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Nuclear magnetic resonance study of polydimethylvinylethynyl carbinol
NUCLEAR MAGNETIC RESONANCE STUDY OF POLYDIMETHYLVINYLETHYNYL CARBINOL* N. M. KOCHA~YA~,
A. P. PIKALOV, S. A. YA~, A. V. KAGRAMANYAX and E. A. MARKOSYAN
Central Physieoteehnical Research Laboratory, Armenian S.S.R. Academy of Sciences, Erevan (Received 8 April 1965)
WE K~OW from [1, 2] that the products of the initial polymerization of dimethylvinylethynyl carbinol (DMVEC) have good adhesion, and for this reason they have been widely used in the manufacture of glues and varnishes. But so far very little attention has been paid to their physicochemical properties. Since the physicochemical properties of glass-like polymers depend on the molecular movement of individual groups and segments, it is exceedingly important to determine the transitions which are characteristic of this movement. In [3] it was found that magnetic fields did not affect the molecular movement, while mechanical forces and electrical fields caused a marked distortion of the true pattern of this movement. For this reason, information derived from an NMI~ study of these processes must give a very accurate description of the actual state of the polymer. For materials in solid aggregate states, Van Vleck in [4] has made a theoretical calculation of the second moment of N M R spectra taking account of different kinds of interaction, where the moment is closely dependent on the internuclear spacing. I t can therefore be taken that there is no interaction between the linear molecule chains of very branched polymers. As found in [5-7], in this case the second m o m e n t can be approximately calculated with an adequate degree of accuracy. B y only taking account of the intramolecular interaction and comparing the theoretical value of the second moment with the experimental, it is possible to determine the contribution due to intermolecular interaction. This fact enables us to use the N M R method to study complex structures of amorphous polymers. The present work deals with a study of an amorphous polymer with quite a complicated structure. According to spectroscopic analyses the polymeric unit of DMVEC is formed b y the cyelization of two molecules of the monomer with formation of cyclopentanone rings. With N M R this kind of polymerization process would have to be changed and the presence of the fourth CH3 groups in the resultant monomer unit explained. * Vysokomol. soyed. 8: No. 4, 635-639, 1966. 697
698
~ . M. KOCItARYANet at.
The repeating unit of the polymer of DMVEC can be represented by the following structural formula [1, 2]: ----CH~--CH CH--CH3 I CH~ ~ C - - C - - C t t a
oCH3--~--0H I _
CH8
el.
_
The measurements were performed on the spectrometer described in [8] with a 15 rain ~race. For a wide temperature range we designed a thermostatted pickup which would give constant temperature within a margin of ~=0.5 °. Figure 1 shows the diagram of the pickup with the stabilization system. Measurements can be made in the temperature range 123-470°K. This is broken down into two bands: 123-225 ° and 220-470°K. This gives a big economy in liquid nitrogen since the coolant for the second half of the range is dry compressed air. The rest of the operation is obvious from the illustration.
I
I
FIG. 1. Thermostatted pickup: / - - m a g n e t , 2--plastic foam ring, 3--dewar, 4-thermocouple, 5-- high-frequency coil, 6-- heat resistance, 7--local modulation coil, 8-- micro-amperometer M- 198/3, 9 -- logohmeter regulator LR 1-02M (photoresistanee fitted with diaphragm and relay replaced), 10--dewar pipe, / / - - h e a t e r , 12--container with dry ice in foam plastic jacket, 1 3 - - i n l e t for compressed air which passes round the outside and inside of coils, 1 4 - - d e w a r vessel SD-15, 1 5 - - h e a t e r . The polymer for the investigation was prepared b y bulk polymerization in the presence of 0.5% benzoyl peroxide at 60-80 °. After reprecipitation in methanol and water and drying at ~ 50 °, the polymer DMVEC was a powder. The good monodispersity of the polymer is mentioned in [2] (dispersion coefficient 1.05-1.08). Since the polymers studied have high
Study of p o l y d i m e t h y l v i n y l e t h y n y l carbinol
699
thermo-reactivity (capable of cross[inking over unsaturated bonds), the specimens were used in powder form. The powder was packed into a fluoroplast-4 container 6 m m diam and 20 m m long, and placed in the high-frequency coil of the spectrometer. Measurements were made over intervals of 3-5 ° , and after each temperature a d j u s t m e n t the conditions set were held for 20 min after which the ~NMR signal was recorded.
Figure 2 shows the value of the second m o m e n t as a function of t e m p e r a t u r e for poly-DMVEC in the range 123-340°K. I t can be seen t h a t in this range of temperatures there are four transitions at 123, 178, 240 and 298°K. The Table sets out the results of an analysis of this dependence. The activation energy on the transition was determined as described in [9, 10]. Calculated in accordance with the structural formula of the repeating unit, the value of the second m om ent for intramoleeular interaction in various different cases of reorientatiou shows t h a t it should diminish b y ~ 2.7 ganss 2 when one of the CH3 groups rotates about the Cs bond. .llH~,gaunt,. ¢2
10
150
Z50
350
T,°K FIG. 2. Temperature dependence of
AH~for poly-DI~IVEC.
I t is evident from the Table t h a t there is a change of ~ 2 gauss 2 in t he second moment at the transition temperatures 240 and 298°K. This is less t h a n the contribution due to the reorientation of one of the CH~ groups. These transitions can therefore be assumed to be due not to the reorientation of CH3 groups about the C3 bond, but, of course, t o rotation about the C--C bonds. This is in good agreement with [11], where it was found t h a t tho reorientatiou of the groups about the C--C bonds in branched polymers makes a contribution of the order of 1-3 gauss ~ to the second moment. Besides this, the presence of h y d r o x y groups as well as unconjugated double and triple bonds enables us to st udy t h e dieletric properties of this polymer. Comparing our results with those of [12], it can be
700
1~. 1Y[.KOCHARYANet
al.
said t h a t the transitions are due to reorientation of the groupings about the C--C bond CHa CHa
I
CHa--C-OH There can only be a change in line width where the reorientation frequency is higher t h a n the initial width of the resonance line of the spectrum, i.e., re> 105 see -~. The reorientation of two chemically equivalent groupings is confirmed by the fact t h a t the second moment undergoes changes of the same magnitude, N 2 gauss 2, on transitions. The big difference in the activation energies, ~ 2.1 keal/mole, points to strong interaction, due of course to the fact t h a t one of the groupings is closer to the linear chain of the polymer. I n accordance with this, it can be taken t h a t the dimethylethynyl carbinol grouping is reoriented with an activation energy of 8.9 keal/mole, and the dimethyl carbinol grouping at ~ 11 kcal/mole. The transition at aprrox. 178°K reduces the value of the second moment b y ~ 3.7 gauss ~. I f this value is compared with the theoretical ( ~ 2 . 7 gauss 2) for the reorientation of a single CH 3 group about the Ca bond, we can assume t h a t this is accompanied by the "defreezing" of one of the CHa groups. The difference of 1 gauss ~ between the experimental and theoretical values can be ascribed to the intermolecular interaction of the CH 3 groups. The transition around 123°K reduces the second moment by more than 11 gauss ~, which indicates the reorientation of the remaining three CH 3 groul)s about the C3 bond. We must draw attention to the fact t h a t there is a difference of ~ 2 keal/mole in the activation energies of one of the CH a groups and the three others. This is commensurate with the difference in the activation energy for the dimethylethynyl carbinol and dimethyl earbinol groups. I t can therefore be assumed t h a t the factors responsible for this slowing down are exactly the same for the two different cases. I t seems to us t h a t the interpretation of this is as follows: the strong interaction of the OH groups in the dimethyl carbinol grouping causes the tetrahedron to rotate about the C--C bond, whereby one of the CHa groups gets rather nearer AH AND ACTIVATION ~NERGY
OF TRANSITIONS AS DEPENDENT
O1~ T H E T E M P E R A T U R E
Transition point, oK
A[t~, g a u s s 2
Activation energy, kcal/mole
< 123 178 240 298
>11 3"7 2"0 2.3
< 4.74 6-6 8.9 11.0
Study of polydimethylvinylethynyl carbinol
701
to t h e linear chain o f t h e p o l y m e r , m a k i n g it energetically n o n - e q u i v a l e n t to t h e t h r e e o t h e r groups. O f course, this a p p r o a c h n o t o n l y slows d o w n t h e m o t i o n of this g r o u p a r o u n d t h e C3bond, b u t also t h a t of t h e entire d i m e t h y l carbinol g r o u p ing. C o n f i r m a t i o n of t h e strong i n t e r a c t i o n w i t h t h e O H g r o u p can b e o b t a i n e d b y s t u d i n g t h e p o l y m e r h o m o l o g u e s of carbinol w h i c h do n o t c o n t a i n t h i s group. T h e a u t h o r s are g r a t e f u l to S. G. M a t s o y a n for p r e s e n t i n g t h e s p e c i m e n s . CONCLUSIONS
(1) T h e s t r u c t u r e of t h e r e p e a t i n g u n i t has b e e n f o u n d m o r e precisely for t h e p o l y m e r d i m e t h y l v i n y l e t h y n y l carbinol e,n d t h e a c t i v a t i o n e n e r g y of t h e t e m p e r a t u r e t r a n s i t i o n s due to r e o r i e n t a t i o n of different molecular g r o u p i n g s d e t e r m i n e d . (2) T h e r e is f o u n d to be s t r o n g i n t e r a c t i o n b e t w e e n O H groups, causing t h e CH3 g r o u p s to b e energeticMly n o n - e q u i v a l e n t . Translated by V. ALFORD REFERENCES
1. S. G. MATSOYAN and N. M. MORLYAN, Izv. Akad. Nauk Arm. SSR, khim. nauki 16: 347, 1963 2. S. G. MATSOYAN and N. M. MORLYAN, Vysokomol. soyed. 6: 945, 1964 3. I. V. ALEKSANDROV, Uspekhi khim. 29: 1138, 1960 4. J. H. VAN VLECK, Phys. Rev. 74: 1168, 1948 5. I. Ya. SLONIM, Uspekhi khim. 31: 609, 1962 6. J. POWLES, J. Polymer Sci. 22: 79, 1956 7. A. LECHE, Nuclear Induction. Foreign Lit. Pub. House, 1960 8. N. M. KOCHARYAN and A. P. PIKALOV et al., Bold. Akad. Nauk Arm. SSR 40:25 1965 9. H. S. GUTOWSKY and L. H. MEYER, J. Chem. Phys. 21: 2122, 1953 10. J, S. WO and E. I. FEDIN, Fiz. tverd, tela 4: 2233, 1962 11. H. S. GUTOWSKY and J. G. POWLES, J. Chem. Phys. 21: 1704, 1953 12. N. M. KOCHARYAN and S. G. MATSOYAN et al., Dokl. Akad. Nauk Arm. SSI:t 37: 7, 1963
A. P. PIKALOV, S. A. YA~, A. V. KAGRAMANYAX and E. A. MARKOSYAN
Central Physieoteehnical Research Laboratory, Armenian S.S.R. Academy of Sciences, Erevan (Received 8 April 1965)
WE K~OW from [1, 2] that the products of the initial polymerization of dimethylvinylethynyl carbinol (DMVEC) have good adhesion, and for this reason they have been widely used in the manufacture of glues and varnishes. But so far very little attention has been paid to their physicochemical properties. Since the physicochemical properties of glass-like polymers depend on the molecular movement of individual groups and segments, it is exceedingly important to determine the transitions which are characteristic of this movement. In [3] it was found that magnetic fields did not affect the molecular movement, while mechanical forces and electrical fields caused a marked distortion of the true pattern of this movement. For this reason, information derived from an NMI~ study of these processes must give a very accurate description of the actual state of the polymer. For materials in solid aggregate states, Van Vleck in [4] has made a theoretical calculation of the second moment of N M R spectra taking account of different kinds of interaction, where the moment is closely dependent on the internuclear spacing. I t can therefore be taken that there is no interaction between the linear molecule chains of very branched polymers. As found in [5-7], in this case the second m o m e n t can be approximately calculated with an adequate degree of accuracy. B y only taking account of the intramolecular interaction and comparing the theoretical value of the second moment with the experimental, it is possible to determine the contribution due to intermolecular interaction. This fact enables us to use the N M R method to study complex structures of amorphous polymers. The present work deals with a study of an amorphous polymer with quite a complicated structure. According to spectroscopic analyses the polymeric unit of DMVEC is formed b y the cyelization of two molecules of the monomer with formation of cyclopentanone rings. With N M R this kind of polymerization process would have to be changed and the presence of the fourth CH3 groups in the resultant monomer unit explained. * Vysokomol. soyed. 8: No. 4, 635-639, 1966. 697
698
~ . M. KOCItARYANet at.
The repeating unit of the polymer of DMVEC can be represented by the following structural formula [1, 2]: ----CH~--CH CH--CH3 I CH~ ~ C - - C - - C t t a
oCH3--~--0H I _
CH8
el.
_
The measurements were performed on the spectrometer described in [8] with a 15 rain ~race. For a wide temperature range we designed a thermostatted pickup which would give constant temperature within a margin of ~=0.5 °. Figure 1 shows the diagram of the pickup with the stabilization system. Measurements can be made in the temperature range 123-470°K. This is broken down into two bands: 123-225 ° and 220-470°K. This gives a big economy in liquid nitrogen since the coolant for the second half of the range is dry compressed air. The rest of the operation is obvious from the illustration.
I
I
FIG. 1. Thermostatted pickup: / - - m a g n e t , 2--plastic foam ring, 3--dewar, 4-thermocouple, 5-- high-frequency coil, 6-- heat resistance, 7--local modulation coil, 8-- micro-amperometer M- 198/3, 9 -- logohmeter regulator LR 1-02M (photoresistanee fitted with diaphragm and relay replaced), 10--dewar pipe, / / - - h e a t e r , 12--container with dry ice in foam plastic jacket, 1 3 - - i n l e t for compressed air which passes round the outside and inside of coils, 1 4 - - d e w a r vessel SD-15, 1 5 - - h e a t e r . The polymer for the investigation was prepared b y bulk polymerization in the presence of 0.5% benzoyl peroxide at 60-80 °. After reprecipitation in methanol and water and drying at ~ 50 °, the polymer DMVEC was a powder. The good monodispersity of the polymer is mentioned in [2] (dispersion coefficient 1.05-1.08). Since the polymers studied have high
Study of p o l y d i m e t h y l v i n y l e t h y n y l carbinol
699
thermo-reactivity (capable of cross[inking over unsaturated bonds), the specimens were used in powder form. The powder was packed into a fluoroplast-4 container 6 m m diam and 20 m m long, and placed in the high-frequency coil of the spectrometer. Measurements were made over intervals of 3-5 ° , and after each temperature a d j u s t m e n t the conditions set were held for 20 min after which the ~NMR signal was recorded.
Figure 2 shows the value of the second m o m e n t as a function of t e m p e r a t u r e for poly-DMVEC in the range 123-340°K. I t can be seen t h a t in this range of temperatures there are four transitions at 123, 178, 240 and 298°K. The Table sets out the results of an analysis of this dependence. The activation energy on the transition was determined as described in [9, 10]. Calculated in accordance with the structural formula of the repeating unit, the value of the second m om ent for intramoleeular interaction in various different cases of reorientatiou shows t h a t it should diminish b y ~ 2.7 ganss 2 when one of the CH3 groups rotates about the Cs bond. .llH~,gaunt,. ¢2
10
150
Z50
350
T,°K FIG. 2. Temperature dependence of
AH~for poly-DI~IVEC.
I t is evident from the Table t h a t there is a change of ~ 2 gauss 2 in t he second moment at the transition temperatures 240 and 298°K. This is less t h a n the contribution due to the reorientation of one of the CH~ groups. These transitions can therefore be assumed to be due not to the reorientation of CH3 groups about the C3 bond, but, of course, t o rotation about the C--C bonds. This is in good agreement with [11], where it was found t h a t tho reorientatiou of the groups about the C--C bonds in branched polymers makes a contribution of the order of 1-3 gauss ~ to the second moment. Besides this, the presence of h y d r o x y groups as well as unconjugated double and triple bonds enables us to st udy t h e dieletric properties of this polymer. Comparing our results with those of [12], it can be
700
1~. 1Y[.KOCHARYANet
al.
said t h a t the transitions are due to reorientation of the groupings about the C--C bond CHa CHa
I
CHa--C-OH There can only be a change in line width where the reorientation frequency is higher t h a n the initial width of the resonance line of the spectrum, i.e., re> 105 see -~. The reorientation of two chemically equivalent groupings is confirmed by the fact t h a t the second moment undergoes changes of the same magnitude, N 2 gauss 2, on transitions. The big difference in the activation energies, ~ 2.1 keal/mole, points to strong interaction, due of course to the fact t h a t one of the groupings is closer to the linear chain of the polymer. I n accordance with this, it can be taken t h a t the dimethylethynyl carbinol grouping is reoriented with an activation energy of 8.9 keal/mole, and the dimethyl carbinol grouping at ~ 11 kcal/mole. The transition at aprrox. 178°K reduces the value of the second moment b y ~ 3.7 gauss ~. I f this value is compared with the theoretical ( ~ 2 . 7 gauss 2) for the reorientation of a single CH 3 group about the Ca bond, we can assume t h a t this is accompanied by the "defreezing" of one of the CHa groups. The difference of 1 gauss ~ between the experimental and theoretical values can be ascribed to the intermolecular interaction of the CH 3 groups. The transition around 123°K reduces the second moment by more than 11 gauss ~, which indicates the reorientation of the remaining three CH 3 groul)s about the C3 bond. We must draw attention to the fact t h a t there is a difference of ~ 2 keal/mole in the activation energies of one of the CH a groups and the three others. This is commensurate with the difference in the activation energy for the dimethylethynyl carbinol and dimethyl earbinol groups. I t can therefore be assumed t h a t the factors responsible for this slowing down are exactly the same for the two different cases. I t seems to us t h a t the interpretation of this is as follows: the strong interaction of the OH groups in the dimethyl carbinol grouping causes the tetrahedron to rotate about the C--C bond, whereby one of the CHa groups gets rather nearer AH AND ACTIVATION ~NERGY
OF TRANSITIONS AS DEPENDENT
O1~ T H E T E M P E R A T U R E
Transition point, oK
A[t~, g a u s s 2
Activation energy, kcal/mole
< 123 178 240 298
>11 3"7 2"0 2.3
< 4.74 6-6 8.9 11.0
Study of polydimethylvinylethynyl carbinol
701
to t h e linear chain o f t h e p o l y m e r , m a k i n g it energetically n o n - e q u i v a l e n t to t h e t h r e e o t h e r groups. O f course, this a p p r o a c h n o t o n l y slows d o w n t h e m o t i o n of this g r o u p a r o u n d t h e C3bond, b u t also t h a t of t h e entire d i m e t h y l carbinol g r o u p ing. C o n f i r m a t i o n of t h e strong i n t e r a c t i o n w i t h t h e O H g r o u p can b e o b t a i n e d b y s t u d i n g t h e p o l y m e r h o m o l o g u e s of carbinol w h i c h do n o t c o n t a i n t h i s group. T h e a u t h o r s are g r a t e f u l to S. G. M a t s o y a n for p r e s e n t i n g t h e s p e c i m e n s . CONCLUSIONS
(1) T h e s t r u c t u r e of t h e r e p e a t i n g u n i t has b e e n f o u n d m o r e precisely for t h e p o l y m e r d i m e t h y l v i n y l e t h y n y l carbinol e,n d t h e a c t i v a t i o n e n e r g y of t h e t e m p e r a t u r e t r a n s i t i o n s due to r e o r i e n t a t i o n of different molecular g r o u p i n g s d e t e r m i n e d . (2) T h e r e is f o u n d to be s t r o n g i n t e r a c t i o n b e t w e e n O H groups, causing t h e CH3 g r o u p s to b e energeticMly n o n - e q u i v a l e n t . Translated by V. ALFORD REFERENCES
1. S. G. MATSOYAN and N. M. MORLYAN, Izv. Akad. Nauk Arm. SSR, khim. nauki 16: 347, 1963 2. S. G. MATSOYAN and N. M. MORLYAN, Vysokomol. soyed. 6: 945, 1964 3. I. V. ALEKSANDROV, Uspekhi khim. 29: 1138, 1960 4. J. H. VAN VLECK, Phys. Rev. 74: 1168, 1948 5. I. Ya. SLONIM, Uspekhi khim. 31: 609, 1962 6. J. POWLES, J. Polymer Sci. 22: 79, 1956 7. A. LECHE, Nuclear Induction. Foreign Lit. Pub. House, 1960 8. N. M. KOCHARYAN and A. P. PIKALOV et al., Bold. Akad. Nauk Arm. SSR 40:25 1965 9. H. S. GUTOWSKY and L. H. MEYER, J. Chem. Phys. 21: 2122, 1953 10. J, S. WO and E. I. FEDIN, Fiz. tverd, tela 4: 2233, 1962 11. H. S. GUTOWSKY and J. G. POWLES, J. Chem. Phys. 21: 1704, 1953 12. N. M. KOCHARYAN and S. G. MATSOYAN et al., Dokl. Akad. Nauk Arm. SSI:t 37: 7, 1963