Mobility of the side chains of polymers containing nitro or nitrate groups

1060

T. 1. BomsovA

13. G. M. BARTENEV, M. M. REZNIKOVSKII and M. K. KHROMOV, Kolloidn. zh. 18: 395, 1956 i4. G. M. BARTENEV, Do -ld. A_~ SSSR 133: 88, 1960 15. G. M. BARTENEV, Vysokomol. soyed. 6: 2155, 1964 (Translated in Polymer Sci. U.S.S.R. 6: 12, 2385, 1964) 16. A. V. TOBOL'SKII, Svoistva i struktura polimerov (Properties and Structure of Polylners) Izd. "Khimiya", 1964 17. B. A. DOGADKIN and Z. N. TARAS0VA, Sb. Vulcanizatsiya rezin (Vulcanization of Rubber). Goskhimizdat, p. 113, 1954 18. A. S. KUZ'MINSKII, N. N. LEZHNEV and Yu. S. ZUEV, Okislenie kauchukov i rezin (Oxidation of Rubbers). Goskhimizdat, 1957 19. V. A. KARGL-N and G. L. SLONIMSKII, Kratkio ocherki po fizikokhimii polimerov (Outlines of the Physico-Chemistry of Polymers). Izd. "Khimiya", 1967 20. G. M. BARTENEV and N. M. LYALINA, Vysokomol. soyed. A12: 362, 1970 (Translated in Polymer Sei. U.S.S.R. 12: 2, 1970) 21. A. V. TOBOLSKY and K. MURAKAMI, J. Polymer Sci. 40: 443, 1959 22. G. M. BARTENEV and A. V. BRYUKHANOV, Ueh. zapiski MGPI im V. P. Potemkina 56: 109, 1"960 23. L. MULLINS and N. TOBIN, Proe. 3rd Rubber Techn. Conf. London, p. 397, 1954; J. Appl. Polymer Sci. 9: 2993, 1963 24. A. MALLINS, Kauehuk i rezina: No. 7, 10, 1968 25. J. J. BRENNAN, T. E. JERMYN and B. B. BOONSTRA, J. Appl. Polymer Sci. 8: 2687, 1964 26. G. M. BARTENEV and L: S. BRYUKHANOVA, Zh. tekhn, fiziki 28, 287, 1958 27. G. M. BARTENEV and L. G. GLUKHATKINA, Vysokomol. soyed. A10: 400, 1968 (Translated in Polymer Sci. U.S.S.R. 10: 2, 467, 1968) 28. G. M. BARTENEV and L. A. VISHNITSKAYA, Vysokomol. soyed. 6: 751, 1964 (Translated in Polymer Sci. U.S.S.R. 6: 4, 824, 1964)

MOBILITY OF THE SIDE CHAINS OF POLYMERS CONTAINING NITRO OR NITRATE GROUPS* T. I. BORISOVA Institute of High Molecular Weight Compounds, U.S.S.R. Academy of Sciences

(Received 10 April 1969) THE conditions of internal r o t a t i o n in t h e p o l y m e r side chain d e t e r m i n e the t e m p e r a t u r e - t i m e p a r a m e t e r s o f dipole polarization o f polar g r o u p s in t h e glassy state. P o l a r groups s i t u a t e d a t t h e end o f the side chain h a v e the highest mobility, i.e. lowest r e l a x a t i o n times o f dipole-group polarization [1]. This s t u d y deals with the m o b i l i t y o f the n i t r o a n d n i t r a t e group o f the e n d o f the side chain * Vysokomol. soyed. AI2: No. 4, 932-937, 1970.

Mobility of side chains of polymers containing nitro or nitrate groups

1061

using the method of dielectric loss and polarization, according to the structure of the side chain in polyalkylmethacrylate derivatives. METHODS OF MEASUREMENTS AND SPECIMENS The temperature-frequency relations of the tangent of the dielectric loss angle (tan ~) and dielectric constant (8') were examined at frequencies of 0.4-200 kc/s and at temperatures ranging from --170 to 130 °. Poly-B-nitroethylmethacrylate ( P N O , E ~ ) , poly-p-nitrophenylmethacrylate (Pl~O2PMA), poly-p-nitratethylmethacrylate (Pl~O3E~IA), and polyvinylnitrate (PV~'03)* were studied. Their structures, densities and refractive indices at 20 ° are tabulated. STRUCTURE DENSITY (p) REFRACTIVE I N D E X (riD) AI~'D GLASS TEMPERATURE OF I~ITRO AI~D NITRATE DERIVATIVES OF POLYMERS

Polymer

PNO,EMA

Structural formula of the mono-unit

p, g/cm s

--CHa--C (CHt)---

no

1.354

1.508

T~, °C

O~0--CH,CH2N0 a

PN02P~

"--CHa--C (CH3)--

PN0,EM_A_

--CHs--C (CHa)---

1.418

1.514

55

PVNOs

O~O.--CH~CH2--ONO~ --CH,--CH-~NO~

1.586

1.522

34

The PNOzPM~ and PVNO3 specimens were reprecipitated twice from acetone solution with methanol and dried to constant weight. PI~O,EM_A_ is insoluble. The u n i t obtained b y polymerization was powdered and repeatedly washed with methanol and dried to constant weight under the same conditions as the two previous polymers. The specimens for electrical measurements were obtained b y moulding at temperatures 20 to 30 ° higher t h a n the glass temperature (Tg), the moulding temperature of PNOzPMA being 135-140 °. P I ~ O , E ~ was prepared b y polymerization of the monomer between two glass plates with benzoyl peroxide (0"5 w%. Yo) The reaction was carried out at 60 ° for two hours and at 80 ° for 48 hr, the films freed from glass were then dried at 80-100 ° a n d a pressure of 10-2ram. Specimens 80-120/~ in thickness with a n electrode diameter of 15-20mm were used for measurement of t a n 6 and e'. The electrodes were prepared b y spraying silver i n v a c u o on a metal base. Electrical measurements were made with bridge circuits with two-electrode

cells in dry air. RESULTS AND DISCUSSION

Figure la and b illustrates the temperature relations of tan ~ and ~' for the polymers studied. Near Tg, or somewhat higher than this temperature, the values of tan increase, depending on the overall losses of dipole-segmental relaxation and ionic conductance. The tan ~n~ region of dipole-segmental type is completely resolved only for PVN03 and partly, as a shoulder of the growing branch tan ~ for * The polymer specimens were obtained in the M. M. K o t o n laboratory of the I n s t i t u t e of High Molecular Weight Compounds, U.S.S.R. Academy of Sciences [2].

1062

T . I . BORISOVA

PNOsEMA. In the case of PNO~E1W_A the temperature upper limit is restricted by degradation changes which take place prior to transition to the high elastic state. In view of the increase in electrical conductivity and polymer degradation the temperature relation of tan ~ at high temperature reaches the value so= ~ (T) only for polymers with nitrate groups (So is the static dielectric constant which decreases at higher temperature).

"tOa I" tOz

~r

q8

8/, J ~

-/60

-80

-6

0

,

80

i

"

,-

-160 -80

0

r

80 T,°C

FIG. 1. Temperature dependenceof tan ~ (a) and 8' (b) for polymers at 1 kc/s: 1--PNO=EMA, 2--PVN08, 3--PNO=PMA, 4--PNOsEMA. In Fig. la the scale on the left refers to curve 3. For PNO~EM-~ at 30 to 80 ° a fully resolved range of tan ~max is observed at 1 kc/s which, as with the results of investigating polyalkylmethacrylates [3] and their derivatives [41, may be due to the motion of CO0 groups of the side chain the glassy State of the polymer. At low temperatures relaxation of dipole polarization of polar groups at the end of side chains of the polymers is observed. The range of tan ~=~ and the corresponding increase in the curve s ' = ~ (T) are clear for nitro and nitrate-flderivatives of polyethylmethacrylate, less clearly defined for PNO=PMA and absent in the case of PVN03: for the latter electrical measurements were continued at lower frequencies. At a frequency of 1 c/s the curve tan ~----~ (T) shows no evidence of low temperature adsorption. Consequently, the motion of the end section of the aide chain of the polymers studied is most free in PNO~EMA and PN03EMA, considerably retarded in PNO~PMA and completely stopped in PVNOa. As for the structure of the side chain of these polymers it may be concluded that addition of the polar group through the ethylene unit imparts maximum mobility. Mobility decreases when the polar group is added with the phenyl ring (in this case in the ID-position). The group is completely retarded in the glassy state when it is directly linked to the main chain.

5Iobility of side chains of polymers containing nitro or nitrate groups

1063

s t u d y o f spin-lattice a n d dielectric r e l a x a t i o n o f c y a n o e t h y l a c e t y l c e l l u l o s e shows t h a t t h e c y a n o e t h y l g r o u p in t h e side c h a i n is a kinetic unit, i n d e p e n d e n t in m o b i l i t y o f t h e r e m a i n i n g p a r t o f t h e r e p e a t i n g u n i t [5]. F r o m s t r u c t u r a l a n a l o g y a n d considering t h a t r e l a x a t i o n o f dipole p o l a r i z a t i o n o f t h e c a r b o n y l g r o u p in the glassy s t a t e is o b s e r v e d a t t e m p e r a t u r e s 100--130 ° higher t h a n t h e A

~r

6 G

6

6

\ 5

i

I

I

//

~ tt

0"3

~ ~

1

b

2

~"

I

~I0 Fzo. 2

3 0

9

14

I

2

b

0.2

L

i

o3

3

2

i

l

01

i

6 logf

2

I

t

#

I

I

6logf

FzG. 3

FzG. 2. Frequency dependences of e' (a) and e" (b) for PNO=EMA: a: 1-- --52, 2-- --60, 3-- --65, 4-- --70, 5-- --80, 6-- --85, 7-- --90, 8-- --98, 9-- --105, 10-- --115, b: 1---52, 2 - - - - 6 0 , 3 - - - - 6 6 , 4 - - - - 7 4 , 5 - - - - 8 0 , 6 - - - - 8 5 , 7 - - - - 9 0 , 8 - - - - 9 8 , 9 - - - - 1 0 5 , 10-- --115. FIG. 3. Frequency dependence of e' (a) and d ' (b) for PNO3EM.A: a: 1-- 0, 2-- -- 10, 3-- -- 20, 4 - - - - 3 0 , 5 - - - - 4 0 , 6 - - - - 5 0 , 7 - - - - 5 5 , 8 - - - - 6 0 , 9 - - - - 7 5 , 1 0 - - - - 8 1 , 1 1 - - - - 9 1 ; b: 1 - - 0 ,

2-- --10, 3-- --20, 4-- --30, 5-- --35, 6-- --45, 7-- --55, 8-- --65, 9-- --75, 11-- --91.

10-- --80,

1064

T.I. BORISOVA

process examined in these polymers it may be assumed that the nitro and nitrate ethyl groups also form a ;~inetic unit, the mobility of which is independent of the kinetic state of the remaining part of the mono-unit and the remaining chain. This is in agreement with the lowest values of the braking potential of rotation round C--O ester bonds in the side chain. By analogy with PNO~P1YIA, the ~ _ / ~ N 0 2 radical, rotating round the C--O bond is apparently the kinetic unit, the motion of which causes polarization of N0~ groups. The relaxation parameters of dipole polarization of nitro and nitrate ethyl groups were compared by analysis of frequency relations of ~' and ~" of corresponding specimens in the temperature range of dipole-group losses (Figs. 2 and 3) (~" is the loss factor).

~rm~

I

~,.o

I

I

z~.z~

I

I

~,.8

I

0-11

5-z 10~/T, oK

FIG. 4

-100

I

i

-60

,

i

:

-20

0

T, oc

FzG. 6

FIG. 4. Dependenceof logf=~ for PNO=EMA (1) and PNOsEMA (2) on inverse temperature in the range of dipole-group losses. FIG. 5. Temperature dependence of the distribution parameter of relaxation times ~: 1-PNO,EI~, 2--PNO=EM-&

Figure 4 illustrates values of logf=ax=~(1/T)PN02EM_A and PNOsEMA, plotted from results shown in Figs. 2 and 3. fmax is the frequency which corresponds to ~a= at temperature T. It follows from Fig. 4 that the low temperature range of dipole-group losses in Pl~02EMA covers lower T values than in PNOsEMA. Consequently, the activation energies of dipole group polarization in these systems (11 and 9 kcal/mole) are determined from the gradient of curves in Fig. 4. Accordingly, polarization of the nitroethyl group is characterized by shorter relaxation times r, but a greater activation energy than for the nitrate ethyl group. This may point to the much higher vibration frequency of the dipole including N0~ in relation to the equilibrium orientation (%) compared with the nitrate group. From results shown in Figs. 2 and 3 relations Of £ " = (0(~') are plotted, which are represented by a circular arc, the centre being below the abscissa axis. From these the distribution parameter of relaxation times ~ introduced by Fuoss and Kirkwood (Fig. 5) is estimated. In the range of polarization relaxation of NO= and NOs groups in PNO~EMA and PNOsEMA polymers, parameter a has the

Mobility of side chains of polymers containing nitro or nitrate groups

1065

values 0.15-0.3 and increases slightly with temperature, i.e. the wide range of relaxation times becomes rather narrower. The absolute values of ~ are higher for PN0~EMA, although it is difficult to explain the higher structural homogeneity of the near order from molecular positions in this polymer, compared with PNO3EMA. Plotting circular curves g ' = ~ (d) helped to evaluate the dielectric dispersion (e0--e=) of the dipole-group process in question, according to temperature. Figure 6 shows that the difference (e0--~) increases linearly with temperature and thus also explains the increase in the em~x values. wr

~emax O'3 2-5

0.2 2"4

°S

Oeb#e /5 2

1.0 1"7

2

-IGO

,

i -60

i

:FIG. 6

i -zo

T,oc

0.5 -100

l

I

I

-60

I

-20

T,°C

FZG. 7

FIG. 6. Dependence of dielectric dispersion (e0--8~) (1, 2) and the loss factor d'max (1", 2"} on temperature: 1, r - - P I ~ O = E M A ; 2, 2 ' - - P N O a E M A . Fzo. 7. Temperature dependences of the effective dipole moment P0~/gl= and the correlation factor g (1', 2') for polymers: 1, I ' - - P N O ~ E M A , 2, 2 ' - - P N O s E M A .

This analysis of the mechanism and parameters of dielectric relaxation of PNO~EMA and PNO3EMA suggests that dielectric dispersion (e0--~oo) at low temperatures is completely due to orientation polarization of nitroethyl and nitrate-ethyl groups. Based on FrShlich's general theory of statistical polarization, the effective dipole moments (P0x/g) of a kinetic unit formed by the end section of the side chain in these polymers were calculated from values of (e0--E~). The values obtained appeared close for both polymers and increased in proportion to T (Fig. 7). The dipole moments of low molecular weight compounds of similar structure--nitro or nitrate derivatives of ethane, propane, etc. (3.3-3.4 and 2.96 Debye, respectively [6]) can be used as/10--dipole moment of the same nitro or nitrate-ethyl group in an isolated state. Using these values of t/0 values g = ~ (T), shown in Fig. 7, were calculated. The correlation factor is very low which indicates that the motion of these groups in a given temperature range is very limited.

1066

T . I . BORISOVA

Since g has a statistical meaning, its low value m a y be the result of a certain number of polar relaxators of this t y p e being completely restricted. Higher g values correspond to less polar nitrate-ethyl groups. I f we compare the values found in this study with those obtained b y similar calculation for dipole polarization of cyanoethyl groups in poly-p-cyanoethylmethacrylate [7] the correlation factor in the latter appears to be lower still, i.e. the retardation of rotation of CNCH2CH~ groups is even greater here/~0=3.5--3"8 Debye [6]). Therefore, the increase in g, representing the hindrance of rotation of the kinetic unit of the type R C H ~ C H 2 - - ( R = C N , N 0 s or N03, respectively) in the side chain of p derivatives of polyethylmethacrylate when T < Tg, can be attributed to weakening of dipole type interactions. We also found a change in the activation energy of polarization of CN, NO~ and N03 groups; the activation energy decreased with a reduction in/~o of the polar group. CONCLUSIONS

(1) A study was made b y relaxation of dipole polarization of the mobility of polar groups (NOz, or NOs) at the end of the side chain in PN0~EMA, PNOsEMA, PNO2PMA and P V N 0 3 polymers. I t was pointed out that the motion of these groups in the glassy state is clearly observed in the first two systems, is considerably more retarded in the third polymer, and is absent from PVN08. (2) Internal rotation within the range of the side chain when T
i. T. I. BORISOVA, G. P. MIKHAILOV and M. lYI.KOTON, Vysokomol. soyed. All: 1140, 1969 (Translated in Polymer Scl. U.S.S.R. ll: 5, 1294 1969) 2. A. I. V0LKOVA and M. M. KOTON, Vysokomol. soyed. 6: 480, 1964 (Translated in Polymer Sci. U.S.S.R. 6: 3, 531, 1964) 3. G. P. M:IKHAILOVand T. I. BORISOVA, Zh. tekhn, fiziki 28, 139, 1958 4. G. P. MIKHAILOV and T. I. BORISOYA, Vysokomol. soyed. 2: 1772, 1960 (Not translated in Polymer Sci. U.S.S.R.) 5. G. P. MIKHAILOV, A. I. ARTYUKHOV and V. A. SHEVELEV, Vysokomo]. soyed. All" 553, 1969 (Translated in Polymer ScL U.S.S.R. ll: 3, 628, 1969) 6. McCELLAN, Tables of Experimental Dipole Moments, San Francisco-London, 1963 7. G. P. M:IKHAILOVA, A. I. ARTYUKIIOV and T. I. BORISOVA, Vysokomol. soyed. A10. 1755, 1968 (Translated in Polymer Sci. U.S.S.R. 10: 8, 2033, 1968)