Effect of paramagnetism of polyconjugated polymers and their complexes on NMR spectra and molecular motion

448

A . I . MAKLAKOVet al. REFERENCES

1. A. V. TOPCHIEV, M. A. GEIDERIKH, B. E. DAVYDOV, V. A. KARGIN, B. A. KRENTSELI. M. KUSTANOVICH and A. S. POLAK, Dokl. Akad. Nauk SSSR 128: 312, 1959 2. V.A. KARGIN, A. V. TOPCHIEV, B. A. KRENTSEL, A. S. POLAK and B. E. DAVYDOV, Zhur. Vseoyuz. Khim. Obshch. ira. Mendeleyeva 5: 507, 1960 3. L. S. POLAK and P. Ya. GLAZUNOV, Sb.: Radiatsionnaya khimiya polimerov (In: The Radiation Chemistry of Polymers). Izd. "Nauka", 164, 1966 4. R. C. HOUTZ, Text. Res. J. 20: 786, 1950 5. R. M. ASEYEYA, Khim. Tekh. Polimerov, No. 8, 98, 1963 6. I. N. YERMOLENKO, R. N. SVIRIDOVA and V. A. POPOV, Russian Authors' Cert. No. 174317, 1963; Byull. Izobret., No. 17, 1965 7. N. N. SEMENOV, Osnovnye problemy khimicheskoi kinetiki (Main Problems of Chemical Kinetics). Izd. Akad. l~auk SSSR, 1959 8. A. A. BERLIN, Khim. Prom., 881, 1962 9. I. S. SKORYNINA and I. N. YERMOLENKO, Doklad. Akad. Nauk. Belorus.SSR 11: 606, 1967 10. S. S. GUSEV and I. N. YERMOLENKO, Zavod. Labor. 30: 181, 1964 11. SUN TUN, S. S. GUSEV, I. N. YERMOLENKO and Z. A. ROGOVIN, Vysokomol. soycd. 3: 1688, 1961 (Not translated in Polymer Sci. U.S.S.R.) 12. A. BELLAMY, The Infrared Spectra of Complex Molecules (Russian translation). Foreign Lit. Pub. House, 1963 13. J. BONSTEIN, Analyt. Chem. 25: 512, 1953 14. N. JONES and K. SANDOROUGE, The Use of Spectroscopy in Chemistry (Russian translation). Foreign Lit. Pub. House, 429, 1959 15. A. R. MONAHAN, J. Polymer Sci. 4, A-I, 2391, 1966

EFFECT OF PARAMAGNETISM OF POLYCONJUGATED POLYMERS AND THEIR COMPLEXES ON NMR SPECTRA AND MOLECULAR MOTION* A. I. MAKLAKOV, V. I. SHEPELEV (dec.), K. A. GOL'DGAMMER, E. A. ZGADZAI, B. G. TARASOV, V. V. PEN'KOVSKII, ]3. V. SOLOV'EV a n d G. P. KARPACHEVA Kazan State University Institute of Physical Chemistry, Ukr. S.S.R. Academy of Sciences A. V. Topchiev Institute of Petrochemical Synthesis, U.S.S.R. Academy of Sciences (Received 14 February 1969)

THE b e h a v i o u r of p o l y m e r s w i t h c o n j u g a t e d b o n d s has been studied in some detail along with t h e f o r m a t i o n of p a r a m a g n e t i c centres (PMC) in these p o l y m e r s [1], b u t t h e n a t u r e of the PMC has n o t been fully elucidated [2]. A n u m b e r o f suggestions was m a d e in reference [3] regarding t h e s t r u c t u r e of c o n j u g a t e d polymers, b u t t h e r e is no d a t a a t all concerning their molecular mobility, a n d p r a c t i c a l l y no N M R studies o f these p o l y m e r s h a v e been u n d e r t a k e n . * Vysokomol. soyed. A12: 2qo. 2, 394--400, 1970.

Effect of paramagnetism of polymers on NMR spectra and molecular motion

449

T h e a i m of this i n v e s t i g a t i o n was to s t u d y t h e effect of PMC on the N M R s p e c t r a of c o n j u g a t e d p o l y m e r s a n d t h e i r complexes, to consider certain c h a r a c t e r istics of t h e PMC a n d to s t u d y t h e m o l e c u l a r m o t i o n in these samples. EXPERIMENTAL AND RESULTS

T h e i n v e s t i g a t e d m a t e r i a l s were a poly-Schiff's base ( p r o d u c t of the polycond e n s a t i o n of 2 , 6 - d i a m i n o p y r i d i n e w i t h glycol), a n d complexes of t h e latter, a n d also p o l y p h e n y l a c e t y l e n e a n d its iodine complexes. T h e m e t h o d s u s e d in t h e p r e p a r a t i o n of t h e s e m a t e r i a l s h a v e b e e n t a b u l a t e d t o g e t h e r w i t h t h e i r c h a r a c t e r istics a n d t h e code n a m e s of t h e s a m p l e s (Table 1). T h e p o l y m e r s a n d t h e complexes b a s e d on t h e m all h a v e a n a r r o w E P R signal w i t h a line-width of ~ 2 - 8 O e r s t e d a n d a g - f a c t o r e q u a l to t h a t of a free electron. T h e c o n c e n t r a t i o n s (N) of t h e PMC b a s e d on these s p e c t r a are g i v e n in T a b l e 1. All the p o l y m e r s a m p l e s u n d e r r e v i e w were coloured (from yellow to black, d e p e n d i n g on the v a l u e of N). T A B L E 1. C H A R A C T E R I S T I C S OF T H E SAMPLES

Sample

Monomer unit

,

Poly-Schiff's base

/%

=CI--I--CH=N--[~/)--N=

Polymer code

PShB

Molee. / wt. of / PMC/g at 77 ° K polymer

800

2× 101~

Method of preparation

[4]

NM

PShB+0.5 Br PShB-i- 0.8 Br PShB + 1"5 Br Polyphenylacetylene PPA+iodine

,, ,, ,, Polyphenylaeetylenc

I

N ----- CH =C (C6H5)-------CI-I =C(CeHs)--

PShB-K1 800 PShB-K~ 800 PShB-K3 800 PPA 1150 PPA-K1 [ 1150 PPA-K2 1150 PPA-K3 1150 PPA-K4 1150 PPA-1 2200

--5 X 10 TM

1017 1.6 X 10TM 2'3 × 10TM 3'8× 10TM 1-4 × 10t9 8× 10TM

[5] [5] [5]

[6] [7] [71] [7] [7] [8]

T h e wide-line N M R s p e c t r a Were t a k e n a t ].8.3 Me/s in t h e t e m p e r a t u r e interval 77 to 330°K. T h e electron spin-lattice r e l a x a t i o n t i m e s were d e t e r m i n e d a t 4 - 5 0 ° K b y t h e i m p u l s e s a t u r a t i o n m e t h o d (frequency ~ 5-7 Mc/s [9], a n d were e x t r a p o l a t e d to 77°K. T h e static m a g n e t i c r e c e p t i v i t y Z was m e a s u r e d b y t h e G o u y m e t h o d in a field of H = 5 5 k O e r s t e d a t r o o m t e m p e r a t u r e . T h e s h a p e of t h e NMI~ a b s o r p t i o n line a n d its v a r i a t i o n s w i t h t e m p e r a t u r e d e p e n d on t h e n a t u r e of t h e samples. T h e s p e c t r u m of P S h B - K 2, a n d particularly t h a t of P S h B - K 3 , i.e. w h e r e t h e c o n t e n t of B r 2 is r e l a t i v e l y high, h a v e a still w i d e r line (with 5 ~ 20 0 e r s t e d ) a t t h e t e m p e r a t u r e of liquid nitrogen, in a d d i t i o n to t h e n o r m a l b r o a d c o m p o n e n t w i t h d ~ 7-8 Oersted. As t h e t e m p e r -

450

A . I . MAKLAXOVe$

al.

ature rises this component disappears at ~ - - 6 0 °. The change in the line shape with temperature for PShB, PPA, PPA-1 and their complexes is characteristic of polymers with conjugated bonds [10]: at low temperatures the line has a single broad component (with & ~ 6-7 Oersted); when the temperature rises a narrow component appears also at a particular temperature depending on the nature of the sample. Figure la shows the temperature dependences of the second moment M s of the absorption line for PShB and its complexes with Br2. In the liquid nitrogen temperature region the PShB-K3 complex with the maximum bromine content has the highest value for M2. Moreover the fall in the curve of M2=f(T) is most abrupt for this complex; even at room temperature its M~ value is the lowest of all the samples investigated. A similar pattern is observed in the behaviour of the temperature dependences of M2 for polyphenylacetylene and its iodine complexes (see Fig. lb). Note t h a t

M2, Oe 2

k,~,3 •

5

t

I

-t50

I

-

6-

I

I

I

-10o

I

r

I

7~x~'~4

I

-50

I

I

I

]

0

I

I

[

I

50 7:, °C

FIG. 1. Temperature dependence of lYl= for PShB (a) and PPA (b): 1--PSI~B; 2 = P S h B - K 1 and PShB-K~; A--PShB-K~, X --PShB-K~; 3--PShB-Ks; 4--PPA; 5--PPA-K=; 7-- PPA-K4.

the curves for P P A and PPA-1, where N differs by almost two orders, are parallel, although the curve of M~=f(T) for PPA-1 is located above the corresponding curve for PPA. Figure 2 shows plots of M2 vs. PMC concentration at a constant temperature. It is seen t h a t at 77°K a rise in N is accompanied by a rise in M2 (curve 1), while at room temperature and above there is a reduction in M2 as N rises (curve 2). The points referring to the pure polyphenylacetylenes (small crosses, in Fig. 2 )fit well on the curve plotted for the iodine complexes of PPA (small circles) at 77°K. Figure 3 shows the temperature dependence of the electron spin-lattice relaxation time Tz, for two of the samples, and it will be seen that Tls~ T -1 in the liquid helium temperature region, which agrees well with the data obtained earlier for irradiated polyethylene [11].

Effect of paramagnetism of polymers on NMR spectra and molecular motion

451

Table 2 contains the m e a s u r e m e n t d a t a for t h e specific magnetic static rec e p t i v i t y Z in the poly-Schiff's base complexes a t r o o m t e m p e r a t u r e . T h e t a b u l a t e d d a t a show t h a t Z is negative for all the complexes, a n d the values f o u n d using t h e additive m e t h o d of Paschal [12], w i t h o u t taking the 7"I3, rnsee

2"0 Mz, Oe~

1"5

~[-

10 ~

×

1.0 2

, [

~

i

0.5

, ,,,,Jtli

t r ,,,,,,Fur

10 is

x

1019

t

t

0.05

I

0.15

N, crn -~

[

I

0.25

7/1, °K

FzG. 2

Fic. 3

Fro. 2. M~ vs. N for PPA, PPA complexes with iodirm, ar~4 PPA-1 1--77, 2--293°K. Fie,. 3. Temperature deperr4ence of eleetro~spimlattice relaxatior~ time T~ for PPA-K~ (curve 1) and PPA-1 (curve 2). PMC into account, are slightly lower t h a n the e x p e r i m e n t a l values. Assuming t h a t the difference in these values is due to the presence of PMC, we obtain values of N based on Curie's law in t h e region of 1019 PMC/g. TABLE

2.

SPECIFIC

MAGNETIC

STATIC

RECEPTIVITY

OF

COMPLEXES

of PShB ÷ Br~. Sample Z x l06 (experiment) Z x 106 (calc.) _h" PMC/g (calc.)

PShB-K1

PShB-K2

PShB-Ks

--0.49 --0.53 2 x l0 TM

--0.47 --0-52 2 x 10.9

--0.45 --0.47 1 × l0 ~

DISCUSSION OF RESULTS

W e k n o w from reference [13] t h a t ill samples wehere there are r e s o n a n t nuclei w i t h spin I as well as PMC w i t h spin S the second m o m e n t of the N M R absorption line is expressed as M2=M2(I--I) ÷M2(I--S),

(1)

where M s ( I - - I ) a n d M 2 ( I - - S ) are the contributions to the second m o m e n t of dipole-dipole I - - I a n d I - - S interactions. I t is n o t difficult to show t h a t the c o n t r i b u t i o n to t h e second m o m e n t of the dipole-dipole i n t e r a c t i o n of r e s o n a n t nuclei (protons) with the nuclei o f halogens in t h e complexes u n d e r review is q u i t e inappreciable in our case. T h e expression M 2 ( I - - I ) is widely known, a n d t o find M 2 ( I - - S ) we m a y use the expression d e r i v e d in reference [14] for a case where t h e PMC are r a n d o m l y d i s t r i b u t e d in the sample and i n t e r a c t only slightly

A.I. MAKLAKOVe~ al.

452

with one another, and are motionless. Slight delocalization of the PMC along the conjugated chains [15] does not affect the equations derived in the paper cited according to which, where the condition of high-temperature approximation is satisfied, i.e. if

~fiSH ---<<1, kT

(2),

Tc~> (~)_/.a') -1

(3)

then when ^

47:

Me(I--S) :M2=~-~'s" ~" (~'2V( -S ( ~ 1))1]'{ 1 -~

yszh2S ( S + I ) H21~/'

3]~eT2

J ,

(3')

and when

"t'c,~<(~I •(~')-1 Ms(I--S) = file_ 47: y~li2S (S + 1) 5'. N . H 9

(4)

kT

2

+-~ua.~i.7~2S ( S + I ) h2.re.6'=A ÷ B ,

(4')

where ?s and ~i are the gyromagnetic ratios for PMC with spill S and for t h e resonant nucleus with spin I, H is the constant magnetic field; k and h are Boltzmann's and Planck's constants, respectively; T is the absolute temperature, r c is the correlation time for PMC; N is the concentration of PMC; 6' is t h e line cutting parameter, equal to the line width at noise-level; a is a parameter equal to [(1--3 cos20)/r3] 2, r is the radius vector connecting I and S, 0 is the angle between r and H; the line above indicates averaging over the region of influence o f PMC [14]. In our case )'s is equal to the gyromagnetic ratio for a free electron, S = 1/2. I f H ~104 Oersted, then (2) is satisfied below liquid helium temperatures, and the second term in the shaped bracket in (3') m a y be disregarded. For all the investigated samples 5' >~20 Oersted, and so in order to satisfy (4) rc must be less than l0 -7 sec. I f we then assume that r averaged over the sphere of influence of PMC is ~ 10-15 A, which is physically correct for the given concentration of PMC, then on roughly calculating parameter a we find that A > B under our conditions, so that the second term in (4') m a y be discarded. We then have from (3) and (4')

" 47: ~]/S(71)) 1]2 6 ' N ,

Me----~- y,/i{ . . . .

M~:~-~ 47: ~,2~2n S (S+I) H . j , .

,

if

:~>>(7:. g')-:

(5)

if

Tc<<(yt"J') -1

(5')

i.e. M2(I--S) is determined exclusively b y the concentration of PMC in the sample. The validity of these determinations is confirmed b y the fact that an expression

Effect of paramagnetism of polymers on I~!~IR spectra and molecular motion

453

similar to (5'), for low values of~c, was derived in reference [16] by authors using a semi-classical method. I n deriving equations (3') and (4') the authors of reference [14] assumed t h a t the PMC do not interact with one another, so t h a t neither the NMR line shape nor the magnitude of the second moment would be valid means of obtaining an approximate estimate of the distribution of PMC in the sample. At the temperature of liquid nitrogen and with our magnetic field strength of H ~ 4 . 3 kOersted it follows [17] from equations (5) and (5') t h a t ~ [ 2 : 3 " 8 X l 0--20A~' ' 5 ',

if

Tc:)f/(~I'5') -1,

(6)

M2= 1.3 × 10-22N. 6 ' ,

if

%~:(yi. 0') -x,

(6')

where M s is expressed in Oersted 2, 8' in Oersted, and N is the number of particles per em 3. Therefore in the case of the polymers under review where N is not more than 1019 and 6 ' ~ 20 Oersted it is clear t h a t a contribution to the total second moment of tile NMR line on account of I - - S interactions would be pc~ssible only in cases where the values of the PMC correlation times (%) are high~ i.e. z¢>) ()'I"5') -1 and where the concentration N of PMC is not less than 10 is particles per enP. In this case it follows from (6) t h a t M.,(I--S)=~[., ~- 10ersted2; and this is a quite measurable value. Let us now consider the experimentally observed dependence of M, on the concentration of PMC in PPA and its complexes at low temperatures (see Fig. 2, curve 1). The Figure shows t h a t as N increases there is a monotonic reduction in the second moment. To elucidate this fact we will use equations (1) and (6), i.e. taking into account the effect of PMC on the second moment of the line, and assuming t h a t T~>>(),'i"5')-1. Then M2=M2(I--I) +M2. In determining the value of M~(I--I) we will make use of the fact t h a t for PPA with N ~ 10~7 cm-3--3~[2<0.10ersted ~, i.e. here the experimental value of the second moment will be M2(I--I ). The experimental and theoretical values of the contributions to ~i2 arising from I - - S interactions are compared in Table 3, and it will be seen t h a t ~I,, does coincide approximately with {5I~--M~(I--I)} in the case of samples with low values of N. The greater discrepancy between the experimental and the calculated values in the case of samples with N-~ 1019 m a y be attributed to the reduced intermolecular contribution of I - - I interactions to Me following the introduction of 12 into the samples, and with curtailment of % accompanying increase in N, with consequent reduction in M..(I--S) (transition fi'om (6) to (6')). Actually a rough estimate of re may be obtained using the expression derived by Khutsishvili [18] r~ l = T-11~+ Tj~ l (7) where TI~ and Tz, are the spin-lattice relaxation time and the spin-spin electron relaxation time respectively. Ta~ extrapolated to 77°K (Fig. 3) amounts to 6h ~ 1 × 10-%ec for PPA-1 ancl ~ 2 × 10-4sec for P P A - K 4, and T2, a n t i where fl

454

A.I.

M_AXLtKOV et al.

is Bohr's magneton, of the order of ~ 10-%ec. Since T2s<
3. EXPERIMENTAL

{M,--M~ (I--I)}

SECOND MOMENT OF T H E N M R

Sample

PPA PPA-K1 PPA-K.~ PPA-K~

AND T H E O R E T I C A L M 2 CONTRIBUTIONS TO T I l E

L I N E ARISII~G OUT OF f - - S

N P M C / {M2--Ms(I--I)}, 1~, Sample /cm s Oersted * Oersted ~ 10 a7 1"6 X 10~8i 2"3× 10~81 3"8× 10 is

0 1"0 0"9 1"1

~0 1.1 1"8 3-0

INTERACTIONS

N (PMC/ {M2--Ms(I--I)}, 1~2, /cm 8 Oersted ~ Oersted 2

P P A - 1 8'0X 10 TM P P A - K , 1"4 × 101~ PShB-K3 5 × 10 TM

1"5 2"0 7"0

6.4 11'2 6'0

the corresponding curve for P P A where owing to the low value of N the PMC have no affect on the NMI~ absorption line. The increased molecular motion is taken as the probable cause of the low thermal stability of these complexes.' Note that a rise in temperature is accompanied b y reduction in M2(I--S) also. For instance, for P S h B - K s (Fig. 1) Ms amounts to 5 . 5 0 e r s t e d 2 at 50 °. Assuming that M s ( I - - I ) ~ 0 at this temperature, which of course is very im-

Effect of paramagnetism of polymers on NMR spectra an4 molecular motion

455

probable, the full second moment of the lines would coincide with M2(I--S ). However, at the temperature of liquid nitrogen Ms(I--S ) is equal to 7 . 0 0 e r s t e d 2 (see Table 3), i.e. M~(I--S) is actually reduced as the temperature rises, though this ought not to be so according to expression (5). This would be possible, assuming t h a t a rise in temperature involves curtailment of Tc--in which case it would be possible to change from formula (6) to (6') in determining the effect of P M C - - a n d assuming also t h a t the theory advanced in reference [14] is incorrect at high temperatures. The position of the points referring to the pure P P A and PPA-1, and to their iodine complexes on curve I in Fig. 2 shows t h a t the magnetic nature of the PMC is identical at the temperature of liquid nitrogen. The authors are deeply grateful to B. D. Davydov for reviewing this paper and for his observations in discussing the experimental results. CONCLUSIONS

The paramagnetic centres (PMC) in polymers with conjugated bonds, and in their complexes, have been investigated and their effect on the NMR spectra of the polymers has been discovered. The conditions under which the second moment (M2) of the NMR spectrum is affected by PMC have been determined. The dependence of M e on the PMC concentration has been observed and accounted for. With the assumptions made in this investigation neither the second moment nor the shape of the NMR line could provide information regarding the distribution of PMC in the sample. The anomalously large effect of halogens on the molecular motion in the polymers with conjugated bonds has been discovered. Considerations in respect to the correlation time (Tc) for PMC have been put forward, and it has been shown t h a t Tc should be reduced with increase in the PMC concentration and in temperature. The paramagnetism of the pure polymers is identical with t h a t of their halogen complexes at 77°K. Translated by R. J. A. HENDI~~ REFERENCES 1. L. A. BLYUMENFEL'D, V. A. BENDERSKII, L. S. LYUBCHENKO and P. A. STUNZHAS,

Zh. strukt, khimii 8: 829, 1967 2. P. EHRLICH, R. J. KERN, E. D. PIERROU and T. P. PROVDER, J. Polymer Sci. B5:

911, 1967 3. I. A. DRABKIN, V. A. TSARUYK, M. I. CHERKASHIN, P. P. KISILITSA, M. G. CHAUSER, A. N. CHIGIR' and A. A. BERLIN, Vysokomol. soyed. A10: 1727, 1968 (Translated

in Polymer Sci. U.S.S.R. 10: 8, 1998, 1968) 4. Yu. A. POPOV, B. E. DAVYDOV, N. A. KUBASOV, B. A. KRENTSEL and I. I. KONSTANTINOV, Vysokomol. soyed. 7: 835, 1965 (Translated in Polymer Sei. U.S.S.R. 7: 5, 921,

1965) 5. G. P. KARPACHEVA, Zh. fiz. khimii 39: 3025, 1965 6. A. A. BERLIN, M. I. CHF_~KASHIN,O. G. SEL'SKAYA and V. Ye. LIMANOV, Vysokotool. soyed. 1: 1817, 1959 (Not translated in Polymer Sci. U.S.S.R.)

G . M . StIAMRAYE¥ et al.

456

7. V. V° PEN'KOVSKII, Zh. teoret, i exper, khimii 3: 106, 1967 8. Ya. M. PAUSHKIN, S. A. NIZOVA, V. S. GAYEVAYA, Karbotsepnye vysokomolekulyarnye soyedineniya, p. 227. Publ. by AN SSSR, 1963 9. N. A. AMENITSKII, L. S. KORNIENKO and A. P. SMIRNOV, Pribory i technika cksperimenta, No. 6, 119, 1963 10. I. Y~. SLONIM, Yg. G. URMAN, V. A. VONSYATSKII, B. I. LIOGON'KII and A. A. BERLIN, Dokl. AN SSSR 154: 914, 1964 11. A. V. KESSENIKH, V. I. LUSHCHIKOV, A. A. MANENKOV and Yu. V. TARAN, Fizika tverdogo tela 5: 443, 1963 12. P. PASCAL, A. PACAULT and $. HOAROU, Compt. rend. 233: 1078, 1951 13. A. ABRAHAM, Yadernyi magnetism (Nuclear Magnetism). Foreign Lit. Pub. House, 1963 14. F. BIGGS a n d S. M. DAY, Phys. Rev. 142: 544, 1966 15. L. L. BUISHVILI ~nd A. V. KESSENIlgH, Fizika tverdogo tela 6: 3016, 1964 16. T. G. STOEBE, T. O. OGURTANI and R. A. HUGGINS, Phys. Rev. 138: 239, 1965 17. A. I. MAKLAKOV, K. A. GOL'DGAMMER, V.I. SHEPELEV and B. G. TARASOV, Fizika tverdogo tela 10: 3421, 1968 18. G. R. KHUTSISHVILI, Uspekhi fiz. nauk 87: 211, 1965

THERMAL TRANSFORMATIONS IN SOME AROMATIC POLYAMID0- AND POLYAMINOAMID0 ACIDS* G. M. SItAMRAYEV,A. A. DuLov, B. I. LIOGOlV'KIIand A. A. BERLIN Chemical Physics Institute, U.S.S.R. Academy of Sciences

(Received 14 February 1969) IN E)~LmR papers [1-3] we reported on the synthesis and properties of thermally stable heterocyclic conjugated poly-(naphthoylene-bis-benezimidazoles) 0

O

-/'\\_ N / - \ =

N-/\-M--

--

where M is absent, -- O, or, -- CH~ and poly-(naphthylene-bis-benzimides) O

r

I

II

O

/~--\

II

where ]VI is absent, or --0--.

* Vysokomol. soyed. AI2: No. 2, 401-408, 1970.

1

I