REDOX INITIATION WITH PERCARBONATE ESTERS J O H N
C .
C R A N O ,
E L I Z A B E T H
K .
F L E M I N G ,
A N D
W I L L I A M
A .
K E l M
Chemical Dicision, PPG Industries, Barberton, Ohio 44803
Redox couples have been discovered which contain diisopropyl peroxydicarbonate (IPP) or ferf-butylperoxy isopropyl carbonate (BPIC) and are effective initiators for emulsion polymerizations a t relatively low temperatures (5' to 30OC.). The couples consist of the percarbonates plus water-soluble reducing agents. Effective reducing agents for IPP are the water-soluble salts of dialkylaminoaromatic acids, sodium metabisulfite, and sodium dithionite. The amino acid salts did not accelerate the decomposition of BPIC in the emulsion systems. However, vinylidene chloride and styrene were rapidly polymerized w i t h the use of BPIC plus sodium metasulfite or sodium dithionite a t 30' C.
DIISOPROPYL peroxydicarbonate
( I P P ) and tert-butylperoxy isopropyl carbonate (BPIC) are examples of two types of percarbonate esters (Strain et al , 1950). As indicated by their structural formulas, IPP is similar to the diacyl peroxide,;, whereas BPIC is related to the tert-butyl peresters of carboxylic acids. These analogies are strengthened when the large difference in the decomposition behavior of the percarbonate esters is considered.
/
\
CH i
CH
2
I PP
CH
\ CH--0-C /
0
I1
CH -0-0-C-CHI
CH
I CH L
BPIC The magnitude of this difference can be readily observed by a study of the half lives of the peroxides (Strong, 1964a). In benzene solution a t a concentration of 0.%iM, IPP undergoes a rapid decomposition a t 30°C. with a half life of about 1 hour. Under the same conditions, BPIC has a half life of well over 500 hours. At 100'C. half of the BPIC decomposes in slightly less than 9 hours. The large difference in stabilities of these percarbonates leads to an equally large difference in their behavior as free radical initiators (Strong, 1964b). I P P can be conveniently used for the suspension polymerization of vinyl chloride at a temperaxure as low as 33.C. With BPIC, much higher temperatures, a t least 80"C., are necessary to achieve a convenie:nt rate of polymerization of vinyl monomers.
T o extend the useful temperature ranges for the percarbonate esters, a study was undertaken to find reducing agents which, when coupled with the peroxides, would afford efficient initiating systems. Some redox couples containing IF'P or BPIC which can be used to initiate free radical emulsion polyinerizations are reported in this paper. Experimental
Procedure. The polymerizations were performed in 7- or 32-ounce beverage bottles. Each bottle was charged with distilled deoxygenated water and then flushed with nitrogen for a t least 03 hour. The surfactant, monomer, reducing agent, and any other ingredient except peroxide were added and the bottle was again flushed with nitrogen, then capped with a crown cap in which a small hole had been drilled. Generally, a neoprene liner (K-1413, Firestone Industrial Products) was used with the cap. I n polymerizations in which vinylidene chloride was used. a special liner consisting of an inner seal of cloth-reinforced butadiene-acrylonitrile rubber and an outer seal of butyl, puncture-sealing nonreinforced rubber was used. The (capped bottle was placed in a guard and then tumbled in a constant temperature water bath. Sufficient time was allowed for the bottle and its contents to reach temperature equilibrium wi1.h the bath. The liquid peroxide was then injected into the polymerization mixture. This point \vas taken as the initiation time (1 := U). The per (cent conversions of monomer to polymer were obtained in the following manner. An approximately 2-ml. sample was taken in a syringe. The syringe plus sample was weighed and the sample was injected into a tared aluminum dish containing 5 ml. of 0.01' ethanolic hydroquinone. The emptied syringe was weighed and the weight of' the sample obtained by difference. The aluminum dish plus residue was heated to constant weight in a 100' C. oven. The conversion was calculated from the weight of the residue corrected for the amount of nonpolymeric solid determined from the polymerization recipe. In some instances the polymer was isolated by coagulation, using isopropyl alcohol or aqueous 10' < CaCI, solutions. The polymers were mashed with water and alcohol several times in a blender. The polymer was vacuum-dried. hlaterials. The diisopropyl peroxydicarbonate used was the commercial grade produced by P P G Industries. Chemical Division. tert-Butylprroxy isopropyl carbonate was obtained by the reaction of tert-butyl hydroperoxide and isopropyl chloroformate in the presence of base a t 0' to 5" C . I t was purified by distillation under reduced pressure (assay 99' c 1. Cumene hydroperoxide (72.8( c ) was obtained from the Hercules Powder Co. VOL. 8 NO. 1 M A R C H 1969
93
Styrene was purified by distillation under reduced pressure. Vinylidene chloride was distilled under nitrogen, The sodium salts of the amino acids were isolated by adding a n equivalent amount of standardized ethanolic sodium hydroxide to a weighed portion of amino acid in ethanol and evaporating the resultant solution t o dryness. Baker and Adamson's reagent grade sodium metabisulfite. J.T. Baker's purified sodium dithionite, and Matheson, Coleman, and Bell's reagent grade sodium thiosulfate were used without further purification. Triethylenetetramine was obtained from the Union Carbide Corp. I n the polymerization studies using IPP, Duponol ME (dry sodium lauryl sulfate) was sometimes used. With BPIC, Duponol ME was replaced by Matheson, Coleman, and Bell's U.S.P. sodium lauryl sulfate. Igepal CO-630 jnonylphenoxypoly(ethyleneoxy)ethanol] was obtained from General Aniline and Film.
Results and Discussion
Diisopropyl Peroxydicarbonate Redox Couples. Using styrene as a diagnostic monomer, several couples, each containing diisopropyl peroxydicarbonate (IPP) plus a watersoluble reducing agent, were found to initiate polymerizations in emulsion systems a t 5°C. The reducing agents can he separated into two classes: water-soluble salts of aromatic amino acids (Crano, 1 9 6 i ) , and salts of dithionous or sulfurous acids. The results obtained in the emulsion polymerization of styrene initiated by IPP-amino acid salt redox couples are given in Table I. An efficient reducing agent contained a tertiary amino group and a water-solubilizing group. When the reducing agent contained a primary amino group (sodium 4-aminobenzoate), essentially no increase in the rate of decomposition of I P P occurred and no polymerization took place in 24 hours. The replacement of the watersoluble amino acid salt with N,L\J-dimethylaniline(DMA) resulted in a very rapid decomposition of I P P with the formation of only a trace of low molecular weight polymer. The IPP-DMA reaction in benzene solution has been discussed (Crano. 1966). The emulsion polymerization of styrene using benzoyl peroxide and the sodium salts of amino sulfonic acids at 25.C. was reported by Hrabak and Bezdek (Hrabak and Bezdek, 1961). The rates of polymerization and terminal conversion obtained using an IPP-amino acid salt redox couple are greatly affected by the type and amount of emulsifying agent employed (Table 11). An added effect was the enhancement of the polymerization rate and terminal conversion that occurred when sodium hydroxide was added to the recipe using the anionic emulsifier. Duponol ME. From the data in Table I1 it can be seen that the use of a mixture of Duponol M E and the nonionic Igepal CO-630 gave better results than the use of a comparable amount of either alone. The necessity for having an emulsion system was indicated by the absence of substantial Table I. Emulsion Polymerization of Styrene with IPP-Amino Acid Salt Redox Complex ( 5 " C.)" ( (
t
Sodium Salt, Parts 3-Dimethylaminobenzoate (0.92) 4-Dimethylaminobenzoate (0.92) 4-Dimethylaminocinnamate(1.07) 4-.4minobenzoate (0.80) 3-Diethylaminobenzenesulfonate( 1.21 None ''
=
y!,
min.
--
Coni~rsion t = 2 t = 24 hr. hr.
10 12
54 30 52
...
., .
0.i
2
...
24
...
73 70 56 Nil
74 Xi1
Recipe. Water, 220 parts; styrene. ZOO parts: lgepal CO-6'30,
10 parts: I P P . 0,47 part.
94
I & E C PRODUCT RESEARCH A N D DEVELOPMENT
Table II. Emulsion Polymerizotion of Styrene with IPP-Sodium 3-Dimethylaminobenzoate Couple ( 5 ' C.)" ((
ConLersion t=& hr.
Part NaOH
t = P hr.
Duponol ME (5) Duponol ME (10) Duponol ME (10)
0.55 0.0 0.55
35 23 60
43 36
Igepal CO-630 (5) Igepal CO-630 (10) Igepal CO-630 (10)
0.0 0.0 0.55
30 54 50
40 73 T3
Duponol ME (3.3) plus Igepal CO-630 (2.2)
0.55
50
52
Duponol ME (2.2) plus Igepal CO-630 (3.3)
0.55
56
61
None
0.0
...
Si1
Emulsifying Agent. Parts
60
Recipe. Water. 3211 parts: styrene. 100 p a r k : ,\odium :i-dimethJiaminubenzuate. 0.92 part: I P I ' . 0 . i i part. Table 111. Emulsion Polymerization of Styrene with IPP-NaiSZO; or IPP-Na&O, Redox Couple ( 5 " C.)"
Conrersion
ReducinE Agent, Part
Na?S,Oi (0.25) SaiS20. (0.2T) SalSIO, (0.27) Ka.S?04 (0.27) Xa,S?O, (0.40) None
Ernuisijj ing Agent, Parts Igepal CO-630 110) Igepal CO-630 (10) Duponol ME (5) Sone Igepal CO-630 (10) Igepal CO-630 (10)
t=.Y
hr. 5 62 47 ,.. ,
, ,
...
t=P'4t=48 hr. hr. 45 77 73 Nil Xi1 Si1
80
. ..
.. ... . .. . .. I
'Recipe. Water. 220 parts: styrene, 100 parts; I P P , U.17 part.
I P P decomposition (less than 5"; in 24 hours) or polymerization when no surfactant was present. The results obtained in the 5.C. emulsion polymerization of styrene initiated by an IPP-sodium metabisulfite (ru'a?S?O-,) or IPP-sodium dithionite (NalS201)redox couple are presented in Table 111. At this temperature, the polymerization rate caused by the IPP-Xa&O couple was rather slow, although it was considerably higher than that caused by I P P alone. This system should provide an attractive initiation rate a t slightly higher temperatures--e.g.. 25' C. A rapid polymerization was initiated by I P P plus sodium dithionite in the presence of Igepal CO-630 or Duponol M E at 5'C. I n the absence of a surfactant there was no acceleration of I P P decomposition (less than 5' decomposition in 24 hours) or polymer formation. Although sodium metabisulfite and sodium dithionite are effective reducing agents for I P P in these emulsion systems, sodium thiosulfate had no effect on the rate of' disappearance of the percarbonate. The I P P redox couples discussed above were compared directly with each other and with the cumene hydroperoxide (CHP)-triethylenetetramine initiating system in the . copolymerization of styrene and vinylidene chloride (5" C.) A copolymerization initiated by I P P alone at 50'C. was also carried out. Each copolymerization was stopped at a 3 0 ' r conversion and the copolymer was isolated for a determination of its composition and intrinsic viscosity (Table I V ) . The IPP-amino acid salt and IPP-sodium dithionite redox couples were comparable to the CHP-amine system
Table VI. Emulsion Polymerization of Styrene with BPIC Redox Couples (30' C.)"
Table IV. Copolymerization of Styrene and Vinylidene Chloride"
Hours Po13mer for 3 0 c c Temn , ComerPropert'es O 6 . sion 5 c VdCl" ( 7 ) '
Initiating System, Part I P P (0.39) + sodium 3-dimethylaminobenzoate (0.78j I P P (0.39) + Na?S?O,(0.22) I P P (0.39) + N a A O ; (0.2%) Cumene hydroperoxide (0.22) plus triethylenetetramine (0.47) IPP (0.39)
5 5 5
2.5 3.5 18.0
31 31 3%
1.1 1.5 2.2
5 50
3.0 10.0
32 34
1.2 0.45
cc
Parts BPIC 0.5 None' 0.5
Reducing Agent lia?SjOi Na2S2Oi Na2S?04
t
=
hr. 19 8 19
1
Conversion t
=
hr. 49 17 63
2
t
24 hr. 86 90 91
=
ilJYnh
I)
3.36 13.2 1.08
Recipe. Water, 200 parts; sty-ene, 100 parts; sodium lauryl sulfate, 2.0 parts; reducing agent, 0.5 p a r t 'Inherent viscosities determined on 0.5 g . d l . polymer solutions i n benrem. '5.0 parts sodium lauryl sulfate used. Inherent ciscosity of polxmer determined on 0.1 g . d l . benzene solution.
Recipe. Water. 186 parts; styrene. 4% parts; cinylidene chloride. 58 parts; Duponol M E , .jparts. " M o l a r percentage determined by chiorine analJsis. ' Determined from relative viscosity measurements on polymer solutions i n benzene at 25>C. ' S o d i u m hxdroxide (0.53 part) added.
with regard to the rate of polymerization and molecular weight of the product. The slower rate obtained with I P P plus sodium metabisulfite had the expected effect of' increasing the molecular weight substantially. The lower molecular weight obtained with the use of I P P alone a t 50°C. was an indication of the ease with which IPP or other materials in the recipe enter into a chain transfer reaction with the gro,wing polymer chain. At 5.C. this tendency is considerably reduced. tert-Butylperoxy Isolpropyl Carbonate Redox Couples. Using vinylidene chloride as a diagnostic monomer, sodium metabisulfite and sodium dithionite were found t o form very active redox couples with BPIC a t 30°C. (Table V) . Sodium 3-dimethylaminobenzoate and sodium thiosulfate were completely inactive as reducing agents for this percarbonate in ennulsion systems. The results obtained with the BPIC-KaiS?Oj couple were complicated by a polymerization initiated by the reducing agent alone. When BPIC was added, a 22'; conversion to polymer had already been attained and the monomer had been in contact with the reducing agent for approximately 30 minutes. There is a report in the patent literature on the use of substances which yield sulfur dioxide in aqueous solution, particularly K?SLOi, for the polymerization of acrylic acid derivatives (Fallows and Mellers, 1946). A probable explanation is that this activity results from a redox couple of the bisulfite and traces of peroxy compounds in the system.
From the data in Table V, it is obvious that the rate of polymerization was substantially increased with the addition of BPIC to the NanS20isystem. Polymerization of vinylidene chloride with sodium dithionite alone was not observed. The BPIC-Ka2S?O4 couple did initiate a very rapid polymerization of this monomer in an emulsion system a t 30" C. Styrene was also polymerized successfully with the BPIC-XarSrOi and BPIC-Sa?S?O? systems a t 30" C. (Table VI). Again, polymerization was achieved with Na,SLOj alone, although the rate was much lower than with the percarbonate present.
Conclusions
The temperature ranges in which IPP and BPIC can be used to initiate emulsion polymerizations can be extended with the addition of certain water-soluble reducing agents. Using IPP, for example, very rapid polymerizations of styrene were achieved a t 5 ° C . with the addition of salts of dialkylaminoaromatic acids or sodium dithionite. The rapid rates of these polymerizations indicate the possibility of using these redox systems a t still lower temperatures. The stability and ease of handling of the liquid tertbutylperoxy isopropyl carbonate provide substantial advantages for its use. This peroxide, coupled with sodium metabisulfite or sodium dithionite, can be used to initiate emulsion polymerizations a t 30" C. or lower.
Literature Cited Table V. Emulsion Polymerization of Vinylidene Chloride with BPIC Redox Couples (30' C.)"
Conversion
1
t = 0
Reducing Agent Sa?S?O-
NaiS?04 Sa?S?O Sodium %dimethylaminobenzoate
t
=
1.j
t
= :j(j
min.
min.
min.
22 0
...
50 64
...
86 85 6il'
...
...
Nil'
Recipe. IVater, 22f/ p w t s ; t in3,lidene chloride, ZOO parts; sodium l a u ~ sulfafe, l 3.0 parts; reducing agent, 0.3 part: E P I C , 0 . j part. " S o pol.vmerization afier Zli hours.
Crano, J. C., J . Org. Chem. 31, 3615 (1966). Crano, J. C., U. S.Patents 3,312,678 and 3,312,679 (April 4, 196'7). Fallows, L., Mellers, E. V., Brit. Patent 579,379 (Aug. 1, 1946). Hrabak, F., Bezdek. M.. Collection Czech. Chem. Commun. 26, 915 (1961). Strain, F . , Bissinger, W. E., Dial, W. R., RudofT, H., DeWitt, B. J.,-Stevens, H. C., Langston, J. H., J . A m . Chem. Soc. 72, 1254 (1950). Strong. W.A., Ind. Eng. Chem. 56 (12). 33 (1964a). Strong, W. A,, IND. ENG. CHEM.PROD.RES. DEVELOP. 3, 264 (1964bj. RECEIVED for review July 5, 1968 ACCEPTED Sovember 27, 1968 VOL. 8 NO. 1 M A R C H 1969
95
