E. F. CARLSTON and F. G. LUM California Research Corp., Richmond, Culif.
rn-Xylylenediamine Polyamide Resins A new diamine shows promise for producing superpolyamides for use in fibers, films, and molding materials
THE
polymer of isophthalic acid and hexamethylenediamine ( 75) is amorphous and has relatively low melting and heat distortion temperatures. T h e present work was undertaken to determine the properties of polymers of mxylylenediamine and various dibasic acids. T h e polymer of m-xylylenediamine and adipic acid shows the effects caused by reversal of the position of the carbonyl groups relative to the amide nitrogen, compared to the polymer of isophthalic acid and hexamethylenediamine previously described. A literature search discloses no references to polymers of m-xylylene$iamine, although p-xylylenediamine polymers have been reported (3,5-7,9, 74. 76). Experimental The m-xylylenediamine used in this investigation was prepared from 99+% pure isophthalic acid by conversion to the dinitrile, followed by hydrogenation to the diamine. T h e crude diamine was purified by vacuum distillation. All of the dibasic acids used were also of 99+% purity. The m-xylylenediamine dibasic acid salts were prepared according to the method of Carothers (4). 4 typical salt is prepared : Adipic acid, 146 grams (1 mole), was added to a solution of 136 grams (1 mole) of m-xylylenediamine in 282 grams of water to form a hot (from heat of neutralization), concentrated solution of the salt. Part of the salt crystallized as the solution cooled. To complete the precipitation of the salt, 1130 ml. of isopropanol was added. After filtering the salt was dried in a vacuum oven a t 60' to 80' C. The yield of salt was approximately 95%.
removed by distillation. A Dow Corning Silicone 710 bath was used for heating, and the following schedule was used : The bath temperature was quickly raised to 180' to 190' C., then slowly (1 to 1.5 hours) to 260' C. The polymer was held a t 260' C. for 1 to 2 hours at atmcspheric pressure before applying vacuum (1 to 5 mm.) for 0.5 to 1 hour to complete the polymerization. By careful heating, especially from 180' to 260' C., the diamine loss was held to 0.1 to 0.3 mole yo. Melting points of the polymers were measured according to the method of Edgar and Ellery (70). The melting point is defined as the temperature a t which the polymer collapses under a load rather than the temperature a t which all equilibrium crystallinity disappears.
Results m-Xylylenediamine reacts with dibasic acids rapidly to form high molecular weight polyamide resins. It has the characteristic high reactivity of aliphatic diamines which are considerably more reactive than the true aromatic diamines (77, 77). Table I shows the melting points and physical appearance of the annealed m-xylylenediamine polymers of several dibasic acids. No data are presented for polymers from dibasic acids with less than six carbons because they either decompose or form low polymers through imide formation. T h e data show that m-xylylenediamine forms crystalline polymers with the even number aliphatic acids. These crystalline polymers form a higher melting series than the amorphous polymers of
280
2 6C
6
24 C
< z E 22c 0
z
I = -J W
200
2 I80
,
I so
A typical polymerization procedure is given:
,
I
H E X A M E T H Y L E N E D l A M I NE A M-XYLYLENLDIAMINE 0 P E N T A M E T H Y L E N E DIAMINE
I40 Excess adipic acid (0.75 mole 70)was added as a stabilizer, and the salt was polymerized in a glass reactor a t atniospheric pressure under a nitrogen atmosphere. The water of reaction was
5
6
7
8
CARBON ATOMS
9
10
II
ti?
13
IN DIBASIC ACID
Figure 1. Melting points of m-xylylene-, hexamethylene-, and pentamethylenediamine polyamide resins VOL. 49, NO. 8
AUGUST 1957
1239
Table I. Melting Points of Polyamides of m-Xylylenediamine Appear-
Pentamethylenediamine
ance of
Dibasic Aoid
Melting Pt., O C .
Adipic Pimelic Suberic Azelaic Sebacic Dodecanedioic Isophthalic Terephthalic
243 192 213 172 193 192 2 15-25' >300
Annealed Polymer Opaque Translucent Opaque Translucent Opaque Opaque Translucent Opaque
Intermittent loading-softening range. the odd number aliphatic acids. Though polymers from the odd number aliphatic acids are amorphous, they are relatively sharp melting softening slightly a t 3" to 5" C . below the melting points reported. Terephthalic acid gives a crystalline, high melting, polymer, while isophthalic acid forms a n amorphous polymer with a broad softening range probably much below its true melting point. An ASTM ( 7 ) heat distortion temperature (fiber stress of 66 pounds per square inch) of over 200" C . was obtained on crystalline poly(m-xylylene adipamide). Attempts to prepare a crystalline sample of poly(hexamethy1ene isophthalamide) by long annealing were unsuccessful. A standard ASTM heat distortion test bar could not be made of the amorphous poly(m-xylylene adipamide) because of rapid crystallization during molding. Samples of amorphous polymer were, however, readily obtained by quick quenching of small amounts of the molten polymer. T h e second order transition temperature of the amorphous polymer as measured by the penetrometer method is 68 'C.
Discussion T h e m-xylylenediamine structure has
a modified linear carbon chain, illustrated by comparison with pentamethylenediamine, and might be considered as a substituted pentamethylenediamine :
m-Xylylenediamine Table II.
Diamine
Specific Gravities of Polyamides Dibasic Specific Acid Gravity
m-Xylylene Hexamethylene
Adipic
1.22 1.14
m-Xylylene Pentamethylene ( 1 ) Hexamethylene
Sebacic
1.15
1 240
1.08
1.09
The presence of the aromatic ring improves the melting point. m-Xylylenediamine polymers have melting points intermediate between those of pentamethylenediamine (8) and hexamethylenediamine (8, 13, 74). The highest values reported are shown in Figure 1. Pentamethylenediamine, however, is unsuitable for high polymer formation because of ring closures during polymerization (72, 78). This cyclization is not possible with m-xylylenediamine because of its rigid structure. T h e data presented show that the m-xylylenediamine-adipic acid polymer is crystalline and has higher melting and heat distortion temperatures than the amorphous polymer of the reverse structure made from hexamethylenediamine and isophthalic acid. The structures of these two polymers are:
n
Poly(m-xylylene adipamide) (This work)
193' C., the melting point of m-xylylenediamine--sebacic acid polymer found in this work. The presence of the aromatic ring in m-xylylenediamine increases the density of the polyamides (Table TI).
Conclusions m-Xylylenediamine forms crystalline polymers from dibasic acids of even carbon number and amorphous polymers from dibasic acids of odd carbon number. The melting points of polymers of m-xylylenediamine and several dibasic acids fall between the melting points of corresponding polymers of pentamethylenediamine and hexamethylenediamine. The reaction characteristics of this new diamine are typical of aliphatic diamines and not of the true aromatic diamines. -4 comparison of poly(m-xylylene adipamide) and of poly(hexamethy1ene isophthalamide) shows that the m-xylylene diamine polymer crystallizes readily on annealing, while the polymer of reverse structure remains amorphous even on long annealing, and is very difficult to crystallize. T h e crystalline form of poly(m-xylylene adipamide) has a melting point of 243 O C. and an ASTM heat distortion temperature of over 200" C. These data indicate that m-xylylenediamine, a new diamine, has great promise for producing superpolyamides for use in fibers, films, and molding materials. Literature Cited (1) ASTM Standards, vol. 6, p, 296,
L
Poly(hexamethy1ene isophthalamide) ( 75) The differences in properties found for these polymers are explained. The m-xylylenediamine polyamide structure contains methylene groups which separate the aromatic rings from the amide groups. The amide groups are thus free to rotate and can hydrogen bond in all directions. Hydrogen bonding in directions perpendicular to the plane of the ring can occur regularly without hindrance by the bulky aromatic ring. I n the hexamethylenediamine polyamide, the amide groups, being conjugated with the aromatic ring, are held in a position essentially coplanar with it by resonance forces. Hydrogen bonding in directions perpendicular to the plane of the ring is, therefore, difficult. This, coupled with the hindrance of the ring resulting from the unsymmetrical meta structure, prevents orderly hydrogen bonding. Other work on related polyamides (2) supports this concept. The unsymmetrical structure also has a considerable effect on the melting point, as shown by the melting point of 300' C. for p-xylylenediaminesebacic acid polymer ( 7 4 , compared to
INDUSTRIAL AND ENGINEERING CHEMISTRY
1955, D 648-45T. (2) California Research Corp., unpublished data. (3) Carothers, W. H., 1J. S. Patent 2,130,523 (Sept. 20, 1938). (4) Zbid., 2,130,947(Sept. 30, 1938). (5) Ibid.,2,130,948 (Sept. 20, 1938). (6) Zbid., 2,163,584(June 27, 1939). (7) Zbid., 2,190,770 (Feb. 20, 1940). (8) Coffmann, D. D., Berchet, G. J., Peterson, W. R., Spanagel, E. W., J . Polymer Sei. 2, 306 (1947). (9) Coffmann, D. D., U. S. Patent 2,193,529 (March 12, 1940). (10) Edgar, 0. B., Ellery, E., J . Chem. Soc. 1952, p. 2633. (11) Flory, P. J., U. S. Patent 2,244,192 (June 3, 1941). (12) Hill, Rowland, "Fibers from Synthetic Polymers," p. 135, Elsevier, Sew York, 1953. (13) Hill, R.: Walker, E. E , J . Polymer Sei. 3, 609 (1948). (14) Izard, E. F., Zbid.,8, 503 (1952). (15) Lum, F. G., Carlston, E. F., IND. ENG.CHEM.44,1595 (1952). (16) Spanagel, E. W.: U. S. Patent 2,163,636(June 27,1939). (17) Triggs, W. W., Brit. Patent 525,516 (Aug. 29, 1940). (18) U. S. Dept. of Commerce, Washington 25, D. C., "Bibliography of Scientific and Industrial Reports," P.B.7416,p. 731,1946.
RECEIVED for review July 21, 1956
L 4 c c ~February ~ r ~ ~7, 1957
Division of Polymer Chemistry, 129th Meeting, ACS, Dallas, Tex., April 1956.
