Acid catalysed degradation of polyoxymethylene in aqueous solutions of hexafluoroacetone

ACID CATALYSED DEGRADATION OF POLYOXYMETHYLENE IN AQUEOUS SOLUTIONS OF HEXAFLUOROACETONE* L. V. IVANOVA, Y r . V. ~[OISEYEV, G. YE. ZAIKOV and A. A. :BERLIN Chemical Physics Institute, U.S.S.R. Academy of Sciences

(Received 8 February 1973) A study was made of the kinetics of degradation of polyoxymethylene oligomers a n d polymers of different molecular weight, with different endgroups, in hydrochloric acid-water-hexafluoroaeetone solutions. I t is shown t h a t the effective rate o f degradation depends on the concentration of hydrochloric acid a n d water in hexafluoroacetone. An equation describing the accumulation of formaldehyde during the degradation of polyoxymethylene is proposed, a n d the depolymerization rate cons t a n t has been calculated.

Ilq EARLIER investigations [1, 2] we described the kinetics of degradation of polyoxymethylene (POM) with methoxy end groups in aqueous solutions of acids, and showed that the process takes place b y an A-1 mechanism [1], and that the end groups have a considerable effect on the reactivity of the oligomers. I t is natural to suppose that an increase in the degree of polymerization will result in these groups having less effect on POM degradation. The degradation of POM cannot be investigated in aqueous solutions of acids under homogeneous conditions as the polymers are insoluble in these solutions. In this paper we report our investigation of the acid catalysed degradation of POM of various molecular weights, with different end groups, in aqueous solutions of hexafluoroacetone (HFA), the latter being the sole common solvent for POM and inorganic acids at low temperatures. EXPERIMENTAL

POM oligomers with methoxy end group~ were prepared by the method described in [3]; the boiling points of the polymers a r e given in Table 1. The p u r i t y of the products was determined b y the NMR a n d GLC methods. POM polymers with methoxy end groups (POM-OCH,) were prepared by t r i o x a n polymerization in presence of methylal with boron fluoride etherate as the catalyst¢. The two methods used to eliminate impurities in the form of polymers with h y d r o x y l end groups (POM-OH) from the samples prepared as above were: 1) heating at 50 ° u n d e r * Vysokomol. soyed. AI6: No. 8, 1831-1837, 1974. ? POM-0CHa were produced at the Milan Research Centre of the M o n t e e a t i n i - E d i s o n Company. 2119

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L. V. IVANOVA et al.

:pressure (11 arm) in a mixture of isopropyl alcohol and an aqueous solution of ammonia; 2) heating at 165 ° for 30 rain in a vacuum (0.1 torr). After purification the samples had not more t h a n 1% polyaeetal bonds; the melting points o f the polymers determined b y differential calorimetry (Perkin-Elmer DS-B-1) are given i n Table 1. TABLE 1. P H Y S I C A L P A R A M E T E R S ~ D

~rikLUES OF keff F O R T H E D E G R A D A T I O N

~0LIGOMERS AND P O L Y M E R S I ~ SOLUTIONS C O N T A I N I N G 0 " 0 0 4 4

MOLE/L. i O l

OF ~ 0 ~ ¢ [

AND 8 " 9 9 M O L E / L .

H~O IN H F A . ~ 30 ° Name Methylat Dihydroxymethylene glycol (n = 2) Dimethyl ether of trihydroxymethylene glycol (n----3) Dimethyl ether of tetrahydroxymethylene glycol ( n = 4 ) Dimethyl ether of hexahydroxymethylene glycol ( n = 6 ) Dimethyl ether of heptahydroxymethylene glycol ( n = 7 ) POM-OCH3 POM-OCH3 POM-OCH3 POM-OCH3 POM-OOCCH3 POM-OH Trioxan Tetraoxan

h~rv

b.p., °C

ketf × lO s,

min-1

76 106

42-46 104.5-105

3.6 5.4

136

152-154

5-1

166

76-78/8 torr

4.7

226

220-230/11 torr 38*

4.2

256 1500 6500 10,500 19,500 100,000 50,000 7000 220,000 9O 120

173" 165-180"

61-62" 112"

3"6 3.8 3.6 3.7 3.9 3.5 3.5 19 3.5 0.3 1.6

* Melting point.

The other polymers and copolymers of trioxan a n d dioxolan were prepared at the K u s k o v Chemical Plant, a n d were used without purification. The physicochemical parameters of the materials are given in Table 1. H F A monohydrate (C3F60.H20) Koch Light Laboratories (U.K.); hydrochloric acid (36% b y wt.) of chemical purity. The kinetics of degradation were investigated as follows. POM polymers and oligomers were dissolved in H F A at 25 °, the dissolution time being from 0.5 to 1.5 hr for the polymers, depending on their molecular weight, and several minutes for the oligomers. H F A is a solvent of a n acidic nature, a n d degradation m a y occur during the dissolution of POM polymers a n d oligomers in this solvent. Changes in"the viscosity of solutions of POM-OH a n d POM-OOCCHa i n H F A were investigated b y Iwabuchi a n d eoworkers [4] at various temperatures. No formation of formaldehyde was observed for the oligomers a n d polymers, a n d 37/~ remained almost constant. The solutions of polymers and oligomers in H F A were thermo,~tatted in a reaction vessel, a n d temperature m a i n t a i n e d to within ±0.02 °. On completion ~ f thermostatting the mixed solution of hydrochloric acid in I-IFA was added to the reaction

Acid catalysed degradation of polyoxymethylene

212I

vessel. The hydrochloric acid concentration in the reaction medium was varied within limits of 4 × 10-3 to 9 × 10-2 mole/1. The concentration of the starting materials was (0.5-2)× 10-~ base mole/1. After predetermined periods of time samples were taken, and these were diluted 100 fold with water to stop the degradation process. The formaldehyde concentration was determined spectrophotometrically, using the Hitachi-139 spectrophotometer, at 520 rim, through the colour reaction with phenylhydrazine hydrochloride and potassium ferrieyanide [5]. Degradation of POM polymers and oligomers is irreversible under the given conditions, as the starting materials are quantitatively converted to monomer. The kinetics of formaldehyde formation are satisfactorily described by a first order equation; for the polymers there is an initial period (5-10~o on the total time of the reaction) when the production of formaldehyde is too slow to be consistent with a first order equation. DISCUSSION OF RESUETS

Effect of water and acid concentration on the effective rate of P O M degradation. As m a y be seen f r o m Fig. 1, the effective first order r a t e constant, keff, o f P O M - 0 C H a d e g r a d a t i o n rises linearly as the acid c o n c e n t r a t i o n rises, a n d is r e d u c e d considerably with increasing H~O concentration. Similar results w e r e o b t a i n e d for t h e POM-OCH~ oligomers a n d p o l y m e r s of different m o l e c u l a r weights. The d e g r a d a t i o n of the P O M oligomers in aqueous solutions of i n o r g a n i c ~ acids takes place b y an A-1 m e c h a n i s m [2] with log keu v a r y i n g linearly with increase in H a m m e t ' s acidity function H 0 [2]

]~rue

log keff-~ H0 ----log - - , K]3~ +

(l)

where ktrue is the t r u e r a t e of disintegration of t h e p r o t o n a t e d form o f the acetal bond; KBR + is t h e basicity c o n s t a n t of the acetal bond. One m a y assume t h a t e q u a t i o n (1) will be correct for t h e H C I - H ~ O - H F A solutions. I n dilute solutions one m a y assume t h a t changes in the acidity o f t h e m e d i u m will be directly p r o p o r t i o n a l to the c o n c e n t r a t i o n of the acid in solution, t h e H 2 0 c o n t e n t being identical, i.e. H0 ~- - - l o g u c l

(2)

Table 2 gives the ktrue/KBR + ratios d e t e r m i n e d f r o m e q u a t i o n (I) t ~ k i n ~ a c c o u n t of e q u a t i o n (2), along with t h e vMues o f the a c t i v a t i o n e n e r g y E a n d a c t i v a t i o n e n t r o p y AS for t h e d e g r a d a t i o n o f m e t h y l a l in H ~ O - H F A solutions oi~ different compositions. E was d e t e r m i n e d in t h e i n t e r v a l 25-40 °.

Effect of molecular weight on the effective rate constant of POM-OCHe degradation. I n a n earlier r e p o r t [2] we dealt with t h e r e a c t i v i t y of POM-OCH~ oligomers in relation to t h e i r chemical s t r u c t u r e in aqueous solutions of m i n e r a l acids; it was p r o p o s e d t h a t t e r m i n a l acetal b o n d scission is followed b y r a p i d d e p o l y m e r i z a t i o n o f polyacetals formed. Given this s c h e m e o f acet~l b o n d seission, one m a y a c c o u n t for the e x t r e m a l t y p e o f relationship b e t w e e n t h e r e a c t i v i t y o f the P O M - O C H a oligomers a n d t h e i r degree of polymerization..

L. V. IVANOVA et al.

2122

T a b l e 1 gives t h e kerr values for the acid c a t a l y s e d d e g r a d a t i o n of POM-OOHa oligomers a n d p o l y m e r s in solutions of 0.0044 mole/1. HC1, 8.99 mole/1. H~O in H F A . T h e highest r e a c t i v i t y is o b s e r v e d for t h e POM-OCH3 dimer, as was also t h e case in aqueous solutions-of acids, a n d kef~ is t h e n r e d u c e d as t h e n u m b e r of a e e t a l b o n d s rises. T h e reactivities o f the POM-OCH3 p o l y m e r s are practically identical. TABLE

2. K I N E T I C PARAMETERS OF D E G R A D A T I O N OF M E T H Y L A L R E L A T I V E TO T H E ~ 2 0

CONTENT IN HFA [HiO],

mole/1. 8"99

9"72 11"30

log (ktrue/

E,

AS*,

IKBH+)

kcal/ /mole

e. units at 30°

[R~O], mole/1.

32± L -24=]= [

11.90 16.20 55.50

at 30 ° 1.05 1.00 0.61

i

29=t=1

I

--

27+1

'

I

log (ktrue/ f /KBH +)

at 30 ° 0"53 -- 0"20 - - 2"50

E, kcal/ /mole w

25!1

AS*,

e. units at 30 °

Y [ 1~1

The effect of the type of end group on the effective rate constant of degradation of _POM. As m a y be seen from Table 1, the reactivities of the P O M p o l y m e r s w i t h v a r i o u s end groups are identical, a p a r t f r o m the P O M - O H w i t h 5iv = 7000. F o r t h e l a t t e r keu is six times higher. T A B L E 3. C H A N G E I N T H E D E G R E E OF CONVERSION AND I N MOLECULAR W E I G H T D U R I N G T H E D E G R A D A T I O N OF P O I ~ c I - O C H a I N

SOLUTIONS

oF 0.0044 mole/1. HC1--8.99 mole/1. H20 IN HFA Time, rain

(mo-- m)

2t)v X

10 -3

m0

0 3 6 14 0 2

0 0"022 0"158 0"386 0 0"053

48 2 1 ~0.5 13-5 2

Reactivity of rings in _POM copolymers. Table 1 gives the kerf values for the d e c o m p o s i t i o n of t r i o x a n , t e t r a o x a n a n d P O M copolymers containing different a m o u n t s of C - - C bonds. As the ring size increases, kefr rises. The n u m b e r of C - - C b o n d s has no effect on t h e r e a c t i v i t y of t h e P O M copolymers (keff = (3"5 ± 0"5) • X 10 -3 min-1). T w o reactions t a k e p l a c e during t h e acid catalysed d e g r a d a t i o n of POM: a chain scission reaction (for the p o l y m e r s it is t h o u g h t t h a t this reaction takes p l a c e b y a r a n d o m law) a n d a d e p o l y m e r i z a t i o n reaction which takes place

Acid catalysed degradation of polyoxyraethylene

2123

when the polymer molecule has O H endgroups, which are active ccntres of depolymerization. Let us now consider the character and quantitative regularities of each of these reaction.

keffxlgZm/n-I /

,

//,/9

{

//

0"01

o.oz

['HG1,],mo/e/~l. FIG. 1. Plots of ]¢ett for POM-OCH3 (h~r~=1500) degradation vs. HC1 concentration in H~O-HFA solutions with total I-I~O concentrations of 8.99 (1), 11.3 (2) and 16.2 mole/1. (3).

The chain scissionreaction. As was noted above, the extremal reactivity of the POM-OCHs oligomers in aqueous solutions and in H F A solutions of acids may be explained if one assumes higher reactivity of terminal acetal bonds. This assumption is favoured b y the dissimilar values of ke~ for linear POM-OCH3 oligomers and POM rings which, in the view of some authors [6] are models of the acetal bond of an "infinite" polymer molecule. Narrow fractions of POM-OCH3 prepared b y fractionation of the polymer with 214v~19,500, using the method described in [7] were used for determining the reactivity of the "middle" bonds. Table 3 gives the variation in molecular weight determined b y the viscometric method [8]. Assuming that for low degrees of conversion chain scission takes place mainly b y a random law, one m a y determine the rate constant of chain scission krand b y using the equation given in [9] 1

1

Pvt Pv.

1

- = 2+~

k~a.d × t

(3)

where Pvt and Pvoare current and initial viscosity average degrees of polymerization respectively, a--is the exponent in the 3~ark-Houwink equation, equal to 0-66i k,a~d----( l ± 0. 2) × 10 -2 rain -1. In view of the above data it m a y therefore be assumed that the reactivity of

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L.

V . I V A N O V A et al.

t e r m i n a l acetal bonds in t h e P 0 M oligomers a n d p o l y m e r s exceeds t h a t of t h e " m i d d l e " bonds. One of the probable reasons for the higher r e a c t i v i t y of t h e t e r m i n a l acetal bonds could well be the possibility of the f o r m a t i o n of cyclic a c t i v a t e d complexes ensuring additional a c t i v a t i o n in the course of a n A-1 reaction H\+

>o(

11/

.CH2~--0~

\CH~

\o

+

6][I~

ROH + CH~.--0CH2--0CH~.--0~,

\/ o

w h e r e R is the e n d g r o u p ( C H s - - or CH3CO--). I n t h e same w a y the f o r m a t i o n of a four m e m b e r e d a c t i v a t e d complex m a y t a k e place. F r o m this s t a n d p o i n t the following conclusions are possible. T r i o x a n is n o t a model of the acetal b o n d of a n "infinite" p o l y m e r molecule in acid catalysed d e g r a d a t i o n reactions as the r a t e constant as a ratio of a single acetal b o n d ( k e f f = l ' 0 × 10 -~ min -1) is lower b y a factor of t e n t h a n the rate of P 0 M chain scission b y a r a n d o m law. T h e lower r e a c t i v i t y of the acetal bonds in t r i o x a n is in all p r o b a b i l i t y due to the rigid ring structure. The r e a c t i v i t y of the acetal b o n d in t e t r a o x a n ( k e f f = 4 . 0 × 1 0 - S m i n -~) is closer to t h a t of the " m i d d l e " acetal bonds, and it is t h e r e f o r e to be e x p e c t e d t h a t t h e larger rings will be a model of the infinite p o l y m e r molecule of POM. TABLE

4. K I N E T I C

GRADATION

OF

PARAMETERS

OF

TRIOXAN--DIOXOLAN

]VIERS I N S O L U T I O N S

.OF 0 . 0 0 4 4

THE

DE-

COPOLY-

mote/1.

HC1--

8.99 mole/1. I-I,O IN HFA 2V/,j× 10-3* 24 61 s 130

C--C-bonds, O/o

krand, rain -~

2'4 4"43 >4"5

1"2 × 10-3 5'5 × 1 0 - 4 3"3X 10-4

* Narrow fractions prepared b y the method described in [7] were used.

I f we t a k e m e t h y l a l as a model of the acetal b o n d of POM-OCHa, t h e ratio o f ]¢true/KBH+ (methylal) to ktrue/KB~+(krand) shows the e x t e n t t o which the t e r m i n a l b o n d in P O M is more reactive t h a n the " m i d d l e " bonds. To a first a p p r o x i m a t i o n ktrue for the t r i o x a n - d i o x o l a n copolymers of different molecular weight m a y be d e t e r m i n e d f r o m e q u a t i o n (3). As m a y be seen f r o m Table 4, krand is r e d u c e d as the n u m b e r of C - - C bonds d e t e r m i n e d b y the m e t h o d described in [10] increases. I t is interesting t o n o t e t h a t value of kr~n a e x t r a p o l a t e d to zero concentration of C - - C bonds ( ( 7 ~ l ) × × 10 -a rain -1) is close to k~nd d e t e r m i n e d for POM.

Acid catalysed degradation of polyoxymethylene

2125

The depolymerization reaction. The depolymerization reaction in the acid catalysed degradation of POM cannot be separately investigated owing to the rate at which the reaction of chain scission takes place. In view of the experimental results two assumptions are possible in regard to the mechanism of the depolymerization reaction. Scission of the POM chain is accompanied by the elimination of one or two molecules of formaldehyde with subsequent closing of the polymer chain, i.e. the kinetic length of the depolymerization chain is equal to unity or to two (mechanism I). A similar mechanism was proposed by Grassie [] 1] for the thermal degradation of POM. Scission of the POM chain is accompanied by the formation of fragments with OH end groups, the depolymerization of which leads to the formation of formaldehyde molecules (mechanism II). To single out mechanism I or I I special experiments involving molecular weight determination during the degradation of POM were carried out. The marked change in molecular weight at low degrees of conversion (see Table 3) confirms mechanism II, and contradicts mechanism I, as in the latter case there ought to be a linear relationship between molecular weight and the degree of conversion. Assuming then that the degradation process takes place by mechanism II, let us find the depolymerization constant. Let us say that the POM chain scission takes place mainly through a random law. The change in polymer mass m during the process will then be described by the equation dm/dt=--k'de p [--OCH2OH],

(4)

where [--OCH2OH] is the number of end groups that are active centres of depolymerization. In the case of stepwise depolymerization of polymers with exponential ~IWD the molecular weight remains constant, i.e. (dMn/dt)de,~--O. Hence

(dN/dt)dep-~(dm/dt) ( N / m ) ,

(5)

where N is the number of POM-OH molecules. Taking into account equations (4) and (5), we obtain

(dNIdt)dep= _ (k'd+pN:lm) ,

(6)

where ]~ep= 2]~dep. In investigations carried out by Berlin and Yenikolopyan [9] a study was made of kinetic regularities (changes in the number of molecules and in polymer mass) for a case where the degradation of polymer molecules takes place through a random law and the length of the kinetic chain of depolymerization is much less than the number average degree of polymerization. Taking account of the

2126

L.V.

IVA~OVA et al.

foregoing assumptions (equation (6)), we obtain

din~dr=

(7)

- - 2krand XV-- ]C~ep N P

dN/dt =

krandm--

2

(s)

3krandN -- kdePN m

m=mo,

Under the initial conditions ( t = 0 , the following solutions:

m/mo=exp{~[ln

N = 0 ) this set of equations has

(2-- ek""~t)-- krandt]},

(9)

where m 0 a n d m are the initial and current polymer mass respectively, a n d -- ~dep m/m o

N*lO 2~nTo

0"5

I

ZO

qO

50

80

T/me, rain

FIG. 2. Kinetic curves of change in polymer mass (I, 2) and in the number of moles N with polyacetal bonds in the sample (3):/--experimental curve; 2, 3--curves calculated on the basis of equations (7) and (8) respectively. Tile experimental d a t a (Fig. 2, curve 1) are satisfactorily described b y equation (7) if kdep is within limits of 0.1-0-2 min -1 (curve 2). Curve 3 shows the change in the n u m b e r of POM-OH molecules (N) with time calculated in accordance with equation (8). I t is seen from the Figure t h a t the highest rate of the reaction determined from the change in polymer mass corresponds to the largest n u m b e r of a c c u m u l a t e d reactive OH groups. I n the case o£ short reaction times (5-10% on the total time) a small n u m b e r of POM-OH molecules are still formed, a n d the polymer mass changes only to a negligible extent, i.e. there is a period t h a t could conventionally be t e r m e d an " i n d u c t i o n " period.

Acid catalysed degradation of polyoxymethylene

2127

The almost identical r e a c t i v i t y ( d e t e r m i n e d f r o m t h e p r o d u c t i o n o f f o r m a l d e h y d e ) o f POiVl of different molecular weights with different end groups m a y therefore be e x p l a i n e d as follows. D u r i n g t h e initial period o f P O M d e g r a d a t i o n a considerable n u m b e r o f P O M - O H molecules are f o r m e d on a c c o u n t o f c h a i n scission t h r o u g h a r a n d o m law, a n d the d e p o l y m e r i z a t i o n of these molecules leads to t h e elimination of f o r m a l d e h y d e ; the a m o u n t o f P O M - O t t is practically i n d e p e n d e n t of t h e molecular weight o f the initial p o l y m e r and the n a t u r e o f its endgroup. TABLE 5. VALUES OF ktrue/KBH+ (1./mole.min) at 30 ° [H,O],

Aeetal borfd seission

mole/1.

terminal

8.99

(3-1 8.0-t-0.2 :~0.2) × 10-3!

55.5

i

middle 2.3±0.2

Depolymerization reaction 30:t: 10 6~: 1 [12]

I n the case o f P O M - O H with M v ~ 7000 (a-oxide) t h e r e are a large n u m b e r o f centres of d e p o l y m e r i z a t i o n a t t h e initial m o m e n t a n d this in the final analysis ensures a high value o f kef~. Owing to the lack o f precise i n f o r m a t i o n r e g a r d i n g t h e initial n u m b e r of O H endgroups, it was u n f o r t u n a t e l y impossible t o c a r r y o u t theoretical calculations o f ke~ for P O M - O H with 2~----7000. W i t h the p r o p o s e d scheme o f P O M d e g r a d a t i o n one m a y c o m p a r e t h e reactivities of t h e t e r m i n a l a n d " m i d d l e " acetal bonds a n d the rates of depolym e r i z a t i o n in H 2 0 - H F A solutions o f v a r y i n g composition (see T a b l e 5). T h e constants were calculated b y e q u a t i o n (1), t a k i n g a c c o u n t of e q u a t i o n (2). Translated by R. J. A. HE,DRY REFERENCES 1. L. V. I ~ V ~ O V A , Yu. V. MOISEYEV, G. Ye. Z A I K O V and V. V. I V ~ O V ,

2. 3. 4. 5. 6. 7.

8.

Izv. A N SSSR,

seriya khimich., 2236, 1970 L. V. IVANOVA, Yu. V. MOISEYEV and G. Ye. ZAIKOV, Izv. AN SSSR, seriya khimieh., 2501, 1970 V. V. IVANOV, A. A. SI-IAGINYAN, V. P. VOLKOV and N. S. YENIKOLOPYAN, Vysokomol. soyed. 7: 1830, 1965 (Translated in Polymer Sci. U.S.S.R. 7: 8, 2015, 1965) S. IWABUCHI, V. JAACKS and W. KERN, Makromolek. Chem. 100: 276, 1967 I. M. KORENMAN, Fotometrieheskii aaaliz (Photometric Analysis). p. 58, Izd. "Khimlya' ', 1970 N. S. YENIKOLOPYAN and S. A. WOLFSON, Khimiya i tekhnologiya poliformal'degida (Chemistry and Technology of Polyformaldehyde). Izd. "Khimiya", 1968 L. M. BOGDANOVA, A. I. VARSHAVSKAYA, G. S. DOMASHNEVA, Ye. M. SAPOZHNIKOV and B. A. ROZENBERG, Vysokomol. soyed. B13: 654, 1971 (Not translated in Polymer Sci. U.S.S.R.) S. R. RAFIKOV, S. A. PAVLOVA and I. I. TVERDOKHLEBOVA, Metody opredeleniya raolekulyarnykh vesov i polidispersnosti vysokomolekulyarnykh soyedinenii (Methods of Determining the Molecular Weights and Polydispersity of High-molecular Compounds). Izd. AN SSSR, 1963

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N . G . MATVEYEVAet al.

9. A.A. BERLIN and N. S. YENIKOIJOPYAN, Vysokomol. soyed. A10: 1475, 1968 (Translated in Polymer Sci. U.S.S.R. 10: 7, 1706, 1968) 10. V. A. lVIININ, A. A. BERLIN, A. I. VARSHAVSKAYA, T. S. KOVTUN, L. V. KARMILOVA and N. S. YENIKOLOPYAN, Vysokomol. soyed. A14: 9, 1972 (Translated in Polymer Sci. U.S.S.R. 14: 1, 9, 1972) 11. N. GRASSIE and R. S. ROCHE, Makromolek. Chem. 112: 16, 1968 12. J. L(}B ERING and V. RANK, Chem. Ber. 70: 2331, 1957

TEMPERATURE DEPENDENCE OF THE MECHANICAL PROPERTIES OF NETWORK POLYMERS BASED ON OLIGOOXYETHYLENE-URETHANE METHACRYLATES* N. G. MATVEYEVA, Z. G. ZEMSKOVA, YU. M. SIVERGIN, 0 . G. SEL'SKAYA, G. V. ]?ODKOLZINAa n d A. A. BERLIN Chemical Physics Institute, U.S.S.R. Academy of Sciences (Received 8 _February 1973)

The glass transition temperature T~ was determined on the basis of the thermomechanical curves for amorphous network polymers based on oligo(oxyethylene-urethane methacrylates) of different molecular weight. It was found that T~ is proportional to the reciprocal of the molecular weight of the original oligomer and ceases to be a function of block length if the oligomer has a molecular weight of > 2000. The limiting values obtained for the stress and the elastic modulus of the network crystalline polymers rise as the length of the oligomerie block increases, and in the case of n ) 6 0 these values become practically constant, which is due to the formation of physical crosslinks increasing the overall network density. For the same polymers in the high elastic state the limiting stress values fall as the block length increases, and at n ) 60 become virtually independent of n. OVR aim in this investigation was to investigate t h e t e m p e r a t u r e dependence o f t h e m e c h a n i c a l properties of n e t w o r k p o l y m e r s of v a r y i n g n e t w o r k d e n s i t y p r e p a r e d b y the h a r d e n i n g of e,~o-bis-(4-methacryloxyethylcarbamatetoluylene-2carbamie) ethers o f oligoethylene glycols ( 0 U M ) of oligoethylene glycols ( 0 U M ) h a v i n g the general f o r m u l a

CH~=C~CHa)COOCH~CH~0CONH--~--CH3 ~-NHC0 [0CH~CH2]n--] /,NHC00 • CH~=C (CH3) COOCI-I~CH~0CONH--~/~z--CH3, where n = 1 - 1 3 6

[1].

• Vysokomol. soved. A16: No. 8, 1838-1843, 1974.

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