Nylon 4

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JOURNAL OF POLYMER SCIENCE: I'AAT A-2 VOL. 4, 899-911 (1966)

Crystallographic Studies of Nylon 4.

Determination of the Crystal Structure

of the (Y Polymorph of Nylon 4*

I.

ROBERT J. FREDERICKS,t Central Research Laboratory, General A ni lin e

& F ilm Corporation, Easton, Pennsylvan ia 18042. THOMAS H. DOYNE,Department of Chemistry, Villanova University, Vil lanova, Pennsylvan ia

19085, and ROBERT S. SPRAGUE, Department of Chemistry, Lehigh

Un iversity, Bethlehem, Pe nnsy lvania 18015

Synopsis

The crystal structure of the 01 polymorph of nylon 4 has been determined from the

x-ray diffraction pa tterns of uniaxially oriented monofilaments. In general t,he crystal

structure of o nylon 4 s similar to that of a nylon 6. Th e unit cell is monoclinic with the

following dimensions: a = 9.29 f .05 A,, b = 12.24f .05 A ., c = 7.97 =t .05 A.,

and p = 114.5 -I 1.0". There are eight monomeric units in the unit cell. The theoreti-

cal density is 1.37 g./cc. and the observed density 1.25 g./cc. The space group is P21.The nylon 4 chains are of the extended planar zigzag type, with the plane of the zigzag

approximately parallel to the a axis of the unit cell. Along the a axis, every other chain

is inverted-an antiparallel arrangement of chains-thus permitting complete hydrogen

bonding and the formation of sheets of nylon 4 chains. Along the c axis of the unit cell,

the second sheet is displaced by3/,,of the b axis, thus leading to a staggered arrangement

of sheets. The sheets are held in place by van der Waals forces.

Introduction

Nylon 4, [-NH(CH,)&O- ]

obtained by polymerizing 2-pyrrolidone

(I),1CH2-CH2

C H r C = OI 1

Ih6

possesses many of the properties characteristic of the polyamides. The

polymer is thermoplastic with a melting point of about 265°C. It may be

combined with suitable fillers or extenders and other conventional con-

stituents such as plasticizers, pigments, and dyes. The polymer can beshaped, spread as a film or surface coating, used as an impregnant, and

* Paper presented a t the First Middle Atlantic Regional Meeting of the American

Chemical Society, Philadelphia] February 4, 1966.

t T o whom the inquiries should be addressed.

899

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900 R. J. FREDERlCKS, T. 11. DOY NE, 1L S. SlMAGUE

extruded into fibers, monofilaments, and other forms. Nylon 4 is insoluble

in most organic solvents and water as well as in aqueous basic solutions and

dilute acid solutions. It is soluble in concentrated hydrochloric acid from

which it can be precipitated by neutrelization with a base. The mechanicalproperties are comparable to those of the other polyamides2while its dye-

ability is somewhat superior.

Nylon 4 also has properties which difTer substantially from those of the

other polyamides. Its resistance to high temperature is poor;2 as the

melting point of the polymer isapproached, depolymerization and decompo-

sition are appreciable. It is adversely affected by boiling water. In its

absorption of water, nylori 4 is quite different from the polyamides and

similar to cotton.

It was felt that a study of the crystal structure of the polymer would be ofinterest in determining whether the above-mentioned unusual properties

resulted from a structure atypical of the polyamides.

Kinoshita3 ook

x-ray fiber patterns of the polymer and stated that nylon 4 existed in two

polymorphic forms, a and p. However, he did no detailed work to eluci-

date the nature of these polymorphs. Vogel~ong,~n structural studies of

the polymorphic forms of nylons 6 and 8, proposed a monoclinic unit cell for

nylon 4 which differs slightly from the unit cell determined by us. Vogel-

song performed no structural work on nylon 4.

We have observed three crystalline forms of nylon 4, which we have calleda, , and 6. The structure of the a polymorph is reported in this paper; the

p and 6 forms are discussed in the following paper.5

Very little x-ray work on nylon 4 has been published.

Experimental Details

The x-ray fiber patterns were taken on monofilaments of nylon 4 which

had been uniaxially oriented during the extrusion process and subsequently

held under tension in boiling water for several hours. Although the boiling

water caused some degradation of the polymer, as inferred from a drop in

molecular weight and a very slight loss in preferred orientation, the crystal-line reflections were considerably sharpened. The boiling water treatment

also converted any p polymorph present to the a orm. Nickel-filtered cop-

per K a x-radiation from a Norelco x-ray diffraction unit was employed. A

cylindrical Charles Supper casette with a diameter of 5.73 cm. was used to

record the fiber patterns. For all but the fifth layer and meridional reflec-

tions, the monofilament was positioned with the fiber axis parallel to the

rotation axis of the Charles Supper Weissenberg mechanism and normal to

the x-ray beam. The fifth layer and meridional reflections were recorded

with the fiber axis mounted normal to the rotation axis of the Charles

Supper Weissenberg mechanism and with the monofilament oscillatedabout the x-ray beam normal. The angle of oscillation was 18" for all re-

flections except the 0.10.0, where it was 67". The intensities of the crys-

talline reflectioris were visually estimated by comparison with a standard

exposure film. The ixiteiisities were determined from exposures of l / 2 ,1 ,2 ,

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CRYSTALLOGRAPHIC STUDIES OF NYLON 4. I 901

4, 8, 16, 32, and 64 hr. Because many of the spots on the films resulted

from more than one reflecting plane, the intensities were proportioned

among the contributing planes on the basis of the magnitude of the cal-

culated structure factors for the model used. Lorentz and polarizationcorrections were made in the usual manner. Spot shape corrections were

made after Franklin and Gosling.6 An isotropic temperature correction

was applied during the refining phase of the structure determination.

The value of the Debye-Waller factor B was determined by trial. The

scattering factors were calculated using the method of Vrtnd et al.' Cal-

culations required during the course of the study were performed on a

GE-225 digital computer at Lehigh University and an IBM-1620 digital

computer a t Villanova University.

The infrared spectra were obtained by using the KBr pellet technique.

Results

In general, the crystal structure of the alpha polymorph of nylon 4 is

quite similar to the a-polymorph of nylon 6 studied by Holmes et a1.*

Figure 1 is the x-ray diffraction fiber pattern of the a polymorph of

nylon 4.

The identity period ( b axis) along the fiber axis was determined from

measurements made of the t coordinate of the fifth layer line on a Bernal

chart. The b axis was found to be 12.24f 0.05 A ., in close agreement with

the expected value of 12.28 A. for extended planar zigzag chains of this

type:9 The dimensionsof the basal plane were determined from a zero layer

line reciprocal lattice net by using the trial-and-error procedures described

by Bunn'O and were as follows: a = 9.29 f .05 A., c = 7.97 f 0.05 A.,

and P=114.5 f 1.0". Reciprocal lattice nets for the higher layer lines

showed that the b axis was normal to the basal plane. Thus, the unit cell

and the symmetry, discussed below, were characteristic of the monoclinic

crystal system. The unit cell dimerisions were verified by calculating the

interplanar spacings for the determined unit cell and comparing these values

to the experimentally determined data. The agreement was quite good.

Fig. 1. X-ray diffraction fiber pattern of the a polymorphof nylon 4. Normal beam

method, cylindrical cassette, camera diamet,erof 5.73 em., CUKOC-radiation, uniaxially

oriented monofilament.

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903 R. J. FREDERICKS , T. H. DOYNE, R. S. SPRAGUE

TABLE I

Observed and Calculated Structure Factors and the Resulting Residual Factor for

LY Nylon 4

1 200

2

3 202

400

-5 204

6

7

8

T02(

-

602

204

604

9 "i206

171.9

411.3

172.0

55.2

67.6

178.1

98.2

116.7

67.6

151.6

402.4

127.8

40.4

110.4

166.9

63.7

100.2

117.8

20.3

8 . 9

44.2

14.8

51.8

11.2

34.5

16.5

50.2

128.9 142.8 13.9

10

404

021I 4a.v

121 67.7 9. 9 57.8

13

14 :iq321

30.8 38.9 8.1

15

92.1 107.1 15.0

(continued)

The theoretical density for a nylon 4 with eight monomeric units in the

unit cell was 1.37 g./cc., and the observed density by physical flotation in a

carbon tetrachloride-toluene system was 1.254 i 0.003 g./cc. at 26.2"C.

Since less dense disordered matter is always present in synthetic polymers,

the experimental density is usually 5-10% less than the theoretical density.

Thus, the experimentally measured density is a further verification of theunit cell dimensions. Attempts were made to induce higher orientation in

the polymer as an aid in determining the unit cell dimensions. Uniaxially

oriented monofilaments were placed in a Loomis 20-ton press with the fiber

axis parallel in some instances and normal in others to the ram axis of the

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CRYSTALLOGRAPIIIC STUDIES OF NYLON 4. I 903

TABLE I (continued)

16

17

18

19

20

21

22

23

24

25

26

27

28

-

325)225 \

622

130

131

230)

333

431

232)

241

341

251

-

351

353,

"3}51

351)

3511451)

65 1

155

353

453

655

361)

104.4

12.3

24.5

36.7

61.3

49.1

115.8

149.6

193.0

130.3

183.4

231.6

30.6

33.0

46.5

63.3

65.9

89.1

25.1

144.6

129.5

213.0

87.8

252.9

180.4

22.4

71.4

34.2

38.5

29.2

27.8

24.0

28.8

20.1

20.0

42.5

69.5

51.2

8 . 2

h?~ x(Fobs - Fcalc)/Z(Foba); 81= 0.273.b The observed data were not put on an absolute scale.

press. A pressure of 19 tons was applied and held for 1min. Other mono-

filaments were flattened between rollers at room temperature and at

100°C. The higher orientation achieved was a t the expense of crystallitesize and perfection and thus ruled out these specimens for x-ray studies.

The space group was determined from a consideration of the systematic

exhct ions . An examination of the observed reflections (Table I) reveals

the following. (a ) There are no systematic absences for reflections of the

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904 R. J. FREDERICKS, T. H. DOYNE, R. S. SPRAGUE

type hkl. ( b ) Only reflections of the

type OkO fork even are observed. This indicates a twofold screw axis along

the fiber axis. ( c ) For the zero layer line (reflections of the type h01), only

reflections for h and 1even were observed. This indicates the presence of aglide plane.

Upon consulting a list of the 230 space groups," the possibilities are:

P21 (primitive, twofold screw axis), P & / m (primitive, twofold screw axis

perpendicular to a mirror plane of symmetry), P g l / c (primitive, twofold

screw axis perpendicular to a glide plane which is parallel to the c-axis).

Consider the geometry of the structural repeating unit, I1 :

The lattice is therefore primitive.

H

CH2 CHz N CHII

CHz CHz CHI

I1Repeat Distance = 12.24f .05 A.

From the positions of the carbonyl oxygens, dictated by the three CH2groups, a twofold screw axis with a translation of one-half the repeat dis-

tance is to be expected. The form of the chain also rules ou t mirror planes

/ \ / \ c / \ / \ /\N

IH

I10

TABLE I1Atomic Coordinates for (X Nylon 4

Atom x Y z Atom x Y z

CHz

CHz

CHzC

0

N

CHz

CHzCHzC

0

N

CH2

CHz

CHzC

0

N

CHzCHI

CHzC0

N

0.044

0.040

0.044

0.040

0.160

0.037

0.044

0.0400.044

0.040

0.160

0.037

0.044

0.040

0.044

0.0400.160

0.037

0.044

0.040

0.044

0.0400.160

0.037

O.OO0

0.102

0.204

0.307

0.307

0.399

0.500

0.6020.704

0.807

0.807

0.899

0.300

0.402

0.504

0.6070.607

0.6990.800

0.902

0.004

0.1070.107

0.199

0.007

0.007

0.007

0.007

0.027

0.006

0.007

0.0070.007

0.007

0.027

0.006

0.507

0.493

0.507

0.4930.473

0.506

0.507

0.493

0.5070.4930.473

0.506

CH2

CHI

CH2N

C

0

CHz

CH2CH2NC

0

CHz

CHzCH2N

C0

CHzCHz

CHzNC0

0.460

0.544

0.460

0.537

0,460

0.340

0.460

0 . 5440.460

0.537

0.460

0.340

0.460

0.544

0.4600.537

0.4600.340

0.460

0.544

0.460

0.5370.460

0.340

0.000

0.102

0.204

0.307

0.399

0.399

0.500

0.6020.704

0.807

0.899

0.899

0.300

0.402

0.5040.607

0.6990.699

0.800

0.902

0.004

0.107

0.199

0.199

0.007

0.007

0.007

0.006

0.007

0.027

0.007

0.0070.007

0.006

0.007

0.027

0.507

0.493

0.5070.4940.507

0.527

0.507

0.4930.507

0.494

0.507

0.527

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perpendicular to the fiber axis. Thus, the possible space groups are

P2* and P21/c. From the systematic extinctions, one would expect the

space group P21/c o be the correct one. However, the three-dimensional

atomic parameters, as eventually determined (Table 11) show that thespace group is the lower symmetry P2*. One can explain this apparent

discrepancy when one considers only the xz parameters, which are what one

0-

0 -

.- HN

-0!c\

i'"=O-HN

\/ = O

-o=3

i= o

Fig. 2. Parallel and antiparallel arrangement of the chains in a nylon 4 and the re-sultant hydrogen bonding: (a) antiparallel placement of the chains permitting thecomplete formation of hydrogen bonds; ( b ) parallel placement of the chains and the

resulting incomplete hydrogen bonding.

would expect for a glide plane along the c axis. Consequently, the h0Z re-

flections would be expected to show the systematic extinctions for this

symmetry element. A similar situation was observed in nylon 6.*

When one is studying the crystal structure of synthetic polymers, the

most practical procedure to follow is trial and error. Since single crystals

large enough to place in an x-ray apparatus are rarely available and since aheavy atom is not usually present in the structure, direct methods for

solving the phase problem and refining the structure are not practical.

The initial model of a nylon 4 was arrived at by considering infrared

spectral data, the usual bond lengths and bond angles for substances

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906 R. .T. FREDERICKS, T. H. DOYNE, R. S. SPRAGUE

Fig. 3. Electron density contour map for the basal plane projection of 01 nylon 4. One

quarter of the basal plane is shown.

Fig. 4. One of the hydrogen-bonded sheets which forms half the unit cell in the 01 poly-

morph of nylon 4.

similar to nylon 4,9 the use of Dreiding stereomodels, the unit cell di-

mensions and the symmetry of the space group.It is well known that the positions of the NH stretching band and the

amide I band are influenced by hydrogen bond formation.12, a In nylon 4

the amide stretching band occurs near 3390 cm.-', compared to 3240 cm.-'

in the monomer while the amide I band attributed to carbonyl absorption

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Fig. 5. X-ray diffraction oscillation pattern of the (Y polymorph of nylon 4. Cylindri-

cal cassette, 67 ' oscillation, camera diameter of 5.73 cm., CuKm x-radiation, uniaxially

oriented monofilament positioned as described in the text.

occurs at 1640 cm.-' in the polymer and 1680 cm.-l in the monomer.

Shifts of this type from the monomer to the polymer indicate hydrogen

bond formation in the latter. Infrared spectra of cast and extruded films,fibers, and powders exhibited similarNH and amide I bands.

The identity period along the fiber axis indicated an extended planar zig-

zag conformation. Dreiding stereomodels of the nylon 4 chains showed

that the possibility of hydrogen bonding was enhanced when every second

molecule in a given plane of molecules was inverted by 180'. This is re-

ferred to as an antiparallel arrangement (see Fig. 2 ) and is similar to the

situation found in nylon 6.s T h e density of a nylon 4 was consistent with

the presence of eight monomeric units or four structural repeating units in

the unit cell. Since it appeared tha t a twofold screw axis passed throughthe chain, it was reasonable to place the four structural repeating units at

the positions of the twofold screw axes in the space group. Structure

factors were then calculated for the h01 reflections and found to be in ap-

proximate agreement with the observed values. Electron density calcula-

tions were performed for the basal plane projection. The resulting electron

density contour map for one quarter of the basal plane, (Fig. 3) shows the

structural repeating units to be identical in projection. The electron

density contours are elliptical with the major axis of the ellipse parallel to

the a axis of the unit cell. Thus the plane of the extended planar zigzag

structural repeats was coincident, or nearly so , with the a axis of the basalplane.

Since the four structural repeating units were located at the posit,ions of

the twofold screw axes, the first half of each unit is related by symmetry

to the second half. The basal Dlane projection showed the plane of the

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908 R. J. FREDERICKS. T. 1%.DOYNE, R. S. SPRAGUE

43/10 b-axis

Fig. 6. Displacement of the nylon 4 sheets by 8/10 of the b axis.

molecules to be parallel to the Q axis and the Dreiding models indicated an

antiparallel arrangement of the chains. Thus a reasonable model of the

structure would have two antiparallel structural repeating units, joined by

hydrogen bonds, forming a sheet along the a axis and the other two

structural repeating units, also hydrogen-bonded, located at z = I/Z, form-

ing a second sheet displaced along the b axis with respect to the first sheet

(one of these hydrogen-bonded sheets is shown in Fig. 4). There wouldhave to be a displacement of the second sheet or the unit cell would be

halved along the c axis. In space group Pgl there are no symmetry re-

strictions on the displacement along the b axis and, consequently, the

possibilities are infinite. The OkO reflections, which depend only on the

y parameters, provided a clue in determining this displacement. The 020

reflection in a: nylon 4 is weak, the 040 reflection medium, the 0.10.0

reflection strong, and the 060 and 080 reflections are not observed (see Fig.

5). The calculated intensities for the OkO reflections for the chosen y

parameters would have to be consistent with these observations. The cal-

culations of the OkO intensities for various arrangements were carried outby using one-dimensional structure factor plots. It is known that an odd

displacement of sheets, that is, by one-tenth, three-tenths or one-half the

b axis, which leads to “crossed” chains, would be a more eecient packing of

CH, groups in the unit cell than would be an even displacement.8 Since

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CRYSTALLOGRAPIIIC STUDIES OF NYLON 4. I 909

the (Y polymorph is a stable conformation, an odd displacement was con-

sidered probable. A displacement of one-tenth b would apparently be an

unstable arrangement because of the proximity of polar groups. For the

three-tenths b displacement, the calculated OkO structure factors were 19.0

for 020, 22.1 for 040,2.1 for 060,4.3 for 080, and 89.5 for 0.10.0, in approxi-

mate agreement with the observed data. Thus, the three-tenths b dis-

placement being considered most likely (see Fig. 6), a set of xyz coordinates

was proposed, and three-dimensional structure factors calculated. The

results showed a fair agreement with the observed values. The structure

was refined by trial and an isotropic temperature factor, B = 0.8, was

applied. The final residual factor (R 1factor), based on the difference in

observed and calculated structure factors, was 0.273 for the atomic pa-

rameters shown in Table 11. The final observed and calculated structurefactors are presented in Table I.

The terms included in Table I were only those reflections for which adiscernible intensity could be measured on the fiber patterns. Many other

reflections would be possible for the a nylon 4 unit cell, but these reflections

were not observed.

The OlcO reflections were not included in the calculation of the residual

factor. The reason for this was that two different oscillation angles were

required in recording these reflections, and consequently the reflections

could not be put on the same scale.

Discussion

The crystal structure of the a-polymorph of nylon 4 has been elucidated

to a degree considered satisfactory for polymer structures. However, as

the R I of 0.273 indicates, additional refinement would be desirable. Be-

cause of the relatively small number of reflections, characteristic of x-ray

diffraction patterns of synthetic polymer fibers, Fourier methods, and least-

squares refinement are not practical. Trial and error procedures are

out of the question because of the large number of nonhydrogen atoms

(48) in the unit cell. In addition the intensities of the reflections are dif-ficult to measure accurately. This is so because of their diffuseness,

especially a t high values of sin 0, caused by various types of disorder in the

structure and by incomplete preferred orientation. It is possible that the

residual factor might be decreased by the application of an anisotropic

temperature correction. High temperature x-ray diffraction studies, re-

ported in the following paper,5show that the (002) (202) composite spacing

is more readily affected by elevated temperature than the (200) spacing.

This is perfectly reasonable when one considers th at the (200) spacing re-

sults from the hydrogen bonded chains in a sheet along the a axis while the

(002) spacing comes from the separation of the van der Waals bondedsheets-a much weaker bond. Holmes et a1.8 observed a marked reduction

in the RI factor after the application of an anisotropic temperature cor-

rection. Unfortunately, the limited memory of our computer precluded

this calculation.

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910 12. J . PHEDERICKS, T. 13. DOYNE, 12. S. SPRAGUE

Despite these limitations, we believe that the overall structure of a! iiyloii

4 is correct. The N H - - - 0 hydrogen bond distance was found to

be 2.93 A., a perfectly reasonable value.14 The distance between sheets

is 3.62A., a typical van der Waals distance.15 The other bond lengths werenormal.

The crystal structure of a! nylon 4 is very similar to that of a! nylon 6.

The staggered placement of the hydrogen bonded sheets and the anti-

parallel arrangement of adjoining chains in the sheets was found also in

nylon 6. Since the structures are so similar, the instability of nylon 4 at

elevated temperatures cannot be explained by the crystal structure. Ap-parently, at elevated temperatures, the equilibrium between monomer

and polymer is shifted to the formation of the stable, five-membered lactam,

2-pyrrolidone.

The IBM-1620 digital computer at Villanova University, used for a number of the

calculations required in this study, was purchased partly through a grant from the Na-

tional Science Foundation.

This paper was abstracted from the dissertation submitted by Robert J. Fredericks in

partial fulfillment of the requirements for the Doctor of Philosophy degree at Lehigh

University.

One of us (RJF) thanks Mr. Harold T. Page of the General Aniline& Film Corporation

for his assistance in taking a number of the x-ray ditrraction patterns used in this study.

References

1. W . 0.Ney, W. R. Nummy, and C. E. Barnes, U.S. Pat. 2,638,463 (May 12, 1953).

2. K . Dachs and E. Schwartz, Ange-w. Chem. Intern. E d ., 1,430 (1962).

3. Y . Kinoshita, Makromol. Chem., 3 3 , l (1959).

4. D. C. Vogelsong, J . Polymer Sci. A , 1,1055 (1963).

5. R. J. Fredericks, T. H . Doyne, and R. S. Sprague, J . Polymer Sci. A-2, 4, 913

6. R. E. Franklin and R. G. Gosling,Acta Cryst., 6,678 (1953).

7. V. Vand, P. F. Eiland, and R. Pepinsky, Acta Cryst., 10,303 (1957).

8. D. R. Holmes, C. W. Bunn, and D. J. Smith, J . Polymer Sci., 17, 159 (1955).

9. L. Pauling and R. B. Corey, Proc. Roy . Soc. (Lond on),B141,lO (1953).

(1966).

10. C. W . Bunn, Chemical Crystallography, Oxford Univ. Press, 1961.11 . N. F. M . Henry and K. Lonsdale, International Tables fo r X-ray Crystallogruphy,

Vol. I , Kynoch Press, Birmingham, England, 1952.

12. A. Miyake, J . Polymer Sci., 44, 223 (1960).

13. L. J. Bellamy, The Infra-red Spectra of Complex Molecules, Wiley, New York,

14. G. C. Pimentel and A. L. McClellan, The Hydrogen Bond, Freeman, San Francisco,

15. C . A. Coulson, Valence, Oxford Univ. Press, 1952.

1960.

1960.

Resume

La structure cristalline du polymorphe LY du nylon 4 a 6th d6termin6e au depart dediagrammes de diffraction aux rayons-X de monofilaments orient& dans un axe. En

general la structure cristalline du nylon LY 4 est semblable ii celle du n$on (Y 6. La

cellule unitaire monocliniqouea les dimensions suivantes: u = 9.29f .05 A , b = 12.24f0.05 A, c = 7.97 f .05 A et @ = 114.5 f . O o . I1 y a huit unites monomeriques par

cellule unitaire. La densite thkorique est 1.37 g/cc et la densite observee est 1.25 g / c c Le

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CHYS?'ALLOGRAPHIC STUDIES OF NYLON 4. I 911

groupe spatial est P d . Les chaines de nylon 4 sont du type zig-zag planaire Btendu avec

un plan du zig-zag approximativement parallele B l'axe a de la cellule unitaire. Le long

de l'axe a, toute l'autre chaine est renvers6e; un arrangement antiparalkle des chaines

permet une liaison hydrogene complete et la formation de feuilles de chaines de nylon 4.

Le long de l'axe c de la cellule unitaire la seconde feuille est dkplac6e de 3/10 de l'axe b,

ceci amenant B un arrangement alterne des feuilles. Les feuilles sont tenues en place

par des forces de van der Waals.

Zusammenfassung

Die Kristallstruktur der a-Form von Nylon 4 wurde aus Rijntgendiagrammen voii

uniaxial orientierten Monofilamenten bestimmt. I m allgemeinen ist die Kristallstruk-

tur von a-Nylon 4 derjenigen von a-Nylon 6 ahnlich. Die Elementarzell~st monoklin

und besitzt folgende Dimensionen: a = 9,29f ,05A, b = 12,24f ,05 A, c = 7,97f0,05 A, und 6 = 114,5 f ,O" . In der Elementarzelle befinden sich acht Monomerein-

heiten. Die theoretische Dichte betragt 1,37 g/cm3 und die beobachtete 1,25 g/cm3.Die Raumgruppe ist P21. Die Ketten von Nylon 4 sind vom gestreckten ebenen Zick-

zack-Typ mit der Zickzackebene abgenahert parallel z u r a-Ache der Elementarzelle.

Langs der a-Ache besteht eine Inversion jeder zweiten Kette-eine antiparallele

Kettenanordnung-, was eine vollstandige Ausbildung von Wasserstoffbindungen

sowie die Bildung von Schichten aus Nylon 4-Ketten erlaubt. Langs der c-Ache der

Elementarzelle ist die zweite Schichte um 3/,0 der b-Achse verschoben, was zu einer

Anordnung mit versetzten Schichten fiihrt. Die Festlegung der Schichten geschieht

durch van der Waals-KrSifte.

Received February 24, 1966

Revised April 23, 1966

Prod. No. 8AF

Documents

Nylon 4