Dichlorostyrenes and Their Polymers J. C. M I C H A L E K AND C. C. CLARK The Mathieson Alkali Works (Inc.), Niagara Falls, Ν . Y. STYRENE, which was first synthesized by Berthelot in 1866, has done much to foster the rapid growth of those two prodigious youngsters of chemical indus try—synthetic rubber and plastics. Poly merized to polystyrene, it has made avail able a thermoplastic with good dimen sional stability and unique insulating properties. Copolymerized with buta diene, it has made possible the widely used GR-S (or Buna-S). Both polystyrene and GR-S have suf fered from a common difficulty. They are adversely affected by heat. The strength of GR-S is greatly decreased at the high temperatures developed by heavy-duty tires (1). Polystyrene wilts below the temperature of boiling water, and, as a result, its uses have been re stricted. Attempts have been made to modify polystyrene and GR-S by the addition of other compounds to the plastic or rub ber-compounding formula. These have been successful in raising the heat resist ance of such materials at the expense of other valuable characteristics, such as the insulating property of polystyrene. The solution of these problems has now been accomplished b y the modification of the styrene nucleus itself to dichlorostyrene. Polymerized to polydichloro styrene, the new compound gives a plastic which combines for the first time the in sulating properties of polystyrene with ex cellent heat resistance. Copolymerized with butadiene, it produces the rubber, recently announced, which is superior t o Buna S, not only in heat resistance, but in many other important properties. Several years ago the investigation of nuclear chlorinated styrènes began in this laboratory. It was soon found that the monomers could be polymerized readily, to form stable polychlorostyrenes, and copolymerized with various other unsaturated bodies to give rubberlike products.
alumina. The properties given in the preceding table have been observed for the dichlorostyrene isomers. In general, these isomers have a surprisingly pleasant odor, particularly the 3,4 isomer which has an odor resembling geraniums. The monomeric dichlorostyrenes are very active. Highly purified samples have been observed to polymerize virtually t o completion in 3 to 4 hours at 60 to 70° C. In spite of this rapid polymerization, i t is possible by working with cross sections of less than 0.5 inch to keep the temperature of the reaction below limits which would be injurious t o the polymer. Styrene normally requires 8 to 14 hours at 130° C., after which time there is usually 1 to 3 per cent of residual monomer. T h e great activity of dichlorostyrene enables the polymerization reaction to go t o such a degree of completion that extractable monomer residues run only about 0.1 per cent by weight. Impurities are found to affect the polymerization reaction, usually in a n adverse manner, such as catalytically breaking the chain reaction of polymerization. On the other hand, some substances are not chain breakers. For example, sulfur as SO2 introduced into the monomer in small amounts seems to aid in the growth of long chains, whereas sulfur as H2S has the opposite effect. Figure 1 shows the effect of temperature on the average molecular weights obtained by polymerizing the dichlorostyrene monomer alone and with small amounts of SO2 or H2S. Polymerization occurs in spite of the presence of 0.1 per cent p-tertiary-butyl catechol, although at a reduced rate. The polymers obtained from each of the isomers described above are all hard,
500
5 400 Dichlorostyrene Isomer 2,6 3,5 2,5 2,4 2.3 3.4
N3T 1.5724 1.5745 1.5788 1.5812 1.5780 1.5840
B.P. ° C. 59 at 2 mm. 53.5atlmm. 74 at 3 mm. 69 at 2 . 5 mm. 61 at 1 mm. 76 at 3 mm.
Density 25/4 1.280 1.237 1.245 1.246 1.264 1.243
.300
Çonfrof
100
The initial field of study was the isomers of dichlorostyrene. Nuclear substituted dichlorostyrenes were prepared from the corresponding dichlorobenzaldehydes by formation of carbinols through the Grignard reaction followed b y dehydration in the vapor phase over activated V O L U M E
2 2,
NO.
1 8
Ο
H2S
20 40 60 80 Polymerization Temperature m °C
IOC
Figure 1 . Effect of SO2 and H2S on molecular weight of dichlorostyrene polymer
SEPTEMBER
25,
1944
ransparent, colorless substances which resemble polystyrene in chemical resistance, solubility and general appearance 1 . With t h e exception of 3,4-dichlorostyrene, t h e polymers are all soluble in aromatic hydrocarbons, chlorinated solvents, some esters, and higher ketones. They are not soluble in aliphatic hydrocarbons, lower alcohols, ethers, and glycols. Some solvents, such as acetone and higher alcohols, swell but do not dissolve dichlorostyrene polymers. The solubility of the polymer of 3,4dichlorostyrene presents interesting possibilities. Although it is a linear polymer, it is insoluble in toluene. Only slight swelling occurs in this solvent at the boiling point. It does not dissolve in CCI4 or CGU-toluene mixtures, but is completely, though slowly, soluble in methyl ethyl ketone. I n addition to mass polymerization, dichlorostyrene can be polymerized in true emulsion which gives a latexlike product before coagulation, and very finely powdered resin after coagulation. For other purposes, the monomer m a y be dispersed in water using gelatin, talc, bentonite, polyvinyl alcohol, or other conventional stabilizers, and polymerized as beads or pearls. Under proper conditions perfectly clear spheroids are obtained as a product.
Mathieson Plastic—A Dichlorostyrene Polymer There are many applications for a plastic material which will maintain its shape and hardness at t h e boiling point of water and above. Mathieson plastic has a distortion temperature of 240° t o 265° F.„ which is higher than that for any plastic which combines excellent electrical characteristics with good strength, machinability, and moldability. High purity and careful control of polymerization c o n ditions are necessary t o prevent impairing the high-temperature properties of t h e product. Mathieson plastic is self-extinguishing according to A S T M D-635-41 T. When held in a flame, i t undergoes pyrolysis and the products of pyrolysis burn. When the flame is removed the pyrolysis stops and there is no further burning. T h e combustion products include CO2, H 2 0 , soot, and HC1, on account of the aromatic structure and chlorine content. 1 T h e trichlorostyrenes, properly prepared by the dehydrohalogenation of chloroethyltrichlorobenzenes, are also surprisingly active monomers having boiling points of 82° to 84° C. a t 2 mm. and n = 1.5943. T h e y polymerize very readily to reams having A S T M distortion temperature of 120° C. a n d higher, and copolymerize to r u b b e r like products.
1559
Other and more detailed properties of Mathieson plastic are shown in Table I.
Table 1. Properties of Mathieson Plastic" MATHIESON PLASTIC
CHARACTERISTIC
Molding qualities Compression molding t e m p . , ° F . Compression molding pressure, l b . / s q . in. Injection molding temp., ° F . Injection molding pressure, l b . / s q . in. 8pecific g r a v i t y I t e f r a c t i v e i n d e x , A'u F l a m m a b i l i t v . i n . / ruin. ( A S T M - D - 6 3 5 - 4 1 T ) Tensile strength, l b . / s q . in. M o d u l u s of e l a s t i c i t y , l b . / s q . i n . X 10 5 Flexural strength, lb. s q . i n . I m p a c t s t r e n g t h , ft. l b s . / i n c h of n o t c h (ASTM-D256-41T) Hardness, Rockwell Distortion under heat, ° F. Dielectric etrength, v o l t s / m i l Dielectric constant Power factor (per cent) W a t e r a b s o r p t i o n , 24 h o u r s ( p e r cent» E f f e c t of w e a k a c i d s Effect of s t r o n g a c i d s E f f e c t of w e a k a l k a l i e s E f f e c t of s t r o n g a l k a l i e s Effeot of o r g a n i c s o l v e n t s
Effact o n m e t a l i n s e r t e Clarity Color possibilities
CELLULOSE
ACETOBTJTYRATE0
Good 350 to 425 2000 to 5000 475 to 525 10.000 to 30,000 1.39 to 1.40 1.62 to 1 . 6 4 Self-Exting. 4600 to 7460 5 . 0 to 7 . 0 14,000 to 19,000
POLTSTTRENE 0 Excellent 275 t o 3 7 5 1,000 t o 10,000 3 2 5 t o 500> 10,000 to 30,000 1 . 0 5 4 t o 1 .070 1.59 0 . 7 5 t o 1 . 50 3,000 to 8,500 1.7 t o 4 . 7 4 , 8 0 0 t o 1Θ.Ο00
1.0 to 1.6 >M100 240 to 265 370 2 . 55 t o 2 6 6
