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5 Applied Crystallization Kinetics. III. Comparison of Polyepichlorohydrins of Different Stereoregularity P. D R E Y F U S S

Downloaded by PURDUE UNIV on November 7, 2017 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/bk-1975-0006.ch005

B. F. Goodrich Research and Development Center, Brecksville, Ohio 44141

Introduction In the course of some of our work on polyethers, we encountered a series of crystalline polyepichlorohydrins which differed quite markedly in their processing characteristics but otherwise seemed quite s i m i l a r . Differences revealed by the infrared and nuclear magnetic resonance techniques then available were too insignificant to be helpful in their characterization. A l l polymers were shown to be crystalline and isotactic by X - r a y analysis. Small differences in optical activity were measurable. However, these differences were too small to be useful for correlation with physical properties. We found that an examination of their crystallization behavior and rates of crystallization was an extremely sensitive and revealing way of characterizing them. Experimental Microscopy. Thin films (1-2 mils) were pressed at 1 5 0 ° C using a Pasedena press fitted with West SCR controllers. T y p i cally, a small sample was placed between Teflon coated a l u m i num foil sheets, preheated for 30 sec, and held at 25, 000 lb. gauge load for 5 min. Samples were then rapidly transferred to a cooling press and held at 25, 000 lb. gauge load for 5 min. Some of the lower melting samples were pressed at 1 0 0 ° C . Portions of these films were placed on a glass slide and covered with a cover glass. Samples were melted in an air oven at the desired temperature, usually 1 5 0 ° C for the desired time, usually 15 min and then rapidly transferred to a hot stage at Current address: Institute of Polymer Science, University of Akron, A k r o n , Ohio 44325. 70 Vandenberg; Polyethers ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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Polyepichlorohydrins

71


constant temperature. The hot stage temperature was controlled by circulating liquid f r o m a Haake NBS bath through the stage. Temperatures, measured by means of a thermocouple in the stage near the sample, were constant to 0. 1 ° C or less. The growth of the spherulites that formed was observed using a Unitron polarizing microscope with crossed polaroids. Photographs were taken with the aid of an A m e r i c a n Optical Co. Photomicrographic camera with a Polaroid Land camera back. Melting was followed using a heating rate of 0. 5 to 1° per min. The slower rate was used in the vicinity of the melting temperature. Dilatometry. Volume-temperature measurements, and c r y s tallization rate measurements were c a r r i e d out in J-shaped dilatometers made f r o m 1 m m P r e c i s i o n bore graduated capillary tubing with mercury as the confining liquid. The procedure followed was very s i m i l a r to that described by Bekkedahl (JJ. Well-fused pellets of appropriate dimensions were pressed at 5 Ram force/lb. Hydraulic Pressure on the gauge and 25 to 120°C (usually 9 0 ° G ) . The pellets were cooled to 4 5 - 5 0 ° C at full pressure before removing f r o m the moid. The sealed dilatometers containing the pellets were evacuated to about 10"* 5 m m Hg while heating at 1 2 5 - 3 5 ° C for about 3 hrs prior to filling with mercury. F o r the rate studies, the prepared dilatometers were placed in a 1 5 0 ° C bath for about 30 min before transferring rapidly to a second bath at the crystallization temperature. Crystallization temperatures were controlled to + 0. 01 °C with the aid of a Dynapac-15 temperature controller. Higher temperatures of the melting bath and longer melting times were tried occasionally. These did not change the observed rates for any of the samples studied. A l l rates are reported in terms of the time, ti., for half the total change in height to occur. Whenever the value of t i was less than about 10 min, we were not able to determine an exact value because crystallization began before thermal equilibrium was achieved. Melting temperatures after isothermal crystallization were obtained in the same bath using heating rates of 0. 3 ° C per min and observing the change in height with temperature which was measured with a calibrated mercury thermometer. Melting temperatures were taken as the temperature where the last traces of crystallinity disappeared.

Vandenberg; Polyethers ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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Results


D e s c r i p t i o n of P o l y m e r s . A wide v a r i e t y of c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n s w e r e e x a m i n e d i n this study. S o m e t y p i c a l e x a m p l e s a r e g i v e n i n T a b l e 1. A l l the p o l y m e r s w e r e p r e p a r e d f r o m r a c e m i c m o n o m e r , but s o m e of t h e m w e r e p r e p a r e d u s i n g i n i t i a t o r s of the type p r e v i o u s l y r e p o r t e d to give p a r t i a l l y o p t i c a l l y a c t i v e p o l y m e r s (2-6). T h e p o l y m e r s w e r e shown to be i s o t a c t i c by c o m p a r i s o n of the o b s e r v e d d - s p a c i n g s with those r e p o r t e d i n the l i t e r a t u r e f o r c r y s t a l l i n e i s o t a c t i c p o l y e p i c h l o r o h y d r i n (8,9). A l s o i n c l u d e d i n T a b l e 1 f o r c o m p a r i s o n a r e s o m e data on p o l y p r o p y l e n e o x i d e s p r e p a r e d with d i f f e r e n t i n i t i a t o r s . Spherulite Morphology. Crystalline polyepichlorohydrin r e a d i l y f o r m s s p h e r u l i t e s on c o o l i n g f r o m the melt. A s shown i n F i g u r e 1, we have o b s e r v e d two k i n d s of s p h e r u l i t e s .

b Figure 1. Polyepichlorohydrin spherulites. Left: Type I spherulites from 329C after melting at 170°C and crystallizing at 50°C for 185 min. (128%). Right: Type II spherulites from 39A after melting at 150°C and crystallizing at 50°C for 222 min. (128x).



Ferric chloride

Polymer from ^ - p r o p y l ene oxide

b

17+5

b

C

c

b c Crystalline, 8.0 , -9.3 c Semicrystalline, 6. 1^, -8 Amorphous, 4 . 9 , + l 25 + 5^, -16 4- 5

0 0 -2. 36 -2.80 -9.75 -10.1

in M - P y r o l at 2 3 ° C

'

7

7

Ref

c

a

D e t e r m i n e d in benzene at 2 0 ° C .

Determined in chloroform at 2 0 ° C .

A is a typical initiator for the preparation of non-optically active but crystalline polymers fr racemic monomer. Β are typical initiators for the preparation of optically active polymer f i racemic monomer.

Potassium hydroxide

Polymer f r o m J - p r o p y l ene oxide

a

Diethyl zincd-borneol

A A Β Β Β Β

Initiate-r

Polymer f r o m racemic propylene oxide

Sample 329C 100Z 162A 2437 2413 2431

Table 1 T y p i c a l Crystalline Polyepichlorohydrins


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B o t h have f i b r i l l a r s t r u c t u r e s but the s t r u c t u r e of T y p e I is c o a r s e r than that of T y p e II. O c c a s i o n a l l y r i n g s a r e o b s e r v e d in T y p e II s p h e r u l i t e s . S o m e t i m e s as shown i n F i g u r e 2 both types of texture a r e o b s e r v e d i n a s i n g l e s p h e r u l i t e . W h e n the s p h e r u l i t e s w e r e o b s e r v e d between c r o s s e d p o l a r o i d s u s i n g a 1st o r d e r r e d plate i n the u s u a l 45° o r i e n t a t i o n , it was found that both types of s p h e r u l i t e s a r e n e g a t i v e l y biréfringent. T h i s is not s u r p r i s i n g s i n c e negative s p h e r u l i t e s have a l s o been o b s e r v e d i n p o l y p r o p y l e n e o x i d e f i l m s (10). N e v e r t h e l e s s , the s p h e r u l i t e s a r e not i d e n t i c a l when v i e w e d with the 1st o r d e r r e d plate. T y p e I is blue i n the s e c o n d and f o u r t h q u a d r a n t s and o r a n g e i n the f i r s t and t h i r d . T y p e II i s s i m i l a r but the q u a d rants a r e s e p a r a t e d by a r e d c r o s s .

Figure 2. Type I and II spherulites both seen in the same spherulite, from 164A melted at 150'C and crystallized at 50°C for 168 min. (128x)

T h e type of s p h e r u l i t e that f o r m s does not s e e m to be a f f e c t e d by the t e m p e r a t u r e at w h i c h the s a m p l e i s m e l t e d o r by the t e m p e r a t u r e of c r y s t a l l i z a t i o n . We have o b s e r v e d the g r o w t h of s p h e r u l i t e s of both types at 30, 50, and 6 0 ° C a f t e r m e l t i n g at 1 5 0 ° C . S i m i l a r m o r p h o l o g y was obtained f r o m the s a m e s a m p l e at a l l t e m p e r a t u r e s . H o w e v e r , as expected, the g r o w t h rate and



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perfection of the spherulites are dependent on the temperature of crystallization. Rates are slower and perfection is greater at temperatures nearer to the polymer melting temperature. We have been able to grow very large spherulites by crystallizing for several days at 5 0 ° C . The morphology does not seem to be affected by the temperature at which the sample is melted prior to crystallization. We have crystallized at 50°C after melting at 130, 150, and 1 7 0 ° C . The morphology obtained f r o m the same sample was similar in all cases. The main difference was that more small spherulites, unresolvable at our usual magnification of 150x, formed after melting at 1 3 0 ° C . Melting Temperatures. The melting temperatures we observe microscopically are usually higher by a few degrees than thoseobserved dilatometrically. Some typical results are given in Table 2 and in Figures 3-5. This is not an unexpected result, since polymer melting temperatures are very sensitive to the rate of heating unless extremely slow heating rates, such as 0. 5 ° C per day, are used. A l s o , the heat transfer in a dilatometer and on a hot stage may be quite different. In addition, Table 2 Microscopic and Dilatometric Melting Temperatures of Crystalline Polyepichlorohydrin Polymer 329C 39A 164A 2413 2431 100Z

Microscopic T

m

115-16 119-20 114 and 117

(°C)

Dilatometric T

m

(°C)

113 115 108.5 and 113 115-17 117.5 111

sample preparation and previous heat history can affect the exact melting temperature observed ( j _ l ) . The important point here is that two different melting temperatures have been observe d_boJhjrujcj^^ the same sample and in different samples. In some of the later experiments, samples were held at temperatures between the higher and lower melting temperatures for several hours to verify that the higher melting polymer was not just slower to melt. Thus, there are two families of crystalline polyepichlorohydrins. A s



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Figure 3.

Melting of 329C and 39A after simultaneously melting at 150°C crystallizing at 50°C on the same slide

and

Figure 4. Melting of spherulites of 164A. At 80°C both Type I and Type II spherulites are visible. By 115°C Type I spherulites are melted. Type II spherulites disappear by 117°C (83%).




DREYFUSS

Figure 5.

Dilatometric melting curve of 164A. Two inflections suggest two different melting temperatures.


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will be discussed below these two families can be related to the stereoregularity of the polymers. Crystallization Rates. We determined growth rates of the spherulites microscopically, but only examined the rates of nucleation qualitatively for reasons that will emerge below. Overall rates of crystallization were determined dilatometrical-


iy. Nucleation of Spherulites. We have examined the rates of crystallization of the two kinds of spherulites microscopically in order to obtain further evidence to aid in understanding the differences observed. We found that different kinds of nucleation apparently occurred in different samples. Some samples gave spherulites of uniform size suggesting instantaneous, heterogeneous nucleation. Other samples gave spherulites of variable size such as would be expected f r o m sparodic, homogeneous nucleation. Only these latter samples were used in the comparison made below in determinations of overall rates of c r y s t a l l i zation. The number of nuclei that appear in the field of view also varies considerably f r o m sample to sample and even f r o m area to area in the same sample. Nevertheless, throughout our studies it appears that spherulites form more readily f r o m Type II spherulites, that is, f r o m more optically active polymer. Growth Rates of Spherulites. A s shown in Figure 6, both types of spherulites grow in the typical fashion observed many times for spherulites: namely, linearly with time. In the particular examples illustrated it was not possible to follow the growth of 39A for as long as 329C was studied because impingement occurred sooner. The fact that a single straight line can be drawn for both types is fortuitous in as much as the particular spherulites examined happened to have the same diameter at the same initial time. But it is significant that the growth rates determined f r o m the slope of the line do not appear to be different. Both are of the order of 1.5 microns per minute. If either type grows faster, the data in Figure 6 suggests that Type II spherulites grow faster. Overall Rates of Crystallization. We divided our studies of overall rates of crystallization into two areas: reproducibility studies and determination of the temperature of maximum rate of crystallization.



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1. R e p r o d u c i b i l i t y . A s stated above, o b s e r v a t i o n s of the o v e r a l l rate of c r y s t a l l i z a t i o n of c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n s t u r n e d out to be a p a r t i c u l a r l y s e n s i t i v e was of c h a r a c t e r i z i n g polyepichlorohydrins. T h u s , we have taken s p e c i a l c a r e to c h e c k the r e p r o d u c i b i l i t y of o u r d i l a t o m e t r i c o b s e r v a t i o n s of o v e r a l l r a t e s . We have c a r r i e d out three d i f f e r e n t kinds of a n a l y s i s to c h e c k r e p r o d u c i b i l i t y . F i r s t , we s h o w e d that the data f r o m a n y given d i i a t o m e t e r w e r e s u p e r i m p o s a b l e o v e r the whole range on r e p e a t e d runs at the s a m e t e m p e r a t u r e . T h i s was t r u e f o r both " s l o w " a n d " f a s t " c r y s t a l l i z i n g p o l y m e r s . Second, we d e m o n s t r a t e d that two d i f f e r e n t s a m p l e s of the s a m e p o l y m e r i n two d i f f e r e n t d i l a t o m e t e r s gave r e p r o d u c i b i l i t y of t i m e a s u r e ments o v e r the whole t e m p e r a t u r e range studied. F i n a l l y , we showed that good s u p e r p o s i t i o n is o b s e r v e d on s h i f t i n g c u r v e s obtained a t d i f f e r e n t c r y s t a l l i z a t i o n t e m p e r a t u r e s . S u c h r e p r o d u c i b i l i t y is t y p i c a l of d i l a t o m e t r i c r e s u l t s on c r y s t a l l i n e p o l y m e r s i n g e n e r a l (11). F r o m these studies we conclude that c r y s t a l l i n e polyepichlorohydrin c r y s t a l l i z e s in a n o r m a l r e p r o d u c i b l e m a n n e r . T h e v a r i a t i o n s r e p o r t e d below a r e due to d i f f e r e n c e s i n the p o l y m e r s * 28,

3

Figure 6. Comparison of spherulite growth rates at 50°C after melting at 150°C. Ο = Type I spherulites from 329C. • = Type II spher ulites from 39A.


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2. D e t e r m i n a t i o n of the m a x i m u m rate of c r y s t a l l i z a t i o n . T h e rate of c r y s t a l l i z a t i o n of any g i v e n p o l y m e r i s v e r y s e n s i t i v e to the t e m p e r a t u r e a t w h i c h the m e a s u r e m e n t i s c a r r i e d out (11). It goes t h r o u g h a m a x i m u m at a f a i r l y w e l l - d e f i n e d t e m p e r a t u r e . A b o v e that t e m p e r a t u r e , as the m e l t i n g t e m p e r a t u r e i s a p p r o a c h ed, the rate of n u c l e a t i o n i s l o w e r a n d l o w e r a n d the o v e r a l l rate d e c r e a s e s . B e l o w that t e m p e r a t u r e as the g l a s s t r a n s i t i o n tempe r a t u r e i s a p p r o a c h e d , the m e l t b e c o m e s i n c r e a s i n g l y v i s c o u s , the rate of d i f f u s i o n of the p o l y m e r chains d e c r e a s e s , and a slowe r o v e r a l l c r y s t a l l i z a t i o n rate is obtained. Therefore, in order to m a k e m e a n i n g f u l c o m p a r i s o n s of p o l y m e r s p r e p a r e d u n d e r d i f f e r e n t conditions i t was n e c e s s a r y to d e t e r m i n e the e f f e c t of t e m p e r a t u r e on the c r y s t a l l i z a t i o n rate of e p i c h l o r o h y d r i n . We have e x a m i n e d the rate of c r y s t a l l i z a t i o n of w e l l o v e r 200 d i f f e r ent p o l y e p i c h l o r o h y d r i n s a t a t l e a s t t h r e e d i f f e r e n t t e m p e r a t u r e s . S o m e of o u r m o r e t h o r o u g h studies a r e i l l u s t r a t e d i n F i g u r e 7. A s the f i g u r e i l l u s t r a t e s , the m a x i m u m rate of c r y s t a l l i z a t i o n

Figure 7. Effect of temperature on the crystallization rate of polyepichlorohydrin


5. DREYFUss


81

(lowest t i ) o c c u r s at about 5 0 ° C . T h e r e a r e s e v e r a l i n t e r e s t i n g a n d u n u s u a l f e a t u r e s about c r y s t a l l i z a t i o n r a t e s of p o l y e p i c h l o r o h y d r i n i l l u s t r a t e d i n F i g u r e 7. E v i d e n t l y , t h e r e a r e not one o r even two p o l y e p i c h l o r o h y d r i n s . Instead t h e r e i s a whole f a m i l y of c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n s . T h e r e a r e the s l o w l y c r y s t a l l i z i n g " m e m b e r s of the f a m i l y l i k e 8 E . T h e s e p o l y m e r s have a r e l a t i v e ly s h a r p m a x i m u m and a n i n t e r m e d i a t e m e l t i n g t e m p e r a t u r e . T h e y c r y s t a l l i z e too s l o w l y and have too n a r r o w a p r o c e s s i n g range to be u s e f u l f o r , say, m o l d e d a r t i c l e s . T h e r e a r e the m e m b e r s with a n " i n t e r m e d i a t e " r a t e of c r y s t a l l i z a t i o n l i k e 100Z. T h e s e p o l y m e r s s u r p r i s i n g l y have a s o m e w h a t l o w e r melting temperature. T h e y too have a r a t h e r s h a r p m a x i m u m in the rate v e r s u s t e m p e r a t u r e c u r v e and would not be e x p e c t e d to p r o c e s s w e l l o v e r a v e r y b r o a d range. F i n a l l y , t h e r e a r e the " f a s t c r y s t a l l i z i n g " m e m b e r s , i l l u s t r a t e d by 2413 and 2431. T h e s e p o l y m e r s have the h i g h e s t m e l t i n g t e m p e r a t u r e s we have o b s e r v e d so f a r and a b r o a d m a x i m u m i n rate v e r s u s t e m p e r a t u r e c u r v e that suggests a b r o a d p r o c e s s i n g range. T h e " f a s t c r y s t a l l i z i n g " p o l y m e r s a l s o have the h i g h e s t o p t i c a l r o t a t i o n s that we o b s e r v e d . T h e y c r y s t a l l i z e i n the f o r m of T y p e II s p h e r u l i t e s . We have studied m a n y e x a m p l e s of e a c h type of polymer. F r o m the c u r v e s and the i n t r i n s i c v i s c o s i t i e s g i v e n f o r the p o l y m e r s , i t a p p e a r s that i n the range studied, i n t r i n s i c v i s c o s ity does not have a n i m p o r t a n t effect on c r y s t a l l i z a t i o n rate. A n a p p a r e n t a n o m a l y i l l u s t r a t e d by the data i n F i g u r e 7 i s the r e l a t i o n s h i p o r r a t h e r l a c k of r e l a t i o n s h i p between the o b s e r v e d rate and the m e l t i n g t e m p e r a t u r e . U s u a l l y a l o w e r m e l t i n g t e m p e r a t u r e c o r r e s p o n d s to g r e a t e r s t r u c t u r a l i r r e g u l a r i t y a n d s l o w e r c r y s t a l l i z a t i o n rate (11). In this c a s e 329C has a l o w e r m e l t i n g t e m p e r a t u r e than 8 E and yet c r y s t a l l i z e s m u c h m o r e r a p i d l y . T h e s e o b s e r v a t i o n s a r e d i s c u s s e d below and an e x p l a n ation is g i v e n .


ff

3. O v e r a l l c r y s t a l l i z a t i o n rate of blends of " f a s t " a n d " s l o w " c r y s t a l l i z i n g p o l y m e r s . We obtained f u r t h e r e v i d e n c e that the g r e a t e r ease of n u c l e a t i o n of o p t i c a l l y a c t i v e p o l y m e r into T y p e II s p h e r u l i t e s is r e s p o n s i b l e f o r the o b s e r v e d i n c r e a s e i n c r y s t a l l i z a t i o n rate by s t u d y i n g s o l u t i o n blends of 2413 and a nonopti c a l l y a c t i v e p o l y e p i c h l o r o h y d r i n . We found that a d d i t i o n of only 6% of 2413 r e d u c e d the t i a t 5 0 ° C of the 'slow" p o l y m e r f r o m 32 m i n to l e s s than 10 m i n .


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D i s c u s s i o n and Conclusions P o l y m e r i z a t i o n of m o n o m e r s l i k e e p i c h l o r o h y d r i n , O C H — ( C H C l ) , l e a d s to p o l y m e r s w h i c h t h e o r e t i c a l l y c a n have m a n y d i f f e r e n t i s o m e r s . A s a r e s u l t of the v e r y elegant w o r k of P r i c e and c o w o r k e r s (12) a n d of V a n d e n b e r g (13) i n t h e i r m e c h a n i s t i c s t u d i e s of the r i n g opening p o l y m e r i z a t i o n of epoxides, the task of a n a l y z i n g these p o l y m e r s i s s o m e w h a t s i m p l i f i e d . F o r exa m p l e , head-to-head, t a i i - t o - t a i l , and h e a d - t o - t a i l p o l y m e r s a r e a l l t h e o r e t i c a l l y p o s s i b l e , but only h e a d - t o - t a i l need to be c o n s i d e r e d f o r the f o l l o w i n g r e a s o n s . We know that p o l y m e r i z a t i o n o c c u r s by r i n g opening i n w h i c h the bond between o x y g e n a n d the c a r b o n l a b e l l e d w i t h a n a s t e r i s k (the a s y m m e t r i c c a r b o n atom) is b r o k e n . F u r t h e r m o r e , we know f r o m studies with o p t i c a l l y a c t i v e p r o p y l e n e o x i d e that p o l y m e r i z a t i o n o c c u r s by i n v e r s i o n at the a s y m m e t r i c c a r b o n and that no r a c e m i z a t i o n o c c u r s on p o l y m e r i z a t i o n . We a l s o know that e v e n when o p t i c a l l y a c t i v e monom e r i s used, s o m e a m o r p h o u s p o l y m e r i s p r o d u c e d . P r i c e a n d c o w o r k e r s (7) have found that these i r r e g u l a r i t i e s a r e l a r g e l y , i f not e n t i r e l y units of head-to-head, t a i l - t o - t a i l s t r u c t u r e f o r m e d as a r e s u l t of s o m e r e a c t i o n i n v o l v i n g c l e a v a g e of the bond c o r r e s p o n d i n g to the C H -O bond i n e p i c h l o r o h y d r i n . In a d d i t i o n we know that a l l c r y s t a l l i n e p o l y e p o x i d e s known to date a r e i s o t a c t i c . S y n d i o t a c t i c p o i y e t h e r s r e m a i n a p r o d u c t of the f u t u r e . 3


2

2

A l t h o u g h s i m i l a r s t u d i e s have not been r e p o r t e d f o r p o l y e p i c h l o r o h y d r i n , there i s no r e a s o n to e x p e c t any d i f f e r e n c e s i n m e c h a n i s m of p o l y m e r i z a t i o n f o r this epoxide. It c a n be a s s u m ed that p o l y m e r i z a t i o n l e a d i n g to c r y s t a l l i n e p o l y m e r o c c u r s p r e d o m i n a n t l y by i n v e r s i o n a t the a s y m m e t r i c c a r b o n a t o m a n d r e s u l t s i n h e a d - t o - t a i l p l a c e m e n t of the m o n o m e r . M a i n l y i s o t a c t i c p o l y m e r w i l l be f o r m e d . O u r s t u d i e s a n d p r e v i o u s w o r k have b o r n this out (8, 9, 14, 15). T h e r e s u l t s of this study f u r t h e r r e v e a l that the c r y s t a l l i n e p o l y e p i c h l o r o h y d r i n we have s t u d i e d c o n s i s t s of i s o t a c t i c s e q u e n c e s that c a n c r y s t a l l i z e i n the f o r m of two d i f f e r e n t kinds of s p h e r u l i t e s . We have shown that the two kinds of s p h e r u l i t e s c a n c o c r y s t a i l i z e . A t p r e s e n t o u r e d u c a t e d guess is that a l l the p o l y m e r s we have e x a m i n e d c o n t a i n e i t h e r T y p e I o r a m i x t u r e of T y p e I a n d T y p e II s p h e r u l i t e s in v a r y i n g p r o p o r t i o n s . The p o l y m e r s that c r y s t a l l i z e m o s t r a p i d l y a n d that have the h i g h e s t m e l t i n g t e m p e r a t u r e s have s o m e o p t i c a l a c t i v i t y a n d t h e i r f i l m s c o n t a i n p r e d o m i n a n t l y T y p e II s p h e r u l i t e s . We c o n c l u d e that the T y p e II s p h e r u l i t e s a r e obtained f r o m o p t i c a l l y a c t i v e p o l y m e r s e q u e n c e s . We do not m e a n to i m p l y that a l l s e q u e n c e s i n these



5.

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p o l y m e r s have the s a m e c o n f o r m a t i o n . We m e r e l y w i s h to s u g g e s t that enough of an e x c e s s of one e n a n t i o m e r has p o l y m e r i z e d to give a m e a s u r a b l e r o t a t i o n and that the o v e r a l l s t r u c t u r e of these p o l y m e r s is m o r e r e g u l a r . We s u g g e s t that T y p e I s p h e r u l i t e s a r e obtained f r o m r a c e m i c p o l y m e r that shows l i t t l e o r no o p t i c a l r o t a t i o n . It is unfortunate f r o m a t h e o r e t i c a l point of v i e w that o u r c o n c l u s i o n s cannot be d e f i n i t e l y r e l a t e d to the d e g r e e of o p t i c a l a c t i v i t y i n the p o l y m e r . T o a c c o m p l i s h this we would need to p r e p a r e p o l y m e r of known and v a r i a b l e a m o u n t s of o p t i c a l r o t a tion, p r e f e r a b l y f r o m o p t i c a l l y a c t i v e m o n o m e r . T h i s we have not done. H o w e v e r , we b e l i e v e that o u r r e s u l t s a r e s u f f i c i e n t l y c o n c l u s i v e e v e n without this c o m p a r i s o n . P o l y m e r s of l o w e r m e l t i n g t e m p e r a t u r e can c r y s t a l l i z e m o r e r a p i d l y than those h a v i n g a h i g h e r m e l t i n g t e m p e r a t u r e b e c a u s e they a r e s t r u c t u r a l l y and m o r p h o l o g i c a l l y d i f f e r e n t . R a c e m i c p o l y m e r c r y s t a l l i z e s i n the f o r m of T y p e I s p h e r u l i t e s . A s long as the p o l y m e r has a s u f f i c i e n t l y low c o n c e n t r a t i o n of a t a c t i c s e q u e n c e s , f a i r l y r a p i d c r y s t a l l i z a t i o n c a n o c c u r . H o w e v e r , the r a t e w i l l be s l o w e r than that of p o l y m e r s that l e a d to T y p e II s p h e r u l i t e s . The f r e e e n e r g y b a r r i e r to n u c l e a t i o n of T y p e II s p h e r u l i t e s s e e m s to be l o w e r . P o l y m e r c o n t a i n i n g s o m e o p t i c a l l y a c t i v e s e q u e n c e s c r y s t a l l i z e m o s t r a p i d l y p r i m a r i l y b e c a u s e the rate of n u c l e a t i o n is g r e a t e r . A n i n c r e a s e d r a t e of n u c l e a t i o n c o m b i n e d w i t h the d e m o n s t r a t e d p o t e n t i a l of c o c r y s t a l l i z a t i o n of T y p e I and T y p e II s p h e r u l i t e s a l s o p r o v i d e s an e x p l a n a t i o n f o r the u s e f u l n e s s of f a s t c r y s t a l l i z i n g p o l y e p i c h l o r o h y d r i n i n i n c r e a s i n g the rate of c r y s t a l l i z a t i o n of s i o w c r y s t a l l i z i n g p o l y e p i c h l o r o h y d r i n . In fact, t h e r e is a d i r e c t p a r a l l e l to s o m e of o u r f i n d i n g s r e p o r t e d i n the c a s e of c r y s t a l l i n e p o l y p r o p y l e n e o x i d e , which is s t r u c t u r a l l y the s a m e as p o l y e p i c h l o r o h y d r i n except that the c h l o r i n e a t o m on the pendant m e t h y l e n e substituent is r e p l a c e d by a h y d r o g e n atom. Two kinds of s p h e r u l i t e s have b e e n o b s e r v e d in c r y s t a l l i n e p o l y p r o p y l e n e o x i d e (14 ). The two w e r e not shown to c o c r y s t a l l i z e . f T

M

n

n

A ck now ledge me nt I a m e s p e c i a l l y indebted to M. P. D r e y f u s s, M. L . D a n n i s , and R. W. S m i t h f o r h e l p f u l d i s c u s s i o n s at c r i t i c a l points i n this study. I a m g r a t e f u l to P. S. N e a l f o r a s s i s t a n c e with s o m e of the e x p e r i m e n t a l work. I w i s h to thank H. A. T u c k e r and C. A. M a r s h a l l f o r p r o v i d i n g the p o l y m e r s u s e d i n this study and M. H. L e h r f o r s h a r i n g the r e s u l t s of h i s study of the m e c h a n i c a l p r o p e r t i e s of the p o l y m e r s .


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Summary The purposes of this study were to determine what chemical and physical structures are present in polyepichlorohydrin and to correlate these structures with the crystallization rates ob served microscopically and dilatometrically. Crystallization rates were shown to be an extremely sensitive way of character izing these polymers. F o r example, the study revealed that the crystalline polyepichlorohydrins examined consisted of isotactic sequences that can crystallize as two different kinds of spheru lites, arbitrarily called Type I and Type II. The two types can cocrystallize. The polymers that crystallize most rapidly and that have the highest melting temperature have some optical activity. Their films contain predominantly Type II spherulites. Polymers that contain Type I spherulites melt lower and show little or no optical activity. These polymers are racemic mixtures. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13.

Bekkedahl, N., J. Research Nat'l. B u r . Standards, (1949), 43, 145. Tsuruta, Τ., Inoue, S., Yoshida, Ν., and Furukawa, J., Makromol. C h e m . , (1962), 53, 215. Tsuruta, Τ., Inoue, S. Yoshida, Ν., and Furukawa, J., (1962), 55, 230. Inoue, S., Tsuruta, T., and Yoshida, Ν., Makromol. Chem., (1964), 79, 34. Tsuruta, Τ., Inoue, S., Ishimori, Μ., and Yoshida, Ν., J . Polym. Sci., C. (1963), (No. 4), 267. Tsuruta, Τ., Macromolecular Reviews, J . Polym. Sci., D, (1972), 179. P r i c e , C. C., and Osgan, M., J. A m . Chem. Soc., (1956), 78, 4787. Kambara, S. and Takahashi, A., Makromol. C h e m . , (1963), 63, 89. Richards, J. R., P h . D . Thesis, University of Pennsylvania, 1961, P a r t III, University M i c r o f i l m s , 61-3547. Magill, J. Η., Makromol. C h e m . , (1965), 86, 283. Mandelkern, L., "Crystallization of Polymers," McGraw - H i l l Book Co., New York, Ν. Υ., 1964. P r i c e , C. C., and Spector, R., J. A m . Chem. Soc., (1965) 87, 2069. Vandenberg, E. J., J. Polym. Sci., A-1, (1969), 7, 525.


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14. Perego, G., and C e s a r i , Μ., Makromol. Chem., (1970), 133, 133. 15. Hughes, L. J., Dangieri, T. J., Watros, R. G., and A i l i n g , J., Polymer Preprints, (1968), 9, 1126.


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Applied Crystallization Kinetics. III. Comparison of ... - ACS Publications

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