molecular confirmation and crystal structure of the β form of poly(ethylene oxybenzoate)

Molecular Conformation and Crystal Structure of the ,i3 Form of Poly(ethy1ene Oxybenzoate)

YASUHIRO TAKAHASHI, TOSHIMITSU KURUMIZAWA, HIROSHI KUSANAGI,* and HIROYUKI TADOKORO, Department of Polymer

Science, Faculty of Science, Osaka University, Toyonaka, Osaka 560, Japan

Synopsis

The crystal structure of the (3 form of poly(ethy1ene oxybenzoate) was analyzed by x-ray diffraction. Four nearly extended molecular chains pass through a unit cell with parameters a = 8.19 A, b = 11.07 A, c (fiber axis) = 19.05 A, (3 = 114.8', and the space group P2l/n-C$,,. The structural difference between the a and (3 forms is mainly due to the internal rotation angles for the virtual bond

and the -CHz-CHz- bond. They are essentially in trans conformation in the (3 form, while the a form contains cis

and gauche (-CHz-CH2-) conformations.

INTRODUCTION

Poly(ethy1ene oxybenzoate)

has two crystal modifications, (Y and p. The molecular and crystal structures of the CY form were reported in a previous paper.l In the (Y form, two molecular chains, in nearly (CTSGT)B conformation, pass through a unit cell with parameters, a = 10.49 .&, b = 4.75 .&, and c (fiber axis) = 15.60 .& and the space group P212121-0;. Here, C, T, S, and G denote cis, trans, skew, and gauche conformations, respectively. For the form, details of the crystal structure were not known, although the fiber period was reported to show that the molecular structure is almost fully extended.l

* Present address: Central Research Laboratory, Unitika Co., Ltd., Uji, Kyoto 611, Japan.

Journal of Polymer Science: Polymer Physics Edition, Vol. 16,1989-2003 (1978) 0 1978 John Wiley & Sons, Inc. 0098- 1273/78/0016- 1989$01 .OO

1990 TAKAHASHI ET AL.

(a) (b)

Fig. 1. X-ray fiber diagrams of poly(ethy1ene oxybenzoate). (a) a form and (b) (3 form.

Fig. 2. End-directional x-ray photograph of a doubly oriented 0-form specimen and indices of the reflections.

In the present study, the crystal structure of the p form was determined by x-ray diffraction for comparison with the a form.

EXPERIMENTAL

Samples

A commercial sample A-Tell (Unitika Co., Ltd.) was used. A uniaxially oriented sample of the p form was obtained by stretching more than fivefold at room temperature immediately after quenching the melt in ice water. Then the sample was subjected to heat treatment a t 18OOC for 1 hr under tension. A doubly oriented specimen of the p form was obtained by rolling the stretched specimen at room temperature and subsequently annealing at 180°C between metal plates. Kuroishi et a1.2 reported that the p form transforms into the a form

POLY(ETHYLENE OXYBENZOATE) 1991

I a m P r. c c "7 0

b = l 1 . 0 7 A --- "

A C

B D

Fig. 3. (a) Relation between chains A and B or C and D on the c projection. Symmetry operations for molecular chain on the b projection in the space groups (a) P211n-Cgh and (b) P ~ ~ / U - C $ ~ .

on annealing without constraints and the a form transforms into the ,6 form by stretching at 120°C. These transitions were confirmed in this study.

X-Ray Measurements

Throughout the present study, nickel-filtered Cu K a radiation was used. Cylindrical cameras with 5- and 10-cm radii were used for measurements of intensities and spacings, respectively. The spacings were calibrated by reference to those of aluminum powder. Intensities of 47 independent reflections were estimated by a microphotometer after measurements by the multiple-film method. Fiber photographs of the a and (3 forms are shown in Figure 1. Figure 2 shows an end-directional x-ray photograph of a doubly oriented sample of the f i form and its schematic representation.


X-RAY ANALYSIS

Unit Cell and Space Group

Forty seven independent reflections could be indexed by a monoclinic unit cell with parameters a = 8.19 8, b = 11.07 A, c (fiber axis) = 19.05 A, and p = 114.8'. This unit cell was confirmed by an x-ray photograph of a doubly oriented sample (Fig. 2). Here, the plane of rolling was found to be parallel to the bc plane. From the fiber period, the molecular conformation is predicted to be nearly in extended form since a fully extended planar chain would have a fiber period of 19.11 A. The observed density (1.31 g/cm3 at 25OC) and cell parameters suggest that four chains, eight monomeric units, pass through the unit cell.

The space group was deduced in the following way. Systematic absences k = odd was found for OkO reflections, but for h01 reflections the three systematic absences, h = odd, 1 = odd, or h + 1 = odd, were indistinguishable because of the small number of observed reflections and the overlapping of reflections. The possible space groups were P21-C;, P2l/m-C;, and P21/n, P21/c, P21/a-C$h at this stage. Since four chains pass through the unit cell, the space group P21-Cz seems unreasonable because two molecular chains would be an asymmetric unit. The space group P21/m-Czh was also excluded because the mirror symmetry prevents good molecular packing in the unit cell. In the space group P21/c-c$h, two kinds of molecular positions are possible; one is on the c glide plane, and the other at the general equivalent position. The former seems improbable because the chains are not related by a symmetry operation. The latter was also excluded by the apparent discrepancy between the observed and calculated structure factors on the equator.

It was found that all but a few very weak reflections could be indexed by a subcell with a' = l/Za = 4.10 A, b' = b, c' = c, and p' = p. This means [Fig. 3(a)] that the symmetry operation between chains A and B or C and D nearly corresponds to the pure translation of l/2a. Figures 3(b) and 3(c) show schematically the molecular packings of chains A and B on the b projection in P21/n and P21/a. The n glide symmetry operation corresponds to the pure translation of 'ha as shown in Figure 3(b) and it is possible to assume the subcell along the a axis. On the other hand, the a glide symmetry operation is not consistent with the pure translation of l/za, e.g., in Figure 3(c), carbonyl groups (1) and ( 2 ) point in op-

TABLE I Crystallographic Data of Two Modifications of Poly(ethy1ene Oxybenzoate)

a Form l3 Form

Crystal system Space group Cell parameters a (A) b (A) c (A) P (") No. of chains in a unit cell Density (g/cm3)

observeda calculated

a At 25°C.

Orthorhombic Monoclinic P212121-08 PZl/n-C$,

10.49 4.15

15.60

2

8.19 11.07 19.05

114.8 4

1.34 1.31 1.40 1.39

POLY (ETHYLENE OXYBENZOATE) 1993

posite. Hence, the subcell is not possible in the case of P2Ja. For these reasons, the space group P21/n-Cgh is most probable. In this space group, the molecule has not a site symmetry. Crystallographic data for the a and /3 forms are sum- marized in Table I.

Structure Determination

The fully extended, planar zigzag model was adopted at the initial stage of structure analysis. The presence of the subcell structure suggests that the molecular axis is approximately y = 0.25 and the molecular plane is almost parallel to the bc plane. Molecular coordinate x = 0.125 was roughly determined by the structure factor calculation for the equator. Furthermore, the coordinate z of the center of the benzene ring was also determined to be 0.44 for the up- pointing molecule by trial and error. Here, the pointing sense is defined by the direction of the bond C(4)-0(2’) (Table 11) and Figures 3(b) and 3(c) show the up-pointing molecules. A small deviation from y = 0.25 and a small rotation about the molecular axis did not improve agreement between the observed and calculated structure factors. Accordingly, an attempt was made to modify the fully extended molecular model. Even if the molecule has no crystallographic

TABLE I1 Numbering of the Atoms and the Conformational Anglesa

H(1) H(2) H(7) H(5) 013) I 1 H V )

I / I

w /c(z+cY C(4) 4 ( 2 ’ ) - C ( Y ) -

I I I I \

- 0 ( 2 1 - - c ( 9 ~ C ( 8 > - 0 ( 1 ) . - c O - C(1)

C(6)-C(5) H(8’) I 1 H(8) H(6)

H(1) H ( & 71: Dihedral angle between planes 0(1)-C(7)-0(2’) and C(9’)-0(2’)-C(7)b 72: Angle around the bond 0(1)-C(7) T3: Angle around the bond C(8)-0(1) 74: Angle around the bond C(9)-C(8) 75: Angle around the bond 0(2)-C(9) w: Internal rotation angle O(l)-C(7)-C(l)-C(6) 6: Internal rotation angle C(3)-C(4)-0(2’)-C(9’)

a Numbering of the atoms in the neighboring monomeric unit are denoted by a prime. b The C(7)-0(2’) can be assumed to be a virtual bond because atoms C(7), C( l ) , C(4), and O(2’)

are on a line.

TABLE I11 Internal Coordinates Assumed for the 0 Forma

Bond length (A) Bond angle (deg)

C(9)-0(2) 1.42 C(9)-0(2)-C(4) 115 0(2)-C(4) 1.37 C(l)-C(7)-0(3) 124 C(1)-C(7) 1.49 0(3)-C(7)-0(1) 122

C(7)-0(1) 1.36 C(7)-0(1)-C(8) 112 0(1)-C(8) 1.43 O(l)-C(8)-C(9) 109.5 C-C (aliphatic) 1.54 C-C-H (aliphatic) 109.5 C-H 1.09 C-C-C (aromatic) 120 C-C (aromatic) 1.40 C-C-H (aromatic) 120

C(7)-0(3) 1.23 C(l)-C(7)-0(1) 114

These values were used in the structure analysis of the a form, ref. 1.


TABLE IV Final Parameters Obtained by Constrained Least-Squares Refinementa

Parameter Value

Fractional coordinates of oxygen atom [0(2)] chosen as the origin X

Y 2

Eulerian angles (deg)b 0

Internal rotation angles (deg) C(9)--C(8) C(8)-0(1) 0(1)-C(7) C(7)-C(1) C(4)-0(2’) O( 2’)-C( 9’) C(9’)-C(8’) C(S’)-O(l’) O( 1‘)-C( 7’)

4 X

C(7’)-C( 1’)

0.168 0.114 0.068 102.8

-159.1 -145.1

158.6 198.1 184.4 178.8

11.2 176.4 147.4 191.8 189.2 182.0

Overall isotropic temperature parameter (A21 B 9.4

a The dihedral angle ym-0(2)-C(9)-C(8) was fixed as 180’ where the ym is t hey axis of the

These are the angles between the orthogonal coordinate systems fixed on the lattice and molecule. coordinate system fixed on the molecule, ref 7.

symmetries in the lattice, it can be expected to have approximately twofold helical symmetry or a glide plane according to the equivalency postulate. At first, the structure factor was calculated from molecular models, in which the benzene rings were rotated about virtual bonds

so as to maintain twofold helical symmetry or glide symmetry, keeping the other internal rotation angles trans. The model with a (2/1) helix gave good agreement between observed and calculated intensities, including the reflections which cannot be indexed with the subcell, while the glide symmetry did not improve the agreement: Moreover, discrepancies were found for the reflections which cannot be indexed with the subcell. This suggests that the molecular conformation is essentially a (2/1) helix.

The conformational energy calculation was performed for the (2/1) helix with a fixed fiber period of 19.05 A. There are six independent conformational angles (71”’75, w ) in a chemical repeat unit (Table 11) and the conformation in the fiber period could be determined by 12 conformational angles. The number of independent angles is reduced by one-half by (2/1) helical symmetry. The presence of the translational symmetry along the fiber axis and the fixed fiber period (19.05 A) reduce the number to 4. Furthermore, 7 2 = 180° was assumed on the basis of the structures of polyesters analyzed so far.l Finally, the number of independent conformational angles was reduced to 3. Details of the calculation are described in the previous paper.l The bond lengths and bond angles used here, which are also used in the previous paper,l are given in Table 111. As a result of the calculation, the minimum-potential model (-1.92 kJ/mole per monomeric


b = 11 .07 A

ro U r-

c C

u1 0

1 --r

-a

Fig. 4. Crystal structure of poly(ethy1ene oxybenzoate) 0 form.

unit) was found to have conformational angles: 71 = 209.5", 7 2 = 180°, 73 = B O O ,

7 4 = 165", 75 = 163.6", o = 0". The structure factor calculation was made on the basis of this molecular model. Here, two molecular arrangements (model I: x = 0.125, y = 0.25, z = 0.44 and model 11: x = 0.375, y = 0.25, z = 0.44) should be distinguished from each other, which give the same structure factors if the molecule is fully extended. I t was found that both models give poor agreement between observed and calculated structure factors. The discrepancy factor R (= Z I a - / Z a ) is 38% for model I and 41% for model 11. In the present work, the discrepancy factor was estimated only for the observed reflections.

I t was also found in the structure analysis of the a form1 that the models obtained by the intramolecular interaction energy calculation give poor agreement between the observed and calculated structure factors. Although the minimum-energy model deviates somewhat from the cis conformation of the internal rotation angle


a l 0 0

a fo rm Pform Fig. 5. Molecular dimensions for the cr and p forms.

Fig. 6. X-ray photograph of commercial A-Tell fiber (macroscopic elastic modulus 7.3 X loLo dyn/cm2).

i.e., 8 = 7 1 - w - 180' = -51', the final structure has the cis conformation (8 = 2'). In the case of the f l form, the internal rotation angle 8 of the minimum- potential model is 29.5'. Furthermore, the internal rotation angles 8 of low- molecular-weight compounds which have chemical structures similar to that of poly(ethy1ene oxybenzoate) are nearly O", e.g., 0" for p,p'- dimethoxybenzo- p h e n ~ n , ~ 4' for deoxyani~oin,~ -2' for fl-5-propoxy-o-benzoquinone-2-oxime (syn form)? -0.4" and 1.5' for 1,4-dietho~ybenzene.~ Therefore, an attempt was made to find models in the potential energy calculation which have cis conformation. A less stable model (4.18 kJ/mole per monomeric unit) with the cis conformation was found; 71 = 194', 72 = 180°, 73 = 180°, 7 4 = 165', 7 5 = BOO, w = 14'. Structure factor calculations were then made with this molecular model. The structure factors for model I gave good agreement with the observed ones ( R = 27%), while model I1 gave poor results no matter how the z parameter was varied.

POLY (ETHYLENE OXYBENZOATE) 1997

TABLE V Fractional Coordinates for the /3 Form

Atom X Y 2

C(1) 0.141 0.163 0.375 C(2) 0.193 0.107 0.447 C(3) 0.177 0.169 0.508 C(4) 0.108 0.287 0.496 C(5) 0.056 0.343 0.424 C(6) 0.072 0.281 0.363 C(7) 0.158 0.097 0.310 C(8) 0.105 0.090 0.181 C(9) 0.097 0.174 0.115 O(1) 0.099 0.160 0.243 O(2) 0.168 0.114 0.068 00) 0.219 -0.006 0.316 H(1) 0.247 0.016 0.456 H(2) 0.218 0.126 0.564 H(3) 0.002 0.434 0.415 H(4) 0.031 0.324 0.307 H(5) -0.009 0.029 0.159 H(6) 0.230 0.038 0.202 H(7) 0.176 0.255 0.140 H(8) -0.042 0.199 0.080 C(1') 0.117 0.298 0.870 C(2') 0.064 0.353 0.923 (33') 0.079 0.290 0.989 C(4') 0.146 0.172 0.002 C(5') 0.199 0.117 0.948 C(6') 0.185 0.180 0.882 (37') 0.101 0.366 0.799 C(8') 0.162 0.374 0.691 C(9') 0.180 0.293 0.629 00') 0.152 0.301 0.751 O(2') 0.092 0.348 0.556 O(3') 0.047 0.471 0.785 H(1') 0.011 0.445 0.913 H(2') 0.037 0.333 0.031 H(3') 0.252 0.025 0.958 H(4') 0.226 0.138 0.841 H(5') 0.278 0.434 0.716 H(6') 0.040 0.429 0.665 H(7') 0.118 0.205 0.629 H(8') 0.322 0.280 0.643

These procedures were also applied to the molecular model with glide symmetry. However, these calculations failed to give a structure with good agreement between the observed and calculated structure factors. This excluded the model with glide symmetry.

The constrained least-squares m e t h ~ d ~ , ~ was then applied to the refinement. During the refinement, the (2/1) helical symmetry assumed so far was removed from the molecule because the molecule has no site symmetry in the lattice, and the bond lengths and bond angles were fixed at the values given in Table 111, which were successfully used in the analysis of the a form. Four Lagrange multipliers were used to keep the bond length and bond angles between neighboring repeating units. The parameters to be refined are a scale factor, three


TABLE VI Observed and Calculated Values of Spacings and Structure Factors for the p Forma

Index do(& d, (A) fl < 1 1 0 ... 6.17 . . . 28 0 2 0 5.55 5.53 154 161 1 2 0 4.50 4.44 108 117 2 0 0 . . . 3.71 . . . 25 2 1 0 3.50 3.52 515 515 1 3 0 ... 3.30 ... 35 2 2 0 . . . 3.08 . . . 30 0 4 0 2.78 2.77 114 102

2.61 2.62 79 67 1 4 0 2.59 3 1 0 . . . 2.41 . . . 110

2.21 2.26 77 79

1 5 0 . . . 2.12 . . . 73 3 3 0 ... 2.05 ... 24 2 5 0 1.90 1.90 78 98

1.85 1.85 106 114

2.22

1.86

0 6 0 1.85 4 1 0 1.83

1.76 1.77 1.79 96 100

0 1 1 ... 9.32 ... 39 -1 1 1 ... 6.58 . . . 1

5.29 5.27 225 225

-1 2 1 4.68 4.58 63 86 1 2 1 4.19 4.06 63 59

3.61 3.75 158 171 3.60

-1 3 1 ... 3.36 ... 10 -2 2 1 3.23

2 1 1) 3.19 3.21 112 133 1 3 1 3.14 2 2 1 . . . 2.87 . . . 9

2.74 2.73 74 76

-1 4 1 ... 2.62 . . . 7 ... 2.51 . . . 11

5.26

2.71

2.48 -2 4 1 2.27

2.19 2.13 63 63 2.13

-3 3 1 2.13

i} 2.19 3 2 1

0 0 2 8.57 8.64 20 19 0 1 2 6.80 6.81 48 60

-1 1 2 ... 6.13 . . . 30 0 2 2 4.64 4.66 129 100

-1 2 2 . . . 4.42 . . . 52

-2 0 2 . . . 4.09 . . . 47 -2 1 2 . . . 3.84 ... 52

1 2 2 ... 3.59 . . . 91

1 1 2 ) 4.35


-; ; :) -1 3 2

2 0 2 1 3 2 2 1 2

0 4 2 -: -3 ; 1 7 2

-3 1 4 2 21 -2 4 21 2

-3 0 5 2 21 -l 0 2 3 31 -2 1 1 3 31

-2 1 3 3 31

-I 0 5 3 31 -l 0 0 4 41 -1 -2 O 2 4 41 -2 2 4 41 -l 0 3 4 41 -2 -3 3 4 41 -3 1 3 4 41 -2 O 1 5 51 -2 O 2 5 51

0 1 3

-1 3 3 -' 0 3 3 ' 'J -1 4 3

-3 2 3 0 4 3 )

0 1 4

-2 1 4 0 2 4

1 2 4

-1 0 5 -1 1 5

-1 2 5

1 0 5 -1 3 5

1 1 5 1

3.39 3.29 3.29 2.99 2.91 2.88 2.74 2.63 2.63 2.62 2.42 2.38 2.32 2.29 2.17 2.14 5.11 4.04 3.99 3.74 3.62 3.22 3.15 3.13 3.10 2.70 2.66 2.50 2.49 2.44 2.07 2.06 4.68 4.32 4.02 3.68 3.57 3.49 3.40 3.07 3.06 2.89 2.80 2.76 2.61 2.60 2.42 2.41 3.80 3.59 3.30 3.18 3.13 2.93 2.84 2.72 2.64 2.64

3.38 59 37

22 34 8

. . .

...

. . .

2.63 83 75

100 . . .

8

44

. . .

2.15

. . .

44

5.04 . . .

60 . . .

42 17

26 ... . . .

3.11 84 48

30 . . . . . .

2.49

2.08

39

51

21

21

32 . . .

9 7

. . .

... . . .

... 19 7

40

...

. . .

. . .

3 . . .

4 40

. . . . . . . . .

32 . . .

4 9

75

. . . 3.53 3.22

. . . 43 74

5 58

. . . 55 2.86

21 36

. . .

. . .


-3 0 5

-2 3 5 1 2 5

-3 2 5 -1 4 5

-2 4 5 -3 3 5

1 4 5 -1 1 6

-2 1 6

0 2 6

1 1 6

-3 2 6 1 2 6

-1 4 6 -3 3 6 -2 4 6

1 3 6 ) 0 4 6

-4 0 6 -4 1 6 -2 5 6

0 5 6 ) -4 3 6 -2 1 7 -1 2 7

-1 3 7

0 4 7

-4 2 7 1 3 7 )

-1 2 8

-2 2 8

-3 1 8

0 0 8)

. . .

2.47

. . .

...

2.15

. . . 2.97 2.90

. . .

. . .

2.60

. . .

. . . 2.26

...

. . .

2.00

. . .

1.77

2.54

2.39 ...

. . .

... 2.13

...

1.93

1.83

...

2.15

...

2.59 2.52 2.52 2.46 2.44 2.34 2.23 2.19 2.16 2.12 2.12 1.94 3.05 2.95 2.88 2.85 2.78 2.75 2.60 2.55 2.40 2.39 2.32 2.27 2.24 2.18 2.08 2.04 2.02 1.99 1.99 1.98 1.95 1.77 1.75 1.75 2.55 2.43 2.41 2.37 2.25 2.24 2.18 2.14 2.12 2.05 2.05 1.96 1.94 1.93 1.84 1.82 1.81 2.34 2.29 2.16 2.16 2.15 2.12 2.09

. . .

44

. . .

. . .

56

. . . 16 26

. . .

...

37

. . .

... 29

. . .

...

73

...

46

36

29 ...

...

. . . 81

. . .

50

58

...

67

...

18

52

31 6

37

21 2

19

13 23

53

42

30 19

2 21

59

16

33

45 3

18

23

3 44

40

39

41

35

59

8


-3 2 8 1.98 -1 3 8 ) 1.97 1.98 95 135 -2 3 8 1.97

1.79 1.78 1.78 60 60

1 2 8 1.77 -4 2 8 1.74

1.70

1 3 8 1.67

1 0 9 1.69

-: :} 1.69 1.68 58 55

1.68 1.70 53 35

a Ellipses (. . .) indicate an unobserved reflection.

fractional coordinates of O(2) atom, three Eulerian angles, ten internal rotation angles, and an overall isotropic temperature parameter (Table IV). Accordingly, the number of independent variables are 18 - 4 = 14. The discrepancy factor was reduced from 27% to 16%. The final parameters obtained by the constrained least-squares refinement and in fractional coordinates are given in Tables IV and V, respectively. Table VI gives comparison between the observed and calculated structure factors. The crystal structure of the p form is shown in Figure 4.

DISCUSSION

Figure 5 shows molecular dimensions for the a and 0 modifications. The molecular chain in the p form has essentially the (2/1) helix conformation, that is, the values of the corresponding internal rotation angles of neighboring monomeric units are almost the same. Differences of the internal rotation angles between two monomeric units seem to be insignificant from the accuracy of the present analysis. The values of ~ 1 , 7 2 , 7 3 , 7 4 , 7 5 , and w are 190°, 184O, 198O, 159O, 171°, and -lo, respectively, in one monomeric unit, while those of a neighboring monomeric unit are 190°, 189", 192", 147O, 176O, and 2 O , respectively. The internal rotation angles 19 correspond to a nearly cis conformation (ll", 8"). The molecule of the p form is approximately a fully extended chain and has twofold helical symmetry. On the other hand, the a form has a contracted large-scale zigzag conformation, each monomeric unit being a large zigzag unit with (CTSGT)2 conformation of the skeletal bonds. The structural difference between the a and p forms is mainly attributed to the internal rotation angles for the virtual bond

and -CH2--CH2- bond. They are essentially trans conformation in the p form, while in the case of the a! form they are cis and gauche conformations.


Intermolecular distances within 5.0 A were calculated for all pairs of atoms: C-C 2 3.17 A, C-0 2 3.03 A, C-H 2 2.50 A, 0.-H 2 2.37 8 ,O-0 2 3.01 A, and

Although the reflections due to the 0 form, as seen on the fiber diagram [Fig. l(b)], are generally broad, their half-widths are not always constant. The x-ray photograph of a doubly oriented 0-form specimen (Fig. 2) exhibits marked differences in the half-widths among the reflections: Half-widths of hkO reflections are much broader than those of OkO reflections. On the other hand, most of the reflections (29 of 38 reflections) observed on the layer lines include Ohl reflections (Table VI). This suggests that there are similar differences in the half-widths on the layer lines and that some of unobserved reflections have intensities stronger than the threshold value but merge nevertheless into the background of x-ray diffraction pattern because of their broadness. Although such phe- nomena can be found in polyglycolide,8 polytetrahydrofuran,9 etc., the variation of the half-widths is not so great as in the present case. Broadening of a reflection is mainly caused by a small crystallite size, crystal imperfection of the second kind, etc. By integral breadth methods and small-angle x-ray scattering from the doubly oriented 0 form, it was possible to distinguish between size and dis- tortion broadening; and it was concluded that the crystallite size in the direction normal to the rolled plane is much smaller than in other directions. The details will be reported in a later paper.

Tashiro et al.1° calculated elastic moduli for the (Y form (2.4 X 1O1O dyn/cm2) and form (57 X 1O1O dyn/cm2), the elastic modulus of the p form being calculated on the assumption of a fully extended conformation. Although the molecular chain deviates slightly from the planar zigzag, the elastic modulus of the p form is considered to be almost the same as that of the planar zigzag. The macroscopic elastic modulus (8.9 X 1O1O dyn/cm2) of commercial A-Tell is larger than the observed crystallite modulus of the a form (6 X 1O1O dyn/cm2).11 This may be attributed to coexistence of the 0 form. In fact, the commercially available A-Tell fiber (macroscopic elastic modulus 7.3 X 1 O 1 O dyn/cm2) gives an x-ray photograph showing coexistence of the (Y and f? forms (Fig. 6).

H*-H 2 1.96 A.

This work was partially supported by a Grant-in-Aid Scientific Research from the Ministry of Education, Japan (No. 147089).

References

1. H. Kusanagi, H. Tadokoro, Y. Chatani, and K. Suehiro, Macromolecules, 10,405 (1977). 2. M. Kuroishi, M. Fujisaki, T. Kajiyama, and M. Takayanagi, Nippon Kagaku Kaishi, 7,1281

3. H. G . Norment and I. L. Karle, Acta Crystallogr., 15,873 (1962). 4. C. Romers, Acta Crystallogr., 17,1287 (1964). 5. M. Haisa and S. Kashino, Acta Crystallogr., B33,485 (1977). 6. S. Arnott and A. J. Wonacott, Polymer, 7,157 (1966). 7. Y. Takahashi, T. Sato, H. Tadokoro, and Y. Tanaka, J. Polym. Sci. Polym. Phys. Ed., 11,233

8. Y. Chatani, K. Suehiro, Y, Okita, H. Tadokoro, and K. Chujo, Makromol. Chem., 113,215

(1972).

(1973).

(1969).


9. S. Kobayashi, K. Murakami, Y. Chatani, and H. Tadokoro, J. Polym. Sci. Polyrn. Lett. Ed., 14,591 (1976).

10. K. Tashiro, M. Kobayashi, and H. Tadokoro, Macromolecules, 10,413 (1977). 11. I. Sakurada and K. Kaji, J. Polym. Sci. C, 31,57 (1970).

Received April 4,1978 Revised June 15,1978

molecular confirmation and crystal structure of the β form of poly(ethylene oxybenzoate)

Documents