I
F. BROWN, F. BERARDINELLI, R. J. KRAY, and L. J. ROSE" Celanese Corp. of America, Summit Research Laboratories, Summit, N. J.
Polymerization of Methyl lsopropenyl Ketone Although the homopolymer and copolymer with styrene are both similar to poly(methy1 methacrylate) in key physical properties, the latter can be iniection-molded more successfully, as it is more stable thermally
M E T H Y L isopropenyi ketone, originally prepared by Merling and Kohler (6) in 1909, polymerizes to a hard, glasslike product. This work was undertaken to develop a commercially acceptable, clear molding powder from this material. Monomer Purification. As received, monomeric methyl isopropenyl ketone contained 15 to 30 p.p.m. of hydroquinone and trace quantities of ethyl vinyl ketone, vinyl isopropyl ketone, and water. Some dimer was usually present. The monomer was purified by distillation in the dark at 65 to 85 mm. of mercury in a stream of nitrogen through a 90 X 25 cm. column packed with glass helices at 3 to 1 reflux ratio. It was then stored in t h e d a r k a t -0Oto -1OOC. Preparation and Properties of Polymers. The homopolymer was readily Present address, Aerojet General Corp., Azusa, Calif.
prepared by bulk, solution, bead, and emulsion techniques. Bulk polymerizations were carried out in borosilicate glass tubes which were flushed with nitrogen and sealed. T h e tubes were immersed in a thermostatically controlled oil bath for a n appropriate time and then were cooled to room temperature as rapidly as possible. The resulting polymer, dissolved in acetone (6% solution) and precipitated by adding cyclohexane, was then filtered, washed with more cyclohexane, and dried a t 70' to 75' C, Typical results are shown in Table I. In the solution polymerizations the best results were obtained by using solvents for the monomer which were nonsolvents for the polymer ( 5 ) . Polymerizations were carried out in a stirred flask fitted with a reflux condenser and a nitrogen inlet. The solution was
Table I. In Bulk Polymerization of Methyl lsopropenyl Ketone, Azobisisobutyronitrile Was Best Catalyst for Producing High Yields of Color-Stable Polymer Initiator Typeb
AN
BznOz MEKP f Co naphthenate
uv
% 0.21 0.41 1.0 2.0 0.24 1.0 1.0 1.0 1.0
1.0 1.0
...
Temp., O
c.
Hr. 16 16 16 15 40 16.5 29 63 24 20.5 92.5
75-76 75-76 75-76 75-76 75-76 75-76 75-76 75-76 87 87 45
Yield,
% 34 62 95 94 86 91
241 17 62
In. Vis. 0.25 0.21 0.23 0.24 0.34 0.33 0.31 0.22 0.29 0.21 0.45
...
Color of Diska
+
Table II. Of
In Solution Polymerization lsopropenyi Ketone, Best
Results Were Obtained by Usina Solvents for the Monomer Which Wer;! Nonsolvents for the Polvmer"
T CB CB CB CB CB CB CB c
d
C
25 336 30 CB UV BzpOr 1.0 25 288 85 0.79 e T = transparent; CB = colorless but brittle. AN = azobisisobutyronitrile; Bz202 = benzoyl peroxide; MEKP = methyl ethyl ketone peroxide; UV = ultraviolet. Polymer was brown. Colored; not molded. e Green and brittle. ~
polymerized under a slow nitrogen purge a t 78O C. for 11 to 11.5 hours, and the resulting cyclohexane slurry of polymer was filtered and the polymer washed and dried a t 75' C. Both products were screened for molding by determining their inherent viscosity and by compression molding as described for the bulk polymer. Typical results are shown in Table 11. Bead polymers were made by charging the reactants to a mechanically stirred flask fitted with reflux condenser and nitrogen inlet and heated by a Gyco thermal mantle. After polymerization, excess monomer was stripped by steam. Subsequently, polymers were isolated by adding magnesium or sodium acetate or if the product was a gummy dispersion it was dissolved in acetone and reprecipitated with water.
ANb, Yield, Solvent 95y0 ethyl alcohol Abs. ethyl alcohol Carbon tetrachloride Cellosolve 2-Ethylbutanol OctaneC 2,2,4-Trimethylpentanea Ligroin, 90-120' C.c Mineral oilc CyclohexaneC
% 1 1 1 1
1.5 1 1 1
1.5 1.5
%
In. Vis. 0.17
36.8 33.5 33.5 25.6 46.4 69.0
0.07 0.07 0.12 0.38
78.5 75.4 91.0 69.0
0.66 0.53 0.45 0.47
0.04
Reaction time, 16 hours at 7.5' C Azobisisobutyronitrile. Nonsolvent for polymer.
VOL. 5 1 , NO. 1
0
JANUARY 1 9 5 9
79
HEAT DISTORTION,
*C
ROCKWELL
WATER
HARDNESS, M SCALE
ABSORPTION, %
TENSILE
FLEXURAL
S T R E N G T H STRENGTH BREAK, LOAD, P.S.I. P.S.I.
AT 2 6 4 R S . I .
30000 26000
22000
too I8000 14000
40
COhlPRESSlVE STRENGTH BREAK, RSI.
1200 IMPACT STRENGTH, FT. LB, PER INCH NOTCH
n
i
20 O
L
Figure 1. In general, poly(methy1 isopropenyl ketone) has mechanical properties similar to poly(methy1 methacrylate)
investigated because of the possibility of improving both light and thermal stability (discussed later). Copolymerizations were carried out i n emulsions following the procedure described. Disks were prepared from rhe polymer by compression molding as previously described and were then heated in an oven for one hour a t 180' C., color change was used as a rough measure of the thermal stability. The effect of the methyl isopropyl ketone to styrene ratio on the properties of the polymer is shown in Table IV. The 60 to 40 copolymer was selected for more intensive study. T o obtain good injection-molding, conditions producing a high molecular weight polymer without too much "rubbery" flow on extrusion were determined. The results of experiments in which modifier concentration was varied are shown in Table V. The 60 to 40 methvl isopropylene -. ketone-styrene emulsion copolymer was rolied for 5 minutes a t 100' C. and then extruded a t 150' C . into rods. The rods were chip-ground, and the pellets Jvere dried a t 50" for 16 hours. The injection molding was then carried out in a Van I k r n injection-molding machine, and physical data were obtained on the injection-molded bars. The Polymer \''as molded at a cylinder temperature of 240' to 250' c. with a 70- to 90-second CYcle. Before the various Physical Properties '''ere determined the specimells were conditioned a t 50% relative humidity and 23' to 30' c. for 24 hours. Test results are compared in Figure 2 with data obtained on polystyrene and poly(methy1 methacrylate), ~
PMIPK Poly(methy1 iropropenyl ketone) PMMA Polyhethyl methacrylate) PS Polystyrene
The polymers were then filtered, washed, dried, and stabilized with dibutyltin dilauryl mercaptide (1.5%). This was added to the dry powdered polymer in the form of an ether solution. The products were then screened for thermal stability. Best results were again obtained when the polymerization was carried out in a n aqueous dispersion in the presence of a monomer solvent which was not a polymer solvent (Table 111). A generalized emulsion polymerization procedure was developed for producing both homo- and copolymers of methyl isopropenyl ketone possessing thermal stability and the molecular weight necessary for injection molding. This procedure is as follows: Charge to Reactor Monomers Water Sodium bicarbonate Nacconal NPSFQ n-Dodecyl mercaptan 10% Aqueous Aerosol
Part.s by Weight 100 200
Potassium persulfate
0-3 for homopolymers 0.15 for copolymers
a Emulsifying Corp.).
(Allied
OT
agent
0.05 1.5
1.5 15.0
Table Ill.
c.
Bead Polymerization Also Produced Best Results When the Monomer Solvent Was Not a Polymer Solvent" MIPK/H20/ Solvent (Weight Ratio) 1/0/5 1/2.5/5 1/2.5/5 1/2.5/5 2/2/1 1/1/2
Temp., Appearance Yield, O C. of Productb % None 16 70 FD Cyclohexane 70 cs 89 Ligroin (70-90' C.) 62 cs 64 80 ED 90 Ligroin (9O-l2O0 C.) Cyclohexane 70 AM 43 Cyclohexanee 74 CFD 43 FD = fine dispersion: CS = coarse suspension: S M Reaction time, 6 hours. Reaction time, 6.5 hours. erated mass; C F D = coarse and fine dispersion. Solvent
In. Vis. 0.15 0.95 1.47 0.58 0.88 0.88 = agglom-
Chemical
These materials were charged to the stirred reactor in the conventional order (emulsifiers, water, initiator, buffer, modifier, and monomers, in that order), and the polymerization was carried out a t 80' C. for 5 hours under a slow purge of the prepurified nitrogen. T h e resulting emulsion was poured into a n equal volume of 3% sbdium chloride solution, heated to 85' C., and cooled
80
to 45' C. It was then filtered through an underdriven centrifuge and washed with water. The resulting cake of polymer contained approximately 50% water. Thermal stabilizers were incorporated by slurrying the wet cake with its own weight of a 1% Nusope 33 or sodium stearate solution, refiltering, and drying a t 60' C. for 16 hours. Both homoand copolymers produced by this process had inherent viscosities of 0.3 which was about the maximum which could be injection-molded satisfactorily. CoPoLYhiERIzATIox WITH STYRENE was
INDUSTRIAL AND ENGINEERING CHEMISTRY
Table IV.
Flow Properties and Thermal Stability Improved as Styrene Content of Copolymer Increased
MIPK/ Styrene Time, Conversion, Olson Flow Color of Disk after Hrs. % Temp., O C." In. Vis. 1 Hr. a t 180' C. Ratio Yellow 138.5 0.21 90/10 3.5 87 0.18 Lt.yellow 3.0 87 131.0 75/25 60/40 3.0 91 125.0 0.17 Trace of yellow 50/50 3.0 97 122.0 0.17 Trace of yellow a Temperature at which 1inch of flow occurs at 1500 p.s.i. in 2 minutes.
KETONE P O L Y M E R I Z A T I O N The methyl isopropylene ketonestyrene copolymer could also be plasticized wilh 5y0 Methox (dimethyl Cellosolve phthalate from Ohio Apex) which had little effect on physical properties but lowered the temperature necessary for injection molding to 227' C. Stability to weathering and the efficiency of various stabilizing agents were evaluated by dissolving pellets of the copoly. mer (prepared as described above) in acetone to give a 30% solution, adding various stabilizers to this solution, and casting films. The films were then seasoned for 10 hours a t 68' C. and exposed in an Atlas Weatherometer. The results are given in Table VI.
Discussion o f Results Bulk polymerization is technically feasible, and molecular weights are in the range for commercial molding. Azobisisobutyronitrie is an efficient initiator for the polymerization. Polymerization Techniques. Solution polymerization produced high yields of polymer (Table 11). Mineral oil, cyclohexane, and 2,2,4-trimethylpentane (iso-octane) gave the best results. For reasons stated previously, azobisisobutyronitrile was selected as the initiator. High molecular weights and good yields in reasonable times were obtained.
'
HEAT ROCKWELL DISTORTION, HARDNESS, AT WSCALE 264 RSJ.
WATER ABSORPTION,
x
TENSILE STRENGTH BREAK,
FLEXURAL COMPRESSIVE IZOD IMPACT STRENGTH STRENWH STRENGTH, LOAD, BREAK, F T L B PER
RS.1.
RSJ.
15,000 13,000
Yield,
0.50
9,000 7,000
5,000
0.20
3,000
0.10
1,000
Figure 2. The 60 to 40 copolymer of methyl isopropenyl ketone with styrene has properties roughly comparable to those of poly(methy1 methacrylate) 60/40 Methyl isopropenyl ketone-styrene copolymer PMM4 Poly(methy1 methacrylate) PS Polystyrene
The results demonstrate that this method has potential for the manufacture of poly(methy1 isopropenyl ketone). I n bead polymerization the main difficulties were obtaining a useful reaction rate and obtaining beads suitable for filtering. Usually fine dispersions or gummy coagulated dispersions resulted. Part of the difficulty possibly
.
% 95 91 98 83 89 84 94
Reaction Time, Hr. 3.75 3.50 2.50 2.00 2.25 2.00 2.75
:i
11,000
Table V. Only 0.2% of Modifier Was Needed to Reduce Molecular Weight of the Methyl lsopropenyl Ketone-Styrene Copolymer to a Level Suitable for Injection Molding N-Dodecyl Mercaptan, % on Monomer 1.00 0.75 0.25 0.11 0.12 0.07 None
In. Vis. 0.21 0.25 0.38 0.47 0.51 0.59 1.00
Flow at 180" C., 1500 P.S.I. Good Good Good
Rubbery Rubbery Rubbery Rubbery
Color of Disk after 1 Hr. at 180" C. Good Good Good Good
Poor Fair Poor
arises from the fact that the monomer has an appreciable solubility in water. The beneficial influence of a nonsolvent for the polymer on the rate of polymerization and molecular weight is shown in Table 111. Ligroin and cyclohexane were very effective. The emulsion polymerization technique was the simplest, most convenient process. Good yields were obtained with azobisisobutyronitrile or potassium persulfate as the initiators. The preferred emulsion process has been described for both the homo- and copolymer systems. Stability. I t was early suspected that small traces of acid residues, either chemically bound or occluded in the polymer, would catalyze the blackening and degradation which occurred in heating. Residues from azobisisobutyronitrile were likely to be neutral as the thermal fission is as follows :
CN-
r r3 N
=
N-
&I3 a Table VI.
INCH AOTCH
RS.1.
-CH2CN-+
(AH1
With Some Stabilizers Weathering Life of the Copolymer Approached That of Commercially Acceptable Plastics4 Stabilizer
None Uvinul 400"
Spectro No. 1 Uvinul 490b Interchemical Corp. 1693c
- 1%
- 1% - 5% - 5% - 1% - 5% - 1% - 5% - 1% - 5%
Hr. in Weatherometer 22 79 22 79 22 79 79 79 68 68 210 210
CH i
0.09 0.06
0.21 0.21 0.30 0.24 0.19 0.31 0.22 0.32 0.21 0.32
Inherent viscosity of copolymer, 0.33. 2,4-Dihydroxybenzophenone (General Aniline & Film Corp.). 2,2'-Dihydroxy-5,5'-dimethoxybenzophenone (General Aniline & Film Corp.).
+ NP
2CN-A-
Inherent Viscosity after Exposure
AH1
On the other hand, compounds such as benzoyl peroxide are likely to yield benzoic acid residues on decomposition as the benzoyl radical may react with water present during the reaction or a t some later stage in the processing. The correctness of this assumption was demonstrated by several factors. A large number of basic organic and inorganic improve-d polY(methYl iSOproPY1 ketone) produced by ultraviolet or gamma irradiation VOL. 51, NO. 1
JANUARY 1959
81
30
20 10 0
5
3 120
130
140
FLOW TEMP
150
(OC.1
Figure 3. Although flow properties improved as styrene content of the copolymer increased, there was no advantage in increasing styrene content beyond 4070
was more thermally stable than that produced by persulfate or peroxide initiators; and deliberate contamination with acids or acid salts invariablb- produced rapid blackening on heating. The mechanism of thermal degradation of poly(methv1 isopropyl ketone) has been described by Marvel and coworkers (7) : CHB
CHz
-cH--&---CH2-A
I
+.
L o
co
CHa
&H3
I
degradation of poly(methy1 vinyl ketone), but this scheme does not necessarily apply to poly(methy1 isopropenyl ketone). Copolymerization. Copolymerization with styrene was the most successful of many attempts to obtain better flohvproperties and improved thermal stability by copolymerizing with an alternating comonomer. The lower alkyl acrylates were also tried but were not as effective as styrene. Interspersing a comonomer in the chain prevents the formation of conjugated cyclic structures because the polymer can then no longer condense readily in a six-membered ring: CH3
I
-CH2-C-CH2-CHI
co
CH, I
This mechanism \vas confirmed by infrared absorption spectroscopy in these laboratories which showed the gradual disappearance of the carbonvl group on heating. The srability of the homopolymer to accelerated weathering tests was much below normal commercial standards in the absence of a n abqorber for ultraviolet light. Compression-molded disks become dark and brittle after only 22 hours of exposure. However, when the homopolymer was reduced in solution with lithium aluminum hydride. the resulting polymer was still tough and moldable and withstood over 200 hours in the weatherometer. I t is assumed that the keto group was reduced to a secondary alcohol group. This supports accepted views that the instability of polyketones to ultraviolet light results from the presence of pendant keto groups. Guillet and Norrish (4)have proposed a scheme for the photo-
82
0 I
Conjugation which occurs in the cvclic structures obtained on thermal degradation of the homopolymer is thought to be responsible for dark colors. Copolymerization with styrene was partially successful in prebenting this cyclization (Table IV). Similar disks of the homopolymer were less stable to heating. Thermal stabilizers for both the homopolymer and copolymer were extensively investigated. The best ones were Susope (sodium naphthenate) and Ivory flakes (sodium stearate). Some lithium fatty acid salts were also effective. The photostability of the copolymer was also investigated. Table V I shows that Uvinul 400, Uvinul 490, and Stabilizer 1693 (Interchemical Corp.) were effective. With these stabilizers the weathering life of the 60 to 40 copolymer approached that of some commercially acceptable plastics such as nylon and polyethylene.
INDUSTRIAL AND ENGINEERING CHEMISTRY
Physical properties of the homopolymer are compared with those of poly(methyl methacrylate) in Figure 1. These were compression moldings, and accordingly compression-molding grades of the reference polymers were employed. In general, poly(methy1 isopropenyl ketone) has mechanical properties similar to poly(methy1 methacrylate). Physical properties of injection-molded 60 to 40 copolymers are compared with polystyrene and poly(methy1 methacryl.. ate) in Figure 2; the 60 to 40 copolymer with styrene is roughly similar to poly(methyl methacrylate). Reference polymers in this instance were injection-molding grades and differ in some physical properties from their compression-molded counterparts. The three barriers to successful injection-molding of both homo- and copolymers were thermal instability, light instability, and flow properties in injectionmolding machinery. The first two, it is believed, have been reduced almost to the commercially acceptable level. Floiv properties are a function largely of molecular weight and freedom from branching. The first factor is more important than the second ( 2 ) . I n general, the more linear the molecule, the higher the maximum molecular weight which can be molded. Varying the modifier concentration, as shown in Table V, indicated that 0.27, of dodecyl mercaptan is sufficient to reduce the molecular weight to a level acceptable for injection molding. Figure 3 shows that flo~vproperties improve as the styrene content of the copolymer is increased until styrene content is 40%. The 50 to 50 curve indicates that no advantage would be obtained by increasing the styrene contenl to this figure. The C0 to 40 and 50 to 50 curves are similar to those of commercial injection. molding grades of poly(methy1 methacrylate) and poi>-styrene (not shown). References
(1) Corner, J. O., kIarvel, C. S.? Riddle, E. H., J . Am. Chem. SOG.64, 92 (1942). (2!‘ Dow Chemical Co., Midland, hfich., Structure and Composition us. Mechanical Behavior of High Polymers. 11. Industrial Application,” Plastics Tech. Service Bull. (3) Dreisbach, R. R., Martin, R. X., IND.ENG.CHEM.41, 2875-80 (1949). (4) Guillet, J. E., Norrish, R. G . \V., Nature 173, 625-9 (1942). (5) Haward, R. N., J . Polymer Sci. 3, 10 (1948). (6) Kohler, H., Merling, G., LT.S. Patents 981,668-9 (1 909). (7) Pilat, H., private communication, Oct. 22, 1953. RECEIVED for review October 11, 1957 ACCEPTEDAugust 21, 1358 Division of Industrial and Engineering Chemistry, 132nd Meeting, ACS, New York, September 1957.
