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16 Characterization of Crystalline Poly(trioxane) and Poly(tetraoxane) Obtained through Plasma-Initiated Polymerization AKIRA ODAJIMA Department of Applied Physics, Hokkaido University, Sapporo, Japan

Downloaded by UNIV OF ARIZONA on June 7, 2017 | http://pubs.acs.org Publication Date: September 24, 1979 | doi: 10.1021/bk-1979-0108.ch016

YOSHIAKI NAKASE Japan Atomic Energy Research Institute, Takasaki, Japan 1

YOSHIHITO OSADA , ALEXIS T. BELL, and MITCHEL SHEN Department of Chemical Engineering, University of California, Berkeley, CA, 94720 C r y s t a l s of t r i o x a n e (TOX) and tetraoxane (TEOX) have been polymerized i n the s o l i d s t a t e by high energy i r r a d i a t i o n followed by post-polymerization, α-ray (1), γ-ray (2,3) as w e l l as x-ray (4) were u t i l i z e d i n i n i t i a t i n g the p o l y m e r i z a t i o n . Recently, i t has been demonstrated that c r y s t a l l i n e polyoxymethylene (POM) can a l s o be obtained through plasma i n i t i a t e d p o l y m e r i z a t i o n i n the s o l i d state (5). Preliminary c h a r a c t e r i z a t i o n studies i n d i c a t e that s t r u c t u r e s of p o l y t r i o x a n e (PTOX) and polytetraoxane (PTEOX) polymerized by both techniques are s i m i l a r . In t h i s work, f u r t h e r f i n e s t r u c t u r a l i n v e s t i g a t i o n s were c a r r i e d out using s m a l l angle x-ray s c a t t e r i n g (SAXS), wide angle x-ray s c a t t e r i n g (WAXS) and d i f f e r e n t i a l scanning c a l o r i m e t r y (DSC). Experimental S i n g l e c r y s t a l s of TOX and TEOX of the approximate dimensions of 1 mm x 10 mm were prepared by sublimation under reduced p r e s sure. R a d i a t i o n - i n i t i a t e d polymerizations of these c r y s t a l s were c a r r i e d out by γ-ray p r e - i r r a d i a t i o n (1 MR) a t room temperature i n air. They were subsequently post-polymerized a t 55°C f o r TOX, and at 62, 81 and 105°C f o r TEOX (6). Plasma i n i t i a t e d polymerizations were conducted bv^ s e a l i n g the c r y s t a l s i n a g l a s s ampule a f t e r degassing a t 10 - 10 t o r r . A glow discharge was i n i t i a t e d i n the gaseous space i n the ampule by i n s e r t i n g the ampule between p a r a l l e l e l e c t r o d e s . E x c i t a t i o n was provided by an I n t e r n a t i o n a l Plasma Corporation Model 3001 Radiofrequency Generator. A power of 40 watts a t 13.56 MHz was used. Post-polymerizations were permitted to proceed a t 45°C FOR TOX AND 110°C FOR TEOX. D e t a i l s of the p o l y m e r i z a t i o n c o n d i t i o n s f o r both techniques were summa r i z e d i n Table 1. X-ray measurements were c a r r i e d out on a Rigaku Denki RU-100PL Rotating Anode X-ray U n i t . N i c k e l - f i l t e r e d copper u

1

Current address: Department of Chemistry, Mito, Japan.

Ibaraki University,

0-8412-0510-8/79/47-108-263$05.00/0 © 1979 American Chemical Society

Shen and Bell; Plasma Polymerization ACS Symposium Series; American Chemical Society: Washington, DC, 1979.


264

PLASMA

POLYMERIZATION

Table I. S o l i d State Polymerizations of Trioxane and Tetraoxane by γ-Ray or Plasma I n i t i a t i o n

Sample

Post-Polymerization Temperature (°C)

Post-Polymerization Duration (hrs)

Yield M.P. (wt %) (°C)

RADIATION INITIATION PTOX-80 55 PTE0X-12 62 PTE0X-25 81 PTEOX-40 105 PTEOX-80 105

20 25 25 6 6

80 12 25 40 80

187 173 181 179 174

PLASMA INITIATION PTOX-20-1P PTOX-20-2P PTOX-40P PTE0X-4P PTE0X-5P PTE0X-83P

18 46 66 24 24 3

20 20 40 4 5 83

189 185 186 183

45 45 45 110 110 110


182


15.

OSADA E T A L .

Liquid

Vinyl

Monomers

265

r a d i a t i o n was generated a t 40 kV and 80 mA. WAXS p r o f i l e s of the (009) and (0018) r e f l e c t i o n s were measured by a step scanning method with a f i x e d time of 80 or 400 sec i n a symmetrical t r a n s m i s s i o n arrangement. For the l i n e broadening a n a l y s i s of PTOX, instrument broadening was c o r r e c t e d by using a TOX s i n g l e c r y s t a l of comparable dimensions as a r e f e r e n c e sample. The x-ray r o t a t i o n diagram of PTOX was obtained p h o t o g r a p h i c a l l y with the f i b e r a x i s as the r o t a t i o n a x i s . To o b t a i n the volume f r a c t i o n of subc r y s t a l s i n the polymer, i n t e g r a l i n t e n s i t i e s were measured by a microdensitometer f o r two (100) r e f l e c t i o n s , i . e . , one produced only by twin o r i e n t a t i o n and the other on the equator with c o n t r i butions from both o r i e n t a t i o n s . Thermal analyses of the polymer samples were conducted on a Perkin-Elmer DSC-1B D i f f e r e n t i a l Scanning Calorimeter. Approximately 1 mg of sample was used i n each determination. The heating r a t e employed was 16°C/min. The instrument was c a l i b r a t e d using indium as a standard. Scanning e l e c t r o n micrographs were taken on an ISI Mini-SEM. Samples f o r observation were coated with an evaporated 60% gold and 40% platinum a l l o y to a thickness of approximately 200A. Results and D i s c u s s i o n The scanning e l e c t r o n micrograph of plasma samples of PTOX i s shown i n F i g u r e 1. The c r y s t a l s a r e seen to c o n s i s t of r o d l i k e f i b r i l s w e l l a l i g n e d with respect to each other. The appearance of these c r y s t a l s i s s i m i l a r to that of the monomer as w e l l as r a d i a t i o n samples of PTOX (7). The PTEOX c r y s t a l (Figure 2 ) , on the other hand, c o n s i s t s of coarse f i b e r s with rather i r r e g u l a r s i z e s and shapes and no p r e f e r e n t i a l o r i e n t a t i o n . There i s a l s o considerable branching i n PTEOX, whereas i n PTOX no branching i s evident* Recent s t u d i e s i n the f i n e s t r u c t u r e s of r a d i a t i o n polymerized PTOX show that they are d i s o r d e r e d c r y s t a l s i n which m a i n - c r y s t a l l i t e s and s u b - c r y s t a l l i t e s a r e arranged i n s e r i e s (7). The f i n e s t r u c t u r e s of PTEOX are even more d i s o r d e r e d and complex than those of PTOX, and are b e l i e v e d to possess an o r i e n t e d l a m e l l a r morphology. However, when the p o s t - p o l y m e r i z a t i o n i s c a r r i e d out at temperatures above 90°C, the s u b - c r y s t a l l i t e s disappear. WAXS studies i n d i c a t e that the (009) and (0018) r e f l e c t i o n s of PTEOX have an asymmetrical p r o f i l e , suggesting the existence of two d i f f e r e n t l a t t i c e spacings along the f i b e r a x i s . Odajima, e t a l . (8) suggested that there may be two kinds of c r y s t a l l i t e s present, namely those with the extended f i b r i l l a r and the f o l d e d l a m e l l a r morphologies. SAXS p a t t e r n of r a d i a t i o n - p o l y m e r i z e d PTOX i n F i g u r e 3A shows only a sharp e q u a t o r i a l s c a t t e r i n g , but no m e r i d i o n a l s c a t t e r i n g . Those f o r PTOX obtained by plasma i n i t i a t e d p o l y m e r i z a t i o n (samples PT0X-20-1P and PTOX-40P shown i n F i g u r e s 3B and 3C) a r e similar. In the case of PTEOX, those polymerized through r a d i a t i o n i n i t i a t i o n but post-polymerized below 80°C (sample PTE0X-12)



266

PLASMA

Figure

Figure

1.

2.

Scanning electron micrograph of polytrioxane (Sample obtained by phsma-initiated polymerization

Scanning electron micrograph of polytetraoxane (Sample obtained by phsma-initiated polymerization

POLYMERIZATION

PTOX-40P)

PTEOX-4P)



16.

ODAJIMA ET AL.

Poly(trioxane)

and

Poly(tetraoxane)

267

a l s o show no m e r i d i o n a l s c a t t e r i n g i n t h e i r SAXS patterns. How ever, f o r those polymerized above 80°C (sample PTEOX-40) both e q u a t o r i a l and m e r i d i o n a l s c a t t e r i n g a r e present (Figure 4A). (This photograph was taken by using a point f o c u s s i n g camera with a mirror-and-monochrometer o p t i c a l system, hence the sharper e q u a t o r i a l s c a t t e r i n g . ) The s p o t - l i k e s c a t t e r i n g s beyond the m e r i d i o n a l s c a t t e r i n g s a r e i n d i c a t i v e of a long spacing of about 100 X a s s o c i a t e d w i t h stackings of the f o l d e d chain l a m e l l a o r i e n t e d p a r a l l e l to the f i b e r a x i s (9). The e q u a t o r i a l s c a t t e r ing i s a t t r i b u t e d to the existence of n e e d l e - l i k e v o i d s between PTEOX f i b e r s oriented i n the d i r e c t i o n of the f i b e r a x i s . The SAXS p a t t e r n f o r PTEOX-5P i s s i m i l a r (Figure 4B), although the s p o t - l i k e s c a t t e r i n g i s very f a i n t . We note that the PTEOX-5P p a t t e r n i s more s i m i l a r to the annealed sample of r a d i a t i o n poly merized PTEOX (10). I t i s not c l e a r why the SAXS data f o r PTE0X-83P e x h i b i t only weak m e r i d i o n a l s c a t t e r i n g , even though the post-polymerization was c a r r i e d out a t the same temperature (110°C). Figures 5A and 5B show the WAXS patterns f o r PTOX obtained through r a d i a t i o n i n i t i a t i o n (sample PTOX-80) and plasma i n i t i a t i o n (sample PTOX-40P). Both show the h i g h l y o r i e n t e d f i b e r diagrams. The (100) r e f l e c t i o n s c l e a r l y i n d i c a t e the twin spots i n a d d i t i o n to spots on the equator. The amorphous halo i s very weak i n both samples. For PTEOX, F i g u r e 6A shows that the r a d i a t i o n polymerized sample (PTEOX-80) a l s o possesses h i g h l y o r i e n t e d f i b e r diagrams. I t appears to have no twin spots, but samples PTE0X-12 and 25 do. In the case of plasma samples, the (100) twin spots a r e present i n PTE0X-5P, though very f a i n t (Figure 6B). Sample PTE0X-83P, on the other hand, shows a r i n g - l i k e WAXS p a t t e r n (Figure 6C). The reason f o r the absence of d i s c r e t e s c a t t e r i n g may p o s s i b l y be a t t r i b u t e d to the i s o t r o p i c s t r u c t u r e of l a m e l l a s t a c k i n g . The amorphous halos i n a l l of the PTEOX samples may be due to the amorphous regions between the lamellae of f o l d e d chain c r y s t a l s . S u b - c r y s t a l f r a c t i o n s i n PTOX from both r a d i a t i o n and plasma i n i t i a t e d polymerizations were determined from the (100) r e f l e c t i o n s and summarized i n T a b l e 2. T h e i r values a r e somewhat, but not s u b s t a n t i a l l y , lower f o r the plasma samples than f o r the r a d i a t i o n samples. However, s i n c e the amount of s u b c r y s t a l f r a c t i o n depends on both the temperature and the y i e l d , meaningful comparisons between these two types of samples a r e d i f f i c u l t on the b a s i s of these r a t h e r l i m i t e d data. In t h e i r recent p u b l i c a t i o n , Odajima and h i s coworkers (11) have shown that the r a t h e r broad and asymmetric (009) and (0018) WAXS p r o f i l e s of PTEOX polymerized above 80°C by r a d i a t i o n i n i t i a t i o n may be r e s o l v e d i n t o two curves. One can be a t t r i b u t e d to the extended chain c r y s t a l s (the only kind present i n sample PTE0X-12), and the other i s the l a m e l l a r type c r y s t a l s with t h i c k nesses of about 100 X. F i g u r e 7 shows that the l i n e shape of the (009) p r o f i l e of the plasma sample PTEOX-5P i s r a t h e r sharp and s i m i l a r to that of the r a d i a t i o n sample PTEOX-25. The h a l f width (Δ2θ)ι = 1.72° or 0.012 S" ) o f the (0018) p r o f i l e i s narrower than those*of PTEOX-25 (2.50° or 0.017 A ) and PTEOX-80 (2.25° o r 1

1



268

PLASMA POLYMERIZATION

Figure 3. Small-angle x-ray scattering patterns of polytrioxane. (A) Sample PTOX-80 by radiation initiation; (B) Sample PTOX-20-1P by plasma initiation; and (C) Sample PTOX-40P by plasma initiation.

Figure 4. PTEOX-40

Small-angle x-ray scattering patterns of polytetraoxane. (A) Sample by radiation initiation; (B) Sample PTEOX-5P by plasma initiation; and (C) Sample PTEOX-83P by phsma initiation.



Figure

5.

Wide

angle x-ray scattering patterns of polytrioxane. (A) Sample PTOX-80 tion initiation; and (B) Sample PTOX-40P by plasma initiation.


by

radia

to

Ci

ο

ο

ο

Ο

>

Η

> w

ο ο >

PLASMA

POLYMERIZATION


270

Figure 6. Wide-angle x-ray scattering patterns of polytetraoxane. (A) Sample PTEOX-80 by radiation initiation; (B) Sample PTEOX-5P by plasma initiation; and (C) Sample PTEOX-83P by plasma initiation.


16.

ODAjiMA E T A L .

Table I I .

and

271

Poly(tetraoxane)

S u b c r y s t a l F r a c t i o n s i n Polytetoxane

Yield (wt %)

Sample


Poly(trioxane)

Sub-crystal Fraction (Vol %)

Post P o l y m e r i z a t i o n Temperature (°C)

RADIATION INITIATION PTOX-80 PTOX-2 PT0X-19 PTOX-50

80 2 19 50

55 50 50 50

36 - 39 ^45 ^40 V30

PLASMA INITIATION PTOX-20-1P PTOX-40P

20 40

45 45

^40 27 - 31

44

Figure

7.

45

46

47 48 2 θ (degrees)

49

50

X-ray diffraction profiles of the (009) and (0018) reflections obtained by plasma initiation (s = 2sin ®/A)

of


PTEOX

272

PLASMA POLYMERIZATION

J


o . o i s r ). On the b a s i s of these f i n d i n g s , one might conclude that PTE0X-5P contains l e s s f o l d e d chain c r y s t a l s and i t s cspacings i n the extended chain c r y s t a l s are longer than those i n the r a d i a t i o n samples. T h i s c o n c l u s i o n , however, must be q u a l i f i e d by the p o s s i b i l i t y that the higher p o s t - p o l y m e r i z a t i o n tem perature used i n the plasma i n i t i a t i o n method may have annealed out some of the l o n g i t u d i n a l compression during the post-polymer i z a t i o n period. On the b a s i s of the p a r a c r y s t a l l i n e theory, the Cauchy-plot method can be employed i n line-broadening a n a l y s i s (12). In t h i s method, the i n t e g r a l breadth of the f i r s t order r e f l e c t i o n i s approximated by ASx

= 1/5

w

+

cOrgSj

2

where Dw i s the weight average c r y s t a l l i t e s i z e along the c - a x i s , c i s the averaged c-spacing, g i s the p a r a c r y s t a l l i n e d i s t o r t i o n parameter and S = 2 s i n θ/λ. From the slope and i n t e r s e c t i o n of a Si v s . S i p l o t , values of g and Dw can be r e a d i l y obtained. For the plasma sample PTOX-40P, D = 650 X and G = 1.25%. By c o n t r a s t , the comparable r a d i a t i o n samples have values of 550 S and 0.7%, r e s p e c t i v e l y . The l o n g i t u d i n a l dimensions f o r both samples are c o n s i d e r a b l y s h o r t e r than the extended length of the m i c r o f i b r i l , which i s of the order of 10* X. The most l i k e l y i n t e r p r e t a t i o n f o r t h i s observation i s that the type of d e f e c t s suggested by the k i n k model (7) must e x i s t i n the c h a i n d i r e c t i o n . DSC thermograms f o r plasma samples of PTOX and PTEOX are shown i n Figure 8. The endothermic p r o f i l e s of PTOX e x h i b i t no superheating phenomenon, resembling those of the r a d i a t i o n samples post-polymerized below 50°C a t high y i e l d or above 50°C a t low yield. I t has been observed that a double endothermic peak appears i n the heating curve of r a d i a t i o n polymerized PTOX a t 55°C with a y i e l d of over 20% (13). Superheating i n these polymers was a t t r i b u t e d to a new type of POM texture produced a t the l a t e r stage of s o l i d s t a t e p o l y m e r i z a t i o n . A l s o shown i n Figure 8 are the thermograms f o r PTE0X-4P and PTE0X-83P. They are very s i m i l a r d e s p i t e the d i f f e r e n c e s i n y i e l d and morphologies. Neither sample shows superheating e f f e c t , a l though both have r e l a t i v e l y long t a i l s e c t i o n s i n the low tempera ture range. For the sake of comparison, we show i n F i g u r e 9 the endothermic p r o f i l e s of r a d i a t i o n polymerized PTEOX. The p r o f i l e of PTE0X-12 i s extremely sharp, with a r e l a t i v e l y low peak tempera ture (170°C). Samples PTEOX-25 and PTEOX-80, on the other hand, have much broader heating curves, i n d i c a t i n g the presence of s u p e r p o s i t i o n of two endothermic curves r e s o l v e d by the dotted lines. I t i s b e l i e v e d that these p r o f i l e s c o n s i s t of two c r y s t a l l i n e forms, namely the lower m e l t i n g f o l d e d chain c r y s t a l l i t e s and the higher melting extended chain c r y s t a l l i t e s (6, _9, 14). It i s of i n t e r e s t to note that only one melting peak i s present i n the plasma samples, even though they were post-polymerized a t e l e v a t e d temperatures. In c o n c l u s i o n , we can s t a t e that PTOX obtained through e i t h e r x

2



16.

ODAjiMA E T A L .

Poly(trioxane)

and

273

Poly(tetraoxane)

I73°C J 120

I

I

I

140

160

180

I— 200

TEMPERATURE ( ° C ) Figure 8. Differential scanning calorimetry polytetraoxane obtained by phsma-initiated

-I 140

I 160

thermograms polymerization

of polytrioxane in the solid

1

1

1—

180

200

220

and state

TEMPERATURE ( C) e

Figure 9. Differential scanning calorimetry thermograms of polytetraoxanes ob tained by γ-ray-initiated polymerizations in the solid state. Dotted curves indi cate the decomposed endothermic profiles caused by the extended chain crystals and folded chain crystals.


P L A S M A POLYMERIZATION

274

plasma or γ-ray i n i t i a t e d polymerizations have r a t h e r s i m i l a r f i n e s t r u c t u r e s . However, there are some d i f f e r e n c e s i n the r a d i a t i o n samples and plasma samples of PTEOX. These d i f f e r e n c e s can not yet be d e f i n i t i v e l y e s t a b l i s h e d , s i n c e the f i n e s t r u c t u r e s are known to depend i n t i m a t e l y on the polymerization c o n d i t i o n s (tem perature, y i e l d , e t c . ) which are not e x a c t l y the same i n the two polymerization techniques.


Abstract Crystals of trioxane and tetraoxane can be polymerized in the solid state by plasma initiation followed by post-polymerization. Scanning electron micrographs indicate that PTOX consists of well aligned fibrils, while PTEOX have irregular coarse fibers with considerable branching. Small and wide angle x-ray scattering patterns indicate that PTOX crystals obtained through plasma initiation resemble those by γ-ray initiation. However, plasma samples of PTEOX appear to consist of one rather than two crys talline forms, as shown by both x-ray and differential scanning calorimetric data. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14.

Coleson, J. P., Reneker, D. Η., J. Appl. Phys., (1970), 41, 4296. Okamura, S., Hayashi, Κ., Nishi, Μ., J. Polymer Sci., (1962), B60, 526. Lando, J., Morosoff, Ν., Morowitz, Η., Post, Β., J. Polymer Sci., (1962), B60, 124. Voigt-Martin, I., Makromol. Chem., (1974), 175, 2669. Osada, Y., Shen, M., Bell, A. T., Polymer Letters, in press. Nakase, Y., Kuriyama, I., Odajima, Α., Polymer J., (1976), 8, 35. Wegner, G., Fischer, E. W., Munoz-Escalona, Α., Makromol. Chem., (1975), Suppl. 1, 521. Odajima, Α., Ishibashi, Τ., Nakase, Y., Kuriyama, E., Rep. Prog. Polymer Phys. Japan, (1976), 19, 161. Kato, T., Nakase, Y., Yoda, O., Kuriyama, Ε., Odajima, Α., Polymer J., (1976), 8, 331. Nakase, Y., Kato, T., Yoda, O., Kuriyama, I., Odajima, Α., Polymer J., (1977), 9, 605. Odajima, Α., Ishibashi, T., Nakase, Y., Kuriyama, I., to be published. Hoseman, R., Bagchi, S. Ν., "Direct Analysis of Diffraction of Matter," North Holland Publ. Co., Amsterdam, 1962. Nakase, Y., Juriyama, I., Nishijima, Η., Odajima, Α., J. Mat'l Sci., (1977), 12, 1443. Nakase, Y., Kuriyama, I., Polymer J., (1973), 4, 517.

Received March 29, 1979.


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