I
HERMANN SCHNELL Farbenfabriken Bayer A-GI Werk Uerdingen, Wiss. Hauptlaboratorium, Krefeld-Uerdingen, Germany
Linear Aromatic Polyesters of Carbonic Acid High-melting, crystallizable polycarbonates fibers, plastics, and coatings In the May 1958 issue of I/EC (page 24 A) appeared a short article entitled Polycarbonates-Attention Getter. It told of the excitement caused at the ACS meeting in San Francisco by disclosure of the manufacturing process for the polycarbonates. The article in May was only prelude to the entire story, told this month on this and the following three pages. It is a story almost certain to result in a new plastic’s being added to our growing list of commercial plastics.
THE
development of thermoplastic polyesters of carbonic acid with high melting points (polycarbonates) has been in progress in these laboratories since 1953. Raw materials for these products are derivatives of carbonic acid and symmetrical aromatic dihydroxy compounds consisting of two phenol residues linked by a joint. The joint between the two aromatic radicals may be a methylene group, an alkyl radical, or a hetero atom-oxygen or sulfur. A particularly easy access is offered by derivatives of 4,4’-dihydroxydiphenylmethane in which one or both hydrogen atoms of the central carbon atom is substituted by aliphatic, aromatic, or cycloaliphatic radicals. A number of these products are easily accessible by condensation of phenols with oxo compounds-4,4 ‘ isopropylidenediphenol [4,4’ - dihydroxydiphenyl- 2,2 - propane (bisphenol A)] from acetone and phenol. The polycarbonate derived from this bisphenol was the first to be produced commercially, but a number of other aromatic dihydroxy compounds have been converted to polycarbonates (5). Polycarbonates from the following bisphenols were investigated :
-
M.P.,
c.
4,4’-Dihydroxy3,3’,5,5’-tetrachlorodiphenyl 3,3’,5,5’-tetrachlorodiphenylmethane 3,3’-dichlorodipheny1-2,2-propane
222 184-5
are
suitable for films,
Commercial Production of Polycarbonates
Phosgenation Method. Slightly more than the equimolecular quantity of phosgene is introduced into a solution or
CH3
CH,
L
.
I
CH 3
3,3’,5,5’-tetrachlorodiphenyl2,Z-propane 133-4 3,3’,5,5’-tetrabromodiphenyl2,2-propane 178-80 3,3’-disulfonic acid diphenylpropane 3,3’,5; 5’-tetrachlorodiphenyl1, l-cyclohexane 147-9 3,3’-dichlorodiphenylsulfone 194-5.5 diphenyl ether 161-2 diphenyl sulfide 151-2 3,3’-dimethyldiphenyl sulfide 120 diphenyl sulfoxide 203 3,3’-dimethyldiphenyl sulfoxide 190 3,3’-dimethyldiphenyl sulfone 268-69 tetraphenylmethane 29697 3,3’,5,5’-tetrachlorodiphenylsulfone 150
Because most of the aromatic dihydroxy compounds mentioned here contain the grouping 4,4’-dihydroxydiphenyl, this term is replaced in the following discussion by bisphenol.
Polycarbonates-Some
suspension of the aromatic dihydroxy compound in aqueous caustic soda solution at 2 0 ” to 30” C . An inert solvent capable of dissolving both phosgene and the resulting polycarbonate is used; methylene chloride is suitable in many cases. A polycarbonate of low molecular weight with -0COCl terminal groups is formed in exothermic reaction and is converted into a material of high molecular weight either by prolonged stirring or, more rapidly, after addition of catalysts suchas quaternary ammonium bases or tertiary amines. The desired molecular weight can be adjusted with chain terminating agents, such as tertbutylphenol. The resulting dough is separated from the salt solution, and any electrolytes are washed out with water. The poly-
of Their Properties
Solubility Insoluble polymers are formed by aromatic dihydroxy compounds of symmetrical structure (hydroquinone and bisphenols derived from alkanes) containing between them the phenol radicals with small substituents. The more assymetrical and bulky the aliphatic radical between the phenol radicals, the higher the solubility.
Melting Range Polycarbonates have no sharp melting point. Melting range is a function of the degree of crystallization. Symmetrical substitution on the bisphenol derivatives gives a polymer with a higher melting range; asymmetrical substitution lowers the melting range.
Crystallization Form clear, transparent solids with favorable mechanical properties which do not change during storage. Radial intensity curves of the X-ray graphs of nonorientated specimens from 2,2-propane bisphenol showed a ratio of crystalline to noncrystalline scattering of 0.4 to 0.5, about as high as that of regenerated cellulose.
89-9 1 VOL. 51, NO. 2
FEBRUARY 1959
157
carbonate can be isolated by evaporating the solvent or by precipitating the polymer with a nonsolvent. After drying at 120" to 130" C., the granular material may be used to prepare solutions. Prior to thermoplastic forming, the granular material must be dried carefully in vacuum a t 120' to 140' C. Polycarbonate intended for injection molding is preferably melted down in the extruder and formed into filaments or tapes which are cut to pellets or chips. This extremely simple method produces, at room or slightly elevated temperatures, polycarbonates with molecular weights well over 200,000. Ester Interchange Method. Equimolecular quantities of aromatic dihydroxy compounds and diary1 carbon-
employed. The rate of ester interchange is increased by the usual alkaline or acid catalysts. The resulting melt is spun off from the reaction autoclaves, by means of nitrogen pressure, in the form of tapes or filaments, which are then cut into pellets or chips to produce a granular material suitable for thermoplastic forming. Molecular weights obtained by this method are limited by the high viscosities of the polycarbonate melts. Polycarbonate Properties
Molecular Weights. Commercially suitable polycarbonates from 2,2-propane bisphenol have molecular weights between 20,000 and 80,000, but it is possible to obtain molecular weights
CH,
L
ates, primarily diphenyl carbonate, are melted with atmospheric oxygen excluded and allowed to react at 150 ' and 300 ' C. to the desired molecular weight, phenol being eliminated. I n the final stages increasingly high vacuum is
well over 200,000. For this polycarbonate, the statistical chain element calculated on the basis of sedimentation, diffusion, and viscosity measurements (7-3) is about 84 A. in tetrahydrofurane and 108 A. in methylene
I.
Physical Properties of Slightly Crystalline Polycarbonate Films Cast from Solution In controst to crystalline polyesters and polyamides, polycarbonates hove no sharply denned melting point
Table
Melting Range, Polycarbonate from
O
c.
SecondOrder Transition Point, O C.
4,4'-Dihydroxydiphenyl>300 methane 290-300 1,2-ethane 130a 185-195 1,l-ethane 123" 150-170 1,l-butane 149" 170-180 1,I-isobutane 149O 220-230 2,2-propane 134a 205-222 2,2-butane 137" 200-220 2,2-pentane 200-220 2,2(4-methylpentane) 180-200 2,2-hexane 148b 190-200 4.4-heptane 170-190 2,2-nonane 176b 210-230 phenylmethylmethane 121b 210-230 diphenylmethane 167b 240-250 1,I-cyclopentane 175' 250-260 1,l-cyclohexane 230-235 ether 220-240 sulfide 230-250 sulfoxide 200-210 sulfone 4,4'-Dihydroxy147' 190-210 3,3'-dichlorodiphenyl-2,2-propane 3,3',5,5'-tetrachlorodiphenyl-2,2180b 250-260 propane 3,3',5,5'-tetrachlorodiphenyl-l, 1163b 260-270 cyclohexane 3,3',5,5'-tetrabromodiphenyl-2,2157b 240-260 propane 95" 3,3'-dimethyldiphenyl-2,2-propane 150-170 Determined by dilatometer. Determined by refractometer.
... ...
158
INDUSTRIAL AND ENGINEERING CHEMISTRY
cc.
Refractive Index
... ...
... ...
1.18 1.20 1.18 1.13 1.14
...
... ...
1.5937 1.5792 1.5702 1.5850 1.5827 1.5745 1.5671
1.16
1.5602
... ... ... ...
1.21 1.27 1.21 1.20
... ... ... ...
1.6130 1.6539 1.5993 1.5900
... ... ... ...
1.32
1.5900
1.42
1.6056
1.38
1.5858
1.91 1.22
1.6147 1.5783
... ...
e
Density, Grams/
1.22
1.17
... ...
chloride. These very high values, compared with known synthetic macromolecular materials, indicate a high degree of rigidity. Accordingly, the second osmotic virial coefficient in methylene chloride and tetrahydrofurane is relatively high. Stretching. Polycarbonates may be orientated by stretching. At room temperature length is approximately doubled accompanied by orientation of chain molecules and an approximately 100% increase of tensile strength in the direction of stretching. However, degree of crystallization is not increased. At elevated temperatures, stretching to approximately four times original length is possible, with concurrent orientation of chain molecules and extensive crystallization as shown by the x-ray diagram of an orientated, crystalline polycarbonate foil from 4,4 '-dihydroxydiphenyl2,2-propane. Evaluation of fiber diagrams and oscillating crystal diagrams for the 2,2propane bisphenol polycarbonate gave an identity period of 21.6 A. ; a rhombic crystallization system with the lattice constants a = 11.9 A., b = 10.1 A., c = 21.6 A.; as well as the space group DZ 2 or D2 3. There are eight basic units in the elementary cell-four molecule chains each with two basic units. Crystal density is 1.3 in comparison with a macroscopic density of 1.20. Melt Viscosity. I n the molten state, polycarbonates remain stable for prolonged periods at temperatures up to 300' C. in the absence of moisture, alkalies, or acids. Rigidity and bulkiness of the macromolecules produce a high melt viscosity. Table II. Water-Vapor Permeability" of Slightly Crystalline Polycarbonates The value for 4,4'-dihydroxy-3,3'-dichlorodiphenyl-2,2-propaneis conspicuously low PermePolycarbonate from
abilityb
4,4'-Dihydroxydiphenyl 3.0 2,2-propane 1.0 1,l-cyclohexane 1.5 1,l-cyclopentane 2.4 methylphenylmethane 4,4'-Dihydroxy3,3'-dichlorodiphenyl-2,2-pro0.56 pane 3,3',5,5'-tetrachlorodiphenyl2.1 2,2-propane 3,3 ',5,5'-tetrachlorodiphenyl1.14 1,l-cyclohexane 3,3',5,5'-tetrabromodiphenyl2.3 2,2-propane Gas permeabilityC of polycarbonate from 4,4'dihydroxydiphenyl-2,2propane," X 1 O-s Hz 1.35 co2 0.75 0 2 0.18 Air 0.04 N2 0.01 Grams/Cm./Hr./Torr X 10-6. 80- t o 100-micron foils cast from solution. C Grams/Cm./Hr./Torr X 20' C., nonstretch films cast from solution 50s thick. a
CARBONIC A C I D POLYESTERS change after 9 months of outdoor weathering. Foils did not discolor when treated a t elevated temperatures over prolonged periods (Table 111). After a relatively short exposure to high temperatures they lost their stretching properties a t room temperature. Elongation then remained unchanged over prolonged periods. No brittleness was encountered. Chemical Resistance. Foils cast from 2,2-propane bisphenol polycarbonate solution, with a thickness of 60 to 80 microns, were stored for 13 weeks at room temperature in acids, alkalies, salt
2,2-Propane Bisphenol Polycarbonate Melt. Vise., Poises 5,800 9,400 14,500 30,000 72,000
5101. Wt. 25,000 27,000 30,000 33,000 40,000
Outdoor Lveathering tests on foils and injection moldings, extending over one year. did not cause discoloration or material changes of physical properties. Specimens buried in garden soil remained unchanged after an exposure of one year. A 179125 filament yarn of stretched polycarbonate showed no
Table Ill.
Stability of Polycarbonate Films to Atmospheric Oxygen at Elevated Temperatures Was Favored
Polycarbonate from 4,4’-Dihydroxydiphenyl-2,2propane
Film T hie kness, Microns
Temp.,
45
140
C.
Time, Weeks
Tensile Strength, Kg./Sq. Cm. 663 664 749 684
54 8 7 8
0
50
150
0 14 26
868 695 705
105 15 12
80
160
0
774 647 635
148 58 14
4
814 769
56 8
0 4 8
1023 1006 1007
7 10 9
65
4,4’-Dihydrox~-3,3’-5,5’-tetrachlorodiphenyl-2,2-propane
Table IV.
% ’
4 8 12
8 12
4,4’-Dihydroxydiphenyl-l,1cyclohexane
Elongat ion,
60
170
190
0
’
Mechanical Properties of Polycarbonate Films Cast from Solution“ Physical properties of films do not change on storage Impact Strength
Polycarbonate from 4,4’-Dihydroxydiphenyl1,l-ethane I , I-isobutane 2,2-propane
Orient at ion Nonstretched Nonstretched Nonstretched 1 :2 stretched 1 :4 , 7 stretched, cryst. 1 :1 1 stretched, Blown foilc Nonstretched Nonstretched Nonstretched Nonstretched Nonstretched
2,2-butane 2,2-pentane methylphenylmethane 1,l-cyclohexane 1,l-cyclopentane 4,4’-Dihydroxy3,3’-dichlorodipheny1-2,2propane Nonstretched 3,3’,5,5’-tetrachlorodiphenyl-2,2-propane Nonstretched 3,3’,5,5’-tetrabromodiphenyl-2,2-propane Nonstretched Film thickness 50 to 60 microns.
Tensile (IG Strength, Method), Kg./Sq. Elongation, Cm. Kg./ Cm. % Cc. 759 775 820 14001700b 2150*
167 147 180 32-40
1013 300 900
Flexing Cycles
> 10,000 > 10,000
...
>10,000 >lO,OOO
15
42 5
35OOb 890 725 665 824 814 708
20 155 70 66 55 56 119
320 700 363 703 172 169 552
> 10,000 > 10,000 > 10,000
5,800 900 1,000 5,000 > 10,000
995
19
65
>10,000
1154
10
33
3,000
1112
8
36
1,000
I n direction of stretch.
e
No additional stretching.
solutions, oxidizing and reducing agents, as well as organic solvents. This polycarbonate is resistant to 20y0 hydrochloric, sulfuric, and nitric acids; 40% hydrofluoric acid, 20 to 100% acetic acid, 10 to 100% formic acid, 10% sodium carbonate; aliphatic hydrocarbons, alcohols, vegetable and animal fats and oils, milk and lactic acid, oleic acid, soap solutions; 30% hydrogen peroxide, 10% potassium dichromate, in 10% sulfuric acid solution, and saturated potassium bromate. I t is not resistant to ammonia and amines. Aqueous alkaline solutions cause gradual decomposition of the film surface, while the remaining film shows no change of physical properties or molecular weight. Prolonged exposure to methanol results in brittleness because of crystallization and degradation. Aromatic hydrocarbons, ketones, esters, and halogenated hydrocarbons either swell this polycarbonate or act as solvents. The polycarbonate from 4,4’-dihydroxy-3,3’, 5,5 ’-tetrachlorodiphenyl-2,2propane is considerably more resistant to hydrolysis. Immersion in 20y0caustic soda for 13 weeks at room temperature caused neither degradation nor change in physical properties. I t is also resistant to methanol. Processing
Because polycarbonates are soluble in commercial solvents and remain stable when melted for long periods, all methods commonly used in forming plastics can be applied. Fibers and films can be manufactured from solutions, especially in methylene chloride, by the usual means. Polycarbonates soluble in paint and varnish solvenls are suitable fixphysically drying coating materials and hot dip coating compounds. Emulsions in water are obtainable from solutions. Appropriately dried polycarbonates can be processed on injection molding machines and extruders into all types of shapes-injection moldings, films, sections, tubing, rods, and blown foils. Polycarbonate foils are highly suited for vacuum forming. Manufacture of fibers by the meltspinning process calls for special technique because of the high viscosity of the polycarbonate melt. With usual techniques, foamed articles with low density, good mechanical properties, and good resistance to elevated temperatures can be produced. Mechanical Properties. FILMS. Polycarbonate forms which can be stretched, such as films and fibers, may be manufactured and used in nonstretched, stretched and noncrystallized, and stretched and crystallized forms (Table IV). VOL. 51, NO. 2
FEBRUARY 1959
159
Mechanical Properties. MOLDINGS, resistant to irreversible distortion under Mechanical properties of polycarbonate stress (cold flow). Polycarbonate moldmoldings are illustrated by the polycarings from 2,2-propane bisphenol to which bonate from 2,2-propane bisphenol, the a 220-kg. per sq. cm. load had been apmost extensively examined type (Table plied for 8 months showed no irreversible V). I t possesses favorable properties distortion. over a wide temperature range, apElectrical Properties. Table V I lists proximately - 70 ’to 140’C. Another electrical data for the polycarbonate important feature of injection moldings is from 2,2-propane bisphenol. For polydimensional stability a t elevated temcarbonates based on bisphenol derivaperature with no change up to 120’ C.; tives without substituents on the aroa t 140’ C. any changes are below 0.2%. matic radicals, electrical characteristics remain constant until approaching the second-order transition point (Table VII). I n many cases, however, polycarbonates from bisphenol derivatives subTable V. Mechanical Properties of stituted on the aromatic radicals show Injection Moldings from 2,2-Propane increases in the tan 6 and dielectric conBisphenol Polycarbonate“ stant with rising temperatures. A numThis material retains its favorable properties ber of these polycarbonates possess no over a wide temperature range defined maximum values of the tan 6 Sp. gr. 1 . 2 0 grams/cc. temperature function. Flexural strength 1100-1 150 kg./sq.
+
~~
Impact strength (notched) Impact resilience Brinell hardness 10 seconds 60 seconds Elongation Modulus of elasticity Tensile strength
cm. 15-60 cm. kg./sq. cm. >50 cm. kg./sq. cm.b Up to 900 kg./sq. em. Up to 870 kg./sq. cm. 7690% Approx. 22,000 kg./ sq. cm. 65CMOO kg./sq. cm.
Standard test rod. None of the specimens broke.
Storage of injection moldings for 5 months under tropical conditions (40’ C., 90% relative humidity) produced no change. Long-term exposure to boiling water or superheated steam resulted in stress cracks and degradation. T h e examined polycarbonate is highly
Table VII.
Table VI. Electrical Properties of 2,2-Propane Bisphenol Polycarbonate
> 100 kv./mm.
Dielectric strengtha Volume resistivity Dryb After 4 days at 80%
1010 ohm cm. 1015 ohm cm.
R.H.b Surface resistance Dry After 24 hr. in waterC Insulation resistance at 100 voltsb 1000 v o w Dielectric constant at 1000 C.P.SP Dielectric lossfactor at looo e.p.s.E
8.10 X 1012 ohms 6.10 X 1012 ohms 8.10 X 1012 ohms 4.10 X 1012 ohms 3.0 ohms tan 6 = 0.5-0.0021
Small standard 4 Foil, 50 microns thick. test rod. e Round disks, 80-mm. diameter, 3 mm. thick.
Electrkal Characteristics of Polycarbonates of Different Composition Some polycarbonates hove no denned maximum values for ton 6
Tan 6 (1000 Polycarbonate from 4,4f-Dihydroxydiphenyl1.1-ethane 1,l-butane 1,l-isobutane 2,2-propane 2,Z-butane 2,a-pentane methylphenylmethane 1.1-cyclopentane 1,l-cyclohexane
C.P.S., 25O C . ) x 104
S.I.C. (1000
C.P.S., 25’
C.)
Tan 6 (1000
S.I.C. (1000
C.P.S., 1000 C . ) x 104
1000 C.)
C.P.S.,
4.9
2.9
4.9
2.9
5.2 5.2 4.9 4.5 4.2 5.0 5.0 11.2
3.3 2.4 2.8 3.1 2.3 3.3 2.9 3.0
5.2 5.2 4.9 4.5 4.2 5.0 5.0 11.2
3.3 2.4 2.8 3.1 2.3 3.3 2.9 3.0
9.9 20.4 11.5 10.0
3.4 2.5 3.3 3.0
90.0 40.0 16.0 37.0
3.6 2.6 3.6 3.0
5.0
2.6
40.0
2.6
2.7
38.0
2.7
4,4’-Dihpdroxy-
3,3f-dimethyldiphenyl-l.l-ethane 3 3 ‘ -dimethyldiphenyl-2,2-propane 3,3’-dichlorodiphenyl-2,2-propane 3,3’, 5,5’-tetrachlorodiphenyl2,2-propane
3,3f,5,5’-tetrachlorodiphenyl-l,lcyclohexane 3,3‘, 5,5’-tetrabromodiphenyl2,2-propane
160
20
INDUSTRIAL AND ENGINEERING CHEMISTRY
Conel us ions Polycarbonates ideally complement the present range of plastics. Their advantages are great ease of processing from solution or by molding; high melt temperature; high fastness to light including ultraviolet radiation ; resistance to air and moisture, even a t elevated temperatures; low water absorption; and favorable mechanical and electrical properties over a wide range of temperatures. I n the nonstretched state they exhibit ease of stretching and crystallization and good resistance to water, acids, salt solutions, oxidizing, and reducing agents, aliphatic hydrocarbons, alcohols, and vegetable and animal oils and fats. I n addition, they have low dirt and color retention. Disadvantages are solubility or swelling properties in a large number of organic solvents, insufficient resistance to strongly alkaline solutions, ammonia, and amines as well as the insufficient resistance to long-term exposure to boiling water and superheated steam. The wide variety of aromatic dihydroxy compounds suitable for producing aromatic polycarbonates, many of which can be produced commercially, makes it possible to develop types with specific properties for certain applications. Acknowledgment
The assistance of Ludwig Bottenbruch, Gerhard Fritz! Heinrich Krimm, and Karl-Heinrich Meyer is particularly acknowledged. Product engineering tests were carried out by Wilhelm Hechelhammer, Gunter Peilstocker, and Lisa R8ssig, and physical measurements were made by Jens Martens, Ulrich Veiel, Horst Hermann, and Otto Petersen. Molecular weights were determined by G. V. Schulz and Alfred Horbach, Institute for Physical Chemistry, Mainz Universi ty. References (1) Debye, P., Bueche, A. M., J . Chcm. Phys. 16,573 (1948); Debye, P., Bueche, A. M., Peterlin, A . , J. Colloid. Sci. 10,
587 (1955).
(2) Kirkwood, J. K., Risemann, J., J.Chem. Pliys. 16, 565 (1948). (3) Peterlin, A . , Makromoi. Chem. 18/19,
254 (1956). (4) Prietzschk, A., lecture, Makromol. Colloquium, University of Freiburg, March, 8, 1957; Kolloid-2. 156, 8 (1958). (5) Schnell, H., Anzew. Chem. 68, 633 (1956). (6) Schulz, G. V., Blaschke, F., J. firakt. C h m . 158,130 (1945). (7) Stua;:, H. A . , “Physik der Hochpolymeren, vol. 11, Springer Verlag, Berlin, 1955. RECEIVED for review March 24, 1958 ACCEPTED August 18, 1958
Division of Industrial and Engineering Chemistry, 133rd Meeting, ACS, San Francisco, Calif., April 1958.
