Properties of Monochlorostyrene as a Vinyl Monomer Richard J. Dolinski, Robert M. Nowak, and louis C. Rubens Physical Research Laboratory, The Dou: Chemical Co., Midland, Mich. 48640 The properties of monochlorostyrene (MCS) are compared with those of styrene and advantages of using MCS in certain applications are discussed. MCS homopolymerizes 1.34 to 13.0 times faster than styrene depending upon the method of initiation and the isomer used. The polymerization rate increases after partial conversion to polymer and the
magnitude of
this
"gel"
effect
i s a function of initiator concentration.
Copolymerization rate data show that polymer formation is faster for MCS than styrene in mixtures with several selected comonomers. MCS monomer-copolymer composition curves reveal nearly ideal copolymer compositions with certain important comonomers such as 1,3-butadiene. MCS can be substituted for styrene in fire-retardant polymer compositions. It burns in air, but can be made fire-retardant by addition of small amounts of SbeOs or copolymerization with about 3%
vinylidene chloride. Its use in fire-retardant high-impact thermoplastics a n d in unsaturated polyester resins i s discussed.
MCS exhibits interesting behavior in cellular plastics applications. Expandable polyMCS beads retain volatile organic blowing agents better than polystyrene. Foams of poly-MCS resist collapse for prolonged periods a t temperatures as high as 225°C. A new concept for using these foams in expandable core molding i s discussed.
STYRENE
and alkyl and halo-substituted styrenes have received extensive research and commercial attention throughout the years (Boundy and Boyer, 1952). Although styrene is a widely used monomer, suitable for many uses, physical and chemical properties in some applications can be significantly improved by substituting monochlorostyrene (MCS) for styrene. These applications of MCS exemplify the uniqueness of this vinyl monomer. Discussion
Properties. Some of the differences in the physical properties of styrene and MCS are illustrated in Table I. The more obvious advantages of MCS are its lower volatility and high chlorine content. Shrinkage during polymerization is less for MCS. For both monomers, shrinkage increases with reaction temperature because of the greater expansion coefficient of the monomer than the polymer. The heat of polymerization of MCS is less per gram than for styrene. The reactivity of MCS in copolymerization is somewhat similar to styrene, as indicated by the Q and e values, but the less negative e value results in less alternating tendency in copolymerization with monomers having positive e values, such as acrylonitrile, methacrylonitrile, and maleate and fumarate polyesters. Polymerization Rates. Polymerization rate studies reveal significant differences between MCS and styrene (Rubens, 1965). As indicated in Table 11, for example, the homopolymerization rates are 1.34 to 13.0 times faster for MCS than for styrene, depending upon the method of initiation and the MCS isomer used. Thermally, the ortho-isomer 292
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 3, 1970
Table I. Properties of Styrene and Monochlorostyrene (MCS) 65/35 Property
Molecular weight B.p., Ci760 mm Sp. gr. 2514" (mono.) Sp. gr. 2514" (poly.) 5; chlorine Q value e value Heat of polymerization, cal g - '
Styrene
ortho/para M C S
104.14 145 0.902 1.048
138.59 186 & 3 1.096 1.245 25.6 1.20 (av.) -0.35 (av.) 116
...
1.o -0.8 168
Table II. Initial Relative Polymerization Rates MCS Method
Thermal (80nC) AIBN-catalyzed (60-80" C) Cobalt 60 (31° C)
Styrene
Ortho
Para
1 1 1
10.7 2.8 13.0
4.0 1.34 8.0
Table Ill. Properties of Injection-Molded Polymers Property
Poly-MCS
Tensile strength, psi Elongation, CC Tensile mod., psi Notched Izod Rockwell (Mj Heat dist, O C 264 psi (unannealed) Dielectric constant lo3 cps Solubility parameter, 6
7,280 1.44 5.7 x lo5 0.5 93 102 2.5 9.3
PS
6,100 1.8 4.6 x 10 0.4 75 87 2.5 8.9
polymerizes 10.7 times faster than styrene, the para-isomer 4 times. Similarly, high energy gamma (y) radiation from a cobalt-60 source is a very effective initiator. There is a smaller difference in polymerization rates between styrene a n d M C S initiated with peroxides or azobisisobutyronitrile ( A I B N ) . T h e MCS homopolymerization rate increases with both catalyst and ortho-isomer concentration in orthoipara-MCS mixtures. The initial polymerization rate follows classical kinetics and varies linearly with the square root of the initiator concentration. The activation energy for polymerization is approximately 20 kcal.mole '. One interesting aspect of the rate curves is the increased polymerization rate observed a t about 40' r conversion. This midconversion acceleration or gel effect is obtained over a range of temperatures (60" to 90.C) and is more pronounced for MCS than for styrene but less than with methyl methacrylate (MMA). The copolymerization characteristics of MCS are similar to styrene, but offer certain advantages. The first of these, shown in Figure 1 with acrylic acid (AA), is an accelerated rate of copolymerization. Rate enhancements are obvious when a 67/33 orthoipara-MCS mixture is substituted for styrene. This effect is observed also for copolymerization with difunctional monomers such as ethylene glycol dimethacrylate (EGDM) and divinylbenzene (DVB). I n addition, the midconversion rate acceleration occurs a t progressively lower conversions with increasing difunctional monomer. While MCS is not greatly different from styrene in copolymerization reactivity, the difference leads to some interesting observations-for example, as illustrated in Figures 2 and 3, the two MCS isomers reveal a nearly ideal system across the entire monomer composition range with 1.3-butadiene and methacrylonitrile. The broken lines in these figures represent the ideal 50150 copolymer composition curves, while the solid lines are the actual data. Similar curves also were generated with other comonomers such as acrylic acid and styrene. With styrene, these comonomers yield curves that deviate somewhat from those obtained with MCS. Physical Properties of Polymonochlorostyrene (PMCS). Table I11 presents data on the physical properties of injection-molded polystyrene (PS) and polymonochlorostyrene (PMCS). The major differences are the higher heat distortion temperature of PMCS compared with PS-i.e., 102" us. 87°C-and the increased hardness of PMCS. The other physical properties given show further advantages of PMCS. Thermogravimetric analysis (TGA) showed PMCS to be a t least as stable as PS, despite its high chlorine content which normally contributes to thermal instability. Weight loss occurs approximately 30" to 40°C lower for PMCS than for PS. Fire-Retardant Applications. PMCS, which contains 2 5 . 6 ' ~chlorine substituted on the aromatic ring, will ignite in a flame and continue to burn after removal of the ignition source. However, PMCS becomes fire-retardant either by copolymerization with halogen-rich monomerse.g.. 3 ' r vinylidene chloride-or by the addition of fireretardant additives such as antimony oxide. MCS finds considerable usefulness in the preparation of fire-retardant copolymers. One such application is fireretardant high impact thermoplastics. Substitution of approximately 7 0 7 MCS for styrene in a high impact formulation containing 3 pph of Sb203 results in a fire-
100
80
..p
. 60
z
0 v)
a w
>
0
40
0
20
0
I60
80
240
TIME, MINUTES
Figure 1. Copolymerization rates of acrylic acid with styrene and MCS
0
20
40
60
100
80
M O N O M E R COMPOSITION IN 1,3 - B U T A D I E N E
%
Figure 2 . Monomer-copolymer composition curve for 1,3butadiene with MCS
IO0
8
M I* P-CH LOROSTYRENJ'
0 0
20
40
60
00
MONOMER C O M P O S I T I O N I N METHACRYLONITRILE
I00
%
Figure 3. Monomer-copolymer composition curve for methacrylonitrile with MCS
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 3, 1970
293
Table IV. Fire-Retardant High-Impact Thermoplastics Containing Monochlorostyrene (MCS)" Tensile, PSI
YO
O h
MCSIS
CI
Yield
Ult.
Tensile M o d . (10 ")
Oil00 50/50 75125
0 12.0 18.0
2,550 3,918 3,546
2,500 3.066 2,651
2.8 3.13 2.91
Elongation, % Yield
Ult.
Vicat H.D. Temp., ' C
lzod Notch
96 108 114
1.2 1.34 1.19
Burn Rate
Burns Burns Nonburningb SE Group I 114 1.04 Nonburninga 100 24.1 2,888 2,496 2.85 1.10 16.7 SE Group I "Each sample contained 6% rubber, 3 pph SblOj, and less than 1 5 of modifiers, antioxidants, etc. 'Terms defined in ASTM D 635-56T and U.L. Subject 94.
Table Chlorendic Anhydride Alkyd
V. Fire-Retardant lsophthalic Alkyd
Properties of Polyesters"
Styrene
MCS
Yo Chlorine
Burn' Rate
50 8 32 12 100 40 24 16 12 60 30 40 0 12 60 "All samples contained 5 pph Sb207. bHLT-15 burn test used. Rating greater than 50 acceptable for most applications. 10 20 30
~
~~
Table VI. Loss of Blowing Agent in Foamed Polymers 20 Hours, Yo Temp.,
25 60 80
O
C
300 Hours, Yo
Styrene
MCS
Styrene
MCS
18 38 48
1.3 12 24
40 72 80
10 33 54
retardant copolymer with good physical properties. Some typical examples are outlined in Table IV. All samples contained 6% of rubber, 3 pph of Sb203, and less than 1% of various modifiers, antioxidants, etc. When compared with the 100% styrene case in the first line of Table IV, the mechanical properties of the fire-retardant highimpact plastic also are good, especially the improved heatdistortion properties for the MCS-containing systems. The advantages of using MCS as a reactive diluent in glass-reinforced, unsaturated polyesters have been cited (Glesner et al., 1966; Rubens et al., 1965). I t is frequently desirable to use MCS as a chlorine source for fire-retardant applications, since faster cure rates and better mechanical properties can also be obtained by using this monomer as a substitute for styrene. I n addition, more of the alkyd of choice may be used as a substitute for a halogencontaining alkyd, thereby obtaining better physical properties while maintaining the same chlorine level, as shown in Table V. Good properties are obtained when MCS is combined with nonchlorinated polyester resins and a filler, such as hydrated alumina, is used as an aid in fire retardancy. Very high ratings (60 to 100) as measured by the HLT-15 test are obtained with this system. Values greater than 50 are acceptable for most applications. I n part because of the ideal copolymer compositions obtained in a butadiene/MCS system cited earlier, excellent properties can be obtained with MCSibutadiene latexes. Systems containing 50% MCS or more easily can be made fire-retardant. Foam Applications. Expandable particles, similar to expandable polystyrene (PS) beads, can be produced from MCS. Volatile five-carbon hydrocarbons and halocarbons as well as Nr-releasing thermosensitive blowing agents are effective for foaming PMCS. Foam densities as low 294
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 3, 1970
1.5 1.41 1.37
30 15.1 14.0
as 0.3 lb per ft3 are obtained by heating in air at 125" to 150°C. The primary blowing agent does not permeate out of the heat-plastified particle very rapidly, and as air permeates into the cells, expansion occurs greatly in excess of the PVT volume of the primary blowing agent. As expected, the temperatures required for expansion of PMCS foams are 20" to 30°C higher than for PS. Well fused bead moldings are produced by steam molding a t 40 to 50 psi (130" to 140°C). Foams of density greater than 1 lb per ft3 are dimensionally stable after demolding. Lower density foams-e.g., 0.25 to 0.5 lb per ft3-will shrink slightly but recover mold dimensions in 24 to 48 hours as air permeates into the cells. The mechanical properties of the foamed PMCS are similar to those of PS foam of comparable density and cell size. Figure 4 shows the relationship of compressive strength us. density for foams molded from expandable beads of PMCS. A similar strength-density curve is observed for foamed PS. The heat-distortion temperature of PMCS foam moldings is about 105" to 110°C and the K factor ranges from 0.22 to 0.28. An important property of PMCS foam is improved retention of entrapped blowing agent (Table VI). Using 40-mesh beads containing 6% isopentane (2-methylbutane) as the blowing agent, PMCS and PS beads were heated a t various temperatures for well over 300 hours. In every case, the loss of blowing agent from PMCS was less than in the comparable case with PS. Advantage was taken of this property to use beads of smaller diameter for production of foam cups with thinner walls and smoother surfaces than normally obtained with larger polystyrene beads.
-.-
60
u)
e.
50
I
& 40 W
K
$ 30
I
s o
0
2 4 6 0 DENSITY (Ibslft')
IO
Figure 4. Compressive strength vs. density for poly-MCS foam
allow the use of MCS in expandable castings, expandable sandwich structures, and foam core moldings. In addition, the significant improvements in physical and /or chemical characteristics inherent in MCS and PMCS lend themselves to several other unique applications for which styrene is not completely satisfactory. Acknowledgment
The authors gratefully acknowledge the technical assistance of D. H. Clarke, W .K. Glesner, W. N . DeLano, and T. 0. Ginter in obtaining the information presented. literature Cited
Boundv, R. H., Boyer, R . F., “Styrene.” Reinhold, Yew York, 1952.
Glesner, W. K., Nowak, R. M., Rexer, J. K., Mod. Plast. 43, 37 (1966). Rubens, L. C., Gordon Conference on Chemistry and Physics of Cellular Materials. New Hampton. N. H., 1969; J . Cell. Plast 6, No. 1, 1 (1970). Rubens, L. C., J . A p p l . Polym. Sci 9, 1473 (1965). Rubens, L. C., Thompson, C. F., Kowak, R. M., SPI 20th Reinforced Plastics Technical and Management Conference, Chicago, Ill., February 1965. RECEIVED for review December 16, 1969 ACCEPTED April 20, 1970 Symposium on Eew Halogenated Monomers, Division of Organic Coatings and Plastics Chemistry, 158th Meeting, ACS, Xew York, N.Y., September 1969.
Cycloaliphatic Epoxy Resins with Improved Strength and Impact Coupled with High Heat Distortion Temperature Anthony C. Soldatos and Allison S. Burhans Chemicals and Plastics Division, Research and Development Department, Union Carbide Corp., Bound Brook, N . J . 08805 The toughness of cycloaliphatic epoxy resins, measured by the impact strength and area under the stress-strain curve, can be significantly improved through modification with several elastomeric materials containing functional groups. The toughness of these systems is proportional to the concentration of the elastomer. Twofold to greater than tenfold improvements in impact have been obtained by the addition of 5 t o 35% carboxyl-terminated butadiene-acrylonitrile copolymer, without significantly degrading the heat-distortion temperature.
Simultaneous improvements were obtained in tensile
strength and elongation. These systems have produced glass cloth reinforced composites with high tensile strength, under both static and dynamic conditions.
THERMOSETTIN(: POLYMERS in general are brittle and susceptible to crack initiation and propagation. Because of this behavior, the usefulness of crosslinked epoxy resins in some of the more critical applications is sometimes limited. This deficiency is often corrected by improving the toughness of the resin through modification with plasticizers or flexible hardeners. As a rule, however, this improvement is accompanied by a severe degradation of some other mechanical properties-modulus, strength, and heat-distortion temperature. In the case of glassy thermoplastic polymers, such as polystyrene. the problem of brittleness has been effectively corrected by the inclusion of elastomeric particles suspended throughout the polymer matrix. More recently, McGarry et ai. (1967) have shown that the toughness of aromatic epoxy resins can be improved under certain limited conditions by incorporating a specific carboxyl-
296
Ind. Eng. Chem. Prod. Res. Develop., Vol. 9, No. 3, 1970
terminated elastomer in concentrations up to 10 pph resin. Our investigation extended this concept to the area of cycloaliphatic epoxies, which have a wide spectrum of outstanding properties. Our goals were to define the parameters affecting the toughness of these resins and develop resin compositions of improved toughness without degrading strength and heat-distortion temperature. This investigation has shown that the toughness of cycloaliphatic epoxy resins can be significantly improved through modification with several elastomeric materials containing carboxyl and mercaptan groups and varying in molecular configuration. The resin selected for this study was the 3,4-epoxycyclohexylmethyl 3,4-epoxycyclohexane carboxylate (ERL-4221).
