An investigation of polyvinylacetate solutions by the diffusion method

74

K.G. BERDN[KOVAand N. P. DOROFEEVA

I t is interesting to note t h a t each of these fibrils is, as it were, made up of two thinner fibrils twisted together. The mechanism of the breakdown of the thick, continuous film into a system of helical fibrils and the "uncoiling" of these into a thinner film is still very puzzling. This micrograph shows t h a t the morphology of the structure can be of a multistage nature, i.e. hyperstructural formations can act as elements for the formation of more complicated forms etc. Another form seen with the electron microscope is shown in Fig. 3 ( × 35,000) where the specimen is a polyester from decamethylene glycol and sebacic acid. Under certain cinditions compact, lenticular particles of complex structure are deposited from solution (a). As the particles become heated in the electron microscope they begin to melt. When the temperature reaches 130 ° they form monolayers (b), of thickness 30-40 A. I t should be emphasized here t h a t this is approximately the thickness of the monolayers in crystals deposited from solution. The electron diffraction pattern (Fig. 4a) indicates a high degree of perfection in the lateral packing of the molecular chains in the crystalline monolayer. At the same time the monolayers in the crystals are not strictly superimposed one above the other. Hence each reflection in the diffraction pattern of some crystalline layers is split into separate points (Fig. 4b). The axes of the chains in the monolayers are perpendicular to the plane of the layer regardless of whether the specimens are obtained from solution or from a melt, or whether they have true, geometrical contours or are shapeless in form. The authors are grateful to A. I. Kitaigorodskii for his interest in this work. Translated by E. O. PHILLIPS REFERENCE

l. Yu. V. MNYUKH, E. M. BELAVTSEVA and A. I. KITAIGORODSKII, Dokl. Akad. Nauk SSSR 133: 1132, 1960

A N I N V E S T I G A T I O N OF P O L Y V I N Y L A C E T A T E SOLUTIONS BY THE DIFFUSION METHOD*

K. G. BERDNIKOVA and N. P. DOROFEEVA Leningrad State University (Received 23 June I960)

THE properties of polymers depend largely on the structure of the macromolecules and on their flexibility, which determines the shape of the chains. A simultaneous study of these characteristics is possible only with dilute solutions, i.e. when it is possible to neglect intermoleeular interaction. /

* Vysokomol. soedin. 3: No. 2, 232-236.

An investigation of p o l y v i n y l a e e t a t e solutionq

75

One of the more important methods of studying polymer solutions is the diffusion method, because the coefficient of self diffusion is dependent on the dimensions and hydrodynamic behaviour of the maeromolecules of dissolved materials. As was shown in references [1] and [2] the geometric dimensions of macromolecules can involve not only the length of linear polymers, but also their structure, for example branching. Thus a study of the dependence of the geometric dimensions of the macromoleeules of a polymer presents the possibility of estimating the degree of branching of the chains. In the present work the diffusion method was used to study the properties of the macromoleeules of a number of fractions of polyvinylacetate. The fractions were obtained b y fractional precipitation from 2 - 4 % acetone solutions b y the addition of water at 20 °. The molecular weights of the fractions were determined from viscosity measurements of solutions of the polymer in acetone. EXPERIMENTAL

Viscosity measurement~ and the determination of molecular weight. The viscosities of solutions of polyvinylaeetate were measured in an Ostwald viscometer in two solvents, acetone and bromoform (the efflux times of the solvents in the viscometer used were: for acetone 56 sec; for bromoform 92 see). The results are shown graphically in Fig. la and b, where the concentration dependence of the specific viscosity of the solutions is shown. t)

77sp/C

ill-c)

a

I0

j'[.<:

,H'(

08

J

YJ

.I /

f w

o.2 o

0.~

0.~

0.6

0.8

l.O

c, (gllOOcrn3)

a

.,.....~.......~*---]['A

o.z

a~

g.6

g.8

~

c, /g/logcrn3)

FI~. 1. The d e p e n d e n c e of qsp/c on c o n c e n t r a t i o n for P V A fractions: (a) in a c e t o n e ; (b) in bromoform,

The values of the intrinsic viscosities It/J, obtained by extrapolation to zero concentration are given in the third and fourth columns of Table 1.

K . (]. B]:RI)?iIKOVA a n d N . P. 1)OIIOFEEVA

76

T A B L E I. CHARACTERISTICS OF POLYVINYLACETATE FRACTIONS !

A × I 0 t6 Frac100 cm a 100 cm a D x I 0 ~ j M × 10 -6 l[q]ac . . . . . . . . . [q]br - - - - (cm2/sec) ergs/ tion I I g g degree

IV-D i 0-0564 !

H-D

0.30 0.47 0.52 0.785

i 0.10811

I-D i II.A i C ~ III-B' i IV-B i II-C I II-O [

0.1253 0"2274 0-4906 0.9462 1.2540 1.9430 2.0660

0.37 0.645 0.71 1.17

1.42

1.89

2.10 2.55 3.45 3.60

2.90 3.30 3.80 4-40

2"07

!

3.86

(h)~ × lO6~

I

1 ×

106

(cm)

(cm)

2.11

0'78

(h )L 2.70

1"08

0.60 0.51 0.415

3.04 2.62 3.38 3-96

0.275 0.275

3.64 3.94

1,00

3.72 4.94 7.48 10.80 15.00 16.00

1.17 1-57 2"30 3"20 3.70 4-60 4.74

3.18 3-14 3-25 3-38 3-26 3.38

The molecular weights of the fractions were calculated from the viscosity m e a s u r e m e n t s in a c e t o n e a c c o r d i n g to t h e e q u a t i o n [3] [q] = 1-58 x 10 -4 M °'69

(1)

w h e r e [q] is t h e intrinsic v i s c o s i t y . E q u a t i o n (1) w a s d e r i v e d for t h e m o l e c u l a r - w e i g h t r a n g e o f ( 1 . 8 5 - 7 . 0 0 ) x 10 '~, h o w e v e r b y c o m p a r i n g thi~ w i t h t h e S c h u l t z e q u a t i o n [4], d e r i v e d for s o l u t i o n s o f p o l y v i n y l a c e t a t e in m e t h y l e t h y l k e t o n e o v e r a r a n g e o f m o l e c u l a r w e i g h t s u p t o 3.]06 we c o n c l u d e d t h a t e q u a t i o n (1) c a n be u s e d for t h e r e g i o n o f h i g h e r m o l e c u l a r weights. Determination of the diffusion coefficient. T h e diffusion coefficients o f t h e p o l y v i n y l a c e t a t e f r a c t i o n s were m e a s u r e d at a c o n s t a n t t e m p e r a t u r e o f 2] ° b y m e a n s o f t h e p o l a r i z a t i o n i n t e r f e r o m e t e r , u s e d a n d d e s c r i b e d in references [5] a n d [6]. W e u s e d a cell in w h i c h t h e liquids are in c o n t a c t in t w o ]a,yers. T h e l o w e r l i q u i d w a s b r o m o f o r m . T h e t h i c k n e s s o f t h e cell a l o n g t h e d i r e c t i o n o f t h e r a y w a s 30 ram. T h e c o n c e n t r a t i o n o f t h e s o l u t i o n w a s 0.5 g / 1 0 0 ml. T h e diffusion coefficients D, m e a s u r e d a t s u c h low c o n c e n t r a t i o n s m a y be c o n s i d e r e d to be t h e s a m e as t h o s e a t infinite d i l u t i o n [7]. t/~.~O z

a

.

"~5

,.iT--

IlK tOz

b

2"5 •

0

5

Ig

15

ZO

25

-I[-0 0 30.10 TLme(sec)

10

20

30

L/O

50

GO'lO ~

FIe. 2a and b. The dependence of 1/K=4Dt on time for PVA fractions in bromoform.

An investigation of polyvinylacetate solutions

77

The diffusion coefficients were calculated by the area method from the maximal ordinate [5]. The experimental results are shown in Fig. 2a where 1/K --4 Dt is plotted against time, t, for the polyvinylacetate fractions in bromoform. Since the determination of the diffusion coefficient D for fraction II-C required a considerably longer time than for the other cases this graph is given on another scale in Fig. 2b. As is seen from these graphs the straight line for 1/K against t passes fairly close to the origin. This indicates t h a t the stratification was fairly good. The slope of the line for 1/K against t is a measure of the diffusion coefficient. The diffusion coefficients derived from Fig. 2a and b are given in the fifth column of the Table l. DISCUSSION

Using the experimental values of the of polyvinylacetate in bromoform, and the equation (1), we plotted the dependence of and 4). As is seen from these graphs this is

"B',9

Log.[7/]

Lo9D

-7

diffusion coefficients D for fractions molecular weightsM, calculated from D o n M on a logarithmic scale (Fig. 3 a straight line relationship within the

.tl

05

~-, >

i

/

I

of

0 #5 I

~.5

5

5.5

I, 6

J

6'5

"0"5 y

Log M

FIG. 3. The dependence of the diffusion coefficient D on molecular weight M for PVA fractions in bromoform.

FIG. 4. The dependence of the intrhlsie viscosity [t/] of PVA on molecular weight. ~I in bromoform.

limits of experimental error, and can be expressed by the equation D----3.63 × l0 -4 ×M -0"57

(2)

A =~loDT -~ (M[t/])½

(3)

The constant was calculated for the polyvinylacetate-bromoform systems. As is known, this differs from the ratio R,/Ro (where R, and RD are the hydrodynamic radii for viscosity and diffusion respectively) only by a numerical factor. The values of A for the fractions investigated are given in the sixth column of the table. It is seen from these figures t h a t A is the same (within the limits of error) for the differer~t fractions. This is illustrated in Fig. 5, which shows the relationship A ----f(P), where P is the degree of polymerization.

'78

K.G. BERDNIKOVA and N. P. DOROFEEVA

T h e m e a n value of A was 3.49 × 10 -1° erg/degree. This result is in good agreem e n t with those o b t a i n e d b y o t h e r a u t h o r s for various systems [6, 8, 9]. As was A 6 "

ZO

.

t~

.

8

.

.

Ig

16

gO

Ztl.lO y P

FIG. 5 Values of the constant A ( ~ goDT -1 (M [t/l)½) at different degrees of polymerization. shown b y T s v e t k o v a n d K l e n i n [6] the root m e a n square distance between the ends of a maeromolecule, (h~)~, can be calculated from diffusion data. I n fact T (h~)½=K ~/0D

(41

where the c o n s t a n t K----7.81 × 10 -s A. B y m a k i n g use of the value of A a n d the diffusion coefficients we calculated the value of (h2)~ for all the fractions. The results are given in the s e v e n t h column of Table 1. Figure 6 shows the d e p e n d e n c e of the root m e a n square distance between t h e ends of the macromolecule on the degree of polymerization. The e x p e r i m e n t a l

/

15

10

50

Igg

/o

150

FIG. 6. The variation of the root mean square length of the PVA chains with degree of polymerization P. points of this relationship lie on a curve with a slight u p w a r d c u r v a t u r e . The eighth c o l u m n of the table gives the lengths of the p o l y v i n y l a c e t a t e molecules, calculated on the a s s u m p t i o n of completely free r o t a t i o n a r o u n d the C - - C bond, from the e q u a t i o n

An investigation of polyvinylacotate solutions

79

1 + cos 0 h~ = n l 2 l - - c o s 0

(5)

-

where n is the number of valence bonds (for polyvinylacetate n :=2P), I is the length of the bond (for a hydrocarbon chain 1= 1.54 x 10-s cm) and 0 is the angle complementary to the valence angle (for the C--C bond 0 = 7 1 °). Substitution of these values in the expression for h 2 gives the equation =3.05 ×

(6)

The theoretical straight line corresponding to this relationship for an undisturbed chain with free rotation around the C--C bonds is shown in Fig. 6. The last column of Table 1 gives the ratio of the lengths obtained from the diffusion measurements to those derived from the free rotation equation. These figures show that over the range of molecular weights investigated the lengths of the polyvinylacetate molecules in bromoform exceed by a factor of 3 the lengths calculated on the assumption of completely free rotation. It is thus seen that these polyvinylacetate fractions follow the relationships characteristic of linear macromolecules. This conclusion is in accord with that drawn from studies of po]yvinylacetate by the light-scattering method [3]. In Fig. 4 we have plotted the dependence of log [t/] on logM, using our experimental values of the intrinsic viscosities of the fractions in bromoform. The relationship between molecular weight and viscosity in this solvent is depicted by a straight line corresponding to the equation [!?] ----1.9 X 10-4 x M °'7°

(7)

The authors express their gratitude to V. N. Tsvetkov for his interest in this work.

CONCLUSIONS

(1) The diffusion coefficients of polyvinylacetate fractions in bromoform, in the molecular-weight range of (0.06--2.00)× l06, have been determined by an optical polarization method. (2) The dependences of the diffusion coefficient D and of the intrinsic viscosity [t/] (for solutions of polyvinylacetate in bromoform) on molecular weight have been determined. (3) The statistical lenghts of the molecules of the polyvinyiacetate fractions in bromoform have been calculated. (4) It is shown that the molecules of these fractions are not noticeably branched. Translated by E. O. PItILLIPS

80

N. M. BAZttENOVet al. REFERENCES

1. 2. 3. 4. 5. 6. 7. 8.

V. N. TSVETKOV, Dokl. Akad. Nauk SSSR 78: 465, 1951 V. N. TSVETKOV, Dokl. Akad. Nauk SSSR 78: 1123, 1951 V. N. TSVETKOV and S. Ya. KOTLYAR, Zh. fiz. khim. 30: 1100, 1956 O. SCHULTZ, J. Amer. Chem. Soc. 76: 3422, 1954 V. N. TSVETKOV, Zh. eksp. i. teoret, fiz. 21: 701, 1951 V. N. TSVETKOV and S. I. KLENIN, Zh. tekh. fiz. 28: 1019, 1958 V. N. TSVETKO¥ and S. I. KLENIN, J. Polymer Sci. 30: 187, 1958 K. G. KISELEVA and I. A. KIZUB, Vestnik LGU (Reports, Leningrad State University), No. 10: 6, 1956 9. V. N. TSVETKOV and R. K. CHANDER, Vysokomol. soedin. 1: 607, 1959

NUCLEAR MAGNETIC RESONANCE STUDIES OF POLYMERS---I. THE TEMPERATURE DEPENDENCE OF MOLECULAR MOBILITY IN DIFFERENT STEREOISOMERIC FORMS OF POLYMETHYLMETHACRYLATE * ~ . M. BAZHENOV, M. V. VOL'KENSHTEIN, A. I. KOL'TSOV a n d A. S. KHACHATUROV Institute of Maeromolecular Compounds, U.S.S.R. Academy of Sciences (Received 8 July 1960)

IN a previous p a p e r [1] we published the first results of a s t u d y of p o l y m e t h y l m e t h a c r y l a t e (PMMA) b y the m e t h o d of nuclear magnetic resonance (NMR) in which the v a r i a t i o n of the N M R line w i d t h t e m p e r a t u r e was studied for a t a c t i c a n d isotactic PMMA. S u b s e q u e n t l y a similar s t u d y of s y n d i o t a c t i c PMMA has been m a d e over the t e m p e r a t u r e range from 20 ° to 240 ° . The results of this investigation are c o m p a r e d in Fig. 1 with those o b t a i n e d previously. I n addition, for all the samples of P M M A investigated, at al] t e m p e r a t u r e s a t w h i c h the derivative contours of the N M R lines were plotted, the second m o m e n t s A H 2 [2], were calculated (from these contours). The results are shown in Figure 2. The value of A / ~ for all the samples decreases at a sufficiently high t e m p e r a ture. This corresponds to an increase in the mobility of the macromolecules. The n a t u r e of the t e m p e r a t u r e dependence of these second m o m e n t s is substantially different for the three stereoisomeric forms of the polymer. * Vysokomol. soedin. 3: No. 2, 290-291, 1961.