PROGRESS IN POLYMER ENGlNEERl" NORBERT PLATZER olecular engineering in polymerization and poly-
M condensation processes is the art of building polymers at will. Understanding of the relationship between molecular structure and performance characteristics enables us to design better macromolecules with improved properties and at reduced cost. Our goal is to make plastics as strong as steel, clear as glass, light as a feather, heat resistant, as thermally stable as quartz, and as inexpensive as paper. In a few instances, we have approached some of our targets, but we never have been able to combine them in a single polymer.
Increased understanding of the relation between molecular s t r uc t ur e a n d in-use c h ara c t e r is-
tics is gradually enabling u s to design polymers having the
Historical Background
Compared with the metal and building industries, the polymer industry is very young. I t was begun a hundred years ago with conversion of a natural material into the first semisynthetic thermoplastic. U p to that time, shellac, gutta percha, India rubber, and horn were the natural plastics. I n 1868, the brothers J. and H. Hyatt found how to modify cotton into celluloid with nitric acid and camphor. The gay nineties and the teens were the great days of billiard balls, washable collars, movie films, spectacle frames, and dentures made of celluloid, which reached an annual production of 40,000 tons. The second semisynthetic thermoplastic was casein or galalith from skim milk, less flammable and easy to fabricate into colorful buttons, handles, knobs, buckles, and beads. At the turn of the century, Bakeland formed the first thermoset by condensing phenol with formaldehyde ( I ) , During LYorld IYar I, production of polyidirnethylbutadiene), the first synthetic rubber, from acetone, was started at Leverkusen. I t was during the twenties that commercial production of cellulose acetate and of the first fully synthetic thermoplastics from vinyl chloride, vinl-1 acetate, and styrene was begun. At that time, Staudinger (2) established the 10
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desired performance properties
existence of macromolecules and proposed linear long chains for polystyrene, polyoxymethylene, and rubber, and Carothers ( 3 ) carried out his investigations which resulted in the foundation of our polymer science. I n the thirties, the first production of acrylics, aminoplasts, polyamides, and polyethylene followed. I n the forties, polyesters, epoxies, fluorocarbons, and ABS appeared. I n the fifties, polyacetals, linear polyolefins, polyurethanes, and polycarbonate were introduced. Finally, in the sixties, the phenoxies, PPO, polyphenylenes, polysulfones, and polyimides were added. Stronger and better polymers have appeared on the horizon to compete with the existing ones, while the originals, like cellulose nitrate, are fading away. Growth of the Polymer Industry T h e polymer industry is not only the youngest, but also the fastest growing section of the chemical industry. Ten years ago there were 85 polymer producers in the U.S. T h a t number has increased to 150. The polymer
industry grew from 4.5 billion pounds (2 million tons) production in 1957 to 14.5 billion pounds (6.6 million outstripping metric tons) in 1967, as shown in Table I (4), production of all nonferrous metals on a volume basis. Nearly two thirds of U.S. plastics production was accounted for by three materials-polyethylene, vinyls, and styrenes. Over 2 billion pounds (1 million metric tons) of each was produced, for a gain of 7 to 7.5y0 over 1966. Polypropylene showed the greatest gain on a percentage basis with 12.1%. Figure 1 illustrates the growth of world production from 1950 to 1967. T h e first graph is subdivided into the seven major polymer-producing countries. T h e second graph shows the growth of the three commodity products-polyethylene, vinyls, and styrenes-during that period ( 4 ) . Because it grew at such a terrific rate from its infancy to its adolescence, that the polymer industry paused in several branches last year startled us. One of the reasons for this slower pace is that commodity products do not
~~
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TABLE 1.
expect that polymer industry production will grow and exceed that of all metals industries within the next 10 years. Then we shall enter the “syntomer age,” as Houwink called it, “when synthetic polymers will become the favorite materials for all applications.”
US. POLYMER PRODUCTION Million Pounds
Year
Polyethylene Vinyls Styrenes Phenolics Urea and rnelamines Alkyds Polypropylene Polyesters Cellulosics Epoxies Others TOTAL
1967
1966
3,825 2,865 2,550 1,100 74 0 680 620 495 195 145 1,255
3,558 2,670 2,384 1,046 718 666 553 470 186 139 1,196
14,470
13,586
Making Plastics as Strong as Steel All polymer chains, regardless of their detailed structure, have approximately the same strength, because they are formed by C-C, C-N, C--0, or C-S covalent bonds, which are in the order of 80 to 100 kcal. However, the strength and rigidity of a plastic depend primarily on interaction between the polymeric chains. Polymer effectiveness can be increased by lengthening the chains or by arranging the chains in a crystalline lattice of helix or chain-folded structure. There are five types of chain interactions, as illustrated in Table 11. Nonpolar bonding. Polyhydrocarbons cohere by van der Waals forces only and require a longer chain length than do chains with strong intermolecular attraction such as the polyamides and polyesters. T h e chain length is generally expressed as degree of polymerization (DP)--i.e., the number of monomeric units in a single chain. T o reach satisfactory mechanical strength, polyhydrocarbons need a D P above 500, whereas polyamides and polyesters reach their strength ceiling at a D P of 150 to 200. Removal of short chains. T h e mechanical strength of thermoplastics is negatively sensitive to the presence
find new applications so easily today. New polymers have to replace existing materials, such as metals, wood, stone, paper, wool, or cotton, and fabricators and consumers look more critically a t these substitutes and judge them less on their good performance characteristics than on their deficiencies. For the use of plastics as building materials and in industrial, automotive, aeronautical, electronic, and furniture applications, we have also raised the specifications for acceptance. Despite these facts, we 40 18
40
35
35 15
30
30
25
25
s z 2 %
= z
10
4
20 g
20
z
s c 3 ” 15 2
15
IO
=
5
IO 5
5
0 1950
1955
I960
YEAR
-
1965
0 1950
INDUSTRIAL
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YEAR
Figure 1. Worldproduction of polymers 12
0 1955
CHEMISTRY
-
1965
TABLE II. SECONDARY BOND FORCES
\ 1. Van der Waals Forces
/CH2\
\ 1
CH2
CH2 /cH2\
/CH2\
CH2
/
/CH2\
/CH2\
CH2
CH2
CH2
CH2
PH2\/ CH2
6+ 6-
2. Dipole Interaction
:
:
I
6-
6'
NaC-C-
3. Hydrogen Bonding
I
-C-O..**
I
1
I
H-O-C-
I
H 0
4. Crosslinking b y Ionic Bonding
5. Crosslinking b y Covalent Bonding
0
II
II
-C-O-Zn-O-C0
0
0
I
l
l
I
l
l
-C-C-C-
of low D P constituents. I t is, therefore, necessary to remove these low molecular weight species if they exist, as they actually do in materials like polystyrene, polyethylene, or cellulose. Crystallization. Crystallization is a physical effect, reversible and strongly influenced by mechanical processes such as orientation and relaxation. For example, the modulus of elasticity of a perfect Nylon-66 crystal has been calculated to be 20 million psi (1.4 million kp/cm2). Commercial Nylon-66, however, is only semicrystalline and has an actual modulus of only 400,000 psi (28,000 kp/cm2). According to density measurements, it consists only of about 50% crystalline regions with regularly folded chains. The irregularly folded chains yield under pressure and cause excessive elongation. I n crystalline materials, the effect of low molecular weight species becomes even more detrimental. Even small weight percentages of low D P species introduce proportionately large number of chain ends which cause widespread lattice distortions, thereby gravely reducing mechanical strength. The behavior of natural rubber also illustrates the influence of crystallization. I n the unstretched form, it is soft, has a modulus of elasticity of only 20 psi, has a low melting point, and is easily soluble. At maximum stretch of 600 to 70070 elongation, elastomer crystals are formed which act as natural reinforcing fillers, the modulus rises to 20,000 psi, and solubility decreases. Polar bonding. If the polymer contains polar groups in the backbone chain, such as -C-0-C-, or as
I I
-c-O-c-
I 1
I
l
l
-cCN-c-
I
I
side chains, such as -CN, -C1, or -NOz, the dipoledipole interaction becomes the dominant influence and the polymer is more rigid. If the polymer contains -CO-NHin the backbone, or -OH and -NHz as side chains, the hydrogen bonding is the decisive factor for the interaction between the macromolecules, as in the case of polyamides, polyurethanes, polyvinyl alcohol, and copolymers of butadiene with acryl amides. Because of their polar and hydrogen bonding characteristics, these polymers exhibit compatibility with small molecules, such as solvents, plasticizers, or water. Covalent and ionic crosslinking. For many years, crosslinking by covalent bonding was the only way to form strong thermosets. Partial crosslinking of polystyrene with p-divinyl benzene or of polyvinyl chloride with dilauryl maleate, di-2-ethyl hexyl maleate, diallyl and triallyl esters, and especially triallyl cyanurate reduces the thermo-processibility and is generally used for surface coating. Under high mechanical stress, the covalent bond breaks and the initial strength is reduced. I n contrast to covalent bonding, ionic (heteropolar) bonding is reversible. It is about 100 kcal and of the same magnitude. Eleven years ago, Cooper (5) copolymerized butadiene with acrylic acid (4 to 20%) and prepared the Zn and Cd salts of the copolymers. These metal salts showed high elasticity after short-time stress. The ionically crosslinked chains were able to glide along each other and to dissociate and associate interchangeably. Du Pont's Ionomers are alkali salts of copolymers of ethylene with acrylic or methacrylic acid (10%). The VOL.
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TABLE Ill.
CROSSLINKING BY IONIC BONDING
-c-c-c-c-c-
-c-c-c-c-cI
I
fiao 0
H
0 I
I
-c-c-c-c-c-
-c-c-c-c-c-
1OOyo ionized
50% ionized
copolymer is made by high-pressure copolymerization with peroxide initiators (6) (Table 111). The monovalent alkali acts only through a n association of polar ion pairs and not, as the bivalent Zn or Cd, through an ionic bonding. This association is considerably less, but allows injection molding and extrusion of Du Pont’s Surlyn A. T h e activation energy of the partially neutralized copolymer is 17 to 20 kcal/mol and that of the copolymer itself is 14 kcal/mol. This comes close to a comparable polyethylene with an activation energy of 7 to 10 kcal/mol. Block copolymerization. One deficiency of polypropylene is its poor impact strength at low temperatures. I n the past, this was overcome either by blending polypropylene with a n elastomer such as polyisobutylene, or by random copolymerization with ethylene. Both procedures resulted in reduced rigidity, hardness, and tensile properties, because crystallization is hindered. I n block copolymerization, the ethylene comonomer is concentrated in segments and allows the formation of a crystalline copolymer. These block copolymers combine the rigidity and higher strength of the crystalline homopolymer with the toughness of the rubber-modified polyblends. Eastman Kodak ( 7 ) , which created the term “Polyallomers,” and Enjay (8) are two of propyleneethylene block copolymer producers. Block copolymers of olefins are generally made by anionic polymerization: the live chains of one homopolymer are reacted with the comonomer. Until recently, block copolymers could be made with nonpolar comonomers only. Jezl (9) and coworkers at Avisun used organic peroxides to convert the living chains into free radicals which now can be block-copolymerized with polar comonomers, such as acrylonitrile or acrylic esters. Polyalloys by blending or grafting. T h e stress needed to break a covalent C-C bond is about 2 million psi (140,000 kp/cm2). However, the tensile strength of commercial thermoplastics is only in the order of 3000 to 17,000 psi (200 to 1200 kp/cm2) and can be raised by a 14
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factor of less than 10 through careful orientation of highly crystalline polymers. T h e discrepancy of a factor of 10 to 100 between the actual and theoretical value arises mainly from flaws and surface cracks in the glassy amorphous regions. As in inorganic glasses, these imperfections can be dimished by annealing or tempering. The possibility of fracture can also be reduced by dispersing an elastomeric phase uniformly through the material. Polyblends or graft copolymers of styrene, SAN, vinyl chloride, and methyl methacrylate upon elastomers, such as polybutadiene, polyisoprene, nitrile rubber, chlorinated PE, EVA, E/PP, butyl acrylate, or butyl hexyl acrylate, are typical examples. T h e amount and effectiveness of the elastomeric phase influences the toughness of the finished product. Most of these elastomers have glass transition temperatures below - 40 OC, with a few being as low as -70 OC, and enhance the cold resistance of the rigid thermoplastics. But they deteriorate rapidly if exposed to temperatures above 150 “C, particularly in the presence of light, air, moisture, or organic solvents. Most developments in this field are in the synthesis and use of more stable elastomers--e.g., the acrylate rubbers, copolymers of propylene oxide with acrylonitrile, or chains of 0 - S : O , C-OC, C-S-C, N-0--N, and -U-C--N, with completely fluorinated substituents such as F or CF3. Composites. For many years, it has been customary to reinforce elastomers and thermosets. Elastomers are blended with finely divided solid fillers, such as carbon black, silica, or alumina. Unsaturated polyesters, epoxies, diallyl phthalate, phenol-formaldehyde, or melamineformaldehyde are crosslinked in glass fiber mats or other fabrics by laminating or molding operations. More recently, thermoplastics have been reinforced with minerals or short glass fibers, so the mix can still be injectionmolded without crosslinking. I n these novel RTP’s (reinforced thermoplastics), the coupling agent between the glass fiber or mineral and the thermoplast is of great importance. I t is frequently a silane and provides the necessary binding force of the same magnitude, as we have seen before between polymer chains. Table I V illustrates that tensile strength of thermoplastics can be increased to approach that of die cast metals through the addition of 20 to 40% cut glass fiber as reinforcement. The tensile strength of polyesters, epoxies, and phenolics reinforced with glass cloth is even greater, while that of the novel RT composites reaches 100,000 to 200,000 psi and approaches the strength of the best steel. The reinforcing material has a n even greater effect on the rigidity of the composite. Table V indicates that the modulus of elasticity of glass fiber-reinforced thermoplastics is on the order of 800,000 to 1,000,000 psi and that of the reinforced polyesters is 1 to 3 million psi. A high modulus of elasticity is required in aircraft construc-
TABLE IV.
STRENGTH OF GLASS FIBER-REINFORCED PLASTICS Tensile Strength, lo00 psi Reinforced
Material
Unreinforced
Short Fiber
Glass Mat
Glass Cloth
RTP (reinforced thermoplastics) Polyethylene, linear
1-3.5
7-1 1
Polypropylene Polyoxymethylene
4.3-5.5 10
8-9 10.5-12.5
Polystyrene
6-8 9.5-1 1
11.5-15 14-19
5-7 8-9.5 9-12
18.5-20
SAN
ABS Polycarbonate Nylon-66 Polysulfone
10
15-19 20-30 18-19
Die cast metals Zinc Aluminum Magnesium
41 33-47 34
RP (reinforced plastics) Polyester
2-13
4-10
2 0-2 5
30-70
EPOXY
5-15
10-20
14-30
20-60
Phenolic
7-8
5-2 0
5- 18
40-60
Novel composite Glass fiber
100-200 250-400
tion to prevent fluttering (IO). T h e novel composites developed by the U.S. Air Force have surpassed the stiffness of metals. By special selection of the reinforcing agent-e.g., graphite or sapphire whiskers-the modulus can be raised beyond that of any engineering material.
...a s Clear a s Glass Amorphous thermoplastics, like polymethyl methacrylate, polystyrene, SAN, PVC, or the cellulose esters, are transparent and used for glazing, photographic film, blown bottles, or clear packaging containers. Only a few crystalline thermoplastics, like polycarbonate or poly(4methyl- 1-pentene), where the crystalline and the amorphous zones have almost identical density and refractive index, are also transparent. Almost no crystalline polymers, like the linear polyolefins, polyacetals, or polyamides, are transparent. T o make glass-clear polymers, we have to prevent crystallization. This can be accomplished by placing bulky side groups onto the main chains. Changing from crystalline to amorphous configuration results in a reduction of rigidity and lower heat distortion temperature. T o maintain high temperature performance, the backbone has to be stiffened by putting aromatic rings into the main
TABLE V.
RIGIDITY OF STRUCTURAL MATERIALS Modulus of Elasticity, 106 psi
Rigid thermoplastics
RTP (reinforced thermoplastics) RP (polyesters, epoxies, phenolics)
0.1-0.6 0.8- 1.0 0.8-5.5
Magnesium
6.5
Aluminum Novel composites with medium modulus reinforcement
10 17-25
Stainless steel Novel composites with high modulus reinforcement
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TABLE VI.
TRANSPARENT AMORPHOUS POLYAMIDES AND POLYPHENYLENES POLYAMIDES
2,4,4-Trimethyl hexamethylene diamine
+
CH3
Terephthalic acid W. R. Grace & Co. U.S. patent 3,150,l17 Dynamit Nobel, A. G.-Trogamid,
amorphous-glass-clear
T.
HDT: 130 "C a t 264 psi; 140 "C at 6 6 psi
Hexamethylene diamine
+
adipic acid
n
0 NH- C H2-CH2-CH2-CH2-CH2-CH2-NH-C-CH
/I
2-C H2-CH2-C H2- C
Crystalline- translucent
Nylon-66
HDT: 6 6 "C a t 264 psi; 183 "C at 6 6 psi
I
POLYPHENYLENES
-
bis-Cyclopentadieneones
+
Diels-Alder
Diacetylenes
+ n
L
i
amorphous- transparent
crystal line -tra nslucenT
chains. Two typical examples are Trogamid T, a glassclear amorphous aromatic polyamide with three methyl side chains made by polycondensation of a trimethyl hexamethylene diamine with terephthalic acid ( I I ) , and a phenylated polyphenylene (12) (Table VI). ,
. .as Light as a Feather
I t has been estimated that replacing metal by high performance composites may reduce aircraft weight by about 20yo (10 to 4070). Through the use of reinforced plastics, a reduction from about 300,000 pounds to 240,000 pounds has been obtained in the new Lockheed C-5A (10). I n many instances, lighter weight, thermal insulation, and cushioning effects are preferred over strength. During the past 15 years, a number of lightweight thermo16
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plastic and thermoset foams with closed and open cellular structure have been developed, using foaming or blowing agents as pneumatogens. Commercial rigid plastic foams and some of their properties are listed in Table VII. Their strength can be significantly increased by sandwich construction or honeycomb patterns. Flammable foam can be made self-extinguishing by incorporating fire retardants or by the addition of lightweight mineral fillers. A new foamable resin is a copolymer of butene-1 with sulfur dioxide, in which excess SO2 acts as a blowing agent (13). ,
. .as Heat Resistant as Quartz
Increasing use temperature through crystallinity. One of the greatest disadvantages of plastics in comparison to natural building materials and ceramics is their
TABLE VII.
RIGID PLASTIC FOAMS
Density, Ib/eu ft2a
Foams
Compressive Strength, psi
Maximum Service Temp, OC
Thermal Conductivity, BTU in./sq ft hr OF
Thermosets
Polyurethane
1.5
20
0.16
120- 125
EPOXY Phenolic Urea formaldehyde
2
17
2
25
0.16 0.25
70 130
2
e . .
...
120
Thermoplastics
Polystyrene
SAN ABS PVC HDPE Cellulose acetate
1 0.8 15 3 35 6-8
5-16
0.26
75-80
6
0.29 0.35
78-88
80
65- 105
125
0.20 0.92 0.3 1
14
200
0.3
350-360
6.3
0.28
350-360
800
70 175
Silicone (R-7002) (XR-713 1) a
3.5
1 Ib/cu ft = 0.01602 g/cc. 1 BTU in./sq ff hr
OF
= 0 . 724 kcal/mol hr "C.
limited-use temperature. The standard test of measuring heat deflection temperature gives an indication of the plastic's softening range. Table VI11 indicates that branched low density polyethylene has a heat deflection temperature of 38" to 50 "C. In linear, high-density polyethylene, the chains are closer packed as crystalline spherulites and the heat deflection temperature is raised by 22" to 38 OC. T h e other example in Table VI11 is polyvinylidene chloride and polyvinylidene fluoride. The first is only 20 to 40y0 crystalline because of its larger chlorine groups. The latter is highly crystalline with a 54 'C higher heat deflection temperature. There is also a difference between linear polymers of different steric configuration. Completely isotactic or syndiotactic polymers are generally much higher melting and more crystalline, and have better mechanical properties than atactic polymers, which are very often amorphous. Increasing use temperature by intermolecular attraction. The two simplest chain molecules are linear polyethylene and polyoxymethylene. Because polyethylene is nonpolar, intermolecular attraction between chains is due to van der Waals forces only. In polyoxymethylene, the C O group is polar and its intermolecular attraction strong. This leads to a higher heat deflection temperature of 170 "C (Table IX). I n polyamides, the -CO-NHgroup in the main chain raises the heat deflection temperature-e.g., of Nylon 66-to 185 "C.
Increasing use temperature through side chain stiffening. Crystalline materials can also be characterized by their melting points, as shown in Table X. T h e top section shows the effect of intermolecular attraction; the second section illustrates that the melting point of crystalline polymers can be raised by placing side groups upon the polyhydrocarbon chains. For instance, polypropylene melts higher than linear polyethylene. Bulky side groups, such as chlorine in PVC, aromatic ring in polystyrene, or AN in polyacrylonitrile, reduce the ability to crystallize and are generally obtained branched in the lower softening amorphous form. O n the other hand, polar groups such as -C1 or -CN raise the softening temperature through intermolecular attraction. The third section of Table X shows that lengthening of the linear flexible hydrocarbon side group depresses the melting point from polypropylene to poly(hexene-1). When the melting point of the crystalline polymer is below the use temperature, elongated samples have a tendency to contract and, as a consequence, the material will be an elastomer. Polybutene- 1 crystallizes in two modifications, a fastcrystallizing unstable form, and a stable higher melting form. This phenomenon can be utilized to thermoform polybutene-1 while it is in its unstable, more easily processed stage. T h e fourth section of Table X illustrates that branching of polybutene-1 in beta position raises the melting point because it restrains the rotational freeVOL.
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TABLE VIII.
INCREASING USE TEMPERATURE THROUGH CRYSTALLINITY Amorphous vs. Crystalline Polymers H e d Deflection Temp, ASTM-D648, O C at 66 psi
High density polyethylene (crystalline)
38-50 60-88
Poly(viny1idene chloride) ( 2 c 4 0 % crystalline) Poly ( v iny I idene floor id e) (hig hI y cry r ta IIine)
95 149
Low density polyethylene (amorphous) . I _
l l _ _ l l _ l _ l _ _ _ _ _ _ _
Steric Configuration Higher melting
isotuctic
synd iotactic
Lower melting
a tactic
18
INDUSTRIAL
AND
ENGINEERING
CHEMISTRY
~
dom. However, branching in gamma position has less effect, as the branch is farther away from the main chain. These few examples demonstrate that we can build polymers with increased use temperature and melting point by selecting and placing the side chains. Increasing use temperature by main chain stiffening. By building a n inflexible ring into the backbone, softening temperature can be raised significantly. Typical ring systems which have pronounced chain stiffening effects are shown in Table XI. They may be aromatic rings or heterocyclic rings, or a combination of both.
TABLE IX. INCREASING USE TEMPERATURE BY INTERMOLECULAR ATTRACTION Heal Deflection Temp, 5STM D648, C at 66 psi
Crystalline
+CH 2-CH
2
+
$-CHz-O -k R-CO-NH-R’
+
High density polyethylene 60-88 Polyoxymethylene 170 -f;i Nylon-66 185
TABLE X.
I
MELTING POINTS OF CRYSTALLINE POLYMERS Melting Point, OC
Polymer
High density polyethylene
138 175 255-265
Polyoxymethylene Polyhexamethylene adipamide (Nylon-66)
A A A A
A
= CH3
Polyvinyl chloride = CGHS Polystyrene
212
= CN
317
I
R
f.CH-CH2 -IT CHR
I
230
Polyacrylonitrile
R = CzH5 Poly(butene-1) R = C3H7 Poly(pentene-1) R = C4H9 Poly(hexene-1)
198-212 ( 1 16), 124-142 130 - 55
R R R R
( 1 16), 124-142 300 360 160
R = CHa +CH-CH2-k
198-212
Polypropylene
= CI
Polypropylene
R’ = H = CH3 R’ = H = C6H5 R’ = H R’ = CsH5 = H
= H
TABLE XI.
Poly(butene-1) Poly(3-methyl butene- 1) Poly(3-phenyl butene-1) Poly(4-phenyl butene- 1)
INFLEXIBLE RINGS FOR CHAIN STIFFENING
Polydiazine
Polyphenylene
r
Polytriazine
Polytriazole
I
Polythiozole
Polydiimide
Polyoxodiazole
Polyimide
Polyimidazopyrrolone
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TABLE XII.
-
n C-C II
f 2 n Na
POLYPHENYLENES
k
p-dichloro benzene metal. Goldfinger, G., J. Poly. Sci., 4, 93 (1949) polyrneriz. (Ziegler cat.)
dehydrat.
'
\
chloranil)
cyclohexadiene Marvel, C. S. & Hartzell, G. A., JACS 8 1, 448 (1959)
f POLYPHENYLENE
I
Marvel, C. S., et al., J. Poly. Sci. A- 1, 2057 (1963)
(d) n
c_'>
AIC13+H20s HCAIC13(0H)-
-I- 2n CuC12
Lewis Acid
Kovacic, P. et al., JACS, 83, 1697 (196 1); J. Org. Ch. 28, 968 (1963).
JM:
CH3 n
c u 20O0C Ullrnan reaction
Kern, W. & Gehm, R., Angew. Chem. 62, 337 (1950)
Bis-cyclopentadienone
+
Diacetylene
-
' POLYTOLYLENE
~ i ~ l ~ - ~ l d ~ ~
-n
Stille, J. K. et al., ACS Meet. Apr. 1968
AROMATIC RINGS IN BACKBONE. Linear p-polyphenylene is a crystalline, brittle, insoluble, and infusible polymer. Its chain is essentially inflexible. I t has been known for many years and was prepared by various methods (1417),as indicated in Table XII. Introduction of CH3group at the ring yields polytolylene (18), which is noticeably less crystalline and has a lower softening range and higher solubility. Phenylated polyphenylenes have been made recently (12) in Diels-Alder reactions which are amorphous, transparent, and stable to 550 "C. Chain flexibility may be introduced by insertion of flexible hinges such as alkyl, -0-, -CO-, -NH-, -Nz-, -S-, or SO2 groups between the rings. Table 20
INDUSTRIAL
AND
ENGINEERING
CHEMISTRY
XI11 shows two commercial products with alkyl and oxygen insertions. The first one, poly-p-xylylene (19), has a melting point of 400 "C and is made by a novel vapor deposition process. p-Xylene is pyrolyzed at 950 "C in the presence of steam, yielding di-p-xylylene. The crude di-p-xylylene is purified to a stable crystalline dimer. I t is heated in a sublimation chamber and pyrolyzed in the vapor phase at 600 "C and reduced pressure to an equilibrium between the divalent radical and a quinonoid structure. Absorption of the monomer on substrates below 30 "C results in immediate and complete polymerization to a linear polymer of a molecular weight of 500,000. Poly-pxylylene has good mechanical
properties, but is insoluble and cannot be thermoprocessed. By substituting one or two hydrogen atoms on the ring by chlorine, bromine, alkyl, acetyl, cyano, or ester, other di-p-xylylenes can be obtained and pyrolyzed under identical conditions. I t was found, however, that each of the monomers has a threshold condensation temperature, Tc. Only a t temperatures lower than this can deposition-polymerization take place at a n appreciable rate. T h e substituted products are less crystalline, have lower melting points, and are soluble in hot chloronaphthalene. The substituted monomers may also be copolymerized by blending them, then depositing them at temperatures below their T c . T h e process is employed to encapsule perishable goods or to coat the inside of tubular heat exchangers for saline water stills.
Polyphenylene oxide (20), the second product of Table X I I I , is made by the copper-catalyzed oxidation of 2,6-xylenol. I n this process, oxygen reacts with active hydrogens from different molecules to produce coupled molecules plus water. If the monomer has two active hydrogens, oxidative coupling can continue and a high molecular weight polymer is formed. The reaction proceeds in pyridine with cuprous chloride as catalyst at room temperature. If the monomer is a methyl-substituted phenol, the polymer remains amorphous and can be thermoprocessed. Oxidative coupling may also be used in the preparation of azopolymers from aromatic diamines, as illustrated in Table XIV. Use of cuprous chloride and pyridine resulted in low molecular weight azopolymers (21). This
~
TABLE XIII.
POLY-p-XYLYLENES and POLYPHENYLENE OXIDE Vapor Phase Deposition
Union Carbide
pyrolysis n
C
H
X
X
3
d CH3
95OoC +steam
'
I
+
C H & 7 3 4 2
0.1 6OO0C mrn
C H 2 a C H 2
100%
F
T,,
p-Xylylene 2-Methyl p-xylylene 2-Ethyl p-xylylene 2-Chloro p-xylylene 2-Acetyl p-xylylene 2-Cyano p-xylylene 2-Bromo p-xylylene Dichloro p-xylylene
"C
30
Polymer Parylene-n
-
X p-xylylene
di-p-xylylene
Monomer
tl
C H 2 n C H2
)z/
X p-xylene
C ' H2-&H2'
M.P., "C 400
60
90 90 130 130 130 130
n = 5000 Pary1ene-c
290
Parylene-d
300
-
POLY p -XY LY LENE linear
OXIDATIVE COUPLING General Electric
2,6-xylenol
POLYPHENYLENE OXIDE amorphous HDT 66 psi) 204 OC
(a
VOL.
61
NO.
5
MAY
1969
21
TABLE XIV.
-
-
AZOPOLYMERS BY OXIDATIVE COUPLING
2 H 2 N e N H 2
+
0 2
cu2+
py r idme
D
N
=
N
$
4- n H 2 0
Monranto: c
r
-Y
disadvantage, that only polymers soluble in pyridine could be made, was overcome (22) through the use of dimethyl acetamide or a mixture of it with pyridine. I n this way, several linear higher molecular weight azopolymers were prepared. These, as shown in Table XIV, are crystalline, have no side branches, and cannot be thermoprocessed. The deficiency of PPO is that it has a "beer bottle" brown color. All azopolymers are even more colored because of their chromophonic azo-groups. By reaction of phenol with acetone, bisphenol-A (p,pisopropylidene diphenol) is made by acid condensation. I t is a raw material for epoxide resins, as well as for several heat-resistant thermoplastics. Table X V shows bisphenol-A as one of the components in the manufacture of polycarbonate, phenoxy, polysulfone, and polysulfonate, all transparent structural plastics. Polycarbonate (23) is made from bisphenol-A either by phosgenation in pyridine, or by interfacial polycondensation or transesterification. I t is known for its toughness, dimensional stability, and self-extinguishing properties. Phenoxy (24, derived from bisphenol-A and epichlorohydrin, is similar in structure to epoxies. It has a free hydroxyl group which can be bound and makes it useful as a strong adhesive. It is inferior to polycarbonate, because it has a lower heat deflection temperature and a greater tendency to stress cracking. Union Carbide is promoting its polysulfone (25) as a n engineering plastic of high heat deflection 22
INDUSTRIAL
AND
ENGINEERING
CHEMISTRY
temperature and good mechanical properties. Sulfone groups are said to draw electrons from the adjacent benzene rings, making them electron-deficient and resulting in good oxidation resistance. The polysulfonates (26) are made from bisphenol-A and disulfonyl chlorides. They are more brittle than polysulfone and have been suggested for use in copolymers with linear polyesters to improve the hydrolytic stability of the latter. The weakest link in the main chain of polysulfone made from bisphenol-A is the isopropylidene group. Building a polysulfone backbone without any aliphatic group, as illustrated in Table XVI, results in a product capable of exceptional resistance to oxidation and of structural use at 260 "C. Such a product is made either by almost quantitative self-condensation of a monosulfonyl chloride or by almost quantitative ferric chloridecatalyzed polycondensation of a disulfonyl chloride with a sulfone (27). Polyphenylene sulfides have been prepared by heating cuprous p-bromo-thiophenoxides. They are semitransparent, tough, and melt at 270" to 290 "C. When heated to 400 OC, they crosslink, providing products of greater toughness and strength. HETEROCYCLIC A N D AROMATIC RINGSIN BACKBONE. The polyimides are the best developed class of high temperature polymers with exceptional oxidation resistance. They are based on the condensation of aromatic dian-
, I
0
2
2,
2
v I
8-3I
I"
uI
I"
8 4u-u-u
I
U
I-
i3.
3
P ;
4I
Q,
E
t
i
fi
+
VOL.
61
NO.
5
MAY
1969
23
TABLE XVI. POLYPHENYLENE SULFONES AND SULFIDES I.C.I., 3M
Polymer 360
Dow
TABLE XVII.
POLYIMIDES
bis-4(aminophenyl)-
pyromellitic dianhydride
SOLUBLE: polyamic acid
ether
S'
$
N I
L
'O
/ ' O
'
y\ N O
O
d
+ 2nH20
I
0
Jn
INSOLUBLE POLYDllMlDE
r o
0
1
Allied Chemicals
,CH2--CH2
'-
CH2 fH
'YH
CH2
0CO
+
N-CI .J-CH~-CI
C H2-COOH @-carboxymethyl caprolactam
24
INDUSTRIAL
AND
&(E amino propyl) glutaric anhydride
ENGINEERING
CHEMISTRY
_L
I
poly-(2,6-dioxo)-1,4-piperidinediyl trimethylene
TABLE XVIII.
POLY(AMIDE-IMIDE),
Trimellitic anhydride
POLYOXADIAZOLE, POLYTRIAZOLE, AND POLYTHIAZOLE
Aromatic diamine
POLY(AMIDE-IMIDE)
{ArJG!$
0 II
,CCl n Ar
\
POLYOXADIAZOLE
+ n "2.
NH2
CCI
8
Diacid chloride
Hydrazine
POLYHYDRAZIDE
POLYTRIAZOLE
?
,C-CH2-Br n Ar
+n
'C-CH2-Br
8
Dibromo Ketone
y
2
C-ArI-C
!
y
2
!
----+
POLYTHIAZOLE
Dithio amide
hydrides with aromatic diamines, followed by intermolecular cyclodehydration. Table X V I I illustrates a commercial process of Du Pont (28) which consists of condensing pyromellitic dianhydride with bis(4-amino phenyl) ether. T h e first step to the polyamic acid intermediate occurs readily in dimethyl acetamide solution at room temperature. T h e polyamic acid is heated to evaporate solvent and can be cast into film a t a 25 to 30% residual solvent content. Upon being heated above 150 "C, it dehydrates by cyclization to form the insoluble polyimide, which is stable for over a year at 275 "C. Du Pont Vespel SP-1 with a heat deflection temperature of 360 O C (at 264 psi), SP-2 with a heat deflection temperature of 243 "C, and its Kapton film, and American Cyanamid's XPJ-182 with a heat deflection temperature of 260 "C are commercial polyimides. Recently, Allied Chemical (29) prepared a polyimide from beta-
carboxy methylated caprolactam by opening the lactam ring, followed by intermolecular cyclodehydration. T h e polymers shown in Table X V I I I have both rigid and flexible links in their backbones, This represents a compromise between chain stiffening and reduction of brittleness and stress-cracking. Placing amide linkages into the backbone is another way to provide flexible hinges. Polyamide-imides, as in Table XVIII, are made by reacting trimellitic anhydride with a n aromatic diamine-materials used in laminating and wire-coating. Like the polyimides, the polyoxadiazoles are made by cyclodehydration. They are heat-resistant materials prepared from polyhydrazide and are obtained from diacid chloride and hydrazine or dihydrazides. When reacted with aniline, polyhydrazides form polytriazoles (30), which are prepared by solution polycondensation of dibromo ketones with dithio amides (31). VOL.
61
NO.
5
MAY
1969
25
H2NmNH TABLE XIX.
n
+
\
H2N
\
SEMILADDER POLYMERS
n Ar,COOH
'COOH
"2
Aromatic tetramine
Dicarboxylic acid
POLYBENZIMIDAZOLE PBI
(AF-R- 100, AF-R- 15 1, AF-A- 12 1)
,CO.CHO
+
n
Ar
n
'CO.CH0 Aromatic tetramine
Bis-o-amino phenol
n H2N I
'
n
Diglyoxalyl benzene
POLYQUINOXALINE
Dicarboxylic acid
POLYBENZOXAZOLE
NH2 + n
I
H5 5H Bis-o-amino thiophenol
n
COOAr Diphenyl ester of aromat. dicarboxylic
POLYBENZOTHIAZOLE
PBT
(AF-R 2506)
acid
Table XIX lists four groups of so-called semiladder polymers: polybenzimidazoles (32),polyquinoxalines (329, polybenzoxazoles (34, and polybenzothiazoles (35), all possessing aromatic and heterorings in the backbones. These polymers can be prepared by polycondensatioa and cyclodehydration from aromatic dicarboxylic or dicarbonyl compounds with aromatic tetramines of diamino phenols or amino-thiophenols. T h e first two groups, the polybenziniidazoles and polyquinoxalines, can be made in two steps with soluble prepolymers similar to the polyimide prepolymers. AF-R-100 and RF-R-15 1, two PBI products developed by the Air Force Materials Laboratory, are made from 3,3' -diamino benzidine and diphenyl isophthalate, resp. isophthalamide, with a prepolymer, soluble in pyridine and fusible a t moderate temperature. They are used in composites with glass cloth or as adhesives for metal-to-metal bond. They are cured at 350" to 550 "C and are characterized by excellent strength properties from -2260" to 650 "C. 26
INDUSTRIAL AND
E N G I N E E R I N G CHEMISTRY
T h e polybenzoxazoles and the polybenzothiazoles become insoluble at a comparatively low degree of polymerization. Therefore, melt condensation techniques are employed to produce insoluble but fusible polymers. AF-R-2506 is a modified PBT with a prepolymer soluble in dimethyl acetamide and made from mixed toluidines, sulfur, and 4-amino phthalimide. Composites made from it possess oxidative stabilities superior to those of the
TABLE XX.
MAXIMUM USE TEMPERATURE 10 min,
Exposure lime
Polyimide (PI) Polybenzimidazole (PBI) Polybenzothiazole (PBT) M o d . Plast. Encyclopedia, 1968, p 1 10.
"C
377
650+ 538
200 hr, OC
358 320 330-343
PBI resins a t 320 OC. Based on available data (36), maximum-use temperatures have been set for the three high temperature resin groups: PI, PBI, and PBT (Table XX). T h e polyimidazopyrrolones, also known as pyrrones and shown in Table XXI, are prepared by polycondensation of pyromellitic anhydride with an aromatic tetra-
TABLE XXI.
0
0
0
0
mine. By varying the heating rate, cyclodehydration takes place either to a semiladder or ladder structure (37). T h e semiladder polybenzimidazolones melt above 400 "C and are soluble in dimethyl formamide, dimethyl acetamide, and dimethyl sulfoxide. When ladder polymers are subsequently formed, they are insoluble in these solvents.
LADDER POLYMERS
NHz
H2N slow
heating
t
\
0
0
n
Semiladder rtruclure
ladder rlructure
Dawans, F., and Marvel, C. S., 1. Polym. Sci. A, 3, 3549 (1965).
ladder
Bailey, W. J., Economy, J., and Hermes, M. E., 1. Org. Chem., 27, 3295 (1962).
polyacrylonitrile
ladder
Hurtz, Textile Res. J., 8 0 , 786 (1950).
ladder
1,2 -polyisoprene
Angelo, R. J., Polym. Prepr., 4 ( 11, 32 (1963). Gaylord, N. G., et a/., 1. Amer. Chem. SOC., 85, 64 1 (1963).
VOL.
61
NO. 5 MAY
1969
27
TABLE XXII,
THERMALLY STABLE HETEROPOLYMERS
Polyperfluorotriazine
r
0-Si-0-Ti
l!?'
1
bR ladder si1 sequioxane
n H
O
p
H
-p
2
H
I
\ -
ligana
I
CH2
0
'
I
crosslinked
Other polymers for high temperature applications are
BBB ( polybisbenzimidazo benzophenanthrolinedione ) and BBL made by polycondensation of naphthalene tetracarboxylic acid with either tetraaminobiphenyl or tetraaminobenzene (38).
Co., 730 Worcester St., lndzan Orchard, M a s s . 01051. Thzs article is based on a pafer given by Dr. Platzer at the 50th Annzversary Meeting of the Socidtd de Chzmze Industrielle, Paris, France, in M a y 1968, and subsequently presented to other scient@ groups zn West Germany, Austria, and Czechoslovakia. AUTHOR Norbert Platzer zs with the Monsanto
28
INDUSTRIAL
AND
ENGINEERING
CHEMISTRY
A true ladder polymer may also be formed from 3methylene pentadiene and p-quinone by means of a Diels-Alder reaction (39). The first ladder pyrone was obtained by the cyclization of polyacrylonitrile at 200" to 320 "C (40). However, lack of perfect head-to-tail structure in polyacrylonitrile formed by free-radical polymerization prevents the formation of a perfect ladder structure, resulting in weak points and poor strength. Further heating leads to evolution of Hz and to aromatization. The final product corresponds in structure to linear graphite, in which one carbon atom of every ring has been replaced by nitrogen, and withstands red heat. 1,2-Polyisoprene lends itself also to cyclization and ladder formation @1), but only to 82%.
...Thermally Stable Through the influence of heat and oxygen, chain breakdown of most polymers occurs on the aliphatic groups in the chain. By linking polyaromatics with oxygen, sulfur, or nitrogen instead of aliphatic groups, polymers are obtained with exceptional resistance to oxidative degradation during permanent exposure to high temperature and air. A typical example is the polysulfone without an isopropylidene bridge. Another principle to improve thermal stability is the replacement of hydrogen atoms of the aliphatic chain by fluorine. This has already been carried out successfully in the production of Teflon, Kel-F, Viton, and other fluorocarbons. A few of the more recent thermally stable polymers are shown in Table X X I I . Polyperfluorotriazine contains alternating heterocyclic rings and totally fluorinated carbon chains. I t is stable above 400 "C and resistant to strong oxidizing agents. Still another very effective method of preparing thermostable products is by incorporating inorganic elements, such as silicon, phosphorus, germanium, magnesium,
TABLE XXIII.
aluminum, titanium, or tin, into the chain (42). T h e first representatives of this system were the well-known silicone polymers of polysiloxanes. Some of them have been made by solid-state polymerization, as their monomers are solid but characterized by a high vapor pressure (43). Although they are thermally very stable, polysiloxanes suffer under the tendency to cyclize into rings with 8, 10, 12, or 14 members, which leads to a progressive softening of the material and loss of toughness, strength, and elasticity. This tendency can be reduced by the introduction of the other elements in the backbone chains. These metal oxanes show excellent thermal stability to as high as 400 "C. Systems of this type can be crosslinked and can form true ladder-type polymers (44),as shown in Table X X I I . By replacing oxygen with nitrogen in polysiloxanes, polysilazanes are obtained. These show promise for hightemperature coatings up to as high as 540 "C and as elastomers with good low-temperature compressibility and stability to radiation. Another method to improve the thermal stability of
US. SELLING PRICES PER WEIGHT AND PER VOLUME
Selling price
$/lb
#/in.3
Selling price
LDPE
11.0 15.5 11.5 19.0 17.0 19.0 18.0 3.0
0.36 0.58 0.60 0.62 0.64 0.66 0.68 0.77
Aluminum SAE 380
24.0 2 1.2
0.79 0.82
26.0 20.0 20.0 22.0 22.0 28.0 35.0 32.0 40.0 36.0 45.0 43.25 40.0 48.5 30.0 4 1.0
0.85 1.oo 1.0 1 1.07 1.08 1.08 1.19 1.23 1.32 1.35 1.5 1.84 1.88 1.95 1.96 2.03
Polystyrene, G.P.
PVC, G.P. Polypropylene Medium impact polystyrene HDPE High impact polystyrene Pig iron, basic Ethylene-propylene cop., med. impact SAN Ethylene-propylene cop., high impact VC-propylene cop. Rigid PVC I, 1, lead stab. Rigid PVC II, 1, lead stab. Rigid PVC II, 1, tin stab. ABS, g.p. EVA (75125) ABS, med. imp. Poly (1-butene) ABS, high imp. lonomer PMMA gen. purp. Cellulose acetate PMMA impact Magnesium AZ-9 1B Polyethylene terephthalate
#/lb
22.5 24.5 62.0 62.0 70.0 70.0 50.0 75.0 75.0 65.0 80.0 16.2 100.0 18.3 126.0 33.0 30.7 39.0 43.0 50.0 50.0 335.0 395.0 325.0 490.0 495.0 1250.0
Aluminum SAE 306 Cellulose acetatelbutyrate
Cellulose propionate
PPO impact blend Ethyl cellulose Polyvinyl dichloride blend
Nylon-6 and -66 Phenoxy Polyacetal Polycarbonate Zinc SAE 903 Polysulfone Zinc Zamac 3 Nylon-6 10 Tool steel Standard 0.95C Brass 403 Stainless steel 204 Brass yellow 405 Stainless steel 304 Brass 85151515 Chlorinated polyether PVDF PTFE PTFCE FEP Polyimide
VOL.
61
#/in.a
2.25 2.45 2.65 2.67 2.68 2.78 2.80 3.09 3.20 3.34 3.46 4.16 4.48 4.5 4.96 9.3 1 9.82 10.8 13.0 14.3 15.8 16.9 25.2 25.4 37.4 38.4 57.8
NO. 5 MAY 1969
29
METRIC T0NS;YEAR
A close relationship exists between the price of a material and its production volume. Figure 2 illustrates that the lower the price, the larger the market for a product. Plotted on a log-log scale, the price-volume curve becomes a straight line. All prices above the line may be considered as unstable, unless the polymer has specific valuable properties, such as the chemical resistance of polytetrafluoroethylene or the transparency of the acrylics.
,n7
Concluding Remarks
IO6
I 07
108
109
10’0
10‘1
10’2
VOLUME, P O U N D S I Y E A R
Figure 2. Price us. production volume (U.S.A.,1967). Log-log scale
organic polymers is the introduction of heavy metals in the form of ions into carboxyl or sulfoxyl groups. Metalloorganic polymers have been prepared from derivatives of bis(8-hydroxy quinoline) and transition metal ions at either 120 “C in fl,N-dimethyl formamide solution, from which the polymer precipitates, or 290 O C in solid state and vacuum (10-3 ton) (45). These polymers are either linear or crosslinked. The trend in thermal stability between the transition metals is shown in the last line of Table X X I I . Transition metal stability was determined by thermogravimetric analysis at 1000 O C . In the’ area of inorganic polymers, the boron polymers have to be mentioned. Olin Mathieson’s monomers have 10 boron atoms and contain silicon-yielding boron polymers, known as carboranes. Space General Corp.’s monomers contain five boron atoms and University of California’s monomers have eight boron atoms plus metal. Boron nitride is thermally stable to 2000 “C. *.
. as Inexpensive as Paper
Plastics are used as replacements for everythingfrom stainless steel, fabric and living tissue to low-cost building material, grass, and turf. We pay a high price for a plastic heart valve, computer part, or space craft component, but we pay little for plastic rugs or tennis courts, ski slopes and sport arenas, or composites for race tracks. For the big commodity polymers, price is the most important factor. The least expensive material which will do the job adequately is chosen. Table X X I I I lists the current U.S. selling prices of polymers and compares them with those of metals on a weight and volume basis. The tendency is to produce polymers of equal properties a t lower costs. Production costs are composed of materials price and conversion cost. Larger units, improved procedures, continuous operation, and automation are a means of reducing conversion cost and increasing yield and output of an existing process. Another means is modification of an existing process or development of a novel, less expensive, process. A typical example is the “solventless” low-pressure polyolefin process of BASF, ICI, Phillips, Amoco, and ESSO, which is less expensive because it eliminates the step of catalyst extraction and solvent recovery. 30
INDUSTRIAL
AND
ENGINEERING
CHEMISTRY
I hope that these few examples have given you the impression that we are able to build one plastic as strong as steel, one as clear as glass, one as light as a feather, one as heat resistant as quartz, and one as inexpensive as paper. However, we have not been able to combine these properties in a single polymer. Whoever does this will be an alchemist changing low-cost raw materials into a product superior to gold. RE FER ENCES (1) Bakeland, L. H., IND.ENO.CHEM.,5 , 506 (1913). (2) Staudinger, H., Eer., 53, 1073 (1920). (3) Carothers, W. N., J . Amer. Chem. Soc., 51, 2548 (1929). (4) Ploste Kautrchuk, 1 4 , 950 (1967); Search 5, Plas. 294 (Feb 1968). (5) Cooper, W., 3. Polym. Sci., 29, 195 (1958). (6) Rees, R. W., and Vaughan, D. J.,Canadian patent 674,593 (1963); ACS, Polym. Div. Preprint 6,287,296 (1965). (7) Vermillion, J. L., Plasf. Des. Proc., 1967 (2), pp 16-20. (8) Tusch, R. L., Pobm. Eng. Sci., 1966 ( B ) , p 255. (9) Jezl, J. L., 155th National Meeting, ACS, San Francisco, April 1968. (10) Spain, G., Aero. Space Eng. Manual Meeting, 660642 (Oct 1966). (11) W. R. Grace & Co., U.S. patent3,150,117; Bier, H., 155th National Meeting, ACS, San Francisco, Calif., April 1968. (12) Stille, J. K . , e1 a / . , Meeting, ACS, San Francisco, Calif., April 1968. (13) Chatelain, J,,155th National Meeting, ACS, San Francisco, Calif,, April 1968. (14) Goldfinger, G., 3.Polym. Sci., 4, 93 (1949). (15) Marvel, C. S., and Hartzell, G. A,, J . Amer. Chem. SOL.,81, 448 (1959). (16) Marvel, C. S., et a/.,J . Polym. Sei.,Part A , 1, 2057 (1963). (17) Kovacic, P., et al., 3.Amer. Chem. Soc., 83, 1967 (1961); 3.Org, Chem., 2 8 , 968 (1963). (18) Kern, W., and Gehm, R., Angew. Chem., 62, 337 (1950). (19) Errede, A., and Szwarc, M., Qunrt. Reu. (London), 12, 301 (1958); Gorham, W. F. 3. PGbm. Scz. Port A-7 4 3027 (1966). Union Carbide U.S. 3,117:168; 3,153,163; 3,155,’71)2; 3,164,6251 3,,342,754; Gdrham, 155th National Meeting, ACS, San Franclsco, Calif., April 1968. (20) Hay, A. G., et al., J . Amer. Cham. Soc., 81, 6335 (1959); Aduan. Polym. Sci.,4, 496 (1967); Coo er G D , and Katchman, A,, 155th National Meeting, ACS, San Francisco, (?aliialii.., April 1968. (21) Kotlyarevckii, I. L., IUPAC Conf., 1965; Izu. Akad. X o u k . SSR, Ser. Khim, 10, 1854 (1964). (22) Bach, H. C., ACS Meeting, 1966 (7, 576); IUPAC Conf., 1967; 155th National Meeting, ACS, San Francisco, Calif., April 1968. (23) Schnell, H., Angew. Chem., 68, 633 (1959); IND.EKG.CHEM.,51, 157 (1954). (24) Union Carbide, Brochures on Phenoxy PRDA, 1966. (25) Spingler, E., Plaitico, 19, 269 (1966); B7it. Plait., 1966 (3), p 132. (26) Conix A. IUPAC Conf. 1959; Schlott, R . J., 155th Kational Meeting, ACS, San FraLciscb, Calif., April i968. (27) SOC.Peiroi. Engrs. 3., 23, 33 (July 1967). Cudby M . E. A. Polymer, 6, 589 (1965); 155th Kational Meeting, ACS, San franciscd, Calif,, A&il 1968. (28) Sroog, C. E., et ai., Polymer Preprints, 5 ( I ) , 132 (1964). (29) Reimschuessel, H. K., 155th Kational Meeting, ACS, San Francisco, Calif., April 1968. (30) Liliquist, M. R., and Holsten, J.R., Polymer Preprints, 4 (2), 6 (1963). (31) Mulvaney, J.E., and Marvel, C. S . , J . Org. Chem., 26,95 (1961); Hurd, R. N., and DeLaMater, G., Chem. Rea., 61, 45 (1961). (32) Vogel, H., and Marvel, C. S., 3. Polym. Sci., 50, 511 (1961). (33) Stille, J. K., and Williamson, J , R., ibid., E , 2, 209 (1964); A , 3, 1013 (1965). (34) Moyer, W. W., et ai., ibid., A , 3, 2107 (1965). (35) Hergenrother, P. M., e1 a/., ibid., 2 , 4795 (1964). (36) Aponyi, T . G., Mod. Plnst. Encyclopedfn, 1968, 110 (1967). (37) Dawans, F., and Marvel, C. S., 3. Polym. Sci., A , 3, 3549 (1965). (38) Berry, C., e f ai., 155th National Meeting, ACS, San Francisco, Calif., April 1968. (39) Bailey, W. J., Economy, J., and Hermes, M . E., J . Org, Chcm., 27, 3295 (1962). (40) Hurtz, Tcixtiie Res. J . , 80, 786 (1950); Bruilant, W. J., and Parsons, J. L., J . Polym. Sci., 22, 249 (1956). (41) Angelo, R. J,,Polymer Preprint,, 4, (I), 32 (1963); Gaylord, K. G., el a / . , J . Amer. Chem. Soc., 8 5 , 641 (1963). (42) Mark, H . F., Pure Appl. Chem., 1 2 , 4-21 (1966). (43) St. Pierre, L. E., 155th National Meeting, ACS, San Francisco, Calif., April 1968. (44) Brown, J.,Poiym. Sei., C, 1, 83 (1963). (45) Horowitz, E., 153rd National Meeting, ACS, Miami Beach, Fla., April 1967; Mod. Plart., 1967, ( l l ) , p 196.
