Delectric Relaxation of PVAc

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Dielectric relaxation o poly vinyl acetate)s. Mashimo R. Nozaki S. Yagihara and S. TakeishiDepartment o Physics, Faculty o Science, Tokai University, Hiratsuka-shi, Kanagawa 259-12, JapanReceived 21 July 1982; accepted 2 September 1982)

Dielectric relaxation measurements of undiluted and diluted poly vinyl acetate) PV Ac have been made attemperatures 288 < T < 366 K over an extremely wide frequency range from 111Hz to 150 MHz. Thecomplex permittivity can be described quantitatively by the Havriliak-Negami equation = + LII1 + jW1 of ]-a , 0 < a , P 1. t has been found that the parameter a is given by a linear equationof dipole moment ratio g as a = 1.09-O.9Ig. This observation suggests that a is connected closely with localchain conformations. On the other hand, P s nearly constant -0 .87 above the glass transition temperatureand is independent of effect of the diluent. This suggests that the constant value of P is an inherentcharacteristic of the relaxation spectrum of PV Ac.

INTRODUCTION

Dielectric relaxation spectrum of polar polymershave long been investigated in both cases of undilutedand diluted polymers. There have been presented sev

eral attempts to explain shape of the relaxation spectrum. 1- 7

Recently, Yoshihara and Work 7 performed precisionmeasurements of undiluted poly 4-chlorostyrene) P4CSat temperatures higher than the glass transition temperature T ~ at frequencies 0.2 Hz-O. 2 MHz and showedthat the Havriliak-Negami H-N) equation gives a complete explanation to the relaxation spectrum. The H-Nequation is

/ - j = ~ + . a . [ 1 + ( j W T O ) 8 1 - ' , 1)

where a is a parameter characterizing asymmetricalbroadening of the spectrum, {3 is that characterizingsymmetrical broadening of the spectrum, ~ is thelimiting high frequency dielectric constant, a is therelaxation increment, To is a relaxation time, and wis the angular frequency. t was found that the parameter a is nearly constant and {3 depends linearly onlog To. Yoshihara and Work have suggested that a characterizes effects of chain connectivity and {3 describeseffects of surroundings of the chain.

t is of particular importance to clarify the physicalmeanings of the shape parameters a and 3 in order tointerpret local chain dynamics from the dielectric r elaxation spectrum of polar polymers.

In the present work, poly vinyl acetate) PV Ac, which

is a typical amorphous and polar polymer, was used tocharacterize the relaxation spectrum of polymer. Thespectrum of undiluted PV Ac was measured in the f requency range from 1 J LHz to 1 MHz at temperatures 301-366 K in order to find an effect of temperature on theshape of the spectrum. Diluted PVAc with benzene(40 by weight) was measured at frequencies 1-150MHz in order to investigate effects of surroundings ofthe chain.

When two or more different but overlapping relaxation processes move along different loci in a temperature-frequency plane, the shape of the apparent relaxation spectrum changes with changing temperature. In

PVAc, twodielectric relaxation

processeswere

cer-

tainly found independently. 8 However, their frequencyregions are quite different from each other at the sametemperature. Furthermore, it is well known thatPV Ac is a typical polymer in which the t ime-temperature supposition principle 9 can be applied to the mainprocess. Therefore, change of the shape of the relaxation spectrum with changing temperature and addingdiluent can be interpreted as an inherent characteristicof the process.

EXPERIMENTAL

The sample of PV Ac wi th viscosity average molecular weight 8. 2x 104 was obtained from Kanto ChemicalCo. A freeze-dried sample was pressed into a film ofthickness 0.656 mm. Gold was evaporated onto bothfaces of the film to form electrodes of radius 10 mmand a guard ring.

In the frequency range from 1 J LHz to 50 mHz, thedielectric relaxation spectrum was obtained from theFourier transformation of dc transient current whichwas measured by a vibrating reed electrometerTR8411; Takeda Riken) and recorded by a pen re

corder. Detailed procedures of this method have beenreported already. 10 The spectrum in the frequencyrange 1 mHz-3 Hz was obtained also by the dc transientcurrent method. However, in this case, a picoammeterTR8641; Takeda Riken) with faster resonance was used

to measure the transient current and a transient recorder SM2100A; Iwatsu Electric) was used to recordand digitize the current. Measurements at frequencies10 Hz-l MHz were made by using a transformer bridge

TR-10A; Ando Electric).Temperatures used for the measurements of undiluted

PVAc were those between 301. 25 and 365.95 K. Temperature was controlled within 0.02 0.

Dielectric measurements of PV Ac diluted with benzene (40 by weight) were made by a Twin-T bridgeDLB-ll01D; Fujisoku Electric) at ten frequencies be

tween 1 and 150 MHz at temperatures 288.2 and 295.2K. The temperature of the solution was controlledwithin 0.10.

The glass transition temperature T of the presentPVAc is 304.0 K which was determined using the same

sample as the present one in the previous paper. 10

J. Chern. Phys. 77 12), 15 Dec. 1982 0219606/82/24625904 02.10 1982 American Inst i tute of Physics 6 59

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6260 Mashimo et al : Dielectric relaxation of poly(vinyl acetate)

1

JI 5

- ,

0 _6 -4 -2 0 2 4 6

og f Hz)

FIG. 1. Dispers ion curves of undiluted PVAc at var ious t emp e ra t u re s . 1 : 301. 25 K; 2 : 301. 71 K; 3 : 302. 90 K; 4 : 303. 60 K:5 :305 .80 K; 6 :309 .16 K; 7 :311 .15 K. 8 :315 .65 K; 9 :326 .25K; 10: 330. 47 K; 11: 335. 05 K; 12: 339. 30 K; 13: 343. 75 K;14 : 349.80 K; 15: 365. 95 K. Solid curves were calculated fromEq. (1).

RESULTS AND DISCUSSION

Frequency dependences of E' - E. for undi lut ed PV Acobtained from dc transient current method and thosemeasured from the bridge measurements are shown inFig. 1. Frequency dependences of dielectric absorptions are also shown in Fig. 2. Both the dispersion andabsorption curves are described completely by the H-Nequation i f appropriate values are chosen to give thecurves best fitted to the experimental curves, as isseen in Figs. 1 and 2. This is in perfect agreementwith the result of P4CS. 7 The values of the parameters chosen are given in Table I.

Dispersion and absorption curves of diluted PV Acwith ~ benzene are also shown in Fig. 3. Thesecurves are described satisfactorily by the H-N equation, too. The values of the other parameters chosenare also listed in Table 1.

Plots of a and {3 against 10gTo are made in Fig. 4which shows that {3 is nearly constant at temperatures

Log f Hz)

FIG. 2. Absorption curves of undiluted PVAc a t var ious t e mpera tures . Solid curves were calculated from Eq. {1l. Temp e ra t u re s are indicated by the sa me numbers as those in Fig. 1.

sufficiently higher than T, but falls with decreaSingtemperature in the vicinity of T,. The constant valueof {3 agrees with that of diluted PVAc.

The parameter a l ies well on a straight line over' awide range of log To. However, the values of the diluted

PV Ac do not lie on the line extrapolated. These resultsof a and {3 seem to contradict to the suggestion ofYoshihara and Work. 7

Square dipole moment per monomer unit I l ~ ) ,obtained from the Onsager equation is listed in Table 1.The Onsager equation used here is

( = kT 2Eo H . ( _ 3 _ ) 2 t.Elv 41TNo 3Eo \E + 2 '

where No is the number of dipoles in unit volume,

2)

k the Boltzmann constant, and Eo is the limiting lowfrequency dielectric constant given by Eo =E. + t.E. Thedens ity of PV Ac g iven in a l i terature U was employed

to obtain the value of No The dipole moment for undiluted PVAc obtained has a negative temperature coefficient. The least square f i t to the plot of In I l ~ )against

TABLE r. Dielec t r ic relaxat ion parameters of undiluted and diluted PV Ac.

Tempera ture TO (K) (s) t.E E., Q 3 (1)2) g

301. 25 5.70 x 10 3 7.922 3.13ga 0.390 0.821 2.458 0.726301. 71 2 . 94x10 3 8.017 3.138 a 0.388 0 .813 2.490 0.735302.90 9 . 25x10 2 8.053 3. 13 5 a 0.402 0.819 2 .515 0 .743303.60 4 . 90x10 2 7.960 3. 13 3 a 0.414 0 .822 2.498 0.738305.80 5. 64x 10 8.040 3. 12 6 a 0.421 0.823 2.549 0.753309.16 1 . 86x10 7.279 3 .117 a 0.450 0.860 2.367 0.699311.15 3.26 7.444 3.111 a 0.445 0 .844 2.440 0.721

315.65 1. 20 6.800 3 .098 a 0.467 0 .864 2.298 0.679326.24 7.16 x 10- 3 6.220 3.068 0.501 0.880 2.231 0.659326.25 1. 38x 10- 2 6.004 3.068 0 .513 0.856 2.161 0.638330.47 4 .1 5 x 10- 3 5.909 3.056 0 .506 0.859 2.174 0.642335.05 1.01 x 10 - 3 5.582 3 .043 0.526 0.868 2 .110 0.623339.30 3 .26 x 10- 4 5,289 3.031 0.530 0 .872 2.050 0.606343.75 1.03x10-4 5.197 3.018 0,551 0,869 2,060 0.609349.80 3.02 x 10 - 5 4.800 3.001 0,560 0 .870 1.972 0 .583365.95 3.23 x 10- 6 4.170 2.955 0.590 0 .873 1.865 0.55160% PV Ac in benzene288.2 1. 20x 10- 8 1.742 2.662 0.719 0.890 1.355 0,400295.2 7. 60x 10 - 9 1.645 2.645 0.750 0 .875 1.334 0,394

Obtained f r o m an equation EO =3. 219 - O. 002 84 T - 273.15) which was obtained exper imental ly

from the br idge measurements ,

J. Chem. Phys., Vol. 77, No. 12, 15 December 1982

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Mashimo t al.: Dielectric relaxation of poly(vinyl acetate) 6261

c

288 2

FIG. 3. Dispersion and absorption curves of diluted PVAc with40% benzene at 288.2 and 295.2 K. Solid curves were calculatedfrom Eq. 0 .

temperature gives a value of - 4. 8X 10 3 for the slope,which seems reasonable if compared with those of vinylpolymers. 12

In order to see more clearly relationships betweenchain conformations and the parameters a and {3, theseparameters are plotted against dipole moment ratiog = J . . L ~ ) / J . . L ~in Fig. 5, where J Lo is the dipole moment ofthe monomer unit. A value of 1. 84 D was employedfor J..Lo which is the dipole moment of ethyl acetate inbenzene. 13 For a , all plots including those of dilutedPV Ac lie on a straight line described by

a = 1 . 0 9 - 0 . 9 1 g

at least in the range of g in this work.

0.9

0.8

0.7:I

tl0.6

0.5

0.4

-10

.~

, , , ,

()(

8 -6 4 2 0 2 4Log To sec)

(3)

FIG. 4. Plots of Q and f against log To for undiluted and dilutedPVAc.

0.9 .0.8

~

0.7


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6262 Mashimo et al : Dielectric relaxation o poly vinyl acetate)

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J. Chern. Phys., Vol. 77, No. 12, 15 December 1982

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Delectric Relaxation of PVAc