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Features of latex copolymerization of acrylic monomers with methylol methacrylamide
1842
V . I . YELISEYEVA and S. A. PETROVA
13. N. M. GELLER, B. L. YERUSALIMSKII, T. P. ZUBOVA,.V.N. KRASULINA, V. A. KROPACHEV, S. S. SKOROKHODOV, Yu. E. EIZNER, Theses of X V I Conf. of High-
molecular Weight Compounds Inst., U.S.S.R. Academy of Sciences, Izd. "Nauka", p. 10, 1970 14. L. E. SUTTON, Interatomic Distances, Sl~ec. Publ., N 11, The Chem. Soe., London, 1958 15. R. DAUDEL, R. LEFEBRE and C. MOSER, Quantum Chemistry, Intersci. Publ., 1959
FEATURES OF LATEX COPOLYMERIZATION OF ACRYLIC MONOMERS WITH METHYLOL METHACRYLAMIDE* V. I, Y E ~ S S r E V X a n d S . A. PETROVX Physical Chemistry Institute, U.S.S.R. Academy of Sciences
(Received 20 May 1969) A s w a s s h o w n in p a p e r s [1,2], colloidally-stable latices are o b t a i n a b l e b y c o p o l y m e rizing lower a l k y l a c r y l a t e s w i t h m e t h y l o l m e t h a c r y l a m i d e (M-hIAA) in t h e a b s e n c e o f emulsifiers a n d w i t h a m m o n i u m p e r s u l p h a t e as initiator. T h e p h y s i c o c h e m i c a l p r o p e r t i e s o f t h e s e latices are similar to those of latices p r e p a r e d in t h e usual w a y w i t h emulsifiers. The colloidal p r o p e r t i e s of t h e s e latices are influenced b y the m o n o m e r - m e t e r i n g p r o c e d u r e as well as b y t h e m o l e c u l a r w e i g h t of t h e p o l y m e r a n d its f u n c t i o n a l g r o u p c o n t e n t ( m e t h y l o l a m i d e groups). T h e a d d i t i o n of MMAA t o t h e c o p o l y m e r c o m p o s i t i o n h a s a stabilizing effect on t h e latices, a n d t h e stab i l i t y of t h e l a t t e r increases w i t h increase in t h e M M A A content. I n t h i s i n v e s t i g a t i o n we s t u d i e d t h e r e a c t i o n kinetics a n d t h e m e c h a n i s m o f t h e rising, g r o w t h a n d stabilization of l a t e x particles in t h e c o p o l y m e r i z a t i o n o f e t h y l a c r y l a t e ( E A ) w i t h M M A A in t h e a q u e o u s phase. DISCUSSION OF RESULTS
The special feature of MMAA as comonomer in the process of emulsion copolymorization with ordinary monomers is its preferential solubility in the aqueous phase. We have shown that with an EA : water ratio of 1 : 1.5 and at a temperature of 60 o the solubility of MMAA is ten times as high in water as in EA. In studying the mechanism of particle formation we adopted the method of emulsion polymerization with staged metering of the monomers and the initiator with access of air and with the following mixture formulation: ethyl acrylate, 100.0; mcthylol methacrylamide, 0-5.0; ammonium persulphate, 1-0; tertiary dodecylmercaptan, 1-0; water, 295.0 pts. by wt. In addition experiments were carried out w i t h the same formulation as above, but using a seeding latex in the form of butyl acrylate-methyl methacrylate-methacrylic acid * Vysokomol. soyed. A12: No. 7, 1621-1625 1970.
Features of latex copolymeriz~tion of acrylic monomers with MMAA
1843
copolymer (60 : 35 : 5) obtained by emulsion polymerization in the presence of sulphanol (3% on monomer wt.). The dilute seed latex in which the polymerization was carried out had the following characteristics: dry residue, 1"04%; surface tension, 58.7 erg/cm2; particle diameter, 0.045 #; number of particles in 1 ml of latex, 1.67 × 10~4. During the polymerization saxaples were removed and the surface tension in the latter was determined by~the ring separation method on a Dew-Nooey device. The particle sizes were determined on aa FEKN-57 nephelometer by the light-scattering method, and the number of particles in 1 ml of latex wa~ calculated. T h e results o b t a i n e d are p r e s e n t e d in Fig. 1 a n d in the Table. ~, e~g/crn ~
58 ~
6,erWcm2 B2--
ff
50
; 2.o
o#
oc 9
38
~6 ~ |
~2
o
!
I
5'
I
I
12
t
I
l#
I
I
2/I
I
I
30
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I
6
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I
12
I
I
16
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I
2~
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I
30
DCUpesidue, % FIG. 1. Change in surface tension (a) in the polymerization without emulsion of EA ((~l)and in the eopolymerization of EA with MM_AA (b): 1 --without seeding, 2-with seeding. I n view of t h e d a t a in Fig. l a we m a y surmise t h a t the p o l y m e r i z a t i o n o f E A (solubility in w a t e r 2.6%) w i t h o u t a n emulsifier s t a r t s in aqueous solution in t h e p o l y m e r i z a t i o n w i t h or w i t h o u t seeding. D u r i n g t h e initial period s u r f a e t a n t oligomers a n d radicals are formed, a n d t h e i r diphilic n a t u r e is a p p a r e n t l y due to the initiator residue (SO~ groups) a t the chain ends which considerably reduces the surface tension o f t h e system. This is confirmed b y the high ~-potential of the particles, a m o u n t i n g to 160 inV. W h e n the p o l y m e r chains h a v e r e a c h e d a particular weight it a p p e a r s t h a t t h e y t h e n form aggregates leading to the n u c l e a t i o n o f latex particles, as is e v i d e n t f r o m the t a b u l a t e d data. Along with the adsorption o f s u r f a c t a n t oligomers a n d radicals t h e r e is f u r t h e r f o r m a t i o n of the l a t t e r in the aqueous phase, as is indicated b y the kinetics of change in 6 during the p o l y m e r i z a t i o n process (Fig. 1). I n view o f these results we would conclude t h a t it is m a i n l y in the aqueous phase t h a t t h e p o l y m e r i z a t i o n of E A proceeds w i t h o u t t h e seed in t h e absence of t h e emulsifier, f u r t h e r evidence of which is seen in the increased n u m b e r of particles per 1 ml o f latex, p a r t i c u l a r l y a t t h e s t a r t of t h e process (see Table). I n the seed p o l y m e r i z a t i o n o f E A t h e n u m b e r of particles per 1 ml o f l a t e x remains practically c o n s t a n t as t h e degree of conversion rises, a n d it is e q u a l to the n u m b e r o f seeding l a t e x particles (see Table). I n this case t h e emerging s u r f a c t a n t
1844
V.I. YELISEYEVAand S. A. PETROVA
oligomers a n d radicals are a d s o r b e d b y t h e surface of the seed l a t e x particles. This is i n d i c a t e d b y t h e increase in t h e size of t h e particles during t h e synthesis. I n t h e seedless c o p o l y m e r i z a t i o n o f E A w i t h MMAA (Fig. lb), a n d also in t h e same process with t h e seeding latex (curves I a n d 2, respectively) the surface tension falls t h r o u g h o u t t h e process, while t h e d i a m e t e r of the particles increases. w i t h t h e degree of conversion. I n t h e seedless p o l y m e r i z a t i o n t h e n u m b e r o f particles remains practically c o n s t a n t a f t e r a certain n u m b e r is r e a c h e d (see Table). I n t h e seed p o l y m e r i z a t i o n d u r i n g t h e initial period, w h e n t h e surface tension is g r e a t l y reduced, t h e n u m b e r of particles remains equal to t h e n u m b e r o f seed l a t e x particles, a n d a f t e r this the t o t a l n u m b e r of particles is increased to t h e n u m b e r f o r m e d in t h e seedless polymerization, a n d remains a p p r o x i m a t e l y constant. T a k i n g all this into consideration we conclude t h a t in t h e emulsionless c o p o l y m e r i z a t i o n of E A w i t h MM_AA the n u c l e a t i o n of particles t a k e s place in the same w a y as in t h e emulsionless p o l y m e r i z a t i o n of EA, and this m e c h a n i s m remains e v e n w h e n t h e seed is introduced. This m e a n s t h a t w h e t h e r or n o t there are seeding l a t e x particles, new particles are f o r m e d in the a q u e o u s phase containing the readily soluble m o n o m e r MMAA. I n this case d i s p l a c e m e n t o f the h y d r o p h i l i c - h y d r o p h o b i c balance o f oligomers f o r m e d in t h e aqueous phase t o w a r d s t h e h y d r o p h i l i c p o r t i o n leads to f u r t h e r "self-stabilization" of the emerging aggregaGROWTH OF PARTICLES AND CHANGE IN THEIR NUMBER PER 1 T H E EM-ULSION-LESS P O L Y M E R I Z A T I O N O F milk A N D I N E 2 ~ - M ~ I A f l k
Without seedeing
rnl
oF LATEX IN
COPOLYMERIZATION
With seeding
dry residue of latex, %
particle diameter, 1~
number of particles in 1 ml of latex × 10-14
3.08 6.9 10.35 13.9 17.1 19.3
0-10 0.11 0.12 0-12 0.13 0.13
EA homo )olymerization 0.56 1.04 (etching) 0.94 7-95 1.11 12.12 1.31 15.45 1.45 17.1 1.50 20.0
1.865 4.315 6.98 9.35 12.05 13.95 15.05 17.3 19.35
0-07 0.10 0-11 0.12 0.13 0.13 0.14 0.14 0.15
EA-MMAA copolymerization 0.90 1"04 (etching) 0-80 5.82 0.92 11.57 0.98 15.2 1.02 18.3 1.13 22.4 1.09 1.05 1.06
dry residue of latex, ~o
particle diameter, lz
number of particles in 1 ml of latex × 10-14
0"04 0"10 0"11 0"12 0"12 0"13
1"67 1"52 1"70 1"69 1"85 1"68
0"04 0"09 0"10 0"10 0"11 0"12
1"67 1"68 2"55 2"56 2"41 2"18
Features of latex eopolymerization of acrylic monomers with MMAA
184~
tes owing to the marked hydxophilization of their surface; this is indicated by the ~-potential of their particles, l l 0 mV, which is lower than in the emulsionless homopolymerization of EA. The lower interfacial tension at the surface of aggregates of methylol-containing oligomers (or radicals) favours increased diffusion of monomers from the aqueous phase into the latter, and in this way the polymerization process is shifted to the volume of the particles. In order to study the kinetics of the process in relation to the amount o f methylol methacrylamide in the reaction system we carried out the emutsionless copolymerization, with access of oxygen, at 65 ° in a reactor providing for the removal of samples and for simultaneous introduction of the total amount of all the ingredients into the reaction as follows*: EA, 100.0; MMAA, 3.0; 5.0 and 7.0; tertiary dodecylmercaptan, 0.5; ammonium persulphate, 0.25; water, 295.0 pts. by wt. As is seen from the kinetic curves in Fig. 2a, a rise in the content of methylol methacrylamide in the copolymer is accompanied by acceleration of the polymerization peocess~. This m a y be due to the more hydrophilic nature of the El
100
10
%8 /40
I/
b
5
~0
20 :..,~.~ _ . r__ ,. --r.. . ~ , . --t- . r--. ¢ - T - -'~--- 3 40 80 120 180 200 290 T/me,
m/n
5
15
25
FIG. 2. Kinetic curves of the emulsionless eopolymerization of EA with different amounts of MMAA in the presence of oxygen (a) and under oxygen-free conditions (b); a: 1--EA+7~o MMAA, 2--EA+5~o MMAA, 3--3% MMAA; b: EAq-3% MMAA, 2--EA, 3--EAq-5% MMAA, 4--EAq-7% MMAA, 5--EA+l.5~o E-30 (emulsifier). Q--Amount of polymer formed (g) per 100 g of aqueous phrase. surface of the emerging particles caused by the introduction of methylol methaerylamide fragments into the macromolecules (with hydrophobic monomers a similar effect is obtained by increasing the amount of emulsifier in the system). The increasingly hydrophilic surface reduces the surface tension at the interface with the aqueous phase, and increases the concentration of monomer in the particles, so t h a t the polymerization rate is increased [4, 5]. * These experiments were performed in collaboration with L. V. Kozlov. t Note that stable latices proved unobtainable [3] in the case of simultaneous addition of the ingredients to the reaction mixture.
1846
V.I. YELISEYEVAand S. A. PETROVA
In the light of the experimental results it was desired to compare the kinetics of the oxygen-free copolymerization of EA, with different amouts of MMAA, with the polymerization kinetics for EA b y itself, with and without the emulsifier. To do this a dilatemetric study was made (under oxygen-flee conditions) of the kinetics of EA copolymerization with different amounts of MMAA in the aqueous phase without the emulsifier, along with the polymerization of EA b y itself in the presence of E-30 emulsifier (sodium salt of sulfo-acids of the f a t t y series C12mC1s) and without E-30; in addition the activation energy for these processes was determined. In carrying out the experiments we used the mixture formulation given above (for the method of gradual introduction of the monomers),but the phase ratio was altered to i : 4 (organic phase : water). The kinetic curves for these processes are depicted in :~ig. 2b. It is seen from this Figure that in the emulsionless polymerization of EA the reaction rate is much lower than in the polymerization with 1.5% of E-30 emulsifier. Without the emulsifier the reaction rate for the EA,MMAA copolymerization in the absence of atmospheric oxygen is reduced with increase in the amount of MM_A_Aintroduced into the reaction, i.e. this monomer has the reverse effect on the reaction rate compared with the polymerization with access of oxygen. This difference m a y well be due to the polymerization of MMAA taking place preferentially in the aqueous phase in the absence of the inhibiting effect of oxygen on this reaction (data on the inhibiting effect of oxygen on the polymerization of water-soluble monomers is given in [6]). The fact that under oxygen-free conditions M-MAA polymerizes mainly in the aqueous phase is further confirmed b y the increased viscosity of the reaction system, while no such increase is observed in the polymerization in the presence of 02. In the presence of the emulsifier the homopolymerization of EA takes place in the polymer-monomeric particles which according to present-day theories gives rise to considerable acceleration of the polymerization process. To determine the activation energy for EA-MM_AA copolymerization in the absence of the emulsifier, and for EA homopolymerization with and without the emulsifier we studied the reaction kinetics in the temperature interval 31-60 °. Figure 3 shows the dependence of the logarithm of the polymerization rate constant on temperature for 4 % conversion. The following are the activation energies for the processes in question. (For the copolymerization of EA with 7 % MMAA the phase ratio was altered owing to the increased viscosity of the system during polymerization when the phase ratio is 1 : 4). Monomers Emulsifier Phase ratio Activation energy, kcal/ /mole
EA 1.5% E-30 1:4
EA None 1:4
EA-}- 7 ~o MMAA None 1:9
12.9
27.1
24.9
Features of latex eopolymerization of acrylic monomers with MMAA
1847
/o#k
lO
05
3"00
3.10
3.2g
330
Fio. 3. Logarithm of polymerization rate constant vs. 1IT: 1 and 2--EA homopolymerization in the presence of 1.5% E-30, and without E-30 (respectively); 3--copolymerization of EA with 7% MMAA, without E-30 emulsifier. The high activation energy for the homopolymerization of EA without the emulsifier (27.1 keal/mole), and the activation energy for the copolymerization of EA with 7% MMAA (24.9 kcal/mole) confirms the conclusions already made to the effect that in both cases the reaction takes place in aqueous solution in the absence of oxygen. The introduction of the emulsifier in the homopolymerization of EA greatly reduces the activation energy of polymerization (12.9 kcal/mole) [7]. This difference in the activation energies points.to differences in the topochemical features of these two processes. We would suggest that in the presence of oxygen, when the polymerization of MMAA :in the aqueous phase is inhibited, the emulsionless process is likewise shifted to the particles, as is confirmed b y the data in Fig. 2a, showing the accelerating effect of MMAA on the process of MMAA-EA copolymerization in the aqueous phase in the presence of oxygen. CONCLUSIONS
(1) I t has been shown that in the mercaptan-regulated polymerization of ethyl acrylate in the aqueous phase in the absence of a special emulsifier a low molecular weight polymer latex is obtainable with fairly high expenditure of the initiator (ammonium persulphate). Moreover the polymerization takes place mainly in the aqueous phase, where surfactant oligomers are formed, the latter separating from aqueous solution and aggregating into particles.
1848
YE. M. MOROZOVA and V. I. YET.mEYEVA
(2) The introduction of methylol methacrylamide (which is preferentially water-soluble) into the reaction system accelerates the polymerization of ethyl acrylate in the presence of oxygen by displacing the site of the reaction into the volume of the emerging particles; this is made possible by increase in the hydrophilic nature of the particle surface by the copolymerizing water-soluble component, and by the higher concentration of monomer in the particles. (3) In the copolymerization of ethyl acrylate with methylol methacrylamide in the absence of oxygen and without the emulsifier the process is displaced into the aqueous phase (compared with the polymerization of ethyl acrylate in the presence of the emulsifier). Translated by R. J, A. HE:NDRY REFERENCES 1. V. I. YELISEYEVA, S. A. PETROVA and I. S. PINSKAYA, P a i n t and Lacquer Materials and their Applications, No. 1, 11, 1968 2. V. I. YELISEYEVA, I. V. NAZAROVA and S. A. PETROVA, Kolloid. zh. 30: 37, 1968 3. V. I. YELISEYEVA, V. F. MALOFEYEVSKAYA, A. S. GERASIMOVA, Yu. A. MAKAROV, I. S. IZMAILOVA a n d K. G. ORLOVA, Vysokomol. soyed. A9: 730, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 4, 813, 1967) 4. M. MORTON, S. KAIZERMAN and M. W. ALTIER, J. Colloid. Sci. 9: 300, 1954 5. H. GERRENS, Dechema Monographien, 49, N R 859-875, 1964 6. G. OZOLS and A. G. PARTS, Makromolek. Chem. 115: 223, 1968 7. S. S. MEDVEDEV, Kinetics and Mechanism of the Formation and Transitions of Macromolecules, p. 11, Izd. "Nauka", 1968
EFFECT OF SOME FACTORS ON THE POLYMERIZATION OF AMINOALKYLMETHACRYLATES IN A THIN FILM IN A I R * Y•. IV[. hIOROZOVAand V. I. YELISEYEVA Chemical Physics Institute, U.S.S.R. Academy of Sciences
(Received 20 May 1969)
MAWr reports have been published on techniques of spontaneous film-formation from monomers by means of a glow discharge [1-3] or an electron beam [4, 5]. These methods involve complicated apparatus and are used in applying protective polymer film coatings to small articles of simple profile. It seemed desirable to study the formation of films from monomers by means of chemical initiation of the polymerization in air with a view to dispensing with * Vysokomol. soyed. A12: :No. 7, 1626-1630, 1970.
V . I . YELISEYEVA and S. A. PETROVA
13. N. M. GELLER, B. L. YERUSALIMSKII, T. P. ZUBOVA,.V.N. KRASULINA, V. A. KROPACHEV, S. S. SKOROKHODOV, Yu. E. EIZNER, Theses of X V I Conf. of High-
molecular Weight Compounds Inst., U.S.S.R. Academy of Sciences, Izd. "Nauka", p. 10, 1970 14. L. E. SUTTON, Interatomic Distances, Sl~ec. Publ., N 11, The Chem. Soe., London, 1958 15. R. DAUDEL, R. LEFEBRE and C. MOSER, Quantum Chemistry, Intersci. Publ., 1959
FEATURES OF LATEX COPOLYMERIZATION OF ACRYLIC MONOMERS WITH METHYLOL METHACRYLAMIDE* V. I, Y E ~ S S r E V X a n d S . A. PETROVX Physical Chemistry Institute, U.S.S.R. Academy of Sciences
(Received 20 May 1969) A s w a s s h o w n in p a p e r s [1,2], colloidally-stable latices are o b t a i n a b l e b y c o p o l y m e rizing lower a l k y l a c r y l a t e s w i t h m e t h y l o l m e t h a c r y l a m i d e (M-hIAA) in t h e a b s e n c e o f emulsifiers a n d w i t h a m m o n i u m p e r s u l p h a t e as initiator. T h e p h y s i c o c h e m i c a l p r o p e r t i e s o f t h e s e latices are similar to those of latices p r e p a r e d in t h e usual w a y w i t h emulsifiers. The colloidal p r o p e r t i e s of t h e s e latices are influenced b y the m o n o m e r - m e t e r i n g p r o c e d u r e as well as b y t h e m o l e c u l a r w e i g h t of t h e p o l y m e r a n d its f u n c t i o n a l g r o u p c o n t e n t ( m e t h y l o l a m i d e groups). T h e a d d i t i o n of MMAA t o t h e c o p o l y m e r c o m p o s i t i o n h a s a stabilizing effect on t h e latices, a n d t h e stab i l i t y of t h e l a t t e r increases w i t h increase in t h e M M A A content. I n t h i s i n v e s t i g a t i o n we s t u d i e d t h e r e a c t i o n kinetics a n d t h e m e c h a n i s m o f t h e rising, g r o w t h a n d stabilization of l a t e x particles in t h e c o p o l y m e r i z a t i o n o f e t h y l a c r y l a t e ( E A ) w i t h M M A A in t h e a q u e o u s phase. DISCUSSION OF RESULTS
The special feature of MMAA as comonomer in the process of emulsion copolymorization with ordinary monomers is its preferential solubility in the aqueous phase. We have shown that with an EA : water ratio of 1 : 1.5 and at a temperature of 60 o the solubility of MMAA is ten times as high in water as in EA. In studying the mechanism of particle formation we adopted the method of emulsion polymerization with staged metering of the monomers and the initiator with access of air and with the following mixture formulation: ethyl acrylate, 100.0; mcthylol methacrylamide, 0-5.0; ammonium persulphate, 1-0; tertiary dodecylmercaptan, 1-0; water, 295.0 pts. by wt. In addition experiments were carried out w i t h the same formulation as above, but using a seeding latex in the form of butyl acrylate-methyl methacrylate-methacrylic acid * Vysokomol. soyed. A12: No. 7, 1621-1625 1970.
Features of latex copolymeriz~tion of acrylic monomers with MMAA
1843
copolymer (60 : 35 : 5) obtained by emulsion polymerization in the presence of sulphanol (3% on monomer wt.). The dilute seed latex in which the polymerization was carried out had the following characteristics: dry residue, 1"04%; surface tension, 58.7 erg/cm2; particle diameter, 0.045 #; number of particles in 1 ml of latex, 1.67 × 10~4. During the polymerization saxaples were removed and the surface tension in the latter was determined by~the ring separation method on a Dew-Nooey device. The particle sizes were determined on aa FEKN-57 nephelometer by the light-scattering method, and the number of particles in 1 ml of latex wa~ calculated. T h e results o b t a i n e d are p r e s e n t e d in Fig. 1 a n d in the Table. ~, e~g/crn ~
58 ~
6,erWcm2 B2--
ff
50
; 2.o
o#
oc 9
38
~6 ~ |
~2
o
!
I
5'
I
I
12
t
I
l#
I
I
2/I
I
I
30
I
I
6
I
I
12
I
I
16
I
I
2~
I
I
30
DCUpesidue, % FIG. 1. Change in surface tension (a) in the polymerization without emulsion of EA ((~l)and in the eopolymerization of EA with MM_AA (b): 1 --without seeding, 2-with seeding. I n view of t h e d a t a in Fig. l a we m a y surmise t h a t the p o l y m e r i z a t i o n o f E A (solubility in w a t e r 2.6%) w i t h o u t a n emulsifier s t a r t s in aqueous solution in t h e p o l y m e r i z a t i o n w i t h or w i t h o u t seeding. D u r i n g t h e initial period s u r f a e t a n t oligomers a n d radicals are formed, a n d t h e i r diphilic n a t u r e is a p p a r e n t l y due to the initiator residue (SO~ groups) a t the chain ends which considerably reduces the surface tension o f t h e system. This is confirmed b y the high ~-potential of the particles, a m o u n t i n g to 160 inV. W h e n the p o l y m e r chains h a v e r e a c h e d a particular weight it a p p e a r s t h a t t h e y t h e n form aggregates leading to the n u c l e a t i o n o f latex particles, as is e v i d e n t f r o m the t a b u l a t e d data. Along with the adsorption o f s u r f a c t a n t oligomers a n d radicals t h e r e is f u r t h e r f o r m a t i o n of the l a t t e r in the aqueous phase, as is indicated b y the kinetics of change in 6 during the p o l y m e r i z a t i o n process (Fig. 1). I n view o f these results we would conclude t h a t it is m a i n l y in the aqueous phase t h a t t h e p o l y m e r i z a t i o n of E A proceeds w i t h o u t t h e seed in t h e absence of t h e emulsifier, f u r t h e r evidence of which is seen in the increased n u m b e r of particles per 1 ml o f latex, p a r t i c u l a r l y a t t h e s t a r t of t h e process (see Table). I n the seed p o l y m e r i z a t i o n o f E A t h e n u m b e r of particles per 1 ml o f l a t e x remains practically c o n s t a n t as t h e degree of conversion rises, a n d it is e q u a l to the n u m b e r o f seeding l a t e x particles (see Table). I n this case t h e emerging s u r f a c t a n t
1844
V.I. YELISEYEVAand S. A. PETROVA
oligomers a n d radicals are a d s o r b e d b y t h e surface of the seed l a t e x particles. This is i n d i c a t e d b y t h e increase in t h e size of t h e particles during t h e synthesis. I n t h e seedless c o p o l y m e r i z a t i o n o f E A w i t h MMAA (Fig. lb), a n d also in t h e same process with t h e seeding latex (curves I a n d 2, respectively) the surface tension falls t h r o u g h o u t t h e process, while t h e d i a m e t e r of the particles increases. w i t h t h e degree of conversion. I n t h e seedless p o l y m e r i z a t i o n t h e n u m b e r o f particles remains practically c o n s t a n t a f t e r a certain n u m b e r is r e a c h e d (see Table). I n t h e seed p o l y m e r i z a t i o n d u r i n g t h e initial period, w h e n t h e surface tension is g r e a t l y reduced, t h e n u m b e r of particles remains equal to t h e n u m b e r o f seed l a t e x particles, a n d a f t e r this the t o t a l n u m b e r of particles is increased to t h e n u m b e r f o r m e d in t h e seedless polymerization, a n d remains a p p r o x i m a t e l y constant. T a k i n g all this into consideration we conclude t h a t in t h e emulsionless c o p o l y m e r i z a t i o n of E A w i t h MM_AA the n u c l e a t i o n of particles t a k e s place in the same w a y as in t h e emulsionless p o l y m e r i z a t i o n of EA, and this m e c h a n i s m remains e v e n w h e n t h e seed is introduced. This m e a n s t h a t w h e t h e r or n o t there are seeding l a t e x particles, new particles are f o r m e d in the a q u e o u s phase containing the readily soluble m o n o m e r MMAA. I n this case d i s p l a c e m e n t o f the h y d r o p h i l i c - h y d r o p h o b i c balance o f oligomers f o r m e d in t h e aqueous phase t o w a r d s t h e h y d r o p h i l i c p o r t i o n leads to f u r t h e r "self-stabilization" of the emerging aggregaGROWTH OF PARTICLES AND CHANGE IN THEIR NUMBER PER 1 T H E EM-ULSION-LESS P O L Y M E R I Z A T I O N O F milk A N D I N E 2 ~ - M ~ I A f l k
Without seedeing
rnl
oF LATEX IN
COPOLYMERIZATION
With seeding
dry residue of latex, %
particle diameter, 1~
number of particles in 1 ml of latex × 10-14
3.08 6.9 10.35 13.9 17.1 19.3
0-10 0.11 0.12 0-12 0.13 0.13
EA homo )olymerization 0.56 1.04 (etching) 0.94 7-95 1.11 12.12 1.31 15.45 1.45 17.1 1.50 20.0
1.865 4.315 6.98 9.35 12.05 13.95 15.05 17.3 19.35
0-07 0.10 0-11 0.12 0.13 0.13 0.14 0.14 0.15
EA-MMAA copolymerization 0.90 1"04 (etching) 0-80 5.82 0.92 11.57 0.98 15.2 1.02 18.3 1.13 22.4 1.09 1.05 1.06
dry residue of latex, ~o
particle diameter, lz
number of particles in 1 ml of latex × 10-14
0"04 0"10 0"11 0"12 0"12 0"13
1"67 1"52 1"70 1"69 1"85 1"68
0"04 0"09 0"10 0"10 0"11 0"12
1"67 1"68 2"55 2"56 2"41 2"18
Features of latex eopolymerization of acrylic monomers with MMAA
184~
tes owing to the marked hydxophilization of their surface; this is indicated by the ~-potential of their particles, l l 0 mV, which is lower than in the emulsionless homopolymerization of EA. The lower interfacial tension at the surface of aggregates of methylol-containing oligomers (or radicals) favours increased diffusion of monomers from the aqueous phase into the latter, and in this way the polymerization process is shifted to the volume of the particles. In order to study the kinetics of the process in relation to the amount o f methylol methacrylamide in the reaction system we carried out the emutsionless copolymerization, with access of oxygen, at 65 ° in a reactor providing for the removal of samples and for simultaneous introduction of the total amount of all the ingredients into the reaction as follows*: EA, 100.0; MMAA, 3.0; 5.0 and 7.0; tertiary dodecylmercaptan, 0.5; ammonium persulphate, 0.25; water, 295.0 pts. by wt. As is seen from the kinetic curves in Fig. 2a, a rise in the content of methylol methacrylamide in the copolymer is accompanied by acceleration of the polymerization peocess~. This m a y be due to the more hydrophilic nature of the El
100
10
%8 /40
I/
b
5
~0
20 :..,~.~ _ . r__ ,. --r.. . ~ , . --t- . r--. ¢ - T - -'~--- 3 40 80 120 180 200 290 T/me,
m/n
5
15
25
FIG. 2. Kinetic curves of the emulsionless eopolymerization of EA with different amounts of MMAA in the presence of oxygen (a) and under oxygen-free conditions (b); a: 1--EA+7~o MMAA, 2--EA+5~o MMAA, 3--3% MMAA; b: EAq-3% MMAA, 2--EA, 3--EAq-5% MMAA, 4--EAq-7% MMAA, 5--EA+l.5~o E-30 (emulsifier). Q--Amount of polymer formed (g) per 100 g of aqueous phrase. surface of the emerging particles caused by the introduction of methylol methaerylamide fragments into the macromolecules (with hydrophobic monomers a similar effect is obtained by increasing the amount of emulsifier in the system). The increasingly hydrophilic surface reduces the surface tension at the interface with the aqueous phase, and increases the concentration of monomer in the particles, so t h a t the polymerization rate is increased [4, 5]. * These experiments were performed in collaboration with L. V. Kozlov. t Note that stable latices proved unobtainable [3] in the case of simultaneous addition of the ingredients to the reaction mixture.
1846
V.I. YELISEYEVAand S. A. PETROVA
In the light of the experimental results it was desired to compare the kinetics of the oxygen-free copolymerization of EA, with different amouts of MMAA, with the polymerization kinetics for EA b y itself, with and without the emulsifier. To do this a dilatemetric study was made (under oxygen-flee conditions) of the kinetics of EA copolymerization with different amounts of MMAA in the aqueous phase without the emulsifier, along with the polymerization of EA b y itself in the presence of E-30 emulsifier (sodium salt of sulfo-acids of the f a t t y series C12mC1s) and without E-30; in addition the activation energy for these processes was determined. In carrying out the experiments we used the mixture formulation given above (for the method of gradual introduction of the monomers),but the phase ratio was altered to i : 4 (organic phase : water). The kinetic curves for these processes are depicted in :~ig. 2b. It is seen from this Figure that in the emulsionless polymerization of EA the reaction rate is much lower than in the polymerization with 1.5% of E-30 emulsifier. Without the emulsifier the reaction rate for the EA,MMAA copolymerization in the absence of atmospheric oxygen is reduced with increase in the amount of MM_A_Aintroduced into the reaction, i.e. this monomer has the reverse effect on the reaction rate compared with the polymerization with access of oxygen. This difference m a y well be due to the polymerization of MMAA taking place preferentially in the aqueous phase in the absence of the inhibiting effect of oxygen on this reaction (data on the inhibiting effect of oxygen on the polymerization of water-soluble monomers is given in [6]). The fact that under oxygen-free conditions M-MAA polymerizes mainly in the aqueous phase is further confirmed b y the increased viscosity of the reaction system, while no such increase is observed in the polymerization in the presence of 02. In the presence of the emulsifier the homopolymerization of EA takes place in the polymer-monomeric particles which according to present-day theories gives rise to considerable acceleration of the polymerization process. To determine the activation energy for EA-MM_AA copolymerization in the absence of the emulsifier, and for EA homopolymerization with and without the emulsifier we studied the reaction kinetics in the temperature interval 31-60 °. Figure 3 shows the dependence of the logarithm of the polymerization rate constant on temperature for 4 % conversion. The following are the activation energies for the processes in question. (For the copolymerization of EA with 7 % MMAA the phase ratio was altered owing to the increased viscosity of the system during polymerization when the phase ratio is 1 : 4). Monomers Emulsifier Phase ratio Activation energy, kcal/ /mole
EA 1.5% E-30 1:4
EA None 1:4
EA-}- 7 ~o MMAA None 1:9
12.9
27.1
24.9
Features of latex eopolymerization of acrylic monomers with MMAA
1847
/o#k
lO
05
3"00
3.10
3.2g
330
Fio. 3. Logarithm of polymerization rate constant vs. 1IT: 1 and 2--EA homopolymerization in the presence of 1.5% E-30, and without E-30 (respectively); 3--copolymerization of EA with 7% MMAA, without E-30 emulsifier. The high activation energy for the homopolymerization of EA without the emulsifier (27.1 keal/mole), and the activation energy for the copolymerization of EA with 7% MMAA (24.9 kcal/mole) confirms the conclusions already made to the effect that in both cases the reaction takes place in aqueous solution in the absence of oxygen. The introduction of the emulsifier in the homopolymerization of EA greatly reduces the activation energy of polymerization (12.9 kcal/mole) [7]. This difference in the activation energies points.to differences in the topochemical features of these two processes. We would suggest that in the presence of oxygen, when the polymerization of MMAA :in the aqueous phase is inhibited, the emulsionless process is likewise shifted to the particles, as is confirmed b y the data in Fig. 2a, showing the accelerating effect of MMAA on the process of MMAA-EA copolymerization in the aqueous phase in the presence of oxygen. CONCLUSIONS
(1) I t has been shown that in the mercaptan-regulated polymerization of ethyl acrylate in the aqueous phase in the absence of a special emulsifier a low molecular weight polymer latex is obtainable with fairly high expenditure of the initiator (ammonium persulphate). Moreover the polymerization takes place mainly in the aqueous phase, where surfactant oligomers are formed, the latter separating from aqueous solution and aggregating into particles.
1848
YE. M. MOROZOVA and V. I. YET.mEYEVA
(2) The introduction of methylol methacrylamide (which is preferentially water-soluble) into the reaction system accelerates the polymerization of ethyl acrylate in the presence of oxygen by displacing the site of the reaction into the volume of the emerging particles; this is made possible by increase in the hydrophilic nature of the particle surface by the copolymerizing water-soluble component, and by the higher concentration of monomer in the particles. (3) In the copolymerization of ethyl acrylate with methylol methacrylamide in the absence of oxygen and without the emulsifier the process is displaced into the aqueous phase (compared with the polymerization of ethyl acrylate in the presence of the emulsifier). Translated by R. J, A. HE:NDRY REFERENCES 1. V. I. YELISEYEVA, S. A. PETROVA and I. S. PINSKAYA, P a i n t and Lacquer Materials and their Applications, No. 1, 11, 1968 2. V. I. YELISEYEVA, I. V. NAZAROVA and S. A. PETROVA, Kolloid. zh. 30: 37, 1968 3. V. I. YELISEYEVA, V. F. MALOFEYEVSKAYA, A. S. GERASIMOVA, Yu. A. MAKAROV, I. S. IZMAILOVA a n d K. G. ORLOVA, Vysokomol. soyed. A9: 730, 1967 (Translated in Polymer Sci. U.S.S.R. 9: 4, 813, 1967) 4. M. MORTON, S. KAIZERMAN and M. W. ALTIER, J. Colloid. Sci. 9: 300, 1954 5. H. GERRENS, Dechema Monographien, 49, N R 859-875, 1964 6. G. OZOLS and A. G. PARTS, Makromolek. Chem. 115: 223, 1968 7. S. S. MEDVEDEV, Kinetics and Mechanism of the Formation and Transitions of Macromolecules, p. 11, Izd. "Nauka", 1968
EFFECT OF SOME FACTORS ON THE POLYMERIZATION OF AMINOALKYLMETHACRYLATES IN A THIN FILM IN A I R * Y•. IV[. hIOROZOVAand V. I. YELISEYEVA Chemical Physics Institute, U.S.S.R. Academy of Sciences
(Received 20 May 1969)
MAWr reports have been published on techniques of spontaneous film-formation from monomers by means of a glow discharge [1-3] or an electron beam [4, 5]. These methods involve complicated apparatus and are used in applying protective polymer film coatings to small articles of simple profile. It seemed desirable to study the formation of films from monomers by means of chemical initiation of the polymerization in air with a view to dispensing with * Vysokomol. soyed. A12: :No. 7, 1626-1630, 1970.