The properties of cellulose acetate molecules in solution in methylene chloride-methanol mixtures

THE PROPERTIES OF CELLULOSE ACETATE MOLECULES IN SOLUTION IN METHYLENE CHLORIDE-METHANOL MIXTURES* M. I. S ~ A ~ P ~ o ~ o v , N. P. Z~KU-I~D~_YEV~kand Y E . K . ~:)ODGORODETSKII M. V. Lomonosov State University, Moscow All-Union Scientific-Research I n s t i t u t e of Cinephotogr~phy

(Received 27 April 1966) Ann published information on the properties of the molecules of cellulose and its derivatives in dilute solution has been discussed and analysed in reference [1]. X-ray analysis and infrared spectroscopy in polarized light dearly shows that intramolecular hydrogen bonding occurs in the molecules of cellulose and its derivatives with incomplete degrees of substitution (?<300). This bonding causes an increase in the skeletal rigidity of the macromolecules. I t was shown in reference [1] that in dilute solution, where there is practically no intermolecular interaction, the rigidity of the molecules of cellulose derivatives is dependent not only on the degree of substitution (?), but also on the ability of the solvent to break the intramoleeular bonds in the polymer molecules. If the solvent molecules do not form strong hydrogen bonds with hydroxyl groups Or oxygen atoms the intramoleeular hydrogen bonds in maeromolecules with ?<300 are preserved and the skeletal rigidity of the molecules will be relatively high. If however the solvent molecules (for example alcohols) can form strong hydrogen bonds of the type O - - ~ . . . X or O . . . K - - X they will break the intramoleeular hydrogen bonds in the molecules of cellulose derivatives. I n these circumstances the skeletal rigidity of the macromoleeules will fall to values characteristic of carbonchain polymers of the vinyl series. The skeletal rigidity of the molecules of fully substituted cellulose derivatives (?~300) is low and is independent of the nature of the solvent. For this reason there is great interest in the study of the properties of extremely dilute solutions of collulose derivatives in two-component solvents, particularly in cases where the molecules of one of the components cannot form strong hydrogen bonds with the polymer molecules and those of the other component can. Then by successively altering the composition of the solvent it would be possible to follow the change in the rigidity of the macromolecules, and consequently to learn how to control their skeletal rigidity and certain other * Vysokomol. soyed. Ag: No. 6, 1212-1220, 1967.

1349

1350

M.I. S-A~P~O~OV et al.

properties. This type of study has not so far been made and the results discussed below represent the first step in this direction.* EXPERIMENTAL

We studied solutions of cellulose acetate (CA) in the methylene chloridemethanol, two-component solvent system. These substances were chosen because of their value in practice. The light scattering and viscosity of solutions of a high molecular weight fraction of a partially esterified sample of CA (7----270-290), prepared by the heterogeneous acetylation method, were studied. In addition a study was made of the viscosity of an tmfraztionated sample of CA with 7=300. The methods of preparation and study were described in detail in reference [5]. RESULTS AND DISCUSSION

Table 1 gives values of the intrinsic viscosity ([t/l), the weight-average and number-average molecular weights (Mw and Mn), the mean square radius of gyration (zt) and the second virial coefficient (A2), obtained by treatment of viscosity, light scattering and osmotic pressure experimental data. The data in Table 1 lead to the following conclusions. 1. For solutions of CA in pure methylene chloride the values of M w and ~ found by treatment of experimental data for one wavelength by the method of Hant, Neiman, Sheraga and Flow, are in good agreement with those found at three wavelengths by the method of Hengstenberg. This enhances the reliability of the values of M w and ~ given in Table 1. 2. For the sample of CA with ?=290 dissolved in pure methylene chloride .Mw/Mn~ 1. Hence our fraction of CA is approximately monodisperse. 3. With decrease in the degree of esterification of the CA the degree of polymerization (Nw) falls from 1160 (7--290) to 1050 (?----270). This can be explained by some degradation of the original CA fraction (?----290) during hydrolysis. 4. The value of M w for all three samples of fractionatcd CA falls with decrease in the concentretion of methylene chloride in the solvent mixture. The light-scattering coefficient in an extremely dilute solution in a mixed solvent is given by the following approximate equation: lim(R00.c~ o.o,,

) 2 n ~ n ~ ( d n On \9 .-:-:

_

(1)

where n o is the refractive index of the mixed solvent, n the refractive index of * The solutions of cellulose acetate in mixed solvents studied in references [2-4] were not extremely dilute. Under these conditions changes in the properties of the solution due to decrease or increase in the number of intramolecular hydrogen bonds in the macromolecules can be masked by the effect of interaction between different maeromoleeules.

P r o p e r t i e s of cellulose a c e t a t e molecules

1351

an

the polymer solution, ~ ~-- characterizes the selective sorption of one of the components of the solvent mixture by the polymer molecules, ~ the volume fraction of the solvent (methylene chloride) in the solvent-precipitant mixture, ~ = - - 0 ~1/ [Oc, and ~1 is the volume fraction of solvent in direct proximity to the dissolved macromolecules. I t is usually assumed that ~>0, i.e. that there is predominant adsorption of the solvent molecules. For solutions of CA in methylene chloridemethanol, however, the derivatives an/at and On/a~have the same sign. Therefore when ~>0 the apparent values of ~l~rw in the mixed solvent should be greater than the true values. Since in fact M~ decreases on addition of methanol it must be assumed that in the region of comppsitions of the mixed solvent studied by us the molecules of methanol and not of methylene chloride are predominantly adsorbed (i.e. ~ <0). In other words at low concentrations of methanol the solubility of CA is improved and not impaired. This assumption is supported by the fact that when small quantities of methanol are added to methylene chloride the rate of solution of CA and the second virial coefficient increase, and as the volume fraction (~) of methanol increases A~ shows a tendency to pass through a maximum. * TABLE 1.

:EXPERI1M:ENTAL V A L U E S O F T H E I N T R I N S I C ~TISCOSITY~ M O L E C U L A ~ VCEIGHT~ R A D I U S

OF G Y R A T I O N AND S E C O N ~ V I R I A L C O E F F I C I E N T F O R C A OF D I F F E R E N T

DEGREES

OF S U B S T I T U T I O N I N E X T R E M E L Y D I L U T E S O L U T I O N S l

7=290, mo=284

?=280, mo=279

7=270, mo=275

7

O

O

7 7 ×~

°

°

V 0

275

1

2 4 6 12 24 30

280 29O 285

350 310 320 265 275 305 300

33*

30 28 28

340?

3OO 360 360

2.1

295

31

340

2"4

285

29

390

1.9

3"7 4"4 3"9

265 245 265 310 300

--30 29 28

310 340 345

5.4 4.6 4.4

265 370 350 325

28 27 26 25

370 370 5OO 650

7"6 5"8 4"3 5'0

* Measurements by Hengstenberg's method gave'~/w~ 32 x 104; ~/n (osmometrie)= 35 x 104. t Measurements by Hengstenberg's method gave zt=370 •, m 0 is the molecular weight of the repeating unit of the macromolecule*.

* T h e a p p a r e n t v a r i a t i o n in ~ r w w i t h change in m e t h a n o l c o n c e n t r a t i o n f r o m 0 to 2 4 % is n o t m o r e t h a n 2 0 % . E q u a t i o n (1) is a p p r o x i m a t e a n d does n o t p e r m i t q u a n t i t a t i v e d e t e r m i n a t i o n of selective sorption of t h e molecules•

1352

lYl. I. SlIA~'.~LROI~'OV et cd.

5. For partially esterified CA samples the values of [t/] and (R2)~ pass through a minimum at ~2___4% with increase in the concentration of methanol. The change in (R2~ is small and at 7----280 is practically within the limits of experimental error. They correlate well with the values of [~/] and among themselves, however, and therefore cannot be adventitious. The position of the minimum in [t]] and (R2)z~ remains practically unchanged at high degrees of substitution. In the case of fully esterified CA there is no minimum in the value of [~/]. On the contrary a small increase in [7] occurs with increase in ~ and at 12% by volume of methanol [~/]evidently passes through a maximum. It follows therefore that the mechanism of adsorption of methanol molecules when the concentration of the latter in the solvent mixture is low is substantially dependent on the extent to which the CA is acetylated. When the CA sample is not completely acetylated adsorption of methanol molecules, when the concentration of the latter is low, causes coiling up of the polymer molecules. Then with increase in ~ the macromolecules again increase in size as a result of continued adsorption of methanol and finally when ~ is large (above 20%) a further quantity of methanol begins to function as a precipitant and then [~]]and A2 show a tendency to decrease. We did not measure [7] at methanol concentrations greater than 24-30~/o but recently published results of the measurement of [7] for solutions of CA in methylene chloride-methanol mixtures [6] show that [7] falls when ~> 30%, and the extent of this is greater at higher degrees of substitution. I f however the CA is fully acetylated coiling of the polymer molecules at low methanol concentrations does not occur. These facts are readily understood when one takes into consideration the fact that in incompletely esterified CA there are intramolecular hydrogen bonds. These bonds remain unbroken in pure methylene chloride because the molecules of the latter are not capable of forming strong hydrogen bonds with oxygen atoms. Consequently CA molecules with 7(300, which are soluble in methylene chloride. must have a fairly high skeletal rigidity, methanol molecules can form strong hydrogen bonds with the oxygen atoms in the CA molecules, and when methanol is present the intramolecular hydrogen bonds will be broken. In some cases the methanol molecules can become attached to the Ott group and in other cases to the oxygen atom of the pyran ring (see Scheme below). Consequently with breakdown of the intramolecular hydrogen bonds a certain number of free hydroxyl groups are formed in the CA molecules. These in turn form hydrogen bonds with other methanol molecules. Thus the methanol molecules play a double role. :By breaking intramolecular double bonds they are the cause of a decrease in the skeletal rigidity of the CA molecules down to a certain minimal limit and cause them to coil up. At the same time, however, they bring about the formation of free hydroxyl groups in the CA molecules, which results in an increase in the energy of interaction of the CA molecules with the solvent, and in the first place with other methanol molecules. As a result of this dimensions of the macromolecules increase. At first the factor

Properties of cellulose acetate molecules

1353

0

a

0

O

H

I

I

tt b

I", H

0

H

] CHz

0' n/"

\0 "~CI_I3 \ C H 3 ¢

Schematic representation of the adsorption of methanol molecules by CA macromolecules; a--unit of an incompletely esterified CA molecule with an intramolecular hydrogen bond; b--adsorption by addition of a CHaOH molecule to the oxygen atom of the pyran ring; c--adsorption by addition of a CHaOH molecule to the oxygen or hydrogen atom of an hydroxyl group freed by rupture of an intramoleeular hydrogen bond. causing coiling of the polymer molecules prevails. As the concentration of methanol increases this factor becomes nullified and the effect of the second factor increases, resultiug in swelling of the macromolecules. Increasing solvation of the CA with methanol occurs as the concentration of the latter increases, and the hydroxyl groups of the CttaOH are directed toward the CA molecules, thus the surface of the solvated CA molecules is mainly occupied by hydrocarbon radicals. Therefore with further increase in~ above 20-30% by volume the energy of interaction of the solvated polymer molecules with the solvent molecules decreases more rapidly when there are fewer free hydroxyl groups in the CA molecules, At this point the so-called repulsion between the hydrocarbon radicals of the solvated CA molecules and free methanol molecules begins. As a result of this the CA molecules again begin to coil up, but for a totally different reason from t h a t at low methanol concentrations. Since we studied products of low degree of hydrolysis, the position of the minima in [~/] and ( R g ~ remains more-or-less unchanged with decrease in the degree of esterification from 290 to 270, and it is well known t h a t in the hydrolysis of CA mainly the primary hydroxyl groups are freed at first. I n these circumstances the number of intramoleeular hydrogen bonds increases only slightly and there is little change in the skeletal rigidity of the macromolecules. The minima in [~] and ~ at low methanol concentrations cannot be due to the presence of associations of CA molecules and the break-up of these b y interaction with methanol molecules for the following reasons. The decrease in [~/] and
1354

M.I.

S ~ o ~ o v

et

eg.

If the fall and subsequent rise in [t/] and ~ with increase in methanol concentration were due to dissociation and subsequent association of the polymer molecules under the influence of methanol the molecular weight of the CA should also pass through a minimum with increase in ~0. Table 1 shows that this does not occur.

In pure methylene chloride the dimensions of CA molecules at different degrees of esterification are evidently mainly determined by the number of intramolecular hydrogen bonds, i.e. by the skeletal rigidity of the macromolecules. I n pure methylene chloride [7] increases with increase in ? (see Table 1), since with decrease in skeletal rigidity the dimensions of the macromolecules increase. In the mixed solvent at ~ 4 ~ , when the intramolecular bonds are broken, the dimensions of the macromolecules are determined by the nature of their interaction with the environment. Therefore with increase in Y, i.e. with decrease in the number of free hydroxyl groups, the intrinsic viseosity of CA in the mixed, methylene chloride-methanol solvent decreases. This follows from Table 1 and is supported by the results of measurements by Uda [6]. As a characteristic of the skeletal rigidity of CA molecules we shall use the parameter a (the steric factor): a=Jo/to: (2) where 0 ~ characterizes the mean radius of gyration of the macromolecules in a 8-solvent and o~Ithe mean radius of gyration of a freely orienting chain. :For CA 0t/=3"16 ~ t (N is the degree of polymerization). Calculations of a made for cellulose and its derivatives by the method of Stockmayer and Fixman show that at 7----300 CA molecules have a skeletal rigidity corresponding to ¢_~ 1.8 [1]. :By making use of these conclusions and the ideas presented above it is possible to calculate the weight-average molecular weight of our sample of unfractionated CA, the sterie factor a, the coefficient of swelling a and other parameters characterizing the state of CA molecules of different degrees of esterification in the mixed solvent at different compositions. The calculations were made in the following way. 1. A graph of [tl]----f (7) was constructed from the data of Table 1 for solutions of our fractions of CA in pure methylene chloride, assuming that Mw~3.1 × 10a. The value of [7] for a fraction of CA of M w~3.1 × 105 and 7~300 was found by extrapolation to be ~550 cmS/g. By means of the formula [1] K~

o AM3=2"87 × 102a(a × 7"75/m0)a

(3)

we find the parameter K in the Stocl~mayer-Fixman equation [~t]=KMt+ 0"51 #o

BM.

(4)

W~en a-~l.8 and mo=288, K was found to be 0.161 cma.g-l.mole -t. :Putting [t/]~550 ema/g, K~0.161 oma.g-l.mole - j and Mw=3.1 × 105 we obtain B ~ 3 . 9 × × 10 -a~ cma.g -1. The parameter B characterizes the energy of interaction of

Properties of cellulose acetate molecules

1355

the polymer molecules with the solvent. Then by means of the known values of K and B it is possible to calculate the weight-average molecular weight of our unfractionated, fully substituted sample in pure methylene chloride. In order to take account of the polydisporsity of this sample it was assumed that the molecular-weight distribution is described by the Schultz equation with the parameter h----1. Then in the above equation 0.94~ 0 should be substituted for ~0. This calculation gave M~ ~ 1.7 × 105. Then by using this value of M w and the values of [r/] in Table 1 the interaction constant B can be found for the polydisporse sample of CA (7~300), in methylene chloride and in methylene chloride-methanol mixtures. The skeletal rigidity of the molecules of the polydisperse sample is independent of their molecular weight, therefore K has the same value as for the monodisporse sample of higher molecular weight. The results of these calculations are presented in Table 2. 2. For calculation of K and B for fractions of incompletely esterified CA the following assumptions were made, in conformity with the above considerations: a) the true molecular weight of the CA in the mixed solvents is the same as in pure methylene chloride; b) when ~ 6 ~ / o all intramolecular hydrogen bonds in the CA molecules are broken and therefore the steric factor is equal to 1.8. By means of this value of a and the values of m0 in Table 1 the values of K for ~ 6 ~ were calculated from equation (3). Correspondingly the values of B were calculated from the intrinsic viscosities (Table 1) by means of equation (4). It was then necessary to find K and B for solutions of incompletely esterified CA at methanol concentrations less than 6% by volume. Here we first found B and then by means of the data on [r/] and M w (Table 1) K was found from equation (4). Firstly B was found for solutions of CA in pure methylene chloride. For this purpose we used the following equation relating B to the second virial coefficient:

B----(AJN ~) F (x) .

(5)

The argument of the function F (x) is given by the equation x=const (BMS/ (h~} ~)

(6)

where (ha) is the mean square end-to-end distance of the polymer chain. From equation (6) it follows that when M and (hS) are constant the parameter x is proportional to B. Function F (x) is known, it decreases monotonically with increase in x. In good solvents a twofold increase in x corresponds to a decrease in F of approximately 15-20~. Consequently when the variation in A s is not very large B is approximately proportional to A s . From the values of A~ in Table 1 it is seen that the second virial coefficient of a solution of CA (?=-290) in pure methylene chloride is less than A~ at ~----24% by a factor of 1.85. The dimensions of the macromolecules under these conditions are practically the same. Thus taking into account the increase in F with decrease in A S it was found that the

1356

M.I.

S~ux~.u~oNov et al.

i n t e r a c t i o n p a r a m e t e r B w h e n 9 = 0 m u s t b e less t h a n B w h e n ~ = 2 4 % b y a f a c t o r o f a p p r o x i m a t e l y 2.15. T h e v a l u e o r b w h e n ~ 0 = 2 4 % h a s a l r e a d y b e e n f o u n d a n d is e q u a l t o 4 . 3 × 10 -2~ c m a . g -1 ( T a b l e 2). C o n s e q u e n t l y t h e v a l u e o f B w h e n q----0 is a p p r o x i m a t e l y 2 . 0 × 10 -2~ c m a - g -1. V a l u e s o f B a t c o n c e n t r a t i o n s {a between 0% and 6% were found by interpolati?n. The values of B and K found i n t h i s w a y a r e g i v e n i n T a b l e 2. TABLE 2. DEPE~D~.~CE OF PARA~T~.aS CH~RAeT~mZrNG Tim PaOPSRTI~S OF CA 3 f A C R O M O L E C U L E S OF D E F I ~ R E N T D E G R E E S OF S]:~BSTITUTIOlq~ O1~ T H E COM:POSITIOlq Ole T H E

0H30H

vol. %,

: I~ , A

K, cm3.g-~. .molel/2

SOLVENT

MIXTURE

B x 102', cm s.g-1

K'

= 300 0 6 12 24

242 243 246 245

0.161 0.161 0.161 0.161

9.15 9.35 9.60 9"60

1.8 1.8 1.8 1.8

1"76 1"77 1"78 1"77

0.008 0.008 0:012 0.012

0"87 0"88 0"87 0"87

0.138 0.083 0.056 0.017 0.016 0.014 0.012

0"62 0"65 0'68 0"76 0'76 0"78 0"78

7 = 290 0 1 2 4 6 12 24

312 304 296 288 296 308 306

0.440 0.310 0-287 0.167 0.165 0.165 0.165

2"0 2"5 2"9 3.5 3.7 4"4 4-3

2.5 2-3 2.1 1.8 1.8 1.8 1.8

1.2 1.3 1.3 1-5 1.5 1.6 1.6

'

2.4 2.1 1-8 1.8 1.8 1.8

1.2 1.3 1"4 1.5 1-6 1"6

0-162 0.076 0.020 0.017 0.014 0.014

0-60 0"67 0"74 0"77 0"79 0"80

2.5 1.8 1.8 1.8 1.8

1"1 1-5 1"7 1.7 1'6

0.324 0.017 0.014 o.o15 0.012

0.54 0.76 0.81 0.80 0.82

7=280 0 2 4 6 12 24

290 282 272 282 300 293

0.380 0.256 0.172 0.169 0.169 0.169

1"9 2"7 3"3 3'8 4.8 4"5 ~----270

0 6 12 24 30

274 278 313 306 298

0.459 0.173 0.173 0.173 0.173

0"9 4.1 6.5 6-1 5-5

3. K n o w i n g K a n d M t h e s t e r i e f a c t o r c a n b e c a l c u l a t e d f o r i n c o m p l e t e l y esterified CA in pure methylene chloride and in methylene chloride-methanol m i x t u r e s c o n t a i n i n g less t h a n 6 % o f m e t h a n o l . A s w o u l d b e e x p e c t e d t h e s k e l e t a l

Properties of cellulose acetate molecules

1357

rigidity of the polymer molecules increases with decrease in the methanol concentration, and is greatest when ~ = 0 . Also when K, B and M are known it is easy to calculate the swelling coefficient a. For calculation of a we used the equations:

~a:I-[-2Z,

(7)

Z = (3/2~z)~ BAM a M ~ : 0 " 9 5 B M ~ / K

(8)

The results of calculation of a, a and the mean square radius of gyration in a P-solvent and in methylene chloride-methanol are given in Table 2. The figures in Table 2 show that the swelling coefficient decreases with increase in the skeletal rigidity of the polymer molecules. The theoretical mean square radius of gyration passes through a minimum at a methanol concentration of about 40/0. As a rule the values are, within the limits of experimental error, in agreement with the experimental values of tz given in Table 1. The deviations are possibly due not only to experimental error b u t also to the fact that the values of ~ in Table 1 were calculated on the assumption that the polymer molecules are Gaussian coils, whereas when a is close to 2 this is not quite true. Finally b y making use of the data on K and B the values of [7] at different molecular weights and of the constants in the M a r k - K u l m - H o u w i n k empirical equations [t/]=K'M a (9) can be calculated b y means of equation (4). The results of such calculations for molecular weights from 5 × 104 to 3 × 10~ are given in Table 2. In the calculation of [7] for the unfractionated sample it was assumed that ~0w=0.94 ¢0 (see above). The values of K' and a in Table 2 are of course approximate and require experimental verification, b u t they are in good agreement with the results of viscosity measurements on CA made b y other authors. For example for fully esterified CA in chloroform at 30 ° the values K ' = 0 . 0 0 6 and a~-0.9 have been obtained, and in tetrachloroethane at 25 ° K'~--0.005 and a = 0 . 9 . These are very close to the values K ' = 0 . 0 0 8 and a = 0 . 8 7 found b y us for CA (?=300) in methylene chloride, which in solvent properties is very similar to chloroform and tetrachloroethane. Also it has been reported in the literature that solutions of CA (degree of esterification not stated) in a mixture containing 800/0 of methylene chloride and 20% of ethanol the constants of equation (9) are K ' = 0 . 0 1 3 9 and a-~0.834. For CA of different degrees of esterification in a mixture containing 80% of methylene chloride and 20% of methanol our values of K ' v a r y from 0.012 to 0.014 and of a from 0.87 to 0.80 (depending on the degree of esterification). I t is seen that the agreement is very good. B y comparing K' and a with a, a and B it is possible to find the relationship between the parameters characterizing the state of the macromolecules in solution with the parameters of the Mark-Kulm-I-Iouwink equation. When the solvent

1358

M.I.

S~d~.KP~a~ONOV et al.

is pure methylene chloride K' increases sharply with decrease in 7 and a falls, approaching 0.5 at 7--~270. It may be assumed that at 7-~ 260 methylene chloride at 20 ° will be a 9-solvent for CA, since experiment has shown that at 7=255 and 20 ° methylene chloride becomes a poor solvent for CA. When mixtures of' methylene chloride and methanol, containing more than 4% of methanol, form the solvent the increase in K ' with decrease in 7 becomes very small and the decrease in a is relatively small. The dependence of K ' and a on methanol concentration for the fully esterified CA sample differs markedly from the dependence of K' and a on q for an incompletely esterified CA sample. V ~ e n 7----300 K ' increases with increase in ~ from 0 to 24% and a remains practically constant, but when 7~290 K' falls rapidly with increase in q and the parameter a increases. CONCLUSIONS

(1) /k study has been made of the light scattering and viscosity of solutions of CA of different degrees of esterification in methylene chloride and methylene chloride-methanol mixtures. The molecular weight (Mw), the steric factor (a), the swelling coefficient (a), the second virial coefficient (As) , the mean square radius of gyration (~) and a number of other parameters characterizing the properties and state of CA molecules in solution have been determined. (2) It was found that when incompletely esterified CA is dissolved in a methylene chloride-methanol mixture selective adsorption of methanol on the CA molecules occurs, and with increase in the concentration of the alcohol the intrinsic viscosity and the dimensions of the polymer molecules pass through a minimum. With further increase in methanol concentration the CA molecules are solvated by methanol by hydrogen bonding. As a result of this the exterior surface of the solvated maeromolecules is occupied by hydrocarbon radicals, which results in a reduction in the energy of interaction of the solvated CA molecules with the excess methanol molecules that have not taken part in solvation. Therefore methanol gradually begins to play the role of a precipitant, which at high concentrations causes coiling up of the solvated polymer molecules. (3) The probable mechanism of the effect of the mixed solvent on the properties of CA molecules in extremely dilute solution is discussed. In incompletely esterified CA the adsorption of methanol molecules is accompanied by breakdown of intramolecular hydrogen bonds and decrease in the skeletal rigidity of the CA molecules to values typical for carbon-chain macromoleeules. This offers the possibility of control of the skeletal rigidity of CA molecules by changing the composition of the solvent mixture. (4) The parameters K and B in the Stockmayer-Fixman equation and K' and a in the Mark-Kuhn-Houwink equation have been calculated for solutions of CA in methylene chloride and methylene chloride-methanol mixtures. The relationship between these parameters and the properties of CA molecules in extremely dilute solution is discussed. Translated by E. O. PHILLIPS

Chemical changes in polyvinylacetate

1359

REFERENCES 1. N. P. ZAKURDAYEVA, Dissertation, 1966 2. R. V. ZUYEVA, R. g. ZHBANKOV, N. V. IVANOVA, P. V. KOZLOV and Ye. K. PODGORODETSKII, Sb. Tselluloza i eye proizvodnye (Collected Papers. Cellulose and its Derivatives). 124, 131, Izd. Akad. N a u k SSSR, 1963 3. V. P. KHARITONOVA and A. B. PAKSHVER, Kolloid. zh. 20: 110, 1958 4. A. B. PAKSHVER and R. I. DOLININ, Zh. prikl, khim. 23: 775, 1950 5. M. I. SHAKHPARONOV, N. P. Z A K U R D A Y E VA and Ye. K. PODGORODETSKII, Vestn. MGU, No. 4, 1966 6. K. UDA, J. Soc. Text. and Cellulose Ind. J a p a n 18: 105, 107, 1962 7. N. P. Z AKUR D A Y E V A and Ye. K. PODGORODETSKH, Khim. volokna, No. 6, 70, 1964 8. N. P. ZAKURDAYEVA, A. A. PETROVA, V. S. BRONSHVAGER and D. K. B E R I D Z E , Zavod. lab. 30: 1407, 1964

CHEMICAL CHANGES IN POLYVINYLACETATE UNDER RADIATION-THERMAL TREATMENT* V. A. LXRIN, Z. A. iViXRKOVX,V. I. Y&KOVEI~KOand N. A. BxK~ Institute of Electrochemistry, U.S.S.R. Academy of Sciences

(Received

25

April

1966)

STUDY of the eleetrophysical and paramagnetic properties of the organic semiconductors formed by radiation-thermal modification of polyvinylacetate has shown [1] that in their basic characteristics they are very similar to the semiconductors obtained by the same method from polyethylene [2]. Since the original polymers differ substantially in composition and structure it was of interest to follow the chemical changes in polyvinylaeetate (PVA) during the successive stages of modification. The method used, which was similar to the method described for polyethylene in reference [3], consisted in chromatographic analysis of the liberated products, determination of the elementary composition of the solid phase and study of the infrared spectra of the latter at various stages of the process. Weighed, v a c c u m treated samples (1-10 g) of bead P V A were irradiated by an electron beam of initial energy 4 MeV to the absorption of dosages of 3 × 10 22 to 1.7 × 10 =4 eV/g. The gaseous products were removed by means of a T~pler pump, measured and fed into a chromatograph. A portion of the irradiated PV A was treated with acetone to ex t r act liquid radiolysis products, and these were also analysed chromatographically. Another portion of the P V A was oxidized at 250 ° in a current of oxygen, and then pyrolysed at 400 °, 600 ° and 800 ° in a current of helium for 2 hr at each temperature. The products liberated were analysed chromatographically at intervals of 5-10 rain, with the use of instruments * Vyaokomol. soyed. A9: No. 6, 1221-1227, 1967.