I
ANDRE CONIX Chemical Research Department, Gevaert Photo-Producten N.V., Mortsel, Belgium
Thermoplastic Polyesters from Bisphenols Film-forming polyesters with good solubility in organic solvents, exceptionally high glass transition temperatures, and high melt viscosity are formed from bisphenols and aromatic and ethylenic dibasic acids
IN
THE past the major research effort in the field of linear polyesters has been directed toward synthesis of fiberforming polymers having a regular and symmetrical structure. These molecular characteristics result in easily crystallizable polymers with high melting points. However, these properties usually imply low solubility in common organic solvents and necessity of shaping polymers from the melt. Besides, the crystallized polymers are opaque and brittle unless their molecules are oriented by a stretching operation. Another characteristic of polyesters studied in the past is low glass transition temperature ( S O 0 to 100" C). Promising new polymers thus possess much higher glass transition temperatures and at the same time poor crystallizability in order not to impair solubility in volatile solvents. High softening points of such polymers are thus not due to a high crystalline melting point but to a high glass transition temperature. The same trend in research is going on in the field of polyamides ( 3 , 8 ) .
presence of esterification catalysts. In the work reported here, this method was applied to polycondensation of 4>4'-isopropylidene diphenol (bisphenol A) with a number of aromatic diacids such as 4,4'-dicarboxylic acid-diphenyl ether and 4,4'-isopropylidene dibenzoic acid. Polyesters obtained by this method had relatively high molecular weights but were slightly discolored. A number of catalysts may be used, but significantly superior results were obtained using titanium compounds, especially butyl orthotitanate or titanium dioxide. Molecular weights obtained using these catalysts were much higher than those obtained with other catalysts such as antimony trioxide or magnesium oxide. The extent of melt polycondensation is limited by the extremely high melt viscosity of the polymers, which prevents effective stirring of the reaction mass. Consequently, eliminating the last traces of acetic acid is seriously hindered, and progression of polycondensation is stopped. The highest intrinsic viscosity
reached by melt condensation of bisphenol A with 4,4'-dicarboxylic acid-diphenyl ether (El, Table I) was 0.8 deciliter per gram, corresponding to an OSmotic molecular weight of approximately 60,000. This is well in the range of molecular weights ( [ q ] > 0.4) where useful mechanical properties of films prepared of this polyester are observed. Polycondensation in Solution. Polyesters have. also been prepared from diacid chlorides and glycols (7). The inherent advantage of using the acid halide procedure is that the reaction is nonreversible. The diacid chloride and the glycol are usually mixed in molecular proportions, and the mixture is warmed gradually to high temperatures. In some cases, reaction is carried out in the presence of a base to neutralize the hydrogen chloride formed. When this procedure was used to prepare double aromatic polyesters, high molecular weight and colorless polymers were not obtainable, but they were produced by polycondensation in a
Synthesis Melt Condensation. Direct polycondensation of bisphenols and aromatic diacids at high temperatures is impracticable, resulting in badly discolored polymers of low molecular weight. According to a patented (70) method, bisphenols are first converted to diacetates, using acetic anhydride, and then polycondensed with aliphatic diacids, such as adipic acid, in stoichiometric proportions in vacuum and in the
LO
30
.-0 I
m
-F S
20
10
Literature Background Subject Basic discoveries in synthesizing linear polyesters Polyesters from glycols and aromatic diacids Polyesters from diphenols and dibasic acids Polycarbonates from bisphenols and phosgene
Ref. (6)
50
100
150
200
(1,5 ) (4.9,10)
( 2 , 7)
2 50 temperature
300
Figure 1. Temperature at which appreciable rise in elongation occurred was taken as softening temperature 11. TI
Birphenol A polyester from irophthalic acid Bisphenol A polyester from terephthalic acid
VOL. 51, NO. 2
FEBRUARY 1959
147
two-phase mixture consisting of an organic solvent for the diacid chloride and water for the bisphenol under the form of a n alkali diphenate. I t is essential that the organic solvent for the acid chloride also dissolves or swells the polymer formed. A particular advantage of this method is that the reaction can be carried out a t room temperature simply by mixing the starting materials, each dissolved in a n appropriate solvent (usually a chlorinated hydrocarbon and water). The reaction is markedly catalyzed by the addition of small amounts of quaternary ammonium or sulfonium compounds. I n the absence of catalysts, no high molecular weights could be obtained. The merit of this polycondehsation technique in solution lies in the unusually high molecular weights of the polyesters. I n some instances, molecular weights as high as 275,000 have been observed, which is much higher than could be obtained using any other known polycondensation technique.
Table I.
Properties of Polyester Films
Softening temperature can b e correlated with chemical structure, but the relationship is often complex Polyesters from Dibasic -4cids and Bisphenole
H
O
~
-
R
~
-
O
H
Softening Temp.,
R
Code
I
c.
Solubi1ityO
CHsCCHs
Terephthalic
250-300 (cryst.)
D
1.5b
T2
C~H&H~
Terephthalic
150-180 (amorph.)
A, C, D
1.lb
Terephthalic
200-220
A-F
0.8b
Terephthalic
250-280
A-F
0.8b
Isophthalic
c, D
1.0'
Isophthalic
120--130 (amorph.) 240-250 (cryst.) 120-130
A-E
1 .3h
Isophthalic
120-130
A-D
1.6b
Isophthalic
135-145
A-F
c. 77'
I5
Isophthalic
160-170
A-F
0.95'
I6
Isophthalic
175-190
A-G
0.75b
Isophthalic
190-200
A-G
0.96*
T4
I1
Using tJle polycondensation techniques described, a large number of polyesters were prepared; films were cast from concentrated solutions (20%) in chlorinated hydrocarbons. Softening temperatures of these films were determined by measuring as a function of temperature the elongation of film strips (4 X 70 mm.) subjected to a load of 0.17 kg. per s q . mm. Heating rate was standardized at 10' C. per minute. The temperature at which an appreciable rise in temperature occurred was taken as the softening temperature (Figure 1). These temperatures have only a comparative value and are not to be confused with melting points. When dealing with unoriented, amorphous films, these softening temperatures cor-
O
T1
I
T3
Chemical Structure and Physical Properties
Dibasic Acid
Intrinsic Viscosity, D1./ Gram
CClsCH
I I CHaCCHa I
I
I2
CzHsCCzHa
I3
CzH5CCH3
I4
(CH3)zCHCCHa
I
'
I
I
I7
I I I
I
I8
CClsCH
Isophthalic
130-150
A-G
1.06
F1
CHsCCHs
Fumaric
150-170
A-F
1.3"
F2
CzHsCCHa
Fumaric
130-135
A-F
0.61°
Fumaric
180
A-F
O.8Jc
F3
I
I
a A = methylene chloride; B = 1,2-dichloroethane; C = 1,2,2-triohloroethane; D = tetrachloroethane; E = dioxane; F = tetrahydrofurane, G = benzene: H = toluene. Measured Measured in 1,2-dichloroethane solution. in tetrachloroethane solution.
Figure 2. X-ray diagram shows unoriented, crystalline film o f bisphenol polyester from isophthalic acid By adjusting film-casting technique, films from this polyester can be obtained in amorphous or semicrystalline condition
148
respond more or less with glass transition temperatures. This was verified in a number of cases in which glass transition temperatures were also determined by a rigorous method, such as the measurement of specific volume as a function of temperature. However, when films have a semicrystalline nature, softening temperatures no longer correspond to glass transitions but are somewhere between the latter and the crystalline melting points of the polymers. Polyesters from Phthalic Acids. Polyesters were prepared from isophthaloyl chloride or terephthaloyl chloride and a number of bisphenols with differ-
INDUSTRIAL AND ENGINEERING CHEMISTRY
ent structures. Properties of these polyesters are described in Table I. The polymer from terephthaloyl chloride and bisphenol A ( T l ) is only soluble in high boiling solvents, shows a softening temperature of about 250' C. (Figure l ) , and has a marked tendency to crystallize. Although it is generally accepted in the field of glycol polyesters that insertion of mphenylene nuclei in polycondensates results in noncrystallizable polymers (7, 5) the bisphenol A polyester from isophthalic acid (11) can be obtained in semicrystalline state. The crystallizability of this polyester is reflected in its
THERMOPLASTIC POLYESTERS Table I.
Properties of Polyester Films (Continued)
Softening temperature can b e correlated with chemical structure, but the relationship is often complex
Polyesters with Repeating Unit
Softening Temp.,
R
Code
I
R'
O
c.
Solubility"
Intrinsic Viscosity, D1.1 Gram
El
CH~CCHI
-0-
200-2 20
A- G
1.1c
E2
CHaCH
-0-
112-130
A-F
0.86c
E3
C?HsCCzHs
-0-
130-140
A-H
0.90
E4
C2HsCCHa
-0-
160-1 75
A-G
0.75c
-0-
175-200
A-F
0.95c
-0-
160-270
A-G
1.3c
160-240
c, D
0.72b
I I
E5 E6
Kl
O - T C HI a
I I
CHICCHI
XI
I co I
M1
CHaCCH3
I
co I
(cryst.)
CHaCCHa
122-130
A-E
0.65b
CHz
170-205
c, D
0.92b
CHaCCHa
130-140
A-F
1.3*
170-200
A-D
1.0b
225-230
A-G
0.6h
1 ~
x2
CHz
M2
CzHsCC2Hs
CHz
x3
CHICCH~
CH3CCHa
s1
CHaCCHs
SO2
190-220
A-F
0.6b
c1
CH~CCHI
ClCCl
220-260
A-G
0 . 90b
I
I
I
I
!
I
I
I I
I
a 4 = methylene chloride; B = 1,2-dichloroethane; C = 1,2,2-trichloroethane; D = tetrachloroethane; E = dioxane; F = tetrahydrofurane, G = benzene; H = toluene. Measured in tetrachloroethane solution. Measured in 1,2-dichloroethane solution.
poor solubility in low boiling solvents such as methylene chloride and 1,Zdichloroethane. Simply by adjusting the film casting technique, films prepared from this polyester can be obtained in amorphous or semicrystalline condition. Figure 2 shows an x-ray diagram of unoriented film in the crystalline condition. The crystallization tendency of this polymer also explains why the films show widely different softening temperatures, depending upon the film casting technique, ranging from 135' to 250' C. (Figure 1). By slow evaporation of the solvent,
is observed when methyl groups in polymer I1 or T1 are replaced by larger substituents preventing close packing of the polymer chains. Introduction of bulkier aliphatic substituents such as an isopropyl instead of methyl, raises the softening point (compare I1 and 14, also I5 and 16). The effect is still more pronounced when introducing large and compact phenyl groups as in polymers 15, 16, and 17, which shoiv muck higher softening points. The effect of crystallizability on solubility properties can be shown Ppreparing copolyesters from mixtures of isophthaloyl and terephthaloyl chloride and bisphenol A. The solubility properties of this copolyester series over the whole composition range show that replacement of only 10 mole yo isophthaloyl chloride by terepthaloyl chloride results in solubility in meth)lene chloride and almost complete loss of crystallization tendency. O n the other hand, softening points and mechanical properties of amorphous films made of the copolyesters d o not seem strongly dependent upon copolymer composition. This observation is explained by the fact that softening temperatures correspond with glass transition temperatures which have been shown to be monotonic functions of the copolymer composition. Polyesters from Diacids with Two Phenylene Nuclei. A large number of polyesters have been prepared from different bisphenols and diacids containing two phenylene nuclei. The chernical repeating unit of this group of polymers is shown in Table I . R' symbols may be oxygen, methylene, carbonyl, sulfonyl, or a substituted methylene, the other R representing a substituted methylene group. Properties of this group of polyesters are given in Table I. Noteworthy is the high softening temperature of polyester E l which is amorphous and soluble in methylene chloride. Of interest in this connection is the isomeric polyester EM1 with structural formula:
I
CHa
opaque films are obtained in which spherulites can be observed by microscopic examination. The crystalline melting point as determined by observation of the disappearance of spherulites was 290' C. Table I shows the effect of chemical structure on softening points. Disturbing the symmetry of the central carbon atom in group R destroys crystallizability of the polyester (compare I1 and I 3 and others). The same effect
Softening temperature of this polymer is only 85' C. compared with 200' C. for the isomeric polyester E l . Considering that both polymers are amorphous, this large difference is surprising. This example again proves that the influence of chemical structure on softening points is rather complicated and not easily predictable. Probably some ill-defined characteristics such as general shape of the chemical repeat unit can have a pronounced influence VOL. 51, NO. 2
FEBRUARY 1959
149
in addition to symmetry factors, stiffness of chains, and attraction forces between chains. The difficulty of interpreting differences in physical behavior as a function of changes in chemical structure is still more apparent by comparing polymers K1 with X1 and M1 with X2. Polymers in which the substituted methylene linkage is found in the bisphenol residue (K1 and M1) are easily crystallizable, as shown by x-ray examination of films cast by slow evaporation from tetrachloroethane solutions. However, isomeric polyesters X1 and X2 in which substituted methylene is situated in the diacid residue are soluble in methylene chloride, show no tendency to crystallize, and have lower softening temperatures. Polyesters from Fumaric Acid. Polyesters derived from bisphenols and aliphatic diacids such as succinic acid are soluble in volatile solvents and form films with rather low softening temperatures (less than 100” C . ) . These low softening points can be explained by the flexibility of the polyester chains caused by an easy rotation between the relatively large number of successive aliphatic bonds. A stiffer polymer chain can be built up by synthesizing a polyester from an unsaturated aliphatic diacid, such as fumaric acid and bisphenols. Properties of these polyesters are given in Table I. Their high softening ternperature is noteworthy. Mechanical and Physical Properties. Mechanical properties of unoriented films made by solution casting are, of
Besides being soluble in chlorinated hydrocarbons, dioxane, tetrahydrofurane, and especially benzene or toluene, most of the polyesters are more or less swollen when contacted with organic solvents except aliphatic hydrocarbons and alcohols. O n prolonged boiling with ethanol, some degradation in molecular weight occurred. Resistance
Table II.
Table 111.
Mechanical Properties of Unoriented Films
Good mechanical properties are retained up to the softening temperatures. Tensile strength, kg./sq. mm. 6 9 Yield strength, kg./sq. mm. 5-7 Elongation at break, % 20-120 Modulus of elasticity, kg./sq. mm. 175-250 Water absorption, YG 0.2-0.5 (after 24-hours in HzO) Density, grams/cc. 1.15-1.25
Table IV.
course, dependent upon the chemical structure of the particular polyester. Furthermore, mechanical properties of crystallizable polyesters such as polymers 11, T1, K1, and M1 are strongly dependent upon the technique employed in casting the films. Mechanical properties of most of the films investigated are listed in Table 11. Good mechanical properties are retained up to the softening temperatures mentioned in Table I. By stretching the films in one or two directions mechanical properties can greatly be enhanced. Typical tensile strengths of stretched films are 15 to 20 kg. per sq. mm. with an elongation of 15 to 30%. An interesting property of the bisphenol polyester films is their exceptional high dimensional stability against changes in temperature or humidity. With unsupported, unstretched films of polyester E l at 150” C. no shrinkage was observed, while at 180’ and 200” C. shrinkage amounted to 1 and 3%, respectively. This property is understandable in view of the high second-order transition temperatures of the polyesters. Chemical Properties
Degradation of Polyesters by Boiling in Ethanol
Resistance to degradation was greater for double aromatic polyesters Poly-
Boiling Time, Polymer Hr. El 0
3 66
[r7 1
Polymer F1
0.82 0.72 0.60
carbonate from Bisphenol -4
1 .o 0.75 0.45
1.3 0.80 Insol.
Effect of Chemicals on Polyesters
Films showed good resistance to hot acid solutions
Time Medium NaOH 1N
Temp., OC. Reflux Reflux Reflux 25’ 25’
NaHCOa (10%) NHiOH (3.5%) NHaOH (25%) H2SOa 1N
J 50
Reflux Reflux 25’ 25’ 25’
Reflux
of
Exposure, Hr. 1
19 90
75 360 24 164 70 164 60
24
0.8 3.5 13.5
2.3
Loss in Weight and Properties, % El F1 (strong and clear) Destroyed (strong and clear) (strong but opaque) Unaffected 19 (brittle and opaque) Unaffected Unaffected 8 . 4 (strong but opaque) (strong and clear) Unaffected Destroyed Unaffected Destroyed Unaffected Unaffected
INDUSTRIAL AND ENGINEERING CHEMISTRY
... ... ... ...
... ...
to such degradation was greater for double aromatic polyesters than for polyesters prepared from fumaric acid (F1 Table 111). The doubly aromatic ester function seems to be generally more resistant to alcoholysis and hydrolysis than the aromatic-aliphatic ester function in polymer F1, or to a lesser extent than the carbonate function in polycarbonates prepared from bisphenol. The resistance of polyesters E l and F1 to alkaline, acid, and oxidizing media was checked by immersion of polymer films (110 microns thick) for different lengths of time at different temperatures. Polymer destruction was followed by measurement of weight loss and inspection of mechanical properties of the films after the test (Table IV). The films were badly attacked by concentrated solutions of ammonia even at room temperature. The resistance of the films to hot acid solutions is very good. Acknowledgment
The skillful assistance of U. L. Laridon, L. M. Dohmen, and L. G. Jeurissen is greatly appreciated. The author thanks his colleagues, especially R. Van Kerpel and J. Bisschops, for many helpful discussions and ,for measurements of physical and mechanical properties. He is also indebted to A. E. Van Dormael, director of the chemical research department, for his continued interest in this work. Literature Cited (1) Bjorksten, J., Toveny, H., Harker, B., Henning, J., “Polyesters and Their Applications,” pp. 199-224, Reinhold, New York, 1956. (2) Bottenbruch, L., Schnell, H. (to Farbenfabriken Bayer A. G.), Ger. Patent 959,497 (March 7, 1957). (3) Caldwell, J. R. (to Eastman Kodak Co.), U. S. Patent 2,756,221 (July 24, 1956). (4) Drewitt, J. G. N., Lincoln, J. (to British Celanese, Ltd.), Brit. Patent 621,102 (April 4, 1949). (5) Hill, R., “Fibers from Synthetic Polymers,” vol. VI, Chap. 6, Elsevier, New York, 1953. (6) Mark, H., Whitby, C. S., “Collected Papers of W. H. Carothers on Polymeric Substances,” Interscience, New York, 1940. (7) Schnell, H., Angew. Chem. 68, 633 (1956); Brit. Patent 772,627 (April 7, 1957) (to Farbenfabriken Bayer A. G.). (8) Schweitzer, G. E. (to E. I. du Pont de Nemours & Co.), French Patent 1,109,902 (Feb. 3, 1956). (9) Wagner, F. C. (to E. I. du Pont de Nemours & Co ). U. S. Patent 2,035,578 (April 1, 1933). . (10) Wallscrove, E. R., Reeder, F. (to Courtaulds. Ltd.), ., Brit. Patent 636,429 (April 26, 1950).
RFCEIVED for review March 24, 1958 ACCEPTEDAugust 21, 1958 Division of Industrial and Engineering Chemistry, 133rd Meeting, ACS, San Francisco, Calif., April 1958.
