or longer. This upward drift is greater with 4-substitution than kvith 3-substitution. Since a minimum amount of drift in either direction is very desirable, 3-isopropyl catechol is believed to have a very desirable combination of properties. An excellent combination of properties was also obtained with 3-n-propyl catechol. Branching on the @-carbon,as shown by the results with 3-isobutyl catechol, is less effective for prevention of downward drift than branching on the a-carbon. Compounds having oxygenated side chains are, in general. much less effective than those containing hydrocarbon side chains. This may be seen by comparing the properties of 4propionyl catechol with 4-n-propyl catechol and 4-n-butyryl catechol with 4-n-butyl catechol. Unsaturation in the side chain also appears to reduce the effectiveness of the compounds as inhibitors (note the weak activity of 3,6-diallyl catechol). The tables also show the results obtained with a variety of disubstituted catechols and of quinones and hydroquinones. In general, p-benzoquinone and hydroquinone are very effective inhibitors and chemical modification of the structure tends to reduce the effectiveness of the parent compound. Hydroquinone derivatives are characterized by their rather strong upward drifts. The results of Table I were obtained Lvith 1.5% benzoyl peroxide, which tends to minimize the up\vard drift. LYhen similar values are obtained with lower amounts of catalyst, the upward drift is considerably greater. Quinones are more effective than the corresponding hydroquinones from which they might be obtained by oxidation. Quinones normally show a downward drift. The last section of Table I s h o w the results obtained with a variety of miscellaneous compounds. Derivatives of phenol are normally rather weak inhibitors, as is shown by the results with Ionol. Derivatives of resorcinol and pyrogallol are also rather ineffective inhibitors.
The last section of Table I1 shows the results obtained with a variety of miscellaneous compounds using polyester B. The most effective compound in this group was 4,4-dihydroxybiphenyl. Most of the other compounds showed very little activity and were not studied further.
Literature Cited
(1) Abrams, I. M., et al. (to Diamond Alkali Co.), U. S. Patent 3,028,361 (April 3, 1962). (2) Anderson, T. F. (to Libbv-Owens-Ford Glass Co.). Zbid., 2,559,837, 2,559,838' (July io, 1951); 2,607,756 (Xug. 19; 1952) ; 2,610,168 (Sept. 9, 1952); 2,632,751,2,632,753 (March 24, 1953); 2,635,089 (April 14, 1953); 2,679,493 (May 25, 1954). (3) Andrews, R. C., Peterson, N. G. (to Glidden Co.), Zbid., 2,777,829 (Jan. 15, 1957). (4) Bjorksten, J., "Polyesters and Their Applications," pp. 288-95, 418-21, Reinhold, New York, 1956. (5) Brooks. M. C.. Praper. I. A. (to United States Rubber Co.). U. S. Paient 3;028,366(April 3, i962). (6) Cass, 1". E., Burnett, R. E., Ind. Eng.Chem. 46, 1619 (1954). (7) Ellis, C. (to Ellis-Foster Co.), U. S. Patent 2,255,313 (Sept. 9,
.,
\-,
, I
~~~~~~
1041)
- '' - 1 .
(8) Fraser, G. L. (to Monsanto Chemical Co.), Ibid., 2,516,309 (July 25, 1950). (9) Gerhart, H. L. (to Pittsburgh Plate Glass Co.), Ibid.. 2,493,343 (Jan. 3. 1950). ---~, (10) Gerhart, H. L., Mod. Plastics 25, NO. 6, 86 (1947). Meyer, I:. \V., Klein, J. G. (to Glidden Co.), U. S. Patent (11) ' 2,846,411 (Xug. 5, 1958). (12) Noller, D. G., Mod. Plastics 39, No. 12, 147 (August 1962). (13) Parker. 15. E. (to Pittsburgh Plate Glass Co.). U. S. Patents ' 2,570,269'(0ct. 9,'1951) ; 2,533,787 (April 12, 1952); 2,627,510 (Frh. 3. 1~ 9 5 3-I )' : 2.643.985 (June 30. 1953): 2.646.416 (Julv 21. ~ 1953) ; 2,664,413 (Dec. 29; 19j3) ; '2,676,9477(Ap'ril2?, 1954) ; 2,698,312 (Dec. 28, 1954) ; 2,740,765 (April 3, 1956) ; 2,829,120 (kpril 1, 1958); 2,844,559 (July 22, 1958). \-----
- I
\----
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- > - - - I - - -
RECEIVED for review November 19, 1962 ACCEPTEDMarch 11, 1963
ENDENE AND CENTRENE POLYESTERS A NT0 N I SZ A Y NA
, Research Center, United States Rubber Go.,
Wayne, A'. J .
Unsaturated polyesters having the double bonds located toward the ends of the chain have physical properties superior to those of the isomers in which the double bonds are located toward the center of the chain. Three pairs of such isomers were synthesized, cured, and tested. HE importance of placing double bonds in polymeric Tn~aterials at the ends of the chain has been recognized theoretically for some time ( 3 ) , but no experimental proof has been given. The present work shows that in the case of polyesters the materials with double bonds located toward the ends of the chain (Endenes) exhibit, upon curing, physical properties substantially improved over those of the isomers having the double bonds in the center (Centrenes). Three pairs of isomeric polyesters have been prepared and tested; in all cases the Endene structures had superior physical properties. In one set (Table I) the Endene A isomer was prepared by first esterifying 2 moles of succinic anhydride with 3 moles of diethylene glycol and then adding to the saturated spine unsaturated terminals in the form of 2 moles of maleic anhydride. The corresponding Centrene B isomer was prepared by first
reacting maleic anhydride with diethylene glycol and then adding the succinic anhydride to that unsaturated spine, forming saturated terminals. I n the above syntheses there is little likelihood of skeletal isomerization (change of relative position of building blocks in the chain), since in the formation of the spine only one kind of acid and glycol is used and the terminal acid anhydride is added to the spine under very mild conditions (120' to 130' C. for 30 minutes) without water formation. No catalysts are used in the procedure. I n the case of both Endene A and Centrene B, use of identical components and proportions as well as identical esterification procedures will result in essentially identical molecular weight distributions ( Z ) , thus eliminating this latter factor from affecting the differentiation of properties of the two isomeric forms. Therefore, we ascribe the differences in physVOL. 2
NO. 2
JUNE 1 9 6 3
105
Table I.
Preparation of Isomeric Polyesters
Structural Isomers Charge I (spine) Maleic anhydride, moles Succinic anhydride, moles Adipic acid, moles Diethylene glycol, moles
Ethylene glycol, moles p-tert-Butyl catechol, €!.
Benzene, ml. Charge I reacted Hours
c.
Charge 11 (terminals) Maleic anhydride, moles Succinic anhydride, moles .4dipic acid, moles Charge I and I1 reacted" Min.
c.
Water of esterification theory, g. .4ctual, ml. Wt. of finished resin, g.
Theory Actual Acid number Theory Actual Av. structure (symbols)
Diethylene Glycol Maleate-Succinate Endene Centrene A B
... 2.0 ...
Ethylene Glycol Maleate-Adifate Endene Centrene C D
2.0
,
2.0
...
...
,..
...
3.0
,.
4.0
...
3.0
...
5 .O
5.0 0.5 15 8
157-205
2.0
...
0.5 15
0.8 30
8 154-207
12 133-202
,
0.8
30 6 132-203
2.0
,.
2.0
..
, . .
,
...
...
30 120-130
31 120-135
120-129
11 hr. 138-206
36 36
36 35
144 143.5
144 134.5
679 681.5
679 679.5
946.5 348
946.5 957
165.2 174.0
165.2 175.6
119
119
A0.0 AOH
MOA0 MOA
4.0
, . .
'/2
hr.
122.7
52.3
A0M.A 0 A0.0.
BOMOA 0 m0A.W
After reaction mixlure was blown with nitrogen 30 minutes.
a1 720-130"
C./or
ical properties between Endene and Centrene types, upon curing, to the difference in the position of double bonds, all other factors being of secondary importance. The geometrical isomerization of maleate to fumarate esters occurs without catalysts a t higher temperatures. The fumarate polyesters exhibit better physical properties than the corresponding maleates. This isomerization occurs to some extent in Centrenes B, D, and F which are prepared by esterification of maleic anhydride with glycols for several hours at temperatures u p to 205' C . ; but in Endenes A, C, and E the maleic anhydride is added to the earlier prepared saturated spine and is reacted only for 30 minutes a t 120' to 130' for Endenes A and C and 120' to 144' for Endene E. These temperatures are too low to cause noticeable isomerization in the absence of catalysts. The fact that Centrenes possess poorer physical properties than Endenes emphasizes the importance and advantage of the position of double bonds a t the end of the chain. The other examples of Endene-Centrene pairs are given in Tables I (second pair) and 111; one with a longer average chain and the other with a very short chain. Many other polyester compositions have been studied (4, as early as 1953. In addition to Endene and Centrene isomers, the intermediate random structures were made by the current 106
l & E C P R O D U C T RESEARCH A N D D E V E L O P M E N T
commercial practice of charging and esterifying all components together. The random polyesters have properties intermediate between the extremes of Endene and Centrene structures of the same composition. An interpretation in terms of Endene us. Centrene structure can be given to the polyesters described by Carlston et al. (7). These authors found that a polyester of isophthalic acid and maleic anhydride with propylene glycol has improved physical properties when the isophthalic acid is first esterified with the glycol, maleic anhydride is added, and the esterification is completed. This procedure is conducive to a product Ivith Endene structure. O n the other hand, in the one-step operation, in which all ingredients are charged a t once, the loivmelting maleic anhydride reacts first, forming the spine, and the high-melting isophthalic acid, with its low solubility, reacts later as the temperature of the mix goes up, and so adds toward the terminals of the chain; thus, a polyester of the Centrene type is formed, which upon curing has physical properties inferior to those of the two-step Endene. Charging the reagents in a particular proper sequence to produce the Endene structure, gives improved resins and is of commercial importance. Using the symbols suggested below, one can visualize the idealized structures of the polyesters.
Idealized Structure
See Table I Composition llfoles Maleic 2 Succinic 2 A0MOM.A Diethylene glycol 3 (Endene A) Maleic 2 Adipic 4 AOMO.OMOMOA Ethylene glycol
5
(Endene C ) See Table I11
Maleic 2 Triethylene glycol 1 or AxA Ethylene glycol 3 (Endene E) A Unsaturated dibasic acid moiety Saturated dibasic acid moiety 0 Glycol moiety x Triethylene glycol moiety
MOAOAO.
(Centrene B) MOMOAOAO.0. .OAOAOMOBOM
or Or
.OAOHO.OAO.
(Centrene D )
OAOAO
(Centrene F)
Comparison of physical properties shows the superiority of Endene structures over Centrenes in spite of imperfections of synthesis and deviations from idealized structures. These are due to molecular distribution, and t o eventual isomerization because of ester interchange and alcoholysis which might have occurred to some degree even though catalysts were absent. Experimental
The esterifications were performed in a flask with a stirrer, thermometer, nitrogen inlet, and a 10-inch packed column headed by a Dean and Stark trap and reflux condenser, under a blanket of nitrogen and in the absence of catalysts. A small amount of a polymerization inhibitor and a few milliliters of benzene were added. T h e benzene carried off water vapors and regulated the boiling temperature in the flask from about 140' to 205' C. Small amounts of benzene were removed or added to regulate the temperature a t the desired level. T h e esterification lasted several hours, during which practically the theoretical amount of water of esterification had
Table II.
Properties of Cured Resins
20% Styrene
+
1 hr. at 110' C.) Resins A and B, Cured with 30% Styrene 3070 Diallyl Phthalate
(Curing with 4% Luperco ATC' and the monomer, 16 hr. at 5 5 ' C.
Structural isomer Endene A Centrene B Endene A Tensile, p.s.i. 870 730 2,200 Elongation, yo 110 41 69 Hardness, Rockwell R Too soft Too soft 52 Elastic modulus at 25" C. 2750(?) 7110 21,550 Impact, notched Izod, ft. lb./inch 3.9 0.94 2.1
Centrene B 1,350 47 35 16,500
Endene A 5,680 19 110 180,500
0.93
8
0.34
Endene C 3,200 63 86 70,900 3.2
Centrene B 2,790 10 116 199,000
0.54
Resins C and D , Curea with 40% Styrene
Centrene D 435 76
