I
E. F. CARLSTON, G. B. JOHNSON, F. G. LUM, D. G. HUGGINS, and
K, T.
PARK
California Research Corp., Richmond, Calif.
Isophthalic Acid in Unsaturated Polyesters The improved properties of these polyesters should make them of interest to manufacturers of reinforced plastics
ISOPHTHALK
and terephthalic acids as modifiers of unsaturated polyesters received little attention until the Oronite Chemical Co. started commercial production from petroleum raw materials. Previous \vork ( 2 ) on condensation polymers showed that isophthalic acid is capable of forming higher molecular \\eight polymers than phthalic anhydride. In the work reported here, isophthalic acid-modified unsaturated polyesters were investigated.
Figure 1. lsophthalic acid reacts more slowly than phthalic anhydride in a large excess of propylene glycol
Comparison with Phthalic Anhydride-Modifled Polyesters
The unsaturated polyesters were made with propylene glycol (1,2-propanedioI), and all formulations contained a 5% excess of glycol. A three-necked, roundbottomed. ?-liter flask \vas used as a kettle, fitted with a stirrcr, inert gas inlet. thermometer. reflux condenser, and receiver for collecting volatile products of the reaction. The reflux condenser \vas fitted \vith a thermometer to measure the temperature of the overhead vapors and with a steam jacket. T h e reflux condenser separated water of esterification from the refluxing glycol and returned the glycol to the kettle with a minimum loss. Polyesters containing appreciable amounts of isophrhalic acid are prepared by techniques someLvhat different from those normally used for phthalic anhydride polyesters. -4 more efficient reflux condenser is needed because more free. reflusing glycol is present during the major part of the reaction. T\vice as much Lvater is formed during esterification; and if the condenser is inefficient, excessive amounts of glycol \vi11 be lost with this larger volume of steam. Boiling water instead of steam in the jacket of the reflux condenser has been used satisfactorily in laboratory and pilot-scale operations. Experimental Procedure.
A.
1 mole PA
8. C.
1 male IP 1 mole PA 1 mole MA 1 male IP f 1 mole MA
D.
+ 2.1 moles propylene glycol + 2.1 moles propylene glycol + 2.1 moles propylene glycol + 2.1 moles propylene glycol
+
Maximum temperature 21 5'
Table I.
C.
Physical Properties of Unsaturated Polyesters
Softening temperatures of isophthalic polyesters are higher than those of phthalic anhydride polyesters
-kid
KO.,M g .
Compn. Mole Ratio
KOH/G.
of Acids
Resin
Softening Temp..
c.
Styrene Content, % 40 50 Viscosity, Cp. at 25' C.
___ 30 -
ti0
One-Step Process PA: M A
1:2 1: 1 2: 1
33 31 32
30 30 32
3,100 2,500 1,800
275 300 225
65 65 50
14 18 14
21 24 17
42
14,800 12,300 9,800
1070 980 760
225 140 125
41 41 22
340 290
85 65
22 15
1520 1630 1290 1630 1630 1630 1070
250 275 200 300 237 250 237
57 65 50 50 45 50 14
1P:MA
1:2 1: 1 2: 1
51 62
Two-step Process PA:MA
1:1 2: 1
18 25
30
2,700
35
2,700
16 14 19 14 14 14 19
60
27,000 30,000
1P:MA
1: 1 2: 1 2.5:1 3: 1 3.5:l 4:1 5: 1
70 85 95 95 100 95
VOL. 51, NO. 3
MARCH 1959
253
Two methods were used to prepare isophthalic unsaturated polyesters, and phthalic anhydride-modified polyesters. In one, all ingredients were charged at the start of the reaction, and esterification was completed in one step. I n the other, the isophthalic acid was esterified with all the glycol to form an essentially neutral ester. The maleic anhydride was then charged, and the reaction carried to completion. T h e two-step procedure has: in general, produced better isophthalic polyesters than the one-step process. Esterification was conducted under a sluw stream uf oxygen-free nitrogen and with vigorous glycol reflux. T h e vapor temperature at the top of the column was maintained at a maximum of 104' C. In the first stage of the twostep procedure, the reaction was taken to a maximum bath temperature of 232' C. In the single-step procedure. the resin reactants were not heated above 251' C. because of the greater sensitivity of maleic anhydride to heat. Commercial chemicals were used. including isophthalic acid supplied by the Oronite Chemical Co. The rates of esterification of isophthalic acid and phthalic anhydride with propylene glycol \cere measured under two sets of conditions. First. 1 mole (166 grams) of isophthalic acid was made to react \vith 2.1 moles (160 grams) of propylene glycol; and 1 mole (148 grams) of phthalic anhydride with 2.1 moles of propylene glycol. Five hundred-milliliter, round- bottomed? threenecked flasks were used, fitted as described. 'The samples taken at halfhour intervals were dissolved in ethylene dichloride and titrated to the end point of bromothymol blue indicator, using 0 . 1 s potassium hydroxide in ethanol. Acidity was expressed in terms of acid number-number of milligrams of potassium hydroxide required to neutralize 1 gram of sample. T h e second set of conditions consisted of conducting the esterification in the presence of 1 mole of maleic anhydride (98 grams) in addition to the amounts of materials described above. T h e softening temperatures of the unsaturated polyesters were measured by placing a sample of the powdered resin on a hot-stage microscope and observing when the resin started to flokv under light pressure of a spatula applied by hand. Melt viscosity of the unsaturated polyesters was measured in a few instances with a vibrating reed instrument (UltraViscoson, Bendix Corp.). The crushed resins passing through a 32-mesh screen were dissolved in styrene a t room temperature and not while hot: as is customary in commercial practice. .411 solutions contained 0.05Yc f - t f r t butylcatechol as inhibitor for room tem-
254
Table II.
Physical Properties of Cured, Unfilled Polyester-Styrene Copolymers
lsophthalic polyesters have higher flexural strength, better flexibility, and greater impact strength than phthalic anhydride polyesters
Heat
Styrene
Distortion
C'oinpii. Mole
('ontent,,
Ratio of Arid.;
c7 I C
Temp., C."
I~lexural Strength, P.S.I. X 10-3h
M o d u l u s of Elasticity P.S.I. X 10-3c
Iiripwt
Strength. E'r,.-Lh.]' ii1.d
One-Step Process PA: M A
1:2
30 40 50 60
99 120 120 109
13 15 15 13
590 560 540 510
2.5 1.9 1.8 1.9
1:1
30 40 50 60
82 94 94 94
14 12 12 11
630 590 560 520
2.6 2.3 2.6 2.6
2: 1
30 40
64 69 70 75
14 12 14 13
610 600 570 530
1.7 2.5 2.2 2.6
12 13 15 14
550 540 510 510
2.4 2.3 2.2 2.4
50 60 IP: M A 1:2
30 40 60
111 129 130 120
1: 1
30 40 50 60
96 102 102 99
15 17 16 16
600 580 550 530
2.2 2.3 2.5 2.3
2: 1
30 40 50 60
70 74 79 80
14 17 18 17
570 570 560 540
2.2 3.6 3.6 3.5
105 114 108 103
16 13 14 16
560 560 530 500
2.4 2:2 2.2 2.2
60
69 76 79 81
15 12 12 14
600 580 550 530
1:2 l:o 1.8 1.6
30 40 50 60
122 125 124 116
18 16 18 17
560 490 490 480
3.0 3.3
30 40
16 19 18 16
550
60
89 96 96 96
30 40 50 60
77 83 85 86
16 17 17 18
530
2.9 3.6 3.8 4.6
30 40 50 60
74 79 83
18 16 17 17
580 550 540 550
2.6 2.7 2.7 4.5
60
71 76 79 82
15 16 18 15
580 530 550 530
2.0 2.7 3.3 3.2
4: 1
30 40 50 60
71 77 76 80
14 18 17 15
570 530 530 510
1.7 3.3 3.4 3.2
5:1
30 40
68 71 75 76
15 16 15 12
560 550 560 540
2.2 2.4 1.4 1.8
50
Two-step Process PA: MA
1:1
30 40
50 60 2: 1
30 40
50 IP: M A 1: I
2: 1
50 2.5:l
3: 1
3.5:l
30 40 50
50 60
ASTM D 648-45T, filler stress 264 p.s i Unnotched h o d .
(8d).
INDUSTRIAL AND ENGINEERING CHEMISTRY
81
,
540 520 500 580 550
550
ASTM D iSO-10T (8h).
3.0 3.0 2.7 3.6 3.7 3.4
ASTM L) 790-49T
UNSATURATED POLYESTERS
IO
0
2
4
6
8
101214
TIME AT 215'C-HOURS
Figure 2. Melt viscosities of unsaturated polyesters as measured b y the Ultra-Viscoson viscometer (Bendix Corp.) The isophathalic-modified polyester, A, i s much more viscous than the phthalic onhydridemodified polyester, B
perature stability. Gardner-Holdt viscosity standards \vere used. Polyester-styrene solutions Lvere cured xvith a mixture of 0.5c0benzob-l peroxide (1% Luperco ATC) and 0.3Yc methyl ethyl ketone peroxide (0.5% Lupersol DDM), \vith 0.01% cobalt (as cobalt naphthenate) for a promoter. The solutions were cured in a circulating air oven held at 38' C. for 4 hours, followed by a gradual increase in the temperature of the oven over 3 more hours to 135' C. and held a t that temperature for 1 hour to complete the cure. Borosilicate glass sheet molds with 0.25-inch stainless steel separators Xvere used with a mold release compound. Vacuum \vas used to deaerate the solutions prior to filling the molds. The cured 0.25-inch sheets of resin were cut into test strips 0.5 inch wide and 5 inches long \vith a high-speed abrasive wheel and Lvith water as a cooling lubricant. This procedure gave edges free of nicks and cracks. A five-bar Tinius-Olsen heat distortion apparatus was used ( 7 ) . Samples were placed in the machine with the load on the 0.25-inch side. Modulus of rupture was measured in an Instron tensile testing instrument, in accordance Ivith the requirements of .i\Slhl Method D 790--49'1' ( 7 ) . A 4inch span in an Instron flexural jig was used. Samples were placed in the machine \vith the load on the 0.5-inch side. -4n Izod-type impact testing instrument (Baldwin-Southwark Serial 120) \vas used. Samples \vere placed in the instrumcnr without notch and struck on the 0.23-inch side.
Discussion of Results. Isophthalic acid reacts more slowly than phthalic anhydride in a large excess of propylene glycol (Figure 1). However. in the presence of maleic anhydride, isophthalic acid is rapidly esterified, and lower acid numbers are obtained than with phthalic anhydride. Unsaturated polyesters made from isophthalic acid have much higher melt viscosity than comparable phthalic anhydride (Figure 2). Table I shows that the softening temperatures of isophthalic polyesters are higher than those of phthalic anhydride polyesters, and become higher as the proportion of isophthalic acid in the polyester i s , increased. Unsaturated polyesters made from isophthalic acid have much higher viscosities in styrene solution than comparable phthalic anhydride polyesters. The heat distortion temperatures of the isophthalic resins are higher than those of the comparable phthalic anhydride resins. isophthalic polyesters have higher flexural strengths and better flexibility than comparable phthalic anhydride polyesters, and the impact strength of the isophthalic polyesters is greater (Table 11). Exotherm curves (Figure 3) for an isophthalic acid polyester and a phthalic anhydride polyester having a mole ratio of 1 to 1 IP or PA to maleic anhydride show that these polyesters cure a t the same rate and reach essentially the same peak temperature during cure. .4s one would expect. the same catalyst system produced a lower cure with a lower peak temperature for polyesters containing less maleic anhydride. Isophthalic polyesters made by the two-step procedure have higher softening temperatures. the solutions in styrene are much more viscous. and the cured polyester-styrene test bars have higher heat distortion temperatures and improved impact strengths, compared with the same polyesters made by charging all ingredients to the kettle a t once. With the phthalic anhydride polyesters.
Table 111.
t
5 0 6 SAUPLE CATALYST = 0 030 % CO 0 8 % MEKP
0 ~ r n TEUP z5.c
l50l
u J J 3 a
c
5
--
130-
a 2
w +
L
POLYESTER
IP/MA
~
______
PA/MA POLYESTER
loLALL> 2 2
4 4
d d
1 -
10 10
d d
12 12
14 14
IO IO
Id Id
TIME, MINUTES
Figure 3. The two types of polyesters cure a t the same rate and reach the same peak temperature during cure the two-step procedure is less effective in increasing the softening temperature and viscosity; heat distortion properties of the cured polyester-styrene resins, however. are improved considerably.
Glass-Filled Laminates Experimental Procedure. Using the two-step method, polyester resins containing isophthalic acid, maleic anhydride. and propylene glycol were prepared. Glass-filled laminates were made with these rmins using both 181 cloth with an organic chrome finish and 2-ounce matting as the reinforcing material. Benzoyl peroxide ( 2 7 , Luperco .4TC) was the catalyst. The laminates were cured in a press a t 104" C. and 15 p.s.i. for 1 hour and postcured outside the press for 1 hour at 149' C. One-eighth-inch stops controlled the thickness of the panels. Oneinch strips were cut from the laminate. and the flexural strength and modulus of elasticity were determined on an Instron tensile tester ( 7 ) .
Physical Properties of Glass Fiber-Reinforced Laminates of lsophthalic Acid Polyesters Containing 40y0Styrene Flexural strength increases with increase in isophthalic acid
Composition of Polyester Mole Ratio,
IP: M.i 4: 1 3: 1 2: 1 1.5:l 1.1 0.5:1 3: 1
2: 1 1: 1 a
Glass Clotha, Plies
14 14 14 14 14 14
... ... ...
Glass Mat? Plies
... ... ... ...
...
... 1 1 1
181 cloth, organic. chrome finish.
Glass Content,
5% 70.1 70.9 69.6 71.6 68.5 70.4
... ...
...
Flexural Strength, P.S.I. x 10-3
Initial Modulus in I'lexure,
P.S.I. x 10-6
68
3.7
85 79 72 75 66 27 24 22
3.8 3.5
3.7 3.4 3.0 1.2 1.2 1.0
Barcol Hardness
60 69 67 70 72 71
_"-ounce mat.
VOL. 51, NO. 3
MARCH 1959
255
Discussion of Results. Tables I11 and IV show the effects of increasing the isophthalic content and increasing the styrene content on the properties of the laminates. T h e flexural strength of isophthalic polyester glass-filled laminates increases as the amount of isophthalic acid in the polyester increases and the maximum flexural strength is obtained at the 3 to 1 isophthalic-maleic mole ratio. These data were obtained lvith polyester solutions containing 407c styrene. T h e properties of the laminates were not appreciably affected by changes in styrene content from 30 to 60';; (Table IV). .All these laminate data \\-ere obtained with glass fiber having an organic chrome finish. Table 1- shows the effect of different finishes on the glass cloth. A 2 to 1 isophthalic-maleic polyester solution containing 40yc styrene by Lveight was used to prepare 14-ply laminates from glass fabrics of Lveave 181 having various finishes. Flexural strength \vas measured before and after the panel \vas immersed in boiling \Yarer for 48 hours. \\Yth this particular polyester? the organic chrome-finished cloth gave the highest flexural strength before being subjected to boiling water, but the silane-treated cloth gave a laminate Ivith the greatest resistance to boiling ivater. \\'hen a polyester-glass fiber laminate is stressed in flexure. failure shoivs u p as a gradual tearing of the laminate accompanied by delamination. Apparently, the degree and speed of delaniina-
Table IV.
have few irregularities in the stressstrain curve before maximum load. TVhen rhe ratio of isophthalic acidmaleic in the polyester is increased to 3 to 1. these irregularities decrease in number and the stress-strain curve approaches a smooth, straight line to maximum load. Conclusions
L
0' 0
01
03
0 2
0 5
0 4
DEFLECTION, INCHES
Figure 4. Laminates made with isophthalic acid polyesters have few irregularities in the stress-strain curve before maximum load
tion are related to the ability of the polyester to \vet the glass fibers during lamination and to adhcrc to the reinforcement. T h e delamination during stress appears in a stress-strain diagram as irregularities in the curve as the load approaches the point of maximum strcss. Figure 4 slioivs that laminates made with isophthalic acid polyesters
Physical Properties of lsophthalic Acid Polyester-Glass Fiber Laminates W e r e Not Appreciably Affected by Styrene Concentration
c o m p n . of
Polyester Mole Ratio, 1P:RIA 1.5:l
3.5:l
Styrene ('ontent,
Glass
C'loth."
70
Plie-:
30 40 50 60
14 14
Flexural
Flexure, Streiigth, P.S.I. x IO-" P.S.I. X IO-." 71 72 75 68
14 14 12 12 12 12
30 40 50 60
Initial Slodulus i n
74 73 68 73
Barcol Hardness
3.1 3.7 3.5 3.3
71 70 68 61
2.9 3.0 2.8 2.9
60 64 63 62
'* 181 cloth, organic chrome finish. Table V.
Effect of Glass Cloth Finish on Flexural Strength of lsophthalic Acid Polyester-Glass Fiber Laminates" Retention
P.S.I.
Glass Cloth Finish Organic chrome Y-1100 NOL-24 Vinyl trichlorosilane Thalco special Organic chrome a
Compn. of Polyester Mole Ratio 1P:MA P.\:hI.4
2: 1 2: 1 2: 1 2: 1 2: 1
...
~t~~~~~~
Content,
7c
Iiiitial
... ... ...
40 40 40 40 40
1:1
30
79 73 71 69 47 58
... ...
14 plies, 181 cloth.
256
INDUSTRIAL AND ENGINEERING CHEMISTRY
x lo-" __
After hoiliiig 48 liours 42 42 41
57 25 17
Acknowledgment
'I'he authors express appreciation 10 Joseph Philipson for assistance and encouragement in obtaining portions of the data and in carrying out these investiqations and 10 Oronite Chemical Cb..\vhich supplied commercial isophthalic acid for this investigation. Literature Cited
The silane-treated cloth had greatest resistance to boiling w a t e r
Flexural Streiigth,
L-nsaturated polyesters made Iron1 isophthalic acid. ivhen cured \\.it11 styrene. are more elastic and have superior flexural strength. impact resistance. and heat distortion properties, compared to similar resins made from phthalic anhydride. Isophthalic unsaturated polyesters can react to higher viscosity than phthalic anhydride resins. which means that more sty-enr may be used to obtain a standard \-iscosity. .L\ t~vo-step method of esterif>-ing unsaturated polysters, compared Xvith the one-step process normally used. results in cured resins that have significantly higher hrat distortion temperatures \viih both phthalic anhydride and isophthalic acid. Consider.abl!- greater \iscositirs are obtained i v i t h isoplitliaiic poi>-rsters by the nvo-step method than \vith cornparable phthalic anhvdride polyesters. .ippreciabl>- more styrene can lie used Lvith isophthalic acid-modified unsaiurated polyesters than is conventionall!. used with phthalic anhydride-modified resins; u p to .50% styrene has no appreciable effect on the properties of the cured resin. In laminate structures isophthalic acid polyesters demonstrate superior adhesion to glass fiber reinforcement. ivith the adhesion increasing as the isophthalic acid-maleic anhydride mole ratio is increased. This excellent adhesion is demonstrated by the resistance of isophthalic polyester-glass fiber laminates to deterioration in boiling- cvater.
of Flexural
Strellgtil
after Roiling 45 Hours,
i';
53 58 58 83 53 29
(1 ) 4 m . Soc. 'Testing Materials. Philadelphia, ".4S'l'M Standards on Plastics," 1955. ( 2 ) Lum, F. G., Carlston, E. F.. I s n . ENG.CHEM. 44, 1595-600 (19521.
RECEIVED for review April 7 . 1958 .ACCEPTED January 2 , 1959 Division of Paint, Plastics, and Printing
Ink Chemistry, New York, N.Y.. September 1954 (in part), and Division of Petroleum Chemistry, Symposium on Kecent Developments in Chemicals from Prtroleum, 133rd Meeting, ACS, San Francisco, Calif., April 1958.
