Dielectric method of studying the molecular movement in polydivinylacetals

DIELECTRIC METHOD OF STUDYING THE MOLECULAR MOVEMENT IN POLYDIVINYLACETALS* G. P. MIKUATT,OV,T. I BORISOVAand A. S. NIGM_&~KHODZHAYEV Institute of MacromolecularCompounds, U S S R Academy of Scmnces (Recewed 25 May 1965) T~E dielectric properties of the polyvlnylacetals prepared by the acetylatmn of polyvmyl alcohol have been stuched m a number of works [1-4] Besides acetal rmgs, the maeromolecules of these polymers also contained a considerable number of umts which carry hydroxyl groups. By forming hydrogen bonds they exert a considerable influence on the kinetic properties of the macromolecule and its segments, increasing the relaxation time of segments and kinetic groups. For this reason we decided to study the polyacetals prepared by the cyclic polymerization of the corresponding monomers of dlvmylacetal, from winch the OH group is absent. The study of the dielectric properties of these polymers [5] showed that the reason for dipole relaxation, particularly the dipole-group process, is the movement of the polar kinetic unit containing the ether oxygen of the side rings [5] The immediate proximity of the polar bonds of the oxygen atoms to the main carbon chain raises the question of the participatmn of the main chain in the process of dipole-group relaxation. The answer can be found by studying the influence of certain factors on the dipole-group loss parameters, the effects of plasticizing low-molecular weight materials on the relaxation time of a given kind of loss for instance Besides this, in view of the ring structure of the maeromoleeule it is interesting to assess the spread of dipole-segmental and chpole-group loss relaxatlon times, and the effective dipole moments of a chain mono-unit. EXPERIMENTAL RESULTS AND DISCUSSION

The preparation of dlvinylacetal polymers has been described in [5, 6], together with some of their properties and the procedure for preparing specimens for electron measurements. The dmlectrm loss angle (tan J ) a n d permittivlty (e') were measured in the frequency range 0.2-150 kc/s at --120 to ~-160°C In this frequency range the loss factor 8"~8' tan J twice passes through a maximum when exposed to temperature variations Figures 1-3 show the frequency dependences of e" and e' of polyvlnylformal (PVF), polydlvlnylethylal (PVE) and polydlvmylbutyral (PVB) in the range 50-100 °, which is the range of dipole-segmental losses. It can be seen that ~ax falls with the temperature. * Vysokomol soyed 8. :hTo 6, 991-996, 1966. 1088

The molecular movement m polychvmylacetals

1089

Figures 4-6 show analogous functions in the range of dipole-group losses (-- 60 to q-10 °) In contrast to the dipole-segmental process, here e " ~ , rises with tem10erature.

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:F~G 1 Frequency dependences of the loss factor 8" a n d permlttlvlty e' for P V F above Tg. The figures lndmate the temperatures at which the meauurements were made FIG. 2. The same as Fig. 1 for PVE

The direct addition of the oxygen atom to the main chain forces us to assume t h a t the kinetic u m t of dipole-group relaxation must contain a certain quantity of the carbon atoms of the mare chain This was verified b y studying the effect of plastmlzlng low-molecular weight ad(htlves on the d]pole-group loss relaxation time The plasticlzers used were dlbutylphthalate, naphthalene and water. The dlbutylphthalate and naphthalene were added to a polymer powder which was then ground m an agate mortar. After this the specimens required for dielectric measurements were press-moulded. To prepare polyvinylacetal with the reqmred amount of water, polymers drmd as powder to constant weight at 60 ° and 10 -~ m m I t g were used (the water content in these specimens was taken as zero). Water was added while the specimens were an a desmcator, in an atmosphere of pre-determined humidity, over an aqueous solution of H~SOa. The increased moisture content was checked b y weighing.

1090

G

P . I~¢IIKHAILOV et

al

Figure 7 shows the temperature dependence of tan tf of polyvinylbutyral specimens containing dlbutylphthalate, naphthalene and water. In the same place we also give the appropriate curve for the imtml unplasticized specimen. It can be r ~r

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seen that the addition of any of the materials mentioned shifts the dipole-group loss range to lower temperatures. The shift increases with the amount of plasticizer. The addition of a polar plastlclzer also increases the height of tan gin.x, while naphthalene lowers ~t The plastwlzatlon of a polymer b y a low-molecular weight material is known to exert a big influence on the relaxation time of those processes which are connected with the increased moblhty of the maeromoleeular segments. The mobility of individual atomic groups only slightly correlated with the chain is not subject to the influence of the plasticizer to the same degree, or it m a y not react at all. On this basis, the drop m the tan 5m.x mentioned above, i e., reduction m the most probable relaxation time of dipole-group losses m polyvmylbutyral, must be taken as indwatmg that the main carbon chain participates to a considerable extent m the movement of a polar kinetic u m t of the chpole-group type. At 11-12 kcal/ mole [1], the activation energy of the dipole-group losses of polywnylaeetal is rather lower than that previously found for this kind of reaction with participa-

1091

The molecular movement m polychvmylacetals

tion of the main chain. For instance, for polymethylmethacrylate it is 18-21 kcal/mole [7], and for polyvinylchlorlde 15 kcal/mole [8]. From the frequency dependences of the loss factor and pernnttivity (Figs 1-6) we plotted mreular

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FIG 5 The same as Fig. 4 for PVE. Fio 6 The same as Fig 4 for PVB diagrams for ~" = ~ (~') Both in the dipole-group and dipole-segmental loss ranges the circular diagrams are regular ares of a circle with some deviation of the experimental points from the are at frequencms where there are also losses of the other kind The dielectric constant of the polymers was determined at zero and infinitely high frequency (e0 and e~ respectively) and also the relaxation time distribution parameter ~. Figure 8 shows the temperature dependences of a reduced to the Fuoss and KIrkwood form For dipole-group losses a rises with temperature, the parameter being different for different homologues of the series studied the lowest value was for polydivmylethylal and the highest for polydivinylbutyral For dipolesegmental losses the relaxation time distribution parameter can be taken as the same for the polymer homologues in question, since the ~ - ~ ( T ) curves follow exactly the same curve along the temperature axis. (For these curves a = q ( T ) for the two homologues must coincide on the sections equal to the difference in glass

1092

G . P . MIXHAILOVet al.

point [5] between the third polymer and each of these two.) We note also t h a t the temperature dependence of ~ is rather h~gher when calculated from the dipolesegmental than from the dipole-group losses.

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Using Buckingham's formula and the ~o and E~ values calculated from the circular diagrams of dipole-group losses, we calculated the effective dJpole moments referred to one mono-umt, t h e y give the polarity of the kinetic u m t of a gwen type of molecular movement (#0~/g)d 8" It can be seen from Fig 9a t h a t th~s value remains constant in the temperature range under review (--60 to + 20 °) and is approximately the same for all three representatives of the polyacetaI series. The effective dipole moments calculated from the dipole-segmental loss circular diagrams (g0~/g)ds are much higher and fall as the temperature rises. It is therefore best to compare the values of (#0~/g)ds with allowance for the difference m the T~ of the homologues, as described above for the relaxation time distribution. This was done by plotting the values T--T~ along the temperature axis m Fig. 9b. The value of (/10~/~d ~ shows the increase in the polarity of a mono-umt as a result of the increased mobility of the maerocham due to segmental movement beginning in it. In the range of the three members of the series studied, the effective dipole moment (/x0~/g)ds rises from 0 74 D at ( T - - T g ) =

The molecular movement m polydzvmylacetals

1098

30 ° for polyvmylformal to 0.98 and 1.15 D for polywnylethylal and polyvmylbutyral respectively. For the homologous series of polyvlnylaeetals, extensmn of the alkyl part of the side chain thus has some effect on the correlatmn of the polar groups, weakening it.

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FIG. 8 Temperature dependences of = for (hpole-group (a) and chpole-segmental losses (b). 1--PVF, 2--PVE, 3--PVB FTG. 9 Temperature dependences of ~o~v/g for chpole-group (a) and dipole-segmental losses (b) 1--PVF; 2--PVE and 3--PVB Calculated from the values of t 0 and n 2, which are for the statm polamzatlon of the polymer (/~0x/g)2, the dipole moments differ very httle m our polymer homologues and have slight temperature dependence. In the temperature range 60-90 ° t h e y have a value of N1.6 D. If/~0 (the dipole moment of the isolated mono-unit) is approximately the same as that for 2-methyl-l,3-dloxane, 1.9 D [9] CH=--CHs--CHs O

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CHa then a rough assessment of the correlation factor g enables us to judge the extent to whmh the movement of the polar group is slowed down as a function of the temperature. At lower temperatures corresponding to the glass-like state for the polymers under review, movement is very hmlted, although the mare chain also takes some part here (g-~0.28) Where there is segmental movement, 1.e., above the transltmn point to the highly elastm state, mtra- and mtermoleeular correlatmn of the polar groups in the side chain becomes insignffieant (g=0 71).

1094

A.V. CHER~OB~ et al. CONCLUSIONS

(1) In the glass-hke state the movement of side polar groups is considerably retarded but, as shown by the results of experiments with plasticized specimens, nevertheless it originates with the help of small sections of the mare carbon chain. (2) Above the glass pomt rater- and intramolecular correlation of the side polar groups is weaker (g-~0 71) Translated by V. AIFO~D REFERENCES

1. 2 3. 4. 5.

6. 7. 8 9.

I. M ERLIKH and P. N. SHCHERBAK, Zh. tekh fiz. 25 1578, 1955

B L FUNT and T. H. SUTHERLAND, Canadian J Chem 30 940, 1952 T. H SUTHERLAND and B L FUNT, J Polymer Sm I1 177, 1953 P. F VESELOVSKII,Izv Tomskogo pohtekhn in-ta 91" 399, 1956 I, A. ARBUZOVA, T I BORISOVA, O. B. Iv, G. P. MIKHAILOV, A. S. NIGMANKHODZHAYEV and K. SULTANOV, Vysokomol soyed 8 927, 1966 L A ARBUZOVA and K. SULTANOV, Vysokomol soyed 2 1077, 1960 G. P. MIKHAILOV and T. I BORISOVA, Zh. tekh fiz. 28 137, 1958 Y. ISH1DA, Kollold Z 168 124, 1960 C. P SMYTH, Dmlectrm Behavlour and Structure, New York, 1955

STRUCTURE THEIR

OF

SOME

REACTIVITY

VINYLAROMATIC IN INITIATED

MONOMERS,

AND

POLYMERIZATION*

A. V. C~ER~OB~, Z]t. S TIR~tK'YX~TSand R. YA DELYATITSKAYA All-Union Research Institute of Single Crystals (Recewed 26 M a y 1965)

VI1V/LAROMATIC monomers, m whmh the polymenzable double bond ~s conjugated with the aromatic ring, are of considerable practical and theoretmal roterest. They polymerlze fairly readily by a radmal mechamsm with the formation of polymers having good electrical insulating properties. I t would be interesting to study the reactivity of thin type of monomer and t r y to ascertain the connection between the activity and structure. As we know, the mare factors affecting the reactivity of monomers are conjugation, polarity and stene effect. The purpose of the present work was ¢o study the influence of the degree of vinyl group conjugation with an aromatic ring on the a c t l w t y of the monomers in initiated polymerization The influence of stene factors on the reactivity of certain monomers was established even before the mvestlgatmn was completed. * Vysokomol soyed 8. ~o. 6, 997-1002, 1966