad.
block-copolymer contains a significant proportion of homopolymer [1, 2]. The yield of block copolymers can be improved using polyfunctional initiators with peroxide groups of varying heat stability [3-5] as initiators of prepolymerization. The variable heat stability of peroxide groups enables high values of ~ and accordingly, ~ to be maintained in the prepolymor at certain temperatures, practically independent of polymerization time. Up to the present time among compounds of this type di- and triperoxide compounds [3, 4] wore only examined for preparing block copolymcrs. This s tu d y is concerned with the possibilities of using oligoperoxides recently prepared [5, 6] with alternating peroxide groups of variable heat stability of general structure --[--C (CH,)n--C00C--CH (CHg)m---C00--]~--,
where R=CH~, C,H., el, Br; n=l-S; r e = l - 7 ; p----8-20, in the synthesis of block copolymers. The structure of this t y p e of initiator, without being restricted by the time factor enables at certain temperatures a prepolymer to be obtained, retaining up to 50% of peroxide groups contained in the macromolecule in isolated form. This opens up the possibility of preparing block copolymers with recurr e n t alternating units of both monomers of t y p e - A - B - A - B . To examine this we dealt with the possibility of preparing block copolymers b y a two-stage system b y radical polymerization initiated with oligo(azelaoyldiperoxy-~-bromo-azelaoyl)peroxide (OP), where n = 7 , m----6, p = 1 8 and R = B r . Preparation, properties and kinetic parameters of stepwise thermal decomposition of OP are described in a previous paper [7]. T A B L E 1. CONDITIONS OF PREPARATION A ~ D PROPERTIES OF ~'ACTIVE~ POLYMERS
(60°, initiator--OP) Code of Initiator Duration of Monomer the speci- concentration polymerizamen base-mole/1, rich, rain Styrene
Butadiene MMA
Degree of polymerization
Number of O--O groups per macromolecnle, according to IR spcotroiodometry scopy
PS-1 PS-2 PS-2 PS-4
0"075 0.075 0.100 0.125
60 120 60 60
292 390 207 180
8-2 6.1 8"3 9.9
8.0 5.9 7"8 10-2
B-1 M-l*
0-125 0.075
120 30
132 --
6-5 8.5
---
* Temperatureof polymerization65% "Active" polymers were obtained by bulk polymerization of corresponding monomers at 60 ° and concentrations of the initiator (OP) of 0.075, 0-100 and 0.125 base mole/1. Comparatively high initiator concentrations were chosen
Preparation of block copolymers
i035
because iodometry and IR spectroscopy for the quantitative determination of peroxide groups in polymers can be used in specimens with a relatively high percentage of active oxygen. For the careful purification of "active" polymer specimens to free them from undecomposed peroxide, the polymer was reprecipitated three times with ethanol from benzene solution.
fn
I 0.4_
~ ~'gO
0"2
~
0
I zx2 J 60 ~20
T/me, min Fro. 1
I ~80
!
2
3
f
Time ~ ht, Fro. 2
Fro. 1. Semi-logarithmictransformations of curves showing the decomposition of peroxide groups in "active" PS, obtained in the presence of OP at 80 (I) and 75° ( I I ) for P8-2 (1) and PS-4 (2); ztD, is the optical density variation of the inhibitor solution (iodine) during the decomposition of peroxide in time v; ~D~--same with complete decompositionof peroxide. FIG. 2. Variation of the degree of polymerization of "active" PS during thermal decomposition in chlorobenzenesolution in the presence of iodine at 70 (1) and 80° (2). As shown by Table 1, as a result of the first stage of polymerization polymers are obtained containing a different number of peroxide groups per macromolecule. The number of peroxide groups in the "active" polymer may be regulated by changing the concentration and time conditions of polymerization. The decomposition of peroxide groups in the polymer was studied using inhibitors at 75 and 80 °. The linearity of semi-logarithmic transformation obtained during the decomposition of an "active" polymer with different numbers of O - - 0 bonds at different temperatures (Fig. 1) is evidence that the reaction is of first order. Rate constants of thermal decomposition of peroxide bonds of "active" polystyrenes (PS) are equal to constants of decomposition of corresponding peroxide bonds in the OP molecule [7]. Therefore, kinetic data of decomposition of oligoperoxides may be used (Table 2) in selecting optimum conditions for preparing high molecular weight "active" polymers and block copolymers.
1036
Y u . L, Z - - - ~ . B m
eJ a/.
A satisfactory agreement between radical yield in vol./~ determined b y t h e inhibition method and the efficiency of initiation of stable 0 - 0 bends of O P derived from results of polymerization [7] indicates that all radicals be~Iin to undergo polymer chain extension. TABLE
2. KINETIC
PAR~TERS
D E C O M P O S I T I O N OF P E R O X I D E
OF THERMAT,
GROUPS OF ACTIVE
POLYMERS
Peroxide groups in PMMA PS
kdeeompX 106,
T, °C
]~
see-1 75 75 80
9.04 9.00 17.20
0.40 0-42 --
Therefore, these OP can be readily used as initiators of block copolymerization with a gradual increase in the temperature of polymerization. At low .temperatures polymerization results in the formation of a polymer with peroxide groups. At higher temperatures these peroxide groups break down to form macroradicals, which ensures the production of block copolymers.
lJJj
"0
I
20 Time, rain
I
I
40
FIo. 3. Kinetic curves showing the accumulation of SM-3 (1-3); SM-2 (4-6) and B8-1 (7-9) block copolymers at 80 (1-3; 7-9); 75° (4-6) and with "active" polymer : monomer ratios of 1 : 1 ( 1 , 7); 1 : 3 ( 2 , 5 , 8 ) ; 1 : 5 (3,6,9) and1:2(4). I t was therefore important to determine position of peroxide bonds in the "active" polymer. I t was found that thermal decomposition of "active" PS in chlorobenzene in the presence of free radical acceptors markedly reduces the degree of polymerization P of the initial macromolecule (Fig. 2). A sudden reduction in macromolecular chain length during the decomposition of peroxide
Preparation of block copolymers
10~
groups in the presence of an inhibitor indicates that peroxide ranged in an isolated position inside the main chain of PS. This icant since, with this arrangement of peroxiiie bonds in "active" low proportion of homopolymer impurities can be expected when
groups are arr e s u l t is s i g n i f PS a relatively preparing block
eopolymers. TABLE 3. P ~ * ~ R S
O~ m.OCK CO~O'.YM~ZA~O~ ~
C~C~S~CS
OF BLOCX
COPOLYMERS
6
~ ~
SM-1 PS-1
SM-~
PS-2
!
0"288 MMA
0"356
75
75
SM-3 PS-3
0"224
80
PS-4
0.200
80
SM.4
BS-1
B-1
MS-1 M-1
0"270 Styrene
80
0.124
85 [
~ ~
~
Composition of reaction
~
~ ~"
freePr°duct'%
1:2
1-62
0"75
7"0
4"0
--
89
1 : 3 1 : 4 1 : 5
1"42 1.25 1.16
1"10 1"49 1-74
7"5 .
6"5 .
--
86
1:6 1:7
1.08
2"30
0.92 1.00
2.68
-----
83 94 95 97
--
98
-2.0 1.0 --
98 95 97 97
1 : 2 1 : 3
1 1 1 1
: : : :
1 :
1 1 1 1 1 1 1 1
: : : : : : : :
5 1 3 5 1 3 7 1 3 5 1 3 5
0'90 0"83 3'00 2"50 1.83 3.01 2"51 .1-34 0-37 0.33 0.26 0.43 0.25 0.16
1"22 1-70 2"00 0"49 0"82 1.16 0.55 0.90 2.04 --~ 0.58 1.00 1.80
. . 9.5 3"0 2.5 0"5 . . 1.0 . . 1.0 3.0 2.0 3.0 . . .
.
. .
. . . .
. . .
. . 7"5 3.0 2.5 2"5 . . 1.0 . . 1.0 ---. . .
.
. .
. . . .
. . .
The "active" polymers obtained without purification were used in the second stage of block copolymerization. Data in Fig. 3 and Table 2 show that "active" polymers used as initiators of block copolymerization, have the conventional properties of peroxide initiators. On increasing the concentration of "active" polymers and increasing temperature, the rate of polymerization increases and intrinsic viscosities of the products formed decrease accordingly. With the same gravimetric ratios of "active" polymer : monomer process rate also depends on the molecular weight of the "active" monomer since in this case molar concentra-
1038
Y~. L. ZHEREBII~ et a~.
tion alters. Intrinsic viscosities of products depend on the type of component taking part in block copolymerization. Tim rate of block copolymerization and the molecular weights of polymers formed can therefore be easily regulated by changing the initial ratio of the polymer-monomer mixture, the concentration of the initiator in the first stage and temperature in both stages of the process.
/00
~
-
/
40d _
I Fro. 4
I
2
I
3y
J
-Z
0
2
4
I
Fro. 5
FIG. 4. Fractional precipitation curves of a synthetic mixture of a PS-PMMA (1) and SM-2 (2) and SM-1 (3) block copolymers. Solvent: THF, precipitant: petroleum ether. FIG. 5. Relationship between Mw app and (VA--VB)/V for copolymer specimen. The figures at the curves are the numbers of specimens in Table 5. An important characteristic of block copolymerization is the practically complete absence of homopolymer impurities (Table 3). This is confirmed by data of a combined method of selective solution and fractional precipitation and the quantitative analysis of I R spectra. When analysing poly(styrene-blockl~riA) specimens homo-PS was extracted with boiling eyclohexane and homoPI~EVIA with acetonitrile [8]. Extraction was also combined with precipitation [9]. After the extraction of homo-PS (or homo-PM:M_A) a mixture of block copolymer and homo-PMMA (or homo-PS) was dissolved in T H F and precipitated with petroleum ether (b. p. 60-80°). Homo-PS was extracted from poly(butadiene-block-styrene) with boiling acetone and homopolybutadiene, with petroleum ether. The amount of PS contained in poly(butadiene-block-styrenes) and poly(styrene-block-~IA) (after selective solution) was determined from the variation of band intensity at 699 cm -1 in I R spectrum typical of the phenyl group. The amount of PM~IA contained in poly(styrene-bloek-MMA) (after active solution) was determined from the variation of band intensity vc=o (1730 cm -1) in 5% polymer solutions in dioxane in cells of constant thickness. The investigations established ~hat the yields of block copolymers when preparing poly(styrene-block-lViMA) and poly(butadiene-block-styrenes) v a r y in the ranges of 83-98 and 91-93%, respectively. This high yield of block co-
Preparation of block copolymers
1039
polymers agrees with the theoretical prerequisites expressed and confirms that OP with peroxide groups of different heat stabilities are effective initiators for preparing polymers with peroxide groups and block copolymers. As a result of examining the fractional precipitation of poly(styrene-blockMMA) specimens optimum conditions were found for precipitation and curves plotted for the precipitation of block copolymers (Fig. 4). Precipitation curves of block copolymers are situated between precipitation curves of PS and PMMA, corresponding to molecular weight, which is confirmed by values of precipitation limits: ~es~2.7-3.2; ?pMMA-~0"33--0.53; 7S~_1--~1.6--2.0; ~SM_2~1.4--1.7 (TiS the volumetric ratio of the precipitant to solvent volume). I f on using diperoxides merely one terminal peroxide bond can be added on average to each "active" polymer macromolecule and A-B type block copolymers obtained, while in the presence of triperoxides [4] (two terminal peroxide bonds) type B - A - B obtained, in our case with internal arrangement in the "active" polymer of a fairly large number of peroxide groups it is evidently possible to obtain an optimum block copolymer structure (with frequent alternation of monomer units) of type - B - A - B - A - B - A . This block copolymer structure is, of course, only probable when monomers are used in the second stage of synthesis, in which chain breakage takcs place exclusively by recombination. Block copolymers will generally be formed of the following main types: A-B, B - A - B , - B - A - B - A - B - A . However, simple calculation shows that in the presence in the "active" polymer molecule of five internal peroxide groups the proportion of structure A-B is under 1.5°/o. TABLE 4. REFRACTIVEINDEX INCREME~CTSOF CORI~ESeO~DI~CGH O ~ [ O P O L Y MERs
Solvent MEK Chloroform Toluene Bromoform
n~2 2 1.3795 1.4460 1.4995 1.6010
! i~
ml/g 0.221 0.151 0.108 0.013
0.115 0.063 -- 0.003 -- 0~)87
As a result of synthesis block copolymers very heterogeneous in molecular weight (molecular heterogeneity) and composition (composition heterogeneity) m a y be formed. Since block copolymers of the same average composition, but different composition variation m a y vary considerably in physical and mechanical properties, the composition heterogeneity of the specimens obtained should be determined quantitatively and the possibility of controlling heterogeneity according to composition, evaluated by changing conditions of synthesis o f block copolymers. We investigated molecular weight characteristics and the composition heterogeneity of several poly(styrene-block-MMA) specimens obtained using both
1040
Y u . L. Z H E ~ . B r ~ et
al.
"active" PS with varying polymerization times and with different PS contents during block copo!ymerization. Light scattering (laboratory visual nephelometer developed from a PI~I photometer), refractometry (IRP-23) and osmometry (Fuoss-!V[ead t y p e osmometer with "finest ultracell filter" membranes) were used for the investigation. Optical measurements were made with ~ = 546nm. TABLE 5. RESULTS OF D~.TER~NI~G THE MOLECULA~WEIGHTSOF BLOCKCOPOLYME~SBY Lm~T SCATr~mNG ~N V~mUS SOLW~TS ~
o
1 2 3 4
• ~
o
SM-1 SM-2
MEK
Chloroform
~ x
~
1:7 1:3 1:3 1:2
0.115 0.133 0.140 0.146
Toluene
~ x~.
470 396 480 305
Bromoform
C) x
-- I . . . . 0.079[ 370 0-017 620 0.022 475 0.087~ 240 0.029 285
x
0.086 --0.0681 --0.065 --0-057
460 598 615 740
Benzene was used as standard scattering liquid. To determine the value of "apparent" Mwap9 the following solvents were used: MEK, chloroform, toluene and bromoform. Refractive indices n~ of the solvents selected and the refractive index increment of styrene ~ and methylmethacrylate VB components of the block copolymer (i. e. corresponding homopolymers) are shown in Table 4. The value of M~ was determined from osmometric results in M E K at 25 °. Table 5 shows values of v and Mwapp of the block copolymer specimens studied. The following equation [10] were used to calculate the "true" M~ value of the block copolymer and components ~(w~) and M (B) and evaluate the composition heterogeneity P and Q of the block copolymer [10]:
M~p.-- ~7~ ~
+ v*(v~v~)~ • ~ ) + v~(v~v*)~ (1-~) ~7~~)
iwapp:/~'W÷
2 P YA-1,'___~B ÷ Q (YA--VB) 2 y2
1 P=~.. ~M,~(x,--x)-----~[(1--x) (A~w-- ~(~B))--X (b~'w-- A~A))]
(2) (3)
(4)
t/
Pmsx:=x (l--x)
(~¢-(A)__)t~(B))
Qraax--~x ( l - - x ) [(l--x) 3,-t'(-~-)÷X_,'~'(B)] ,
(6) (7)
Preparation
of block copolymers
1041
where x is the weight average content A in the block copolymer determined from refractometri6 data V=XVA-~- (l--x)
VB
(8)
~i is the gravimetric proportion of molecules with molecular weight Mtj and x~ composition; Pmax and Qmax correspond to the case of maximum composition heterogeneity for a given block copolymer, i. e. a homopolymcr mixture with the same values of M(A) ~ W and ~71//tB) tO • The numerical average values of M~A) and M~B) were determined from the equations
M~)=xM.
(9)
M~)----(1--x) Mn
(10)
It should be noted that averaging in eqns. (9) and (10) covers all macromoleeules of the specimen, therefore, the presence of homopolymer A results in a lower value of ~(nB) and of homopolymer B, to a reduced value of M(nA) (Table 6). TABLE
6.
RESULTS
OF DETERMINING
M O L E C U L A R W E I G H T :AND C O M P O S I T I O N H E T E R O G E N E I T 1 ~
OF THE
SPECIMENS
STUDIED
•
* x
Pm.~lQm.~
N
I 1
3
465
160
2.9
10
--
--
465
160
2.9
2
18
450
--
~0
~0
~
--
112
--
--
490
--
--
--47.2
22.4
0.84
0-80
3 4
23 29
520 410
190 240
~0
2.7 1-7
110 93
44 70
2.5 1.3
473 520
146 170
3'2 3"0
--29.1 --85-1
11.2 41-7
0-45 0-93
0.32 0"94
It follows from eqn. (3) that for a block copolymer of homogeneous composition ( P = 0 , Q=o) ~tTwappis independent of v i. e. of the solvent used and is equal to the "true" value of Mw and the relationship between Mwapp and (vA--VB)/V takes the form of a straight line parallel to the abscissa axis. For a block copolymet of heterogeneous composition the relationship is represented by a parabola. Figure 5 and Table 6 indicate that only specimen 1 obtained with a ratio of "active" PS : PM:MA of 1 : 7 was homogeneous in composition. A low content of the styrene constituent makes it difficult to obtain accurate quantitative data about the composition of this block eopolymer by the methods used and suggests that there is no composition variation with molecular weight. The other specimens studied show varying heterogeneity in composition. They are characterized by P < 0 , which is expressed in a displacement to the right of parabolic
1042
Yu. L. Zll3EREBrLqet
al.
curves from the ordinate and confirms that with an increase in molecular weight, the block eopolymer molecules are enriched with MMA units. The composition heterogeneity of specimen 4 is very high and raises doubts as to whether this specimen is a mixture of homopolymers. For verification we turn to values of/14n. For a homopolymer mixture it is correct to say that
/1~ and 21~ values previously derived were found assuming the absence of homopolymers from the product of block copolymerization and cannot therefore be used in eqn. (11). We can, however, evaluate the maximum value of (~ixtm)max which corresponds to a mixture of monodispersed homopolymers, i. e. when ~14A--/14 x and M--B 223 vA 10a, n-w n = M --r w . For specimen 4 we obtain /~mixture~ tl,-n ]max= which within the range of experimental error, is the same as J~n=240X 10a. However, some polydispersion of components A and B m a y be expected as regards molecular weight, i. e. MXn<~wA and 2tinr<~l~w~. Then, 214m~tu~e#214n and therefore, the specimen examined is not a homopolymer mixture. A considerable heterogeneity of composition of this block copolymer is due to the close relation between macromolecular composition and molecular weight. This is also confirmed b y the low polydispersion of the styrene constituent of macromolecules (2t~wA/~=l'3), i. e. the overall weight of PS blocks in the block copolymer molecule depends slightly on the molecular weight of the latter. For specimen 3, of which composition heterogeneity is much lower, the high value of JTwA/J4n A is due to a more proportional distribution of polystyrene units in block copolymer molecules of different molecular weight. This is confirmed b y the fact that values of 2~w/Y~n, -~ws ~I?A/j,~An and ~tB/M w/ n~ are similar. A s t u d y of the effect of conditions of block copolymerization on polymer structure shows that the composition heterogeneity of poly(styrene-block-MMA) increases with an increase in the proportion of "active" PS during block copolymerization and if the content of "active" PS is the same, with a reduction of molecular weight. A variation in conditions of block copolymerization has little effect on 2~w of the block eopolymer, ~ w~ and the polydispersion of 2t~wB/;l~. At the same time the value of MnA decreases with a reduction in the content of , , active 7, PS, while the polydispersion of/~wA//~n~ decreases with an increase in composition heterogeneity of the block copolymer. It m a y be assumed that high composition heterogeneity of the block copolymer obtained with a high proportion of "active" PS and a reduction of molecular weight, is because the polystyrene macroradicals formed are large and have a low diffusion coefficient, consequently, on being formed they do not react at a great distance from each other and the probability of meeting and reacting with a radical containing a low number of monomer units of MMA, is high. This results in the formation of block copolymer molecules enriched with PS units. After the PS radicals had been used up to some extent the extension of PMMA segments begins to predominate which
Hydrolysis of but~liene-nitrile rubber in alkaline medium
1043
results in the formation of block copolymer molecules of higher molecular weight enriched with MMA units. Finally, we note that by altering conditions of block copolymerization both in the first and second stages of synthesis, block copolymers with a varying degree of composition heterogeneity may be obtained, in order to synthesize various optimum block copolymer structures according to requirements of use. Translated by E. SEMERE REFERENCES 1. N. S. TSVETKOV, R. F. MARKOVSKAYA, Khimiya i khimich, tekhnol. 11: 936, 1968; Vysokomol. soyed. 7: 169, 1965 (Translated in Polymer Sci U.S.S.R. 7: 1, 185, 1965) 2. G. SMETS, L. CONVENT and Y. BORGHT, Makromolek. Chem. 23: 162, 1957 3. S. S. IVANCHEV, A. I. YURZHENKO, V. I. GALIBEI, A. I. PRISYAZHNIKOV and Yu. N. ANISIMOV, Auth. Cert. 218431, 1968; Byull. izobr. No. 17, 1968 4. S. S. IVANCHEV, V. L GALIBEI, T. A. TOLPYGINA, Auth. Cert. 278116, 1970; Byull. isobr., No. 25, 1970 5. S. S. IVANCHEV, Yu. L. ZHEREBIN, V. I. KUZNETSOV and Yu. I. DERKACH, Auth. Cert. 359251, 1972; Byull. izobr. No. 35, 1972 6. Yu. L. ZHEREBIN, S. S. IVANCHEV, V. I. GALIBEI, Zh. organ, khimii 7: 1660, 1971 7. Yu. L. ZHEREBIN, Dissertation, 1972 8. T. OTSU, J. Polymer Sci. 26: 236, 1957 9. R. TSEREZA, Metody issledovaniya polimerov (Methods of Investigating Polymers). Izd. inostr, lit., 1961 10. W. BUSHUK and H. BENOIT, Compt. rend. 246: :3167, 1958; Canad. J. Chem. 36: 1616, 1958
KINETIC STUDY OF HYDROLYSIS OF BUTADIENE-NITRILE RUBBER IN ALKALINE MEDIUM* 1~. SIt. FRENKEL', T. I . KIRILLOVA a n d E . A. KUZ'MINA All-Union Scientific Research and Design Institute of the Rubber I n d u s t r y
(Received 21 August 1972)
A kinetic study was made of the interaction of butadiene-nitrile rubber dissolved with alkali in o-xylene. I t was found that, in the complex process of hydrolysis of polymer molecules, hydrolysis of the polyamide obtained is the decisive stage. The activation energy of hydrolysis of polyamide was determined at temperatures of 125 to 145 °. * Vysokomol. soyed. AI6: No. 4, 902-905, 1974.
(Received 21 August 1972) The prospects were indicated of using diacyl oligoperoxide initiators with peroxide groups of variable heat stabilities for the synthesis of poly(styrene-block-methylmethacrylate) and poly(butadiene-block-styrene) with high ( ~ 83 %) yields. Optimum process conditions were found. I t was found possible to regulate the composition of block copolymers, prepare block copolymers with frequently alternating blocks of both monomers. A s t u d y of composition heterogeneity of poly(styrene-block-methylmethacrylate) b y light scattering, refractometry and osmometry enabled us to establish t h a t it increases with an increase in the proportion of " a c t i v e " polystyrene during block copolymerization and with a reduction in the molecular weight of the latter. Pm~A~ON of block copolymers b y radical polymerization involves in every case the polymerization of one of the monomers using initiating systems to enable a polymer to be obtained which contains peroxide groups ("active" prepolymer) and polymerization of a second monomer initiated b y the prepolymer obtained. Pol3rfunctional peroxide compounds of different structures appeared to be the most suitable for obtaining "active" prepolymers with initiating systems [1-4]. I t has been pointed out [1] t h a t the yield of the block copolymer depends on the content of "inactive" polymer in the prepolymer, of which the gravimetric proportion ~ m a y be determined b y the ratio
~=(1-~)/(p-~),
(1)
where ~ is the average proportion of undecomposed peroxide groups of the polyfunetionM initiator during polymerization; p is the number of peroxide groups in the initiator; ~ is the average number of peroxide groups remaining in the prepolymer macromoleeule. I t is easy to see t h a t the efficiency of block copolymerization can be easily regulated b y changing t h e / 9 - - f u n c t i o n a l i t y of the initiator used. I f when using diperoxide compounds (/9=2) the gravimetric proportion of the "inactive" polymer reaches 25%, for oligoperoxide with /9~10 it is less t h a n 1%. This is the significant advantage of oligoperoxide compounds proposed b y Tsvetkov [1] for preparing block eopolymers. However, the initiators indicated have shortcomings owing to the equivalence of peroxide groups in the peroxide molecule. Values of ~ and !c are proportional to the time of polymerization, which does not always enable us to reach high degrees of conversion with the retention of requisite values of a n d ~. I n addition, peroxide groups are contained in the polymer maeromolecule as blocks, which also reduces the efficiency of bloek-copolymerization. This explains the experimental fact t h a t even in the case of sufficiently high functionality of the initiator (/9----10-20) the * Vysokomol. soyed. A16: No. 4, 893-901, 1974. 1033
1034
Yu. L. ZKERERINet ad.
block-copolymer contains a significant proportion of homopolymer [1, 2]. The yield of block copolymers can be improved using polyfunctional initiators with peroxide groups of varying heat stability [3-5] as initiators of prepolymerization. The variable heat stability of peroxide groups enables high values of ~ and accordingly, ~ to be maintained in the prepolymor at certain temperatures, practically independent of polymerization time. Up to the present time among compounds of this type di- and triperoxide compounds [3, 4] wore only examined for preparing block copolymcrs. This s tu d y is concerned with the possibilities of using oligoperoxides recently prepared [5, 6] with alternating peroxide groups of variable heat stability of general structure --[--C (CH,)n--C00C--CH (CHg)m---C00--]~--,
where R=CH~, C,H., el, Br; n=l-S; r e = l - 7 ; p----8-20, in the synthesis of block copolymers. The structure of this t y p e of initiator, without being restricted by the time factor enables at certain temperatures a prepolymer to be obtained, retaining up to 50% of peroxide groups contained in the macromolecule in isolated form. This opens up the possibility of preparing block copolymers with recurr e n t alternating units of both monomers of t y p e - A - B - A - B . To examine this we dealt with the possibility of preparing block copolymers b y a two-stage system b y radical polymerization initiated with oligo(azelaoyldiperoxy-~-bromo-azelaoyl)peroxide (OP), where n = 7 , m----6, p = 1 8 and R = B r . Preparation, properties and kinetic parameters of stepwise thermal decomposition of OP are described in a previous paper [7]. T A B L E 1. CONDITIONS OF PREPARATION A ~ D PROPERTIES OF ~'ACTIVE~ POLYMERS
(60°, initiator--OP) Code of Initiator Duration of Monomer the speci- concentration polymerizamen base-mole/1, rich, rain Styrene
Butadiene MMA
Degree of polymerization
Number of O--O groups per macromolecnle, according to IR spcotroiodometry scopy
PS-1 PS-2 PS-2 PS-4
0"075 0.075 0.100 0.125
60 120 60 60
292 390 207 180
8-2 6.1 8"3 9.9
8.0 5.9 7"8 10-2
B-1 M-l*
0-125 0.075
120 30
132 --
6-5 8.5
---
* Temperatureof polymerization65% "Active" polymers were obtained by bulk polymerization of corresponding monomers at 60 ° and concentrations of the initiator (OP) of 0.075, 0-100 and 0.125 base mole/1. Comparatively high initiator concentrations were chosen
Preparation of block copolymers
i035
because iodometry and IR spectroscopy for the quantitative determination of peroxide groups in polymers can be used in specimens with a relatively high percentage of active oxygen. For the careful purification of "active" polymer specimens to free them from undecomposed peroxide, the polymer was reprecipitated three times with ethanol from benzene solution.
fn
I 0.4_
~ ~'gO
0"2
~
0
I zx2 J 60 ~20
T/me, min Fro. 1
I ~80
!
2
3
f
Time ~ ht, Fro. 2
Fro. 1. Semi-logarithmictransformations of curves showing the decomposition of peroxide groups in "active" PS, obtained in the presence of OP at 80 (I) and 75° ( I I ) for P8-2 (1) and PS-4 (2); ztD, is the optical density variation of the inhibitor solution (iodine) during the decomposition of peroxide in time v; ~D~--same with complete decompositionof peroxide. FIG. 2. Variation of the degree of polymerization of "active" PS during thermal decomposition in chlorobenzenesolution in the presence of iodine at 70 (1) and 80° (2). As shown by Table 1, as a result of the first stage of polymerization polymers are obtained containing a different number of peroxide groups per macromolecule. The number of peroxide groups in the "active" polymer may be regulated by changing the concentration and time conditions of polymerization. The decomposition of peroxide groups in the polymer was studied using inhibitors at 75 and 80 °. The linearity of semi-logarithmic transformation obtained during the decomposition of an "active" polymer with different numbers of O - - 0 bonds at different temperatures (Fig. 1) is evidence that the reaction is of first order. Rate constants of thermal decomposition of peroxide bonds of "active" polystyrenes (PS) are equal to constants of decomposition of corresponding peroxide bonds in the OP molecule [7]. Therefore, kinetic data of decomposition of oligoperoxides may be used (Table 2) in selecting optimum conditions for preparing high molecular weight "active" polymers and block copolymers.
1036
Y u . L, Z - - - ~ . B m
eJ a/.
A satisfactory agreement between radical yield in vol./~ determined b y t h e inhibition method and the efficiency of initiation of stable 0 - 0 bends of O P derived from results of polymerization [7] indicates that all radicals be~Iin to undergo polymer chain extension. TABLE
2. KINETIC
PAR~TERS
D E C O M P O S I T I O N OF P E R O X I D E
OF THERMAT,
GROUPS OF ACTIVE
POLYMERS
Peroxide groups in PMMA PS
kdeeompX 106,
T, °C
]~
see-1 75 75 80
9.04 9.00 17.20
0.40 0-42 --
Therefore, these OP can be readily used as initiators of block copolymerization with a gradual increase in the temperature of polymerization. At low .temperatures polymerization results in the formation of a polymer with peroxide groups. At higher temperatures these peroxide groups break down to form macroradicals, which ensures the production of block copolymers.
lJJj
"0
I
20 Time, rain
I
I
40
FIo. 3. Kinetic curves showing the accumulation of SM-3 (1-3); SM-2 (4-6) and B8-1 (7-9) block copolymers at 80 (1-3; 7-9); 75° (4-6) and with "active" polymer : monomer ratios of 1 : 1 ( 1 , 7); 1 : 3 ( 2 , 5 , 8 ) ; 1 : 5 (3,6,9) and1:2(4). I t was therefore important to determine position of peroxide bonds in the "active" polymer. I t was found that thermal decomposition of "active" PS in chlorobenzene in the presence of free radical acceptors markedly reduces the degree of polymerization P of the initial macromolecule (Fig. 2). A sudden reduction in macromolecular chain length during the decomposition of peroxide
Preparation of block copolymers
10~
groups in the presence of an inhibitor indicates that peroxide ranged in an isolated position inside the main chain of PS. This icant since, with this arrangement of peroxiiie bonds in "active" low proportion of homopolymer impurities can be expected when
groups are arr e s u l t is s i g n i f PS a relatively preparing block
eopolymers. TABLE 3. P ~ * ~ R S
O~ m.OCK CO~O'.YM~ZA~O~ ~
C~C~S~CS
OF BLOCX
COPOLYMERS
6
~ ~
SM-1 PS-1
SM-~
PS-2
!
0"288 MMA
0"356
75
75
SM-3 PS-3
0"224
80
PS-4
0.200
80
SM.4
BS-1
B-1
MS-1 M-1
0"270 Styrene
80
0.124
85 [
~ ~
~
Composition of reaction
~
~ ~"
freePr°duct'%
1:2
1-62
0"75
7"0
4"0
--
89
1 : 3 1 : 4 1 : 5
1"42 1.25 1.16
1"10 1"49 1-74
7"5 .
6"5 .
--
86
1:6 1:7
1.08
2"30
0.92 1.00
2.68
-----
83 94 95 97
--
98
-2.0 1.0 --
98 95 97 97
1 : 2 1 : 3
1 1 1 1
: : : :
1 :
1 1 1 1 1 1 1 1
: : : : : : : :
5 1 3 5 1 3 7 1 3 5 1 3 5
0'90 0"83 3'00 2"50 1.83 3.01 2"51 .1-34 0-37 0.33 0.26 0.43 0.25 0.16
1"22 1-70 2"00 0"49 0"82 1.16 0.55 0.90 2.04 --~ 0.58 1.00 1.80
. . 9.5 3"0 2.5 0"5 . . 1.0 . . 1.0 3.0 2.0 3.0 . . .
.
. .
. . . .
. . .
. . 7"5 3.0 2.5 2"5 . . 1.0 . . 1.0 ---. . .
.
. .
. . . .
. . .
The "active" polymers obtained without purification were used in the second stage of block copolymerization. Data in Fig. 3 and Table 2 show that "active" polymers used as initiators of block copolymerization, have the conventional properties of peroxide initiators. On increasing the concentration of "active" polymers and increasing temperature, the rate of polymerization increases and intrinsic viscosities of the products formed decrease accordingly. With the same gravimetric ratios of "active" polymer : monomer process rate also depends on the molecular weight of the "active" monomer since in this case molar concentra-
1038
Y~. L. ZHEREBII~ et a~.
tion alters. Intrinsic viscosities of products depend on the type of component taking part in block copolymerization. Tim rate of block copolymerization and the molecular weights of polymers formed can therefore be easily regulated by changing the initial ratio of the polymer-monomer mixture, the concentration of the initiator in the first stage and temperature in both stages of the process.
/00
~
-
/
40d _
I Fro. 4
I
2
I
3y
J
-Z
0
2
4
I
Fro. 5
FIG. 4. Fractional precipitation curves of a synthetic mixture of a PS-PMMA (1) and SM-2 (2) and SM-1 (3) block copolymers. Solvent: THF, precipitant: petroleum ether. FIG. 5. Relationship between Mw app and (VA--VB)/V for copolymer specimen. The figures at the curves are the numbers of specimens in Table 5. An important characteristic of block copolymerization is the practically complete absence of homopolymer impurities (Table 3). This is confirmed by data of a combined method of selective solution and fractional precipitation and the quantitative analysis of I R spectra. When analysing poly(styrene-blockl~riA) specimens homo-PS was extracted with boiling eyclohexane and homoPI~EVIA with acetonitrile [8]. Extraction was also combined with precipitation [9]. After the extraction of homo-PS (or homo-PM:M_A) a mixture of block copolymer and homo-PMMA (or homo-PS) was dissolved in T H F and precipitated with petroleum ether (b. p. 60-80°). Homo-PS was extracted from poly(butadiene-block-styrene) with boiling acetone and homopolybutadiene, with petroleum ether. The amount of PS contained in poly(butadiene-block-styrenes) and poly(styrene-block-~IA) (after selective solution) was determined from the variation of band intensity at 699 cm -1 in I R spectrum typical of the phenyl group. The amount of PM~IA contained in poly(styrene-bloek-MMA) (after active solution) was determined from the variation of band intensity vc=o (1730 cm -1) in 5% polymer solutions in dioxane in cells of constant thickness. The investigations established ~hat the yields of block copolymers when preparing poly(styrene-block-lViMA) and poly(butadiene-block-styrenes) v a r y in the ranges of 83-98 and 91-93%, respectively. This high yield of block co-
Preparation of block copolymers
1039
polymers agrees with the theoretical prerequisites expressed and confirms that OP with peroxide groups of different heat stabilities are effective initiators for preparing polymers with peroxide groups and block copolymers. As a result of examining the fractional precipitation of poly(styrene-blockMMA) specimens optimum conditions were found for precipitation and curves plotted for the precipitation of block copolymers (Fig. 4). Precipitation curves of block copolymers are situated between precipitation curves of PS and PMMA, corresponding to molecular weight, which is confirmed by values of precipitation limits: ~es~2.7-3.2; ?pMMA-~0"33--0.53; 7S~_1--~1.6--2.0; ~SM_2~1.4--1.7 (TiS the volumetric ratio of the precipitant to solvent volume). I f on using diperoxides merely one terminal peroxide bond can be added on average to each "active" polymer macromolecule and A-B type block copolymers obtained, while in the presence of triperoxides [4] (two terminal peroxide bonds) type B - A - B obtained, in our case with internal arrangement in the "active" polymer of a fairly large number of peroxide groups it is evidently possible to obtain an optimum block copolymer structure (with frequent alternation of monomer units) of type - B - A - B - A - B - A . This block copolymer structure is, of course, only probable when monomers are used in the second stage of synthesis, in which chain breakage takcs place exclusively by recombination. Block copolymers will generally be formed of the following main types: A-B, B - A - B , - B - A - B - A - B - A . However, simple calculation shows that in the presence in the "active" polymer molecule of five internal peroxide groups the proportion of structure A-B is under 1.5°/o. TABLE 4. REFRACTIVEINDEX INCREME~CTSOF CORI~ESeO~DI~CGH O ~ [ O P O L Y MERs
Solvent MEK Chloroform Toluene Bromoform
n~2 2 1.3795 1.4460 1.4995 1.6010
! i~
ml/g 0.221 0.151 0.108 0.013
0.115 0.063 -- 0.003 -- 0~)87
As a result of synthesis block copolymers very heterogeneous in molecular weight (molecular heterogeneity) and composition (composition heterogeneity) m a y be formed. Since block copolymers of the same average composition, but different composition variation m a y vary considerably in physical and mechanical properties, the composition heterogeneity of the specimens obtained should be determined quantitatively and the possibility of controlling heterogeneity according to composition, evaluated by changing conditions of synthesis o f block copolymers. We investigated molecular weight characteristics and the composition heterogeneity of several poly(styrene-block-MMA) specimens obtained using both
1040
Y u . L. Z H E ~ . B r ~ et
al.
"active" PS with varying polymerization times and with different PS contents during block copo!ymerization. Light scattering (laboratory visual nephelometer developed from a PI~I photometer), refractometry (IRP-23) and osmometry (Fuoss-!V[ead t y p e osmometer with "finest ultracell filter" membranes) were used for the investigation. Optical measurements were made with ~ = 546nm. TABLE 5. RESULTS OF D~.TER~NI~G THE MOLECULA~WEIGHTSOF BLOCKCOPOLYME~SBY Lm~T SCATr~mNG ~N V~mUS SOLW~TS ~
o
1 2 3 4
• ~
o
SM-1 SM-2
MEK
Chloroform
~ x
~
1:7 1:3 1:3 1:2
0.115 0.133 0.140 0.146
Toluene
~ x~.
470 396 480 305
Bromoform
C) x
-- I . . . . 0.079[ 370 0-017 620 0.022 475 0.087~ 240 0.029 285
x
0.086 --0.0681 --0.065 --0-057
460 598 615 740
Benzene was used as standard scattering liquid. To determine the value of "apparent" Mwap9 the following solvents were used: MEK, chloroform, toluene and bromoform. Refractive indices n~ of the solvents selected and the refractive index increment of styrene ~ and methylmethacrylate VB components of the block copolymer (i. e. corresponding homopolymers) are shown in Table 4. The value of M~ was determined from osmometric results in M E K at 25 °. Table 5 shows values of v and Mwapp of the block copolymer specimens studied. The following equation [10] were used to calculate the "true" M~ value of the block copolymer and components ~(w~) and M (B) and evaluate the composition heterogeneity P and Q of the block copolymer [10]:
M~p.-- ~7~ ~
+ v*(v~v~)~ • ~ ) + v~(v~v*)~ (1-~) ~7~~)
iwapp:/~'W÷
2 P YA-1,'___~B ÷ Q (YA--VB) 2 y2
1 P=~.. ~M,~(x,--x)-----~[(1--x) (A~w-- ~(~B))--X (b~'w-- A~A))]
(2) (3)
(4)
t/
Pmsx:=x (l--x)
(~¢-(A)__)t~(B))
Qraax--~x ( l - - x ) [(l--x) 3,-t'(-~-)÷X_,'~'(B)] ,
(6) (7)
Preparation
of block copolymers
1041
where x is the weight average content A in the block copolymer determined from refractometri6 data V=XVA-~- (l--x)
VB
(8)
~i is the gravimetric proportion of molecules with molecular weight Mtj and x~ composition; Pmax and Qmax correspond to the case of maximum composition heterogeneity for a given block copolymer, i. e. a homopolymcr mixture with the same values of M(A) ~ W and ~71//tB) tO • The numerical average values of M~A) and M~B) were determined from the equations
M~)=xM.
(9)
M~)----(1--x) Mn
(10)
It should be noted that averaging in eqns. (9) and (10) covers all macromoleeules of the specimen, therefore, the presence of homopolymer A results in a lower value of ~(nB) and of homopolymer B, to a reduced value of M(nA) (Table 6). TABLE
6.
RESULTS
OF DETERMINING
M O L E C U L A R W E I G H T :AND C O M P O S I T I O N H E T E R O G E N E I T 1 ~
OF THE
SPECIMENS
STUDIED
•
* x
Pm.~lQm.~
N
I 1
3
465
160
2.9
10
--
--
465
160
2.9
2
18
450
--
~0
~0
~
--
112
--
--
490
--
--
--47.2
22.4
0.84
0-80
3 4
23 29
520 410
190 240
~0
2.7 1-7
110 93
44 70
2.5 1.3
473 520
146 170
3'2 3"0
--29.1 --85-1
11.2 41-7
0-45 0-93
0.32 0"94
It follows from eqn. (3) that for a block copolymer of homogeneous composition ( P = 0 , Q=o) ~tTwappis independent of v i. e. of the solvent used and is equal to the "true" value of Mw and the relationship between Mwapp and (vA--VB)/V takes the form of a straight line parallel to the abscissa axis. For a block copolymet of heterogeneous composition the relationship is represented by a parabola. Figure 5 and Table 6 indicate that only specimen 1 obtained with a ratio of "active" PS : PM:MA of 1 : 7 was homogeneous in composition. A low content of the styrene constituent makes it difficult to obtain accurate quantitative data about the composition of this block eopolymer by the methods used and suggests that there is no composition variation with molecular weight. The other specimens studied show varying heterogeneity in composition. They are characterized by P < 0 , which is expressed in a displacement to the right of parabolic
1042
Yu. L. Zll3EREBrLqet
al.
curves from the ordinate and confirms that with an increase in molecular weight, the block eopolymer molecules are enriched with MMA units. The composition heterogeneity of specimen 4 is very high and raises doubts as to whether this specimen is a mixture of homopolymers. For verification we turn to values of/14n. For a homopolymer mixture it is correct to say that
/1~ and 21~ values previously derived were found assuming the absence of homopolymers from the product of block copolymerization and cannot therefore be used in eqn. (11). We can, however, evaluate the maximum value of (~ixtm)max which corresponds to a mixture of monodispersed homopolymers, i. e. when ~14A--/14 x and M--B 223 vA 10a, n-w n = M --r w . For specimen 4 we obtain /~mixture~ tl,-n ]max= which within the range of experimental error, is the same as J~n=240X 10a. However, some polydispersion of components A and B m a y be expected as regards molecular weight, i. e. MXn<~wA and 2tinr<~l~w~. Then, 214m~tu~e#214n and therefore, the specimen examined is not a homopolymer mixture. A considerable heterogeneity of composition of this block copolymer is due to the close relation between macromolecular composition and molecular weight. This is also confirmed b y the low polydispersion of the styrene constituent of macromolecules (2t~wA/~=l'3), i. e. the overall weight of PS blocks in the block copolymer molecule depends slightly on the molecular weight of the latter. For specimen 3, of which composition heterogeneity is much lower, the high value of JTwA/J4n A is due to a more proportional distribution of polystyrene units in block copolymer molecules of different molecular weight. This is confirmed b y the fact that values of 2~w/Y~n, -~ws ~I?A/j,~An and ~tB/M w/ n~ are similar. A s t u d y of the effect of conditions of block copolymerization on polymer structure shows that the composition heterogeneity of poly(styrene-block-MMA) increases with an increase in the proportion of "active" PS during block copolymerization and if the content of "active" PS is the same, with a reduction of molecular weight. A variation in conditions of block copolymerization has little effect on 2~w of the block eopolymer, ~ w~ and the polydispersion of 2t~wB/;l~. At the same time the value of MnA decreases with a reduction in the content of , , active 7, PS, while the polydispersion of/~wA//~n~ decreases with an increase in composition heterogeneity of the block copolymer. It m a y be assumed that high composition heterogeneity of the block copolymer obtained with a high proportion of "active" PS and a reduction of molecular weight, is because the polystyrene macroradicals formed are large and have a low diffusion coefficient, consequently, on being formed they do not react at a great distance from each other and the probability of meeting and reacting with a radical containing a low number of monomer units of MMA, is high. This results in the formation of block copolymer molecules enriched with PS units. After the PS radicals had been used up to some extent the extension of PMMA segments begins to predominate which
Hydrolysis of but~liene-nitrile rubber in alkaline medium
1043
results in the formation of block copolymer molecules of higher molecular weight enriched with MMA units. Finally, we note that by altering conditions of block copolymerization both in the first and second stages of synthesis, block copolymers with a varying degree of composition heterogeneity may be obtained, in order to synthesize various optimum block copolymer structures according to requirements of use. Translated by E. SEMERE REFERENCES 1. N. S. TSVETKOV, R. F. MARKOVSKAYA, Khimiya i khimich, tekhnol. 11: 936, 1968; Vysokomol. soyed. 7: 169, 1965 (Translated in Polymer Sci U.S.S.R. 7: 1, 185, 1965) 2. G. SMETS, L. CONVENT and Y. BORGHT, Makromolek. Chem. 23: 162, 1957 3. S. S. IVANCHEV, A. I. YURZHENKO, V. I. GALIBEI, A. I. PRISYAZHNIKOV and Yu. N. ANISIMOV, Auth. Cert. 218431, 1968; Byull. izobr. No. 17, 1968 4. S. S. IVANCHEV, V. L GALIBEI, T. A. TOLPYGINA, Auth. Cert. 278116, 1970; Byull. isobr., No. 25, 1970 5. S. S. IVANCHEV, Yu. L. ZHEREBIN, V. I. KUZNETSOV and Yu. I. DERKACH, Auth. Cert. 359251, 1972; Byull. izobr. No. 35, 1972 6. Yu. L. ZHEREBIN, S. S. IVANCHEV, V. I. GALIBEI, Zh. organ, khimii 7: 1660, 1971 7. Yu. L. ZHEREBIN, Dissertation, 1972 8. T. OTSU, J. Polymer Sci. 26: 236, 1957 9. R. TSEREZA, Metody issledovaniya polimerov (Methods of Investigating Polymers). Izd. inostr, lit., 1961 10. W. BUSHUK and H. BENOIT, Compt. rend. 246: :3167, 1958; Canad. J. Chem. 36: 1616, 1958
KINETIC STUDY OF HYDROLYSIS OF BUTADIENE-NITRILE RUBBER IN ALKALINE MEDIUM* 1~. SIt. FRENKEL', T. I . KIRILLOVA a n d E . A. KUZ'MINA All-Union Scientific Research and Design Institute of the Rubber I n d u s t r y
(Received 21 August 1972)
A kinetic study was made of the interaction of butadiene-nitrile rubber dissolved with alkali in o-xylene. I t was found that, in the complex process of hydrolysis of polymer molecules, hydrolysis of the polyamide obtained is the decisive stage. The activation energy of hydrolysis of polyamide was determined at temperatures of 125 to 145 °. * Vysokomol. soyed. AI6: No. 4, 902-905, 1974.