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Synthesis of polyethylene glycols of molecular weight above 10,000 by anionic polymerization
Synthesis of polyethylene glycols of molecular weight above 10,000
2779
5. P. P. K-USHCH, G. V. LOGADZINSKAYA, B. A. KOMA~OV a n d B. A. ROZENBERG, Vysokomol. soyed. 22A: 2012, 1980 (Translated in Polymer Sci. U.S.S.R. L~: 9, 1980) 6. B. E. READ and G. wrLI.;JkMS, Trans. Faraday Soc. 57: 1979, 1961 7. G. PEZZIN, G. AFROLDI and C. GARBUGLIO, J. Appl. Polymer Sci. 11: 2553, 1967 8. P. KA-RRER, Kurs organichcekoi khimii (Organic ChomistrT Course). Izd. Goekhimizdat, p. 1015, 1962
Polymer Sc'i~mceU.S.S.R. Vol.22, Yo. 11. pp..°779-2786. 19,~0 Prated in PoJand
0002-$050'80/1t2779-06507.50/0 I~81 PersamonPre~ Ltd.
SYNTHESIS OF P O L Y E T H Y L E N E GLYCOLS OF MOLECULAR W E I G H T ABOVE 10,000 BY ANIONIC POLYMERIZATION* N. V. PTITSY~A, S. V. OVSYA~-~OVA, Ts. M. G~L'FER and K. S.
K Az~.'qSKII
Chemical Physics Institute. U.S.S.R. Academy of Sciences (Rec~vcd 16 October 1979) A s t u d y has been made of the anionic polymerization of ethylene oxide in bulk at 90--140 ° in the presence of initiating systems based on K O H and triethylene glycol. Experiment4 were run in glsu~ ampoules and metal reactors, v a r y i n g the conditions of introduction of ethylene oxide. Meamxrement of MW values of the resulting polyethylene glycols brought to light discrepancies in calculations based on weighed portions of the ethylene oxide and initiator. The discrepancies stem from the presence of coinitiators, pexticxflarly water, in the system, and m a y he minirniTed when ~ latter are taken into account. The feaaibility of obtaining high molecular weighte has been assessed. The polymerization kinetics do not obey a first-order equation; the reaction rate i n c r e u e e along with the degree of conversion. The haLf-conversion times tally with catalyst concentrations. I t is seen from the reaction rate conatemts ( ~0-015 1./ /mole-sec at 90 °) that the active centres are associatee of alcoholate and hydroxyl groups. I t was found that the overall reaction rate increases on replacing K O H b y CeOH. Ways of increasing the polymerization rate are discussed.
E~mTLZ~-Z oxide (EO) polymers are materials whose applications cover a singulaxly wide range of molecular weight extendln~ from several millions down to dimers. The synthesis of these polymers naturally calls for the development of a variety of methods, the most important being those of aaxionic polymerization (low molecular weight range) and suspension polymerization used for the synthesis of "polyox" type polymers. The standard method of synthesizing polyethylene glycols (PEG) is based on the controlled addition of OE to a starting material (water, or a glycol) in the * Vysokomol. soyed. A ~ : No. 11, 2534-2539, 1980.
2780
N. V. P T r r s ~ A
~ a/.
presence (generally) o f alkaline catalysts. I n f o r m a t i o n in t h e p a t e n t [1] a n d o t h e r l i t e r a t u r e [2] shows t h a t the l a t t e r m e t h o d h a s i n h e r e n t limitations s t e m m i n g f~om t h e reaction ~-----~CHsCH sONa - , ---:'-CH ----CH s-i- Y a O H , (1) as well as f r o m processes of c a t a l y s t d e a c t i v a t i o n , m o n o m e r isomerization to a c e t a l d e h y d e , splitting o f the p o l y e t h e r chain b y alkalis or b y alcoholates, etc. [3]. On t h e o t h e r h a n d , a detailed i n v e s t i g a t i o n o f the anionic p o l y m e r i z a t i o n mec h a n i s m o f EO [4] has failed to confirm t h a t the process takes place strictly b y a " l i v i n g " p o l y m e r i z a t i o n m e c h a n i s m , i.e. w i t h o u t a n y sort of chain t e r m i n a t i o n . This p a p e r relates to o u r analysis a n d e x p e r i m e n t a l s u b s t a n t i a t i o n o f t h e feasibility o f direct synthesis o f P E G s w i t h molecular w e i g h t s a b o v e 10,000. A p a r t f r o m theoretical considerations t h e i n v e s t i g a t i o n was u n d e r t a k e n in view o f the d e m a n d for p o l y m e r s of the t y p e in question r e c e n t l y e n c o u n t e r e ~ in a n u m b e r of fields o f Soviet engineering. I n f o r m a t i o n on the applications o f P E G s o f differing molecular w e i g h t s is g i v e n in [3]. The experimental procedure was baeed on a ~ g prepexation of the initiator systems, and on the utilization of commercial l:n&teri&ls, a s well as the duplicating of labora. tory teets by experiments in metal hydroxyethylation reactors simulating the technological apparattm involved. The EO used in the inveetigation ("Orgsynthmis", State Standard 7563-73) had average charactermtice as follows: moisture content 0.01%, acetaldehyde content 0.01%, acidity (calculating for acetic acid) 0-004%0, nonvolatile residue {of polymer)0.005O/o. The characteristice of the grade A triethylene glycol (TEG) were: hydroxyl number 22.9, acidity 0-0007%, moisture content 0"022%0. Initiator syetema were prepared by reacting molten KOH with TEG at 330--360 K under vacuum (residual prmeure 0.1-0-01 tort), whilst stirring conti. nuoualy. The prvce~ was accompanied by complete dimolution of the alkali and by alight ooloratioa. The progrem of the reaction w u monitored by acid titration and by Fischer analysis, which allowed separate determinations of the amounts of alcoholate, alkali and water. For instance, in one of the experiments the amount of KOH + H,O was 0.07%, which ;a equal to 1% of the ~lkAli not entering into the reaction. Acid titration in the same experiment gave 1.91 × 10-J mole, of alcoholate where the initial KOH amounted to 1.93 × 10-' molee. The potamium concentration in the starting system= w u (6"0-7"5) × 10-4 mole/g or 3-5-4.2 wt.% on the initial KOH. The preparation time for the starting systen~ w u 8--12 hr. Polymerization was carried out under laboratory conditions in glaee ampovdee and in s 200 ml metal re•etor, the oo--iponents being fed in e~muJtaneoualy under p ~ equal to the EO vapour premure at the temperature of an experiment. For instance, the monomer preasure at 353 K, according to calculations, is 9 arm. The starting system was fed, in • current of dry argon, into containeru heated under vacuum and filled with argon. EO w ~ eonden~d from vaporizers. Te~t portions of the component~ were obtained by weighing. The polymerization kinetice were monitored by calorimetric means in the c u e of poly. merization in ampoules, and through pre~mn~e changee in the oa~ of polymerization in the reactor. Molecular weights were measured with the aid of an Lrbbelohde viscosimeter in water • t 26°. Viscoaity-average MW calculations were based on the equation [~]=6.7 x 10-' -~/~w obtained by analysis of published data calibration baaed on standard PEG specimens produced by the Fluka A6 Buclm Company and having MW values of 1000, 1500, 2000, 3000 and 4000 (see F~. 1).
Synthesis of polyethylene gl~ols of molecular weight above I0,000
278!
Initial systems for the synthesis of P E G were prepared by dissolving the alkali in a standard substance, normally a glycol HO--R--OH+MeOH
=~ H O - - R - - O M e + H s O
(2)
The water evolved was partially removed by a variety of methods, including evacuation, purging with an inert gas, azcotropic distillation, etc. Clearly, incomplete elimination of water from the system may lea<] to additional chains forming and lowering the total molecular weight of the product. Likewise the role of coinitiator may be played by any proton-containing impurities t h a t axe present in monomer, in connections, in the initial alkali, etc. The role to be played by these additional macromolecules will largely depend on the MW envisaged for the product. Certainly, the MW of the resulting polymer is given correctly by the relation ~,=
gzo n0+Yn,'
(3)
where gRo is the amount of EO polymerized (g), and n 0 and ~. ~ axe amounts (in t
moles') of the initiating substs~ace, including the &lcoholate, and transfer agents (coinitiators) respectively. The contribution of the second term in the denominator will obviously be particularly significant if conditions for the preparation of high-molecular PEGs call for low values of no. If relation (3) is rewritten as 1
M,
_
n0
,
1
gso + gEo = ~Mcffilc + X ,
(4)
it becomes particularly obvious that a discrepancy between planned and realized molecular weights will be entirely the result of coinitiators present in the system. With precisely the above considerations in view we planned a series of experiments and adopted experimental procedure envisaging a m a x i m u m passible elimination of the foregoing coinitiators or allowing quantitative control of the latter. The experimental results were plotted in line with equation (4) (see Fig. 2). The theoretical M W was given by the relation M~lc=
~-r
,
g~-o , nn,o + n ~ + r,u
(5)
where terms in the denominator refer respectively to TEG (or PEG), water, acid and acetaldehyde; the amounts of the latter substances were calculated on the basis of batch data and weighed portions of the materials. The curve in Fig. 2 has a slope of 1.0, which corresponds to a complete participation of the initiator in the process, and the intercepts in Fig. 2 are equal to 30,000 for the experiments in ampoules, and to ~ 100,000 for those in the reactor. It may well be t h a t this difference stems from a marked adsorption of water present on the glass ampoule
2782
N.V.
PTrrsYz~A ~ a/.
qa
walls. It follows from Table 1 that hydroxyethylation experiments in standard reactors provide direct confirmation that polymers with MW values of up to 40,000 may be synthesized. Similar correlations between calculated and observed molecular weights were reported in [4, 5] for the auioaic polymerization of specially purified E 0 in the presence of alkali-metal complexes of naphthalene, and show that the values in question are completely identical for MWs at any rate up to 3x108.
!o .! o2
q
I'0
l
• .
1 J
! ~
I~o. 1
I
I
i
I
IogM,, FIo. 2
1~o. 1. Intrm~c v i ~ t y
ver~as molecular weight of PEG, water, 25°: 1--data in [8]; 2--data obtained in tho preeent inveetigation. 1~o. 2. Relationship between calculated and observed molecular weights for EO polymerization, uging TEG-KOH initiator ~O~stoms:1 - i n ampoulee, 2--in metal reactors.
Thus the results of these experiments show that under conditions simulating technological ones it is feasible to prepare high-molecular PEGs, and that in each case there will be a molecular weight maximum determined by the practical impossibility of reducing to zero the value o f ~ n~ in equations (3) and (4) i.e. it is e6sentially a matter of technology. Among factors leading to additional chains forming one has also to consider that of moisture adsorption on reactor walls and on the walls of connecting equipment, as well as mechanodegradation of polymer at the stage of synthesis, and the participation of products responsible for coloration appearing in starting systems. Moreover it may well be that the batch data m a y not fully reflect the degree of purity of the monomer. The molecular weights of polymers generally make up only one side of the problem. Another side is the practicability of the weights being attained within a reasonable time, i.e. kinetic features of the polymerization process are involved. Molecular weight requirements mean that in this case one will be forced to use low initial concentrations of active centres, which will necessitate a search for new kinetic auproaches.
S y n t h e e s Of p o l y e t h y l e n e glycols of m o l e c u l a r w e i g h t a b o v e 10,000
ETI[rY'L~IqlO X I D E POLYMERIZATION IN THE PRESENCE S Y S T E M S IN MZTAL REACTOP~8 •
TABLE
I gv.o, ment, lqo.
go [ 100.7 ] 104.7 i i13"6 125"0
1
2 3 4 5 6 7 8 9 10 11
1132.o 180"0 300.0 270"0 35O'O 270"0 390.0
g~'~,.,..,
$
Polymerization conditions
i
I R O K x 10', I
g
mole
0.319
1.94
1.836
11 "62
1.447 1.292 0-978 0-462 0-577 0.728 0-654 0"985 1"069
9"18 8" 18 6"21 6.71 8.32 10.50 9.44 14"27 15.43
, !
',
I i
OF
I
T°
time, hr
98 98 98 98 98 100-130 100-140 130-140 120- 140 120-130 90-140
25 8 12 17 15 28 20 14 28 14 14
2783
TEG-KOH
*~COHOL~C
Mere e x 10
M, x 10-'
X 10-' 34"5 8"2 9"2 13"2 17"7 32"8 38"0 37"5 38"5 26"8 31"7
27"5 7"8 9"6 12.0 15.0
31.6 30.7 47.5 30.8 10.8
28-0
• E x p e r t m e ~ t , 1-5 w ~ e carried out in • laboratm, y reactor, EO w i r e r o~ate.nt 0"01%; e,r p e r t m e a h t O-11 took pl•ce i a • ledtada.-d h y d r o x y e t h y l a t i o n reactor, EO motstm~e cont4mt 0-02.%. *" A m o u n t o f the l n l t h t t o r system.
Figure 3a shows kinetic curves of EO polymerization plotted on the basis of a thermometric method in ampoules. I t can be seen tlmt for the systems in question there is an initial autoacceleration such as occurs in most processes of this kind. The kinetic curves do not obey a simple first-order equation, probably in view of a TABLE
2. KXNET~C P~,~Mrr~'~ for E O X~OLY~'EmZ~TXO~," n~- T ~ Z Fg~SZNC~ o r T E G - K O H A N D T E G - C o O H xrn'rxAToR 8YPCTEM$ m AMYOL'TLF.S
[ROMe] × I n i t i a t o r sy.q~em
TO
×
10t,
: ~ , , rain
'=u' min
mole/l. TEG-KOH
"I'EG-CeOH
kt**×lO*, i k,×lOt l./mole. :. l./mole. •80C I .SOC (==0.5) (==0.85)
ii
o.63
77 77 90 90 90 9(, 98 98
5"15 5"25 1 "50 2"14 2"55 2"81 0"68 0-69
61 60 68 49 39 37 54 48
98 96 115 83 71 65 89 86
0.37 0.37 1.13 1.10 1.11 3.15 3.48
5.22 5.33
90 90 90
0"85 0"87 ! .20
75 68 52
137 120 93
1.81 1.94
3.02
1.85
2-83
• Tim,~ for at~inl~q~ col~v~r*io~m (=) 0.b and 0-85 m~n. i
** Rate eon~tanL* with r~pecUve v~lue* of a: ~ - - - ~ _ _ ~ t n ( l - =).
1.16
0"64 1 "83 1 "78 1"75 1.74
)-)
N.V. P~U'rS~A ~ a~.
2784
major change in the properties of the medium. With a view to kinetic characterization we accordingly selected times for the a t t a i n m e n t of varying degrees of conversion (see Table 2); Fig. 3b shows the polymerization rate constant relative to alcoholate concentrations. The sate constant increases slightly with increasing conversion, and amounts, on average, to about 1.5 × 10 -2 l./m~e.sec (at 363 K). In metal reactors the induction periods were much longer, and the polymerization rates lower. The reasons for this call for further investigation, which we are carrying out. Polymerization rates in a reactor which allows complete loading at the start of an experiment came closest to the "ampoule" rates, since in the latter case the system undergoes no volume increase such as would be typical for standard hydroxyethylation reactors involving continuous feeding of EO.
k, oC t~8 2 t~q I ~1
1
1
¢0
1
80
I
1
120
o.ol
o~oz [ROK],mo{e/,
T/me , rain
Fla. 3. Kinetic~ of the bulk polymerization of EO in the pr~ence of initiator ry~tevas at 90°: a-[ROK] ==0-016 (1), 0.022 (2) and 0.034 (3) mole/]. ; b-rate constant versus alcoholate concentration, at degreee of conversion 0.5 (1) and 0-85 (2). With PEG as the initiator autoacceleration is partially eliminated and the take-up of monomer is better described by a first-order equation. This is a pointer in favour of technology involving the use of PEG of medium, MW (e.g. 1000 or 5000). The rate constants observed for the system under study are considerably lower titan the free alcoholate reactivities determined on the basis of propagation rate constants. According to [4] we have for the bulk polymerization kp=2.4 × I0 -x= exp (--20,700/RT) 1./mole.sec, which gives kp= 7-45 l./mole sec for 363 K. Factors underlying reduced reactivity in these systems are, on the one hand, association of alcoholates to trimers ( K ~ = = 1.4× l0 ts exp (-- 15,300/RT), i.e. approrlmately 8 × 106 l.ffimole' at 363 K), and, on the other hand, alcoholates associating with alcohol and forming inactive complexes of varying composition [6J. In particular, it should be noted t h a t complete elimination of moisture from the system also has serious kinetic consequences, as was demonstrated in [7], as polymerization is inhibited as a result of inactive complexes formed with alcoholates. In view of the foregoing equilibria the reaction rates observed for polymerization in presence of the starting systems are fully in line with the results of more
Synthesis of pol~ethylene glycols of molecular weight above 10,000
2785
detailed kinetic investigations, and may accordingly ~ r v e as a basis in regard to technological calculations. On the other hand it should be possible in the light of the material presented above to obtain intensified processes of anionic polymerization of EO. As the main factors attention is drawn to the following considerations. 1. The use of alcoholate-enriched starting systems, i.e. this amounts to an increased absolute catalyst concentration in the system. Disadvantages in this case are coloration of starting systems and polymerizates, becoming more marked as the alkali concentration increases, as well as the increased viscosity of a starring system, which may impede proper dehydration of the system. 2. A change to higher-pressure apparatus and hence to higher concentrations of monomer in the reaction zone. 3. The use of catalysts based on other alkali metals, e.g. such as cesium. This follows directly from the results of kinetic investigations [4], since cesium alcoholates are more active and less stably associated, as was further confirmed by the results of independent tests (see Table 2). Thus in view of the experimental results and conclusions reached in the present investigation it m a y . b e said that it is feasible to proceed with direct synthesis of P E G s of high molecular weight, using standard methods. The conclusions reached are in our view also of major significance in regard to the synthesis of a number of other important products. For instance, if due regard is not made for the role of coinitiators and chain transfer agents in the synthesis of nonionogenic surfactants this will lead to a considerable amount of P E G appearing in the products in question, and the homogeneity and functional properties of the latter will be affected. In the case of block copolymers of a-oxides, e.g. ethylene and propylene oxides, which have wide-ranging applications in a number of fields, failure to take the role of coinitiators into account W~ll inevitably result in the formation of homopolymers. In other cases, e.g. in the synthesis of statistical copolymers, products prepared by these same methods will have molecular weights below the levels envisaged, for the reasons outlined above. The authors thank S. G. Entelis and K. G. Mizuch for their interest in this investigation and for helpful comments in this connection. Tra,s/ated by R. J. A. ~ t t ~ "
I. U. K. Pat. 821203, 1959; USA Pat. 2923690, 1960 2. G. M. POWI~.LI. and F. E. BAILY, Encyclopedia of Chemlcal Technology, Second Suppl. vol., I~. Y., 1960
3. Water.soluble Reel.ha, Second edition, Ed. by R. L. Davidaon and M. Sittig,'N. Y., 1968; O. N. DYMENT, K. S. KAZANI~KII s,-~d A. M. MIROSHNIKOV, m their book Gl~koli i drugiye proizvodnye okisei etilena i propilena (Glycols and Other Derivativee of Ethylene and Propylene Oxide6). Izd. "Khlmiya", 1977 4. A. A. BOLOVYANOVand K~ B. KAZANRK~, Vysokomol. soyod. 12A: 2114, 1970; 14A: 1063, 19"/2 (Translated in Polymer Sci. U.S3S.R. I~: 9, 2396, 19"/0; 14: 5, 1186, 1972)
2786
I. I. B a a a s E x o v , and A. M. V~jss,r--,~
5. IL S. ]KAZKNSgII~ A. A. SOLOVJANOV and S. G. ENTEIA[8, Europ. Polymer J. 7: 1421, 1971 6. A. A. 8OLOVYANOV and K. S. ILAZ&NSlk~I~ Vyeokomol. Soyed. 19B: 498, 1977 (Not translated in Polymer Sci. U.S.S.R.) 7. A. BAR-ILAH and A. Zrl.gR&, J. Macromolec. Sci. A4: 1727, 1970 8. C. RO88I and C. CUNIBERTI, Polymer Letter 2: 681, 1964
8¢ieace U.s~q.R. VoL 22, .'~0. I L PP. 27'8e--2791,
~
1980
In Pohuad
oo~.,-a~/$Ol l 1 ~ , T S $ ~ lO't.60lO © 1~1 Pa..'~aon ~ Ltd.
ROTATIONAL AND TRANSLATIONAL MOBILITIES OF A SPIN PROBE IN A POLYMER-SOLVENT SYSTEM* I. I. B a ~ s ~ x o v A and A. M. V a s s ~ s Chemical Physics L-mtitute, U.S.S.R. Academy of Scienoee
( ~ t u ~ d 22 Ocgober 1979) A study has been made of the rotational and translational diffusion of a spin probe, the 2,2,6,6-tetramethylpiperidine.l-oxyl stable radical, in a polymer (SKS-30 rubber) --eolvent (m-xylenel system, whilst varying the polymer concentration from 0 to 100 wt. o//o. On going from liquid phase to polymer the rotational diffusion coefficient is reduced by 2-2.5 orders, and the translational diifumon coefficient by 3-3.5 orders. Changes in the rotational and translational mobilitiee of the probe are most mm-ked o/ This stems t~om an inwhen the concentration of polymer in solution is > 40 wt./o. local density of the macromolecular unite in the low molecular particle region. I f a low molecular particle in polymer is displaced to an extent (distance) of the order of ite diameter, the n u m b e r of timee it is able to change its orientation is considerably greater in polymer compared with the n u m b e r in the case of an equal degree of displacement in the Liquid phase.
RADICALreactions in solid polymers are subject to a number of kinetic anomalies t h a t do not occur in the liquid or gas phases [l, 2]. These anomalies are due to peculiarities of the polymeric matrix, the most important of the latter being the limitation of molecular mobility. The intensity and character of molecular motion of the medium determines the dynamics of the reacting particles, which influence the elementary step in chemical transformations [,3-6]. Factors underlying kinetic anomalies in reactions of low molecular particles in polymers can be understood only by means of a detailed investigation shedding light on the mechanism of their movement. It is therefore of interest to investigate the rotational and translational diffusion of the particles and to compare their movements * Vy~okomol. soyed. A22: .N'o. 11, 2540-2544, 1980.
2779
5. P. P. K-USHCH, G. V. LOGADZINSKAYA, B. A. KOMA~OV a n d B. A. ROZENBERG, Vysokomol. soyed. 22A: 2012, 1980 (Translated in Polymer Sci. U.S.S.R. L~: 9, 1980) 6. B. E. READ and G. wrLI.;JkMS, Trans. Faraday Soc. 57: 1979, 1961 7. G. PEZZIN, G. AFROLDI and C. GARBUGLIO, J. Appl. Polymer Sci. 11: 2553, 1967 8. P. KA-RRER, Kurs organichcekoi khimii (Organic ChomistrT Course). Izd. Goekhimizdat, p. 1015, 1962
Polymer Sc'i~mceU.S.S.R. Vol.22, Yo. 11. pp..°779-2786. 19,~0 Prated in PoJand
0002-$050'80/1t2779-06507.50/0 I~81 PersamonPre~ Ltd.
SYNTHESIS OF P O L Y E T H Y L E N E GLYCOLS OF MOLECULAR W E I G H T ABOVE 10,000 BY ANIONIC POLYMERIZATION* N. V. PTITSY~A, S. V. OVSYA~-~OVA, Ts. M. G~L'FER and K. S.
K Az~.'qSKII
Chemical Physics Institute. U.S.S.R. Academy of Sciences (Rec~vcd 16 October 1979) A s t u d y has been made of the anionic polymerization of ethylene oxide in bulk at 90--140 ° in the presence of initiating systems based on K O H and triethylene glycol. Experiment4 were run in glsu~ ampoules and metal reactors, v a r y i n g the conditions of introduction of ethylene oxide. Meamxrement of MW values of the resulting polyethylene glycols brought to light discrepancies in calculations based on weighed portions of the ethylene oxide and initiator. The discrepancies stem from the presence of coinitiators, pexticxflarly water, in the system, and m a y he minirniTed when ~ latter are taken into account. The feaaibility of obtaining high molecular weighte has been assessed. The polymerization kinetics do not obey a first-order equation; the reaction rate i n c r e u e e along with the degree of conversion. The haLf-conversion times tally with catalyst concentrations. I t is seen from the reaction rate conatemts ( ~0-015 1./ /mole-sec at 90 °) that the active centres are associatee of alcoholate and hydroxyl groups. I t was found that the overall reaction rate increases on replacing K O H b y CeOH. Ways of increasing the polymerization rate are discussed.
E~mTLZ~-Z oxide (EO) polymers are materials whose applications cover a singulaxly wide range of molecular weight extendln~ from several millions down to dimers. The synthesis of these polymers naturally calls for the development of a variety of methods, the most important being those of aaxionic polymerization (low molecular weight range) and suspension polymerization used for the synthesis of "polyox" type polymers. The standard method of synthesizing polyethylene glycols (PEG) is based on the controlled addition of OE to a starting material (water, or a glycol) in the * Vysokomol. soyed. A ~ : No. 11, 2534-2539, 1980.
2780
N. V. P T r r s ~ A
~ a/.
presence (generally) o f alkaline catalysts. I n f o r m a t i o n in t h e p a t e n t [1] a n d o t h e r l i t e r a t u r e [2] shows t h a t the l a t t e r m e t h o d h a s i n h e r e n t limitations s t e m m i n g f~om t h e reaction ~-----~CHsCH sONa - , ---:'-CH ----CH s-i- Y a O H , (1) as well as f r o m processes of c a t a l y s t d e a c t i v a t i o n , m o n o m e r isomerization to a c e t a l d e h y d e , splitting o f the p o l y e t h e r chain b y alkalis or b y alcoholates, etc. [3]. On t h e o t h e r h a n d , a detailed i n v e s t i g a t i o n o f the anionic p o l y m e r i z a t i o n mec h a n i s m o f EO [4] has failed to confirm t h a t the process takes place strictly b y a " l i v i n g " p o l y m e r i z a t i o n m e c h a n i s m , i.e. w i t h o u t a n y sort of chain t e r m i n a t i o n . This p a p e r relates to o u r analysis a n d e x p e r i m e n t a l s u b s t a n t i a t i o n o f t h e feasibility o f direct synthesis o f P E G s w i t h molecular w e i g h t s a b o v e 10,000. A p a r t f r o m theoretical considerations t h e i n v e s t i g a t i o n was u n d e r t a k e n in view o f the d e m a n d for p o l y m e r s of the t y p e in question r e c e n t l y e n c o u n t e r e ~ in a n u m b e r of fields o f Soviet engineering. I n f o r m a t i o n on the applications o f P E G s o f differing molecular w e i g h t s is g i v e n in [3]. The experimental procedure was baeed on a ~ g prepexation of the initiator systems, and on the utilization of commercial l:n&teri&ls, a s well as the duplicating of labora. tory teets by experiments in metal hydroxyethylation reactors simulating the technological apparattm involved. The EO used in the inveetigation ("Orgsynthmis", State Standard 7563-73) had average charactermtice as follows: moisture content 0.01%, acetaldehyde content 0.01%, acidity (calculating for acetic acid) 0-004%0, nonvolatile residue {of polymer)0.005O/o. The characteristice of the grade A triethylene glycol (TEG) were: hydroxyl number 22.9, acidity 0-0007%, moisture content 0"022%0. Initiator syetema were prepared by reacting molten KOH with TEG at 330--360 K under vacuum (residual prmeure 0.1-0-01 tort), whilst stirring conti. nuoualy. The prvce~ was accompanied by complete dimolution of the alkali and by alight ooloratioa. The progrem of the reaction w u monitored by acid titration and by Fischer analysis, which allowed separate determinations of the amounts of alcoholate, alkali and water. For instance, in one of the experiments the amount of KOH + H,O was 0.07%, which ;a equal to 1% of the ~lkAli not entering into the reaction. Acid titration in the same experiment gave 1.91 × 10-J mole, of alcoholate where the initial KOH amounted to 1.93 × 10-' molee. The potamium concentration in the starting system= w u (6"0-7"5) × 10-4 mole/g or 3-5-4.2 wt.% on the initial KOH. The preparation time for the starting systen~ w u 8--12 hr. Polymerization was carried out under laboratory conditions in glaee ampovdee and in s 200 ml metal re•etor, the oo--iponents being fed in e~muJtaneoualy under p ~ equal to the EO vapour premure at the temperature of an experiment. For instance, the monomer preasure at 353 K, according to calculations, is 9 arm. The starting system was fed, in • current of dry argon, into containeru heated under vacuum and filled with argon. EO w ~ eonden~d from vaporizers. Te~t portions of the component~ were obtained by weighing. The polymerization kinetice were monitored by calorimetric means in the c u e of poly. merization in ampoules, and through pre~mn~e changee in the oa~ of polymerization in the reactor. Molecular weights were measured with the aid of an Lrbbelohde viscosimeter in water • t 26°. Viscoaity-average MW calculations were based on the equation [~]=6.7 x 10-' -~/~w obtained by analysis of published data calibration baaed on standard PEG specimens produced by the Fluka A6 Buclm Company and having MW values of 1000, 1500, 2000, 3000 and 4000 (see F~. 1).
Synthesis of polyethylene gl~ols of molecular weight above I0,000
278!
Initial systems for the synthesis of P E G were prepared by dissolving the alkali in a standard substance, normally a glycol HO--R--OH+MeOH
=~ H O - - R - - O M e + H s O
(2)
The water evolved was partially removed by a variety of methods, including evacuation, purging with an inert gas, azcotropic distillation, etc. Clearly, incomplete elimination of water from the system may lea<] to additional chains forming and lowering the total molecular weight of the product. Likewise the role of coinitiator may be played by any proton-containing impurities t h a t axe present in monomer, in connections, in the initial alkali, etc. The role to be played by these additional macromolecules will largely depend on the MW envisaged for the product. Certainly, the MW of the resulting polymer is given correctly by the relation ~,=
gzo n0+Yn,'
(3)
where gRo is the amount of EO polymerized (g), and n 0 and ~. ~ axe amounts (in t
moles') of the initiating substs~ace, including the &lcoholate, and transfer agents (coinitiators) respectively. The contribution of the second term in the denominator will obviously be particularly significant if conditions for the preparation of high-molecular PEGs call for low values of no. If relation (3) is rewritten as 1
M,
_
n0
,
1
gso + gEo = ~Mcffilc + X ,
(4)
it becomes particularly obvious that a discrepancy between planned and realized molecular weights will be entirely the result of coinitiators present in the system. With precisely the above considerations in view we planned a series of experiments and adopted experimental procedure envisaging a m a x i m u m passible elimination of the foregoing coinitiators or allowing quantitative control of the latter. The experimental results were plotted in line with equation (4) (see Fig. 2). The theoretical M W was given by the relation M~lc=
~-r
,
g~-o , nn,o + n ~ + r,u
(5)
where terms in the denominator refer respectively to TEG (or PEG), water, acid and acetaldehyde; the amounts of the latter substances were calculated on the basis of batch data and weighed portions of the materials. The curve in Fig. 2 has a slope of 1.0, which corresponds to a complete participation of the initiator in the process, and the intercepts in Fig. 2 are equal to 30,000 for the experiments in ampoules, and to ~ 100,000 for those in the reactor. It may well be t h a t this difference stems from a marked adsorption of water present on the glass ampoule
2782
N.V.
PTrrsYz~A ~ a/.
qa
walls. It follows from Table 1 that hydroxyethylation experiments in standard reactors provide direct confirmation that polymers with MW values of up to 40,000 may be synthesized. Similar correlations between calculated and observed molecular weights were reported in [4, 5] for the auioaic polymerization of specially purified E 0 in the presence of alkali-metal complexes of naphthalene, and show that the values in question are completely identical for MWs at any rate up to 3x108.
!o .! o2
q
I'0
l
• .
1 J
! ~
I~o. 1
I
I
i
I
IogM,, FIo. 2
1~o. 1. Intrm~c v i ~ t y
ver~as molecular weight of PEG, water, 25°: 1--data in [8]; 2--data obtained in tho preeent inveetigation. 1~o. 2. Relationship between calculated and observed molecular weights for EO polymerization, uging TEG-KOH initiator ~O~stoms:1 - i n ampoulee, 2--in metal reactors.
Thus the results of these experiments show that under conditions simulating technological ones it is feasible to prepare high-molecular PEGs, and that in each case there will be a molecular weight maximum determined by the practical impossibility of reducing to zero the value o f ~ n~ in equations (3) and (4) i.e. it is e6sentially a matter of technology. Among factors leading to additional chains forming one has also to consider that of moisture adsorption on reactor walls and on the walls of connecting equipment, as well as mechanodegradation of polymer at the stage of synthesis, and the participation of products responsible for coloration appearing in starting systems. Moreover it may well be that the batch data m a y not fully reflect the degree of purity of the monomer. The molecular weights of polymers generally make up only one side of the problem. Another side is the practicability of the weights being attained within a reasonable time, i.e. kinetic features of the polymerization process are involved. Molecular weight requirements mean that in this case one will be forced to use low initial concentrations of active centres, which will necessitate a search for new kinetic auproaches.
S y n t h e e s Of p o l y e t h y l e n e glycols of m o l e c u l a r w e i g h t a b o v e 10,000
ETI[rY'L~IqlO X I D E POLYMERIZATION IN THE PRESENCE S Y S T E M S IN MZTAL REACTOP~8 •
TABLE
I gv.o, ment, lqo.
go [ 100.7 ] 104.7 i i13"6 125"0
1
2 3 4 5 6 7 8 9 10 11
1132.o 180"0 300.0 270"0 35O'O 270"0 390.0
g~'~,.,..,
$
Polymerization conditions
i
I R O K x 10', I
g
mole
0.319
1.94
1.836
11 "62
1.447 1.292 0-978 0-462 0-577 0.728 0-654 0"985 1"069
9"18 8" 18 6"21 6.71 8.32 10.50 9.44 14"27 15.43
, !
',
I i
OF
I
T°
time, hr
98 98 98 98 98 100-130 100-140 130-140 120- 140 120-130 90-140
25 8 12 17 15 28 20 14 28 14 14
2783
TEG-KOH
*~COHOL~C
Mere e x 10
M, x 10-'
X 10-' 34"5 8"2 9"2 13"2 17"7 32"8 38"0 37"5 38"5 26"8 31"7
27"5 7"8 9"6 12.0 15.0
31.6 30.7 47.5 30.8 10.8
28-0
• E x p e r t m e ~ t , 1-5 w ~ e carried out in • laboratm, y reactor, EO w i r e r o~ate.nt 0"01%; e,r p e r t m e a h t O-11 took pl•ce i a • ledtada.-d h y d r o x y e t h y l a t i o n reactor, EO motstm~e cont4mt 0-02.%. *" A m o u n t o f the l n l t h t t o r system.
Figure 3a shows kinetic curves of EO polymerization plotted on the basis of a thermometric method in ampoules. I t can be seen tlmt for the systems in question there is an initial autoacceleration such as occurs in most processes of this kind. The kinetic curves do not obey a simple first-order equation, probably in view of a TABLE
2. KXNET~C P~,~Mrr~'~ for E O X~OLY~'EmZ~TXO~," n~- T ~ Z Fg~SZNC~ o r T E G - K O H A N D T E G - C o O H xrn'rxAToR 8YPCTEM$ m AMYOL'TLF.S
[ROMe] × I n i t i a t o r sy.q~em
TO
×
10t,
: ~ , , rain
'=u' min
mole/l. TEG-KOH
"I'EG-CeOH
kt**×lO*, i k,×lOt l./mole. :. l./mole. •80C I .SOC (==0.5) (==0.85)
ii
o.63
77 77 90 90 90 9(, 98 98
5"15 5"25 1 "50 2"14 2"55 2"81 0"68 0-69
61 60 68 49 39 37 54 48
98 96 115 83 71 65 89 86
0.37 0.37 1.13 1.10 1.11 3.15 3.48
5.22 5.33
90 90 90
0"85 0"87 ! .20
75 68 52
137 120 93
1.81 1.94
3.02
1.85
2-83
• Tim,~ for at~inl~q~ col~v~r*io~m (=) 0.b and 0-85 m~n. i
** Rate eon~tanL* with r~pecUve v~lue* of a: ~ - - - ~ _ _ ~ t n ( l - =).
1.16
0"64 1 "83 1 "78 1"75 1.74
)-)
N.V. P~U'rS~A ~ a~.
2784
major change in the properties of the medium. With a view to kinetic characterization we accordingly selected times for the a t t a i n m e n t of varying degrees of conversion (see Table 2); Fig. 3b shows the polymerization rate constant relative to alcoholate concentrations. The sate constant increases slightly with increasing conversion, and amounts, on average, to about 1.5 × 10 -2 l./m~e.sec (at 363 K). In metal reactors the induction periods were much longer, and the polymerization rates lower. The reasons for this call for further investigation, which we are carrying out. Polymerization rates in a reactor which allows complete loading at the start of an experiment came closest to the "ampoule" rates, since in the latter case the system undergoes no volume increase such as would be typical for standard hydroxyethylation reactors involving continuous feeding of EO.
k, oC t~8 2 t~q I ~1
1
1
¢0
1
80
I
1
120
o.ol
o~oz [ROK],mo{e/,
T/me , rain
Fla. 3. Kinetic~ of the bulk polymerization of EO in the pr~ence of initiator ry~tevas at 90°: a-[ROK] ==0-016 (1), 0.022 (2) and 0.034 (3) mole/]. ; b-rate constant versus alcoholate concentration, at degreee of conversion 0.5 (1) and 0-85 (2). With PEG as the initiator autoacceleration is partially eliminated and the take-up of monomer is better described by a first-order equation. This is a pointer in favour of technology involving the use of PEG of medium, MW (e.g. 1000 or 5000). The rate constants observed for the system under study are considerably lower titan the free alcoholate reactivities determined on the basis of propagation rate constants. According to [4] we have for the bulk polymerization kp=2.4 × I0 -x= exp (--20,700/RT) 1./mole.sec, which gives kp= 7-45 l./mole sec for 363 K. Factors underlying reduced reactivity in these systems are, on the one hand, association of alcoholates to trimers ( K ~ = = 1.4× l0 ts exp (-- 15,300/RT), i.e. approrlmately 8 × 106 l.ffimole' at 363 K), and, on the other hand, alcoholates associating with alcohol and forming inactive complexes of varying composition [6J. In particular, it should be noted t h a t complete elimination of moisture from the system also has serious kinetic consequences, as was demonstrated in [7], as polymerization is inhibited as a result of inactive complexes formed with alcoholates. In view of the foregoing equilibria the reaction rates observed for polymerization in presence of the starting systems are fully in line with the results of more
Synthesis of pol~ethylene glycols of molecular weight above 10,000
2785
detailed kinetic investigations, and may accordingly ~ r v e as a basis in regard to technological calculations. On the other hand it should be possible in the light of the material presented above to obtain intensified processes of anionic polymerization of EO. As the main factors attention is drawn to the following considerations. 1. The use of alcoholate-enriched starting systems, i.e. this amounts to an increased absolute catalyst concentration in the system. Disadvantages in this case are coloration of starting systems and polymerizates, becoming more marked as the alkali concentration increases, as well as the increased viscosity of a starring system, which may impede proper dehydration of the system. 2. A change to higher-pressure apparatus and hence to higher concentrations of monomer in the reaction zone. 3. The use of catalysts based on other alkali metals, e.g. such as cesium. This follows directly from the results of kinetic investigations [4], since cesium alcoholates are more active and less stably associated, as was further confirmed by the results of independent tests (see Table 2). Thus in view of the experimental results and conclusions reached in the present investigation it m a y . b e said that it is feasible to proceed with direct synthesis of P E G s of high molecular weight, using standard methods. The conclusions reached are in our view also of major significance in regard to the synthesis of a number of other important products. For instance, if due regard is not made for the role of coinitiators and chain transfer agents in the synthesis of nonionogenic surfactants this will lead to a considerable amount of P E G appearing in the products in question, and the homogeneity and functional properties of the latter will be affected. In the case of block copolymers of a-oxides, e.g. ethylene and propylene oxides, which have wide-ranging applications in a number of fields, failure to take the role of coinitiators into account W~ll inevitably result in the formation of homopolymers. In other cases, e.g. in the synthesis of statistical copolymers, products prepared by these same methods will have molecular weights below the levels envisaged, for the reasons outlined above. The authors thank S. G. Entelis and K. G. Mizuch for their interest in this investigation and for helpful comments in this connection. Tra,s/ated by R. J. A. ~ t t ~ "
I. U. K. Pat. 821203, 1959; USA Pat. 2923690, 1960 2. G. M. POWI~.LI. and F. E. BAILY, Encyclopedia of Chemlcal Technology, Second Suppl. vol., I~. Y., 1960
3. Water.soluble Reel.ha, Second edition, Ed. by R. L. Davidaon and M. Sittig,'N. Y., 1968; O. N. DYMENT, K. S. KAZANI~KII s,-~d A. M. MIROSHNIKOV, m their book Gl~koli i drugiye proizvodnye okisei etilena i propilena (Glycols and Other Derivativee of Ethylene and Propylene Oxide6). Izd. "Khlmiya", 1977 4. A. A. BOLOVYANOVand K~ B. KAZANRK~, Vysokomol. soyod. 12A: 2114, 1970; 14A: 1063, 19"/2 (Translated in Polymer Sci. U.S3S.R. I~: 9, 2396, 19"/0; 14: 5, 1186, 1972)
2786
I. I. B a a a s E x o v , and A. M. V~jss,r--,~
5. IL S. ]KAZKNSgII~ A. A. SOLOVJANOV and S. G. ENTEIA[8, Europ. Polymer J. 7: 1421, 1971 6. A. A. 8OLOVYANOV and K. S. ILAZ&NSlk~I~ Vyeokomol. Soyed. 19B: 498, 1977 (Not translated in Polymer Sci. U.S.S.R.) 7. A. BAR-ILAH and A. Zrl.gR&, J. Macromolec. Sci. A4: 1727, 1970 8. C. RO88I and C. CUNIBERTI, Polymer Letter 2: 681, 1964
8¢ieace U.s~q.R. VoL 22, .'~0. I L PP. 27'8e--2791,
~
1980
In Pohuad
oo~.,-a~/$Ol l 1 ~ , T S $ ~ lO't.60lO © 1~1 Pa..'~aon ~ Ltd.
ROTATIONAL AND TRANSLATIONAL MOBILITIES OF A SPIN PROBE IN A POLYMER-SOLVENT SYSTEM* I. I. B a ~ s ~ x o v A and A. M. V a s s ~ s Chemical Physics L-mtitute, U.S.S.R. Academy of Scienoee
( ~ t u ~ d 22 Ocgober 1979) A study has been made of the rotational and translational diffusion of a spin probe, the 2,2,6,6-tetramethylpiperidine.l-oxyl stable radical, in a polymer (SKS-30 rubber) --eolvent (m-xylenel system, whilst varying the polymer concentration from 0 to 100 wt. o//o. On going from liquid phase to polymer the rotational diffusion coefficient is reduced by 2-2.5 orders, and the translational diifumon coefficient by 3-3.5 orders. Changes in the rotational and translational mobilitiee of the probe are most mm-ked o/ This stems t~om an inwhen the concentration of polymer in solution is > 40 wt./o. local density of the macromolecular unite in the low molecular particle region. I f a low molecular particle in polymer is displaced to an extent (distance) of the order of ite diameter, the n u m b e r of timee it is able to change its orientation is considerably greater in polymer compared with the n u m b e r in the case of an equal degree of displacement in the Liquid phase.
RADICALreactions in solid polymers are subject to a number of kinetic anomalies t h a t do not occur in the liquid or gas phases [l, 2]. These anomalies are due to peculiarities of the polymeric matrix, the most important of the latter being the limitation of molecular mobility. The intensity and character of molecular motion of the medium determines the dynamics of the reacting particles, which influence the elementary step in chemical transformations [,3-6]. Factors underlying kinetic anomalies in reactions of low molecular particles in polymers can be understood only by means of a detailed investigation shedding light on the mechanism of their movement. It is therefore of interest to investigate the rotational and translational diffusion of the particles and to compare their movements * Vy~okomol. soyed. A22: .N'o. 11, 2540-2544, 1980.