Oscillatory flow birefringence of polymer solutions

Oscillatory flow birefringence of polymer solutions

631

REFERENCES 1. Yu. V. MITIN, Zh. obsheh, khim. 28: 3302, 1968 2. British Pat. 846616, 1960; RZhKhim., 9L143, 1961 3. E. BLATT, Monomery (Monomers). p. 155, 1961; p. 174, 1953, Foreign Literature Publishing House (Russian translation) 4. V. V. KORSHAK, H. S. KOLESNIKOV and A. V. KHARCHEVNIKOVA, Dokl. Akad. Nauk SSSR 56: 196, 1947 5. V. V. KORSHAK and H. S. KOLESNIKOV, Dokl. Akad. :Nauk SSSR 70: 6259, 1950 6. N. N. TSYURUPA, Praktikum po kolloidnoi khimii (Practical Handbook of Colloid Chemistry). p. 139, Izd. "Vysshaya shkola", 1963 7. K. NAKANISI, IK-spektry i stroyenie organicheskikh veshchestv (Infrared Spectra and the Structure of Organic Substances). Izd. "Khimiya", 1965 8. K. A. KUN and R. KUNIN, J. Polymer Sci. A-I, 6: 2689, 1968 9. G. V. SAMSONOV, Ye. B. TROSTYANSKAYA and G.E. YEL°KIN, Ionnyl obmen (Ion Exchange). Xzd. " N a u k a " , 1969 10. A. S. TEVLINA, H. S. KOLESNIKOV, A. Ya. VAINER and L. Ire. FRUMIN, Plast. massy, No. 4, 8, 1969

OSCILLATORY FLOW BIREFRINGENCE OF POLYMER SOLUTIONS* S. N. P ~ ' x o v and Yr. L. VAGrN A. A. Zhdanov State University, Leningrad (Received 13 October 1969)

THE hydrodynamic and optical properties of macromolecules in solution have been described in many papers [1-3], in which important characteristics have been given, one of which is the rigidity of the polymer chain. On the other hart4 there are few experimental data on the kinetic properties of macromolecules [4, 5]. I n t e r e s t in t h e s t u d y of t h e oscillatory flow birefringence ( O F B R ) o f p o l y m e r solutions h a s p r o v i d e d t h e p o s s i b i l i t y of d e t e r m i n i n g kinetic characteristics, especially t h e r e l a x a t i o n s p e c t r u m d e t e r m i n e d b y t h e n a t u r e of t h e r o t a t i o n a l B r o w n i a n m o v e m e n t of t h e molecule a n d of t h e m i e r o - B r o w n i a n m o v e m e n t o f its component parts. U n f o r t u n a t e l y t h e difficulties i n v o l v e d in s t u d y of O F B R limit t h e choice of p o l y m e r s a n d s o l v e n t s a n d t h e results o f such m e a s u r e m e n t s are r e p o r t e d in o n l y a small n u m b e r o f p a p e r s [6-8]. * Vysokomol. soyed. A13: No. 3, 555-564, 1971.

632

S. N. PEN'KOV and Yu. L. VAor~

T h e s o l v e n t s u s e d i n r e f e r e n c e s [6] a n d [8] w e r e A r o c l o r s o f d i f f e r e n t d e g r e e s o f s u b s t i t u t i o n (the-- 1 0 0 P , t / , = 2 . 3 P ) . T h e d i f f i c u l t i e s i n v o l v e d i n m a k i n g f r e q u e n c y measurements was the reason for the use of the method of reduced parameters [9], t h e a p p l i c a b i l i t y o f w h i c h t o t h e O F B R o f d i l u t e p o l y m e r s o l u t i o n s h a s n o t been proved. We have examined the possibility of measuring OFBR in the gap not covered i n r e f e r e n c e s [6] a n d [8], i.e. w i t h l e s s v i s c o u s s o l v e n t s i n t h e f r e q u e n c y r a n g e s of 0-3.6 kHz and 0-10.7 kttz.

EXPERIMENTAL The optical p a r t of the apparatus was the sta~cl~rd equipm~rtt [10] used for m e a s u r e m e n t of flow birofringoneo (with a mica compensator without a half-shadow device). The light source was a DRSh-250 lamp, with a current supply from a constant current network. A schematic d i a g r a m of the dynamo-optimoter, in the gap of which O F B R arises, is given in Fig. 1. I n this a p p a r a t u s the permanent m a g n e t from a moving-coil loudspeaker w~s used to p r o d u c e a radial magnetic field and oscillating motion was produced b y interaction of the c u r r e n t from a sound generator in the power coil and the radial magnetic field. A slightly convergent light beam is focussed inside the gap 3 (Fig. 1) ( d = 0 . 0 2 ram) formed b y the oscillating plato 4 and the wall 1. The gap is fixed b y throe nickel spacers 2, glued to 1. The length of the gap in the direction of the light r a y is 40 ram. The cell containing the test liquid, in which the blade 4 a n d wall 1 are immersed is t h e r m o s t a t i c a l l y controlled b y the water from a t h e r m o s t a t b a t h ( z f T = ~ 0 . 0 5 ° ) , which is passed through a j a c k e t surrounding the cell (the cell is not shown in Fig. 1). The light flux passing t h r o u g h t h e s y s t e m is detected b y an F E U - 3 3 photomultiplier. The recording p a r t of the a p p a r a t u s is shown in Fig. 2. F o r a free wave (d = co) and variation in the velocity of oscillation of the blade a~3oording to the law v = % oxp ¢cot in the direction o~, perpendicular to the plane of vibration, a w a v e propagates with t h e ' v e l o c i t y [ 11]: v (~, t) = % oxp [ico~--(1 +i) flz].

(1)

F o r pure liquids its damping and the wave vector are given b y the f o r m u l a

where co is the cyclic frequency of vibration of the plato a~4 p arid ~ are the d e n s i t y a n d viscosity of the liquid respectively. Simple calculation shows t h a t for a bourldod wave (1/B~d) its field is defined b y t h e value of rid. Only whoa fld<
Oscillatory flow birefringence of polymer solutions

//

ff

633

Y

fl"9 ~8

M

~/7 H ~6

~2 FIG. 1

FIG. 2

FIG. 1. Schematic diagram of the d y n a m o - o p t i m e t e r for measurement of O F B R in the audio-frequency region: / - - f i x e d plate, 2 - - n i c k e l spacers, 3 - - g a p , 4 - - g l a s s blade, 5 - - t r a c t i o n rod to control the pressure of the plate on the glass blade, 6 - glass prism, 7--velocity measuring coil, 8 - - r i g i d rod, 9 - - p o w e r coil, lO--interchangeable elastic element for production of resonance vibrations. FIG. 2. Outline of the recording system: / - - s o u n d generator, 2 - - p h a s e shifter, 3--osciUograph, d--selective amplifier, 5 - - g a l v a n o m e t e r , 6, 7, / / - - s w i t c h e s , 8 - photomultiplier, 9 - - p o w e r coil, / 0 - - v e l o c i t y measuring coil. the solution [12]. Thus when its value is smM1 a t the o u t p u t of the selective amplifier 4 (Fig. 2) connected to the photomultiplier, a voltage of frequency co is produced V = A sin 2~ .sin 2~ "go sin cot.

(3)

I-Iere a and ~ are the azimuths of the m i c a compensator a n d the anisotropie layer in the gap respectively. The coefficient A (in t h e general case a complex cooflleiont) is d e p e n d e n t on the thickness of the compensator, the magnitude of the light flux, the coefficient of amplification of the F E U - a m p l i f i e r system a n d An/g of the solution (g is the velocity gradient a n d An the refractive index difference between the ordinary and e x t r a o r d i n a r y rays). Since to a first approximation [2] for dilute solutions a n d a low velocity g r a d i e n t 2~=~/2--Vog, where ro=(rc/2--2~)/g=(2)~/g)~o, then V = A sin 2e 1 - - ~og0 - go sin cot.

(4)

Thus a linear relationship between V a n d g in a relaxing solution occurs only when (~ogo)' << 1 •

(5)

I t is easy to see t h a t whoa condition (5) is satisfied the phase difference between the signals, V, of relaxing and non-relaxing liquids (if their kinematic viscosities do not differ g r e a t l y ) will be dependent only on the phase difference between An and g of t h e relaxing solution, because in the reference solution Ar~ and g v a r y in phase. This phase difference is i n d e p e n d e n t of the magnitude of the light flux. The modulus (An~g) of the solution [7] (in a r b i t r a r y units) is proportional to the experimentally d e t e r m i n e d value of K sin 2 20 K = sin 2 a '

(6)

634

S. N. PEN'xOV a n d Yu. L. VAGnV

where 8 is the angle of rotation of the compensator giving a fixed (in all instances) photocurrent at the o u t p u t of the photomultiplier when v0 =0, and ~ is the azimuth of the compensator at which the amplitude of V0 (on the oscillograph screen) when v0 ~ 0 is the same as the amplitude of the voltage at the o u t p u t of the amplifier (with the F E U photocathode

tp, de# b 0 0

i

®I

I,

2

0

I

3 0

-lol-tn/g 1'8~J'n ~ o 1.7tT

0

a

0

O

, 1

I 2

I

3 f, kHz

FIG. 3. a - - R e l a t i v e value of Jn/g of =-methylnaphthalene and a 2-5~/o solution of castor oil in T B E as a function of frequency; b--phase difference of the O F B R of these liquids.

closed) when the voltage from the velocity measuring device is switched in a t the input. F o r a given value of = i n each instance the reading of the position of the pointer of the amplifier is fixed. E q u a t i o n (6) also defines the sign of An/g, because sin 2= is a n odd function. W i t h this method of measurement we have

gpoly~er

(~)polymer

(7)

The relative O F B R of the solution is found from equation (7) and this can be recalculated to the absolute value after measurement of the flow birefringence (FBR) of the polymer solution a n d the reference material. For measurement of the phase difference between ~ n a n d g the method of reference (7) was used. This is based on determination of the phase difference of V for the test solution a n d the reference material in relation to the reference signal, i.e. the voltage on the plates of the oscillograph when the velocity measuring device is switched in to the amplifier. The average relaxation time can be calculated from the formula tan =--

(8)

09

where ~ is the phase shift between An and g. The amplitude of the velocity % (and the amplitude of the velocity gradient) is found from the voltmeter reading, previously calibrated a n d connected to the velocity measuring system. I n our case 50sec-l~
Oscillatory flow birefringence of polymer ~olutions

635

factor of three there is satisfactory agreement with the results of measurement of F B R . I t is also seen t h a t the relative value of An/g and the zero phase difference in O F B R in t h e measured frequency range corresponds to (0v<
RESULTS AND DISCUSSION

One of the samples studied was poly-7-benzyl-L-glutamate (PEG) (fraction III, molecular weight 3.17 × 105), which has also been studied by other methods [14, 15]. This fraction was studied in solution in TBE.

,,

I

q

i

I

I

7

I

I

12

I

20

I

28

t

I

38

f , /O'fHz

F i e . 4. The t a n ¢ = F ( f ) relationship for a solution of PBG fraction I I I in DCE (c =0.011 Yo) (1); the dispersion of An/g of this solution (relative values) (2); the form of the function ztn/g=F(.f) for a single relaxation time ( T = I . S x 10 -4 sec) (3); dispersion in the Kerr effect for P B G fraction I I I in DCE [14] (4); representation of zln]g on the complex plane (g).

According to the literature [14-16] PBG in dichloroethane (DCE) has the conformation of a rigid a-helix. The OFBR of two fractions of polystyrene (PS-I, molecular weight 6.0× 10 -e and[ PS-II, molecular weight 0.46× 10s), obtained by fractional precipitation by methanol from solution in benzene, was also measured. The molecular weights were found from the intrinsic viscosities in benzene. The solvents were TBE (PS-I and PS-II) and bromoform (BF) (PS-I). From the general theory of relaxation phenomena it follows that N

A =Bg ,=1

~p

(9)

where B is the optical factor, zp the OFBR relaxation time and Cp a numerical

S. N. PEN'KOVand Yu. L. VAGl~

636

characteristic of the contribution of a relaxation mechanism num ber p to the total 0 F B R . I f ~ is the phase shift between ~n and g we obtain from (9) ~p~p

~ 1+o)'z~,

--tan~

-----~ co

(10)

Cp

~ l+~'~ tan~ . ¥= IS the averaged (at a given frequency) relaxation time which gives rise (D

to this phase shift, as in a simple system with a single relaxation time z = tan F ( c o ) = t a n ~ in the case of a complex system gives a qualitative measCO

CO

ure of the breadth of the relaxation spectrum. The greater the value of z~.0/~. the broader is the spectrum.

0

1"0

2"0

3"0 f, kHz

f'lO'2,Hz

F,a. 5

Fro. 6

FIG. 5. Dispersion in OFBR of a solution of PBG fraction H I in TBE (c = 0.0033 ~): 1--tan

~, 2-- (Arb/g)rel.

FIG. 6. Frequency dependence of ¥ =

tan co

: 1--PBG fraction III in TBE

(c=0"0033~), 2--PBG in DCE (c=0.011~). Figure 4 shows the relationships z l n / g = F l ( f ) and t a n ~ = F , ( f ) for P B G fraction I I I in DCE (c=0.011%). The Cole-Cole diagram is also included. Figure 5 represents F l ( f ) and F~(f) for the same sample in T B E (c=0.0033%). Curves tan of ¥ - for this fraction in both solvents are given in Fig. 6. The complex co O F B R values of the PS samples are shown in Fig. 7. The initial p a r t of the functan tion ¥ - for PS-I is given in Fig. 8. (D

Oscillatory flow birefringence of polymer solutions

637

A macromolecule in the field of action of a velocity gradient sinusoidal in time on the background of intense Brownian movement in the general case undergoes additional changes of state, due to vibrational rotation of the molecule as a whole, with periodic change in its end-to-end distance and complex (also periodic) change in the micro-conformation. a

b 212 ~7 108 iOSO.." " ~ . x - - x - - " - x . . . . 53

o

8.0 ~g 1.5

FIG. 7. Complex value of An/g for PS solutions: a--PS-I in TBE (c=0.10~); b--PS-I in BF (c=0.13yo); c--PS-II in TBE (c=0.3~). Dotted lines--results accoding to Zimm [18]. The contribution of these changes to the total 0FBI~ is substantially dependent, in addition to the optical factor, on the relaxation time z, which determines the time scales of these processes. When cot >> 1 these changes do not occur and there is no such contribution to the OFBR. I f in the complex spectrum of relaxation times ~I>>T~ there is a region of frequencies (coy1>>1) in which the contribution of the mechanism ,with the relaxation time ~ can be neglected. For this reason under certain conditions [17] the predominant factor in O F B R could be either orientation or deformation of the macromolecule. I f a very extended, rigid ellipsoid is taken as a model of the molecule the O F B R is associated with a single relaxation time (the orientation effect). To the extent t h a t the model is made more complex [18, 19] (the possibility of taking up new conformations) it becomes necessary to take account of additional relaxation times. I f these conformations are improbable because of high potential barriers, in the overcoming of which new states arc involved, then the macromolecule has a small number of relaxation times and a narrow spectrum.

638

S.

•. Pv.N'KOVand Y~. L. VAoIN

From the results presented in the graphs it follows that the spectrum of PBG ->To_____(2X~ • in DCE is narrower than in TBE and in both instances /| -t -a]n ~ The dotted curve 3 (Fig. 4) shows the variation in the OFBR for a single relaxation time ( r = 1.5 × 10-4 see). Curve 4 illustrates the dispersion in the Kerr effect [14] in DOE. ~,I0 Q

sec

3: 2 !

0

I

I

I

--~=

I00

200

dO0

4OO f , Hz

Fzo. 8. Initial sections of the curves of the frequency dependence of ~ = ]--solution of PS-I in TBE (c=0.10~); 2--PS-I in BF (c=0"13yo).

tan

eo

Although the values of v0 from F B R and from OFBR, and T from the Kerr effect are similar (Table) the spectra of the electrical birefringence (EFBR) and OI~BR differ considerably, l~rom the value of ¥=~0->3o (Table) we obtain the coefficient of rotational diffusion [2], D,----1/(6T0)=900 CGSU. This is close to the value obtained in reference [15] (/9,----720 CGSU). Since 1), ~ 1/H 8 (H is the long axis of the equivalent ellipsoid modelling the PBG molecule), the data given in reference [15] and obtained from OFBR give values of H differing by 7%. Thus the small breadth of the OFBR relaxation spectrum of PBG in DCE (high kinetic rigidity) is confirmed by independent results obtained by different methods

[14, 15]. The relaxational characteristics of solutions of PBG in TBE are described by a broader spectrum. In reference [16] this is explained by greater polydispersity due to the formation of solvated molecules. From the complex diagrams (Fig. 7) it follows that the OFBR spectrum of PS solutions is broader than that of PBG fraction I I I (Table), but the relaxation spectrum of PS-II is much narrower than the spectrum of PS-I. For kinetically flexible molecular coils the theory predicts considerable broadening of the spectrum, even for monodisperse samples. This is associated with micro-Brownian movement of individual elements of the molecules (sub-chains). For example, for "non-free-draining" coils [18] the theory gives M,t [,fl

(11)

Oscillatory flow birefringence of polymer solutions

639

Here p is the number of the sub-chain and 2~ the tabulated value of the parameter characterizing hydrodynamic interaction. Since p----1,2, ..., N (N is the number of subchains) broadening of the spectrum with increase in molecular weight is inevitable. Of course in addition to the specific effect of micro-Brownian movement, molecular and conformational polydispersity play a very substantial paxt. an ~Gt,el.

3O

°

.

-x~

-x o

"~'7

o

~

o

08

~ O'05

I 0'1

I 0'15

J g'2

.,~

10 0

c,g/IOOcma

~8

FIG. 9. Dependence of the modulus An/gc on frequency and concentration for PS-I in TBE: 1--0, 2--30, 3--60, 4--110, 5--200, 6--400, 7--640, 8--1500 and 9--2000 ttz. Although the polydispersity of the fractions was not investigated there are grounds for asserting that the main cause of the broadening lies in the kinetic properties of the polymer molecules. Since the main contribution to O F B R is made b y mechanisms with a long relaxation time (small p), it follows from (11) that if polydispersity plays a substantial part the fractionated sample would have a molecular weight distribution (Table) described approximately b y A (M 1"5) ~ 100 with a small difference, in the percentage content, because v0 and T~ differ b y two orders of magnitude, and short relaxation times are reliably observed in the experiment. The fact that the breadth of the.spectrum is dependent (mainly) on individual properties of the macromoleeules is illustrated b y the considerable narrowing that occurs on passing to a sample of lower molecular weight (Table). Further study is of course necessary for quantitative assessment of the role of the various factors. The dotted curves in Fig. 7 represent the complex An/g values according to Zimm [18] for "non-free-draining" coils. The frequency and concentration dependence of An/gc for PS-I in T B E is given in Fig. 8. It is possible from these graphs to compare the results of theory [18, 19] and experiment, because An/gc is dependent on concentration only at low frequencies.

640

S. N. PEN'KOVand Yu. L. VAGrs

It is seen from Fig. 7 that there is only semi-quantitative agreement with the deductions of reference [18]. The discrepancy is particularly large in the lowfrequency region. R~T+AXATmNALO~A~Ae~PJsTIeS OF PBG A~D PS ~ACaOMOLECULES OFBR Sample

PBG fraction III in DeE PBG fraction III in TBE PS-I in TBE PS-I in BF PS-II in TBE

o o

xT 2.2

0-317 0-8 0.3171 9.8

6.0 6.0 I 9.8 2.0 0.46 9.8

3-1 7-5 1.4

1.9 9.0 40 32 2.4

1.7 8.0 35 30 2.6

1.6 5.3 120 160 8

200 300 18

• In the theory of Peterlin [19] account is taken of internal viscosity, which increases the relaxation time according to the equation

+,4) Here ~ is the relaxation time according to Zimm [18], f the coefficient of translational friction of the sub-chain and cpp a factor taking account of internal viscosity. Unfortunately to present the results of the theory of reference [19] would be a very laborious operation. We shall state only that taking account of internal viscosity reduces the discrepancy between theory and experiment in the low-frequency region, b u t it does not explain the long relaxation times observed experimentally (the sharp fall in zln/g at low frequencies). It is seen from Fig. 8 that the relaxation spectra of PS-I in T B E and B F differ little, though the viscosities of the solvents differ b y a factor of five and [r/] b y a factor of two. This provides independent confirmation of the role of internal viscosity, which has an important effect in the orientation of F B R under certain conditions [17, 20, 21]. Analysis of the results presented in Fig. 9 (the independence of An/gc on c for PS-I at f~>400 Hz) leads to the possible conclusion that the short relaxation times relate to micro-Brownian movement of the internal sub-chains of the molecule, because their movement varies little with change in concentration. In conclusion we note that according to Zimm [18] the F B R "extinction angle" is given b y the equation

}+o P

Oscillatory flow birefringence of polymer solutions

641

and tan ~ by the formula

tan~=

Z 1 +co2~ Tp

(14)

E 1 +c09"v~ It follows from (13) and (14) that

g /g~o--\

co ]~,~o "

This last equation has been confirmed experimentally for the PS fractions. Since in Peterlin's theory [19] r~ is equivalent to vp, T~ and 1/(l+co2v~) is analogous to 1/(1-}-co2(~) 2 it is easy to see that equation (15) must be applicable in that theory also. It is evident that condition (15) is universal, because it applies also to rigid polymer molecules (Fig. 6). The authors are very grateful to V. N. Tsvetkov for assistance in the work. CONCLUSIONS

(1) A method has been developed permitting measurement of the oscillatory flow birefringence (OFBR) of polymer solutions (in the audio-frequency region) in solvents with viscosity q ~0.008 P. (2) The relaxational characteristics of solutions of poly-7-L-benzylglutamate (PBG) in dichloroethane (DCE) and tetrabromoethane (TBE) are in agreement with the conclusion t h a t the PBG molecule has high kinetic rigidity (especially in DCE). (3) Solutions of polystyrene (PS) in TBE and bromoform (BF) have broad relaxation spectra (broader in a fraction of high molecular weight). The main cause of this broadening of the spectra is the high kinetic flexibility. (4) The weak dependence of the relaxation spectra of PS-I in TBE and BF on the viscosity of the solvent is clue to the large part played by internal viscosity. (5) The validity of equation (15), derived from the theory of references [18] and [19], has been confirmed experimentally. (6) There is only semi-quantitative agreement between the results of references [18] and [19] and the dispersion of the OFBR of the PS samples in TBE and BF. (7) The contribution of short relaxation times to the total value of An/gc is independent of concentration. Translated by E. O. P~ILLIPS REFERENCES

1. V. N. TSVETKOV, Vestnik LGU 22: 39, 1961 2. V. N. TSVETKOV, V. Ire. ESK1N any S. Ya. FRENKEL', Struktura maeromolekul v rastvorakh (The Structure of Macromolecules in Solution). Izd. "l~auka", 1964

642

O. G. TARAKA~OVand L. N. KOI~'DRAT'EVA

3. V. N. TSVETKOV, I. N. SHTENNIKOVA, Ye. I. RYUMTSEV, L. N. ANDREYEVA, Yu. P. GETMANLrHUK, Yu. L. SPIRIN and R. I. DRYAGILEVA, Vysokomol. soyed. A10: 2132, 1968 (Translated in Polymer Sci. U.S.S.R. 10: 9, 2482, 1968) 4. I. LEARY, J. Polymer Sci. 23: 167, 1957 5. V.N. TSVETKOV and V. P. BUDTOV, Vysokomol. soyed. 6: 1209, 1964 (Translated in Polymer Sci. U.S.S.R. 6: 7, 1332, 1964) 6. C. THURSTON and I. SCHRAG, J. Chem. Phys. 45: 3373, 1966 7. S. N. PEN'KOV, Vestnik LGU 16: 84, 1964 8. C. THURSTON and I. SCHRAG, J. Polymer Sci. 6: 1331, 1968 9. J. FERRY, Vyazkouprugie svoistva polimerov (The Viscoelastic Properties of Polymers). Foreign Literature Publishing House, 1963 (Russian translation) 10. E. V. FRISMAN and V. N. TSVETKOV, Zh. eksp. i teor. fiz. 23: 690, 1952 11. W. MASON, Trans. ASME 69: 359, 1947 12. S. N. PEN'KOV, Optika i spektroskopiya 1O: 787, 1961 13. S. N. PEN'KOV and V. S. STEPANENKO, Optika i spektroskopiya 14: 156, 1963 14. V.N. TSVETKOV, I. N. STENNIKOVA, Ire. I. RYUMTSEV andV, S. SKAZKA, Vysokomol. soyed. 7: 1111, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 6, 1231, 1965) 15. V. N. TSVETKOV, I. N. STENNIKOVA, Ye. I. RYUMTSEV and G. I. OKHRIMENKO, Vysokomol. soyed. 7: 1104, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 6, 1223, 1965) 16. A. WADA, J. Polymer Sci. 45: 145, 1960 17. W. KUHN and H. KUHN, J. Colloid Sci. 3: 11, 1947 18. B. ZIMM, J. Chem. Phys. 24: 269, 1956 19. A. PETERLIN, J. Polymer Sci. B5: 113, 1967 20. R. CERF, J. Chem. Phys. 48: 59, 1951 21. R. CERF, J. Polymer Sci. 23: 125, 1957

E F F E C T OF T H E NATURE OF URETHANE AND CARBAMIDE GROUPS ON T H E OXIDATION OF POLYHYDROXYPROPYLENE

GLYCOL* O. G. TARAKANOVand L. N. KONDRAT'EVA Vladimir Scientific Research Institute for Synthetic Resins

(Received 13 October 1969)

WE HAvE previously [1] noted the synergetic effect of urethane and carbamide groups in the thermo-oxidative degradation of polyhydroxypropylene glycol (PttPG). Carbamide groups introduced into pure PHPG exer~ a weak stabilizing effect, but when they are introduced into polyesterurethane (PEU) the rate of oxidation of the latter falls considerably, and an induction period is found which depends on the amount of earbamide introduced. * Vysokomol. soyed. A13: No. 3, 565-569, 1971.