The synthesis and oxidative reactions of allylcellulose

THE SYNTHESIS AND OXIDATIVE REACTIONS OF ALLYLCELLULOSE*t 0 . P. KOZ'MINA, E. P. PROSVIRYAKOVA and 0 . V. KALLISTOV Institute of Macromolecular Compounds, U.S.S.R. Academy of Sciences (Received 9 November 1964)

ALLYLCELLULOSE is an interesting substance, both from the point of view of the s t u d y of the mechanism of oxidation of cellulose ethers and of the modification of the properties of cellulose. It has already been shown that allylcellulose is easily oxidized b y atmospheric oxygen, giving an insoluble polymer, and the formation of peroxide and carboxyl groups in the macromolecules of the ether, and elimination of lowmolecular products, was noted [1]. In this communication some new experimental results are reported, on the oxidation and other properties of allylcellulose (AC) and on its synthesis. These results were in part included in a general report on the mechanism of oxidation of cellulose ethers and esters [2]. Samples of the ether ranging from insoluble products or products soluble in alkaline solution and of low degree of substitution, to products of high degree of substitution (~ ~200) and soluble in organic solvents were synthesized. In the preparation of AC it is not always possible to obtain reproducible results with respect to the solubility of the final ether. We have shown that in the presence of traces of impurities, for example when peroxides are formed in the alkyl halide or when the reaction mixture comes into contact with atmospheric oxygen, the solubility of the ethers is impaired. We found that the interchange method, starting from acetylcellulose, can be used for the production of soluble allyl ethers under laboratory conditions. An example of this method of preparation is given in the experimental section. The properties of solutions and films of AC were studied. The average molecular weights of the ethers were in the region of 40-70 x 108, i.e. of the same order as for ethylcellulose [3]. Freshly-prepared films of AC possess the fair mechanical strength on stretching of 450-500 kg/cm 2. However under atmospheric conditions the films age rapidly, losing their solubility and becoming brittle. Study of the oxidation of cellulose allyl ethers was undertaken for the purpose of elucidating the initial stages of the process. Samples were oxidized both under * Vysokomol. soyed. 7: No. 10, 1701-1706, 1965. t Communication 23 in the series "The mechanism of oxidation of cellulose ethers and esters by oxygen". 1874

Synthesis of allylcellulose

1875

heterogeneous conditions, in the form of films and powders, and in dilute solution, at 20-70 °. In this temperature region AC normally oxidizes without an induction period. The primary products of oxidation of AC, as in other cellulose ethers [2], are undoubtedly peroxides (Fig. 1). Alongside formation of peroxides of the ethers decomposition of these occurs, with elimination of acrolein*, formaldehyde, allyl alcohol, formic acid and water, and also with formation of low-molecular peroxidic compounds. Carbonyl, carboxyl, ester and epoxide groups accumulate in the AC macromolecules, and the ether loses its solubility. Figure 1 shows the accumula-

g20

.~2i

0

/ /

0"2 04 ~6 Holes02pepgtucoseunit

08

FIG. 1. Oxidation of allylceUulose film at 40°: 1--peroxide content of allylcellulose molecule, 2--elimination of aldehydes (aerolein), 3, 4 and 5--epoxide-, ester- and carboxyl-group content of ether molecule respectively, 6--alkoxide-group content. tion of the main reaction products. The other substances were determined in separate experiments. The formation in this instance of epoxide groups, and the loss of solubility of t h e ether as oxidation proceeds, are undoubtedly the result of secondary reactions due to the presence of the double bond in the eter group. Epoxide groups arise :most probably as a result of reaction of secondary reaction products--low-molecular peroxide compounds--with the double bond of the allyl group b y the Prilezhayev reaction [4]. The formation of formaldehyde in the oxidation of the ether groups of AC can be attributed to opening of the a-oxide ring of epoxygroups, for example b y the action of free radicals. I t should be noted that the formation of formaldehyde together with acrolein has also been observed in the oxidation o f allyl ethers of low-molecular alcohols [5]. Because of the impairment or loss of solubility of films of the ether on oxidation it was not possible to follow change in intrinsic viscosity to find whether degradation of the polymer chain occurs, as in the oxidation of saturated cellulose * In reference [1] the formation of acrolein was not mentioned, only the elimination of formaldehyde, whereas in this reaction more acrolein than formaldehyde is formed.

O. P..Koz'~i~a et,al.,

1876'

ethers [2]. However~when AC was oxidized in dilute solution at 20-50 ° we observed that in t h e v e r y beginning of the process the intrinsic viscosity falls, and only later begins to rise (Fig. 2). It m a y be assumed that this fall in viscosity is due to degradation~ of the macromolecules, and the subsequent rise to "micro-crosslinking" of the polymer chains, which can occur through t h e unsaturated bonds b y the action of free radicals accumulating in the system as oxidation proceeds. When the temperature of oxidation is increased from 20 to 40 ° bothprocesses, degradation and erosslinking, are accelerated (Fig. 2, curve 2). At 50 ° the minimum in the curve is shifted to the right and the rise is steeper (Fig. 2, curve 3). At higher temperatures the curves smooth out and rise steadily until the ester begins to precipitate from solution.

2"5

o

o

o

2

2"0

t"5

!

V

I

8

I

]2

.

r

t5

I

2g

T/me ~ houz'3

FIG. 2. Variation in intrinsic viscosity of a 1~o solution of allylcellulose: /--at 20°, 2--at 40°, 3--at 50°. These results indicate the degradative nature of the oxidation of AC, which is normally masked b y secondary reactions of the polymer molecules, involving the double bonds of the ether groups. For quantitative characterization of these reactions it is necessary to determine the molecular weight of specimens of the ether during the course of oxidation. This forms a special, independent part of the study of the mechanism of degradation and crosslinking of the polymer molecules and will be undertaken later. The change in intrinsic viscosity shown in the three curves of Fig. 3 was studied with the same solution of AC. The slight difference in the values of the initial (at v ~ 0 ) intrinsic viscosity, [~], is explained b y the fact that it falls to some extent with increase in temperature. This sligh t fall in [~/] is not associated with oxidation, and is a general property o f maeromolecules i n solution.

Synthesis of allylcellulose

1877

In order to find the effect of secondary products on the process the action of peroxidic compounds on AC was Studied. It was found that alkyl and acyl h y d r o p e r o x i d e s a n d p e r o x i d e s r e a c t w i t h A C (in s o l u t i o n ) t o f o r m e p o x i d e g r o u p s at the double bonds. In this reaction alkyl and acyl hydroperoxides are reduced to the alcohol and acid, ' respectively, and acyl peroxides to acid anhydrides, as w a s f o u n d p r e v i o u s l y b y o n e o f u s [6]. F u r t h e r d e t a i l s o n t h e r e a c t i o n o f A C a n d other unsaturated ethers with peroxidic compounds will be reported in a separate communication. EXPERIMENTAL

Allylation of celluloee. The ethers were prepared from purified cotton linters and freshly distilled allyl bromide, free from peroxidic compounds. Well teased out linters were mercerized in 50% sodium hydroxide solution for 18-24 hours. The alkali-treated cellulose was squeezed out to four to five times the original weight and esterified in a current of nitrogen with an excess (from 5 to 20 moles) of allyl bromide in benzene (thiophene-free) or freshly purified CC14, with stirring and with or without the addition of d r y alkali. The reaction was carried out at the boiling point of the solvent for 4-8 hours. The volatile components were then distilled off in vacuo (or in a current of nitrogen), the AC was washed with hot water until free from salts and alkali, and dried to constant weight in vacuo over phosphorus pentoxide. I n some experiments the water was removed b y distillation with benzene. Highly substituted, soluble ethers were further purified b y reprecipitation from solution. Preparation of allylcellulose by interchange with acetyl cellulose. Allyl bromide and 50% sodium hydroxide solution in four- to fivefold excess were a d d e d dropwise a n d simultaneously, with vigorous stirring over a period of 2-3 hours, to an 8% solution of cellulose diacetate in acetone a t the boiling point of acetone. The reaction ceased after 4-5 hours. Allylcellulo~e precipitated from solution in the form of a white, resinous, swollen product, which was purified as described above after evaporation of the volatile materials. The yield was 70-75~o, calculated on the weight of dia~etate taken. The degree of substitution was 1"5-1"75 (by iodine value). E x a m p l e s of such preparation are given in the Table, from which it is seen t h a t b y varying the q u a n t i t y of the allylating reagent, a n d the reaction time, under otherwise equal conditions, it is possible to prepare allylcelluloses of different composition and properties. The analyses of various samples of the ether b y combustion, iodine ( K a u f n ~ n n method [7]) a n d bromine values are in agreement a n d can be used to calculate the degree of etherification of the cellulose. The determination of alkoxyl groups b y the Zeisel method gave somewhat lower results. As an example we quote the results of two analyses of sample 2 b y the three methods: b y elementary analysis b y iodine a n d bromine values b y the Zeisel m e t h o d

1-78 1"74 1"62

1.74 1.74 1-60

AllylceUuloses with degrees of substitution f r o m i-5 to 2"2 are soluble, or partially soluble in methylene chloride, an alcohol-benzene mixture, toluene, acetone, ethyl acetate etc.

The intrinsic viscosity of the AC's was determined in a suspended-level, Ostwald viseometer, and the molecular weight b y the light scattering m e t h o d ~in solution in ethyl acetate, in a polarizing nephelometer [8]. Oxidation of allylcellulose by oxygen. AC in the form of a film, powder or dilute solu-

1878

O.P.

KOZ'MI~A etal.

EFFECT OF CONDITIONS OF PREPARATION ON THE COMPOSITION AND PROPERTIES OF ALLYLCELLULOSE Experiment ~o.

8 11 4 12 17 18 6 14 15 21 26 27 29 34

Preparative conditions excess o f allyl bromide, moles

time, hours

5 5 15 20 10 20 15 4 4 15 15 20 20 20

4 6 8 4 6 8 8 6 4 6 8 8 6 8

dry NaOH added

Characteristics of product elementary composition

~*

solubility

swells 50 95 50 swells 95 90 90 60 95 80 85 60 90

5 5 10 2 2 10 10

54.6 56"2 58"4

7"2 7"8 7"4

52"6 59"8

7"2 7"5

10 5 10 10 10

59"1

7"9

115 141 178 137 88 206 183 175 156 191

59"9

7"8

209

60"0

7"8

210

[~3

1"9 3"6 1"8 4"2 3"8 2"4 3"6 3"4 3"7

Remarks. All experiments in the Table (except Nos. 14 and 15) on the direct allylation of alkaliceilulosewere carried in benzene (No. 12 in CCI,). In experiments Nos. 14 and 15 AC was prepared by interchange from acetylcellulose in acetone. The "solubility and intrinsic viscosity, [~], were determined in alcohol-benzene solution. Thc molecular weights of samples 4 and 18 were determined by the light scattering method (45 × 10a and 60× 10a respectively). * ~ is the number of alkoxyl groups per 100 glucose units. out

t i o n w a s o x i d i z e d in a glass vessel w i t h a p o r o u s b o t t o m , p l a c e d in a n u l t r a t h e r m o s t a t . F o r o x i d a t i o n s i n s o l u t i o n t h e vessel w a s p r o v i d e d w i t h a n a d d i t i o n a l n e c k for r e m o v a l o f t e s t s a m p l e s (the c o n c e n t r a t i o n o f e a c h s a m p l e w a s d e t e r m i n e d a c c u r a t e l y b y t h e g r a v i m e t r i e m e t h o d ) . I n o r d e r t o m e a s u r e t h e u p t a k e o f o x y g e n t h e e x p e r i m e n t s w e r e c a r r i e d o u t in a closed s y s t e m i n t h e a p p a r a t u s d e s c r i b e d p r e v i o u s l y [9]. T h e s p e c i m e n s w e r e o x i d i z e d a t c h o s e n , c o n s t a n t t e m p e r a t u r e s . T h e r a t e o f p a s s a g e (or circulation) o f o x y g e n w a s f r o m 1"5 t o 3 1./hr in d i f f e r e n t e x p e r i m e n t s . T h e volatile p r o d u c t s w e r e c o n d e n s e d in t r a p s cooled t o - - 8 0 °, c a r b o n d i o x i d e w a s a b s o r b e d in b a r i u m h y d r o x i d e s o l u t i o n a n d CO w a s o x i d i z e d t o CO s b y m e a n s o f h o p c a l i t e . Analysis of the volatile oxidation products. P e r o x i d i c c o m p o u n d s w e r e d e t e r m i n e d iodom e t r i c a l l y in a c u r r e n t o f n i t r o g e n (with allowance for c o n s u m p t i o n o f iodine b y d o u b l e b o n d s in c o n t r o l e x p e r i m e n t s ) , a n d polaxographically. Aldehydes were determined by means of their reaction with hydrazine sulphate, and for i d e n t i f i c a t i o n t h e y w e r e p r e c i p i t a t e d b y solutions o f 2 , 4 - d i n i t r o p h e n y l h y d r a z i n e a n d dim e d o n e . T h e h y d r a z o n e s w e r e s e p a r a t e d in a m a g n e s i u m o x i d e c h r o m a t o g r a p h i c c o l u m n b y t h e m e t h o d o f N e b b i a a n d Garrieri [10]. T w o d i s t i n c t a b s o r p t i o n b a n d s w e r e o b t a i n e d , c o r r e s p o n d i n g in R f v a l u e a n d colour t o t h e 2 , 4 - d i n i t r o p h e n y l h y d r a z o n e s o f acrolein a n d f o r m a l d e h y d e , a n d a f e w diffuse b a n d s o f c a r b o n y l c o m p o u n d s t h a t could n o t b e i d e n t i f i e d b e c a u s e o f t h e s m a l l q u a n t i t y p r e s e n t . I n a d d i t i o n t h e d i m e d o n e - d e r i v a t i v e p r e c i p i t a t e was h e a t e d w i t h 1 1~ N a O H , d u r i n g w h i c h t r e a t m e n t t h e f o r m a l d e h y d e l i b e r a t e d p a s s e d i n t o solution. T h e alkali-insoluble r e s i d u e h a d m . p . 163-164 ° a n d c o r r e s p o n d e d t o t h e d i m e d o n e d e r i v a t i v e ( a n h y d r o u s form) o f acrolein (m.p. 163°).

Synthesis of allylcellulose

1879

Formaldehyde was also identified by means of its reaction with p-naphthol [11]. A condensation product in the form of long, thin needles of m.p. 192° was obtained. Melting points of 192-195 ° are quoted in the literature for dinaphthylmethane. From the salts obtained by neutralization of the condensate with 1 N NaOH the acids were liberated, after evaporation of aldehydes, by acidification with sulphurie acid and distillation. They consisted mainly of formic acid (identified by reduction of silver nitrate etc.) and acrylic acid, determined by the method of Critchfield after careful neutralization [ 12]. Alcohols (allyl) were determined by the nitrate method by means of ultraviolet spectroscopy. Analyais of oxidized aUylceUu~oae. During the course of oxidation the elementary composition and functional groups were determined, after the AC specimens had been washed and vacuum treated to remove adsorbed reaction products of low molecular weight. Peroxide groups were determined iodimetrically in a current of nitrogen (with a correction for iodine absorbed by double bonds) and by other conventional methods. Carboxyl groups were determined by titration by the method of Van der Wyk [14] (after decomposition of peroxides), with Methylene Blue as indicator. Epoxide groups were determined from the quantity of combined chlorine or nitrogen after treatment of an oxidized sample with a hydrochloric acid solution containing calcium chloride (812 g CaC1t- 2H=Oq-600 ml HtO-~ 95 ml cone. HC]), or dry, gaseous ammonia. Amino-compounds, including hydrazines and hydroxylamine, alsto react with epoxido groups. I t is therefore difficult to determine earbonyl groups in oxidized AC. When the latter is reacted with 2,4-dinitrophenyl hydrazine condensation occurs with both epoxide and carbonyl groups (forming derivatives of a bright-yellow colour}. These methods show the presence of carbonyl groups only by the difference between the total combined nitrogen and the chlorine taken up by the epoxide groups in a control experiment. Aldehyde groups were determined by condensation with dimedone. The infrared spectroscopic method is the most suitable for determination of carbonyl groups in this case. This was used successfully for determination of functional groups containing C = O in oxidized ethylcellulose [15]. For determination of ester groups a weighed quantity of AC, after neutralization of carboxyl groups (to Methyl Red), was saponified in 1 N NaOH. The solution was filtered off and the ether was washed free from alkali. The combined filtrate and wash-water was evaporated in the water bath in the presence of copper turnings (to prevent polymerization), followed by acidification and distillation of the acid. The acrylic acid in the distillate was determined by the method of Critchfield [12].

CONCLUSIONS The m e c h a n i s m o f o x i d a t i o n o f ally]cellulose is similar t o t h a t ofethylcellulose a n d o t h e r ethers. The a c t i o n of o x y g e n p r o d u c e s h y d r o p e r o x i d e groups, m o s t p r o b a b l y on the e t h e r C - a t o m o f t h e allylic radical. As a result of d e c o m p o s i t i o n of these acrolein, ally] alcohol, peroxidic c o m p o u n d s , formic acid, water, C02 a n d CO are liberated. The a l k o x i d e - g r o u p c o n t e n t o f t h e p o l y m e r molecule falls accordingly, the carbonyl-, carboxyl-, ester- a n d e p o x i d e - g r o u p c o n t e n t s o f the polymer a n d o t h e r c o m p o u n d s rise a n d t h e intrinsic viscosity of t h e ether decreases. Specific features of t h e process, associated w i t h t h e presence of ally]ic double b o n d s are t h e s e c o n d a r y reactions of f o r m a t i o n of epoxide g r o u p s in t h e m a c r o molecule a n d o f a" n e t w o r k s t r u c t u r e due t o cross]inking of t h e macromolecules. Tran~/ated by E. O. PHILLIPS

i880

A. I . KURILENK0 et all REFERENCES

1 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15.

S. N. DANILOV a n d O . P . KOZ'MINA, Zh. obshch, khim. 18: 1823, 1948 O. P. K 0 Z ' M I N A , ' Izv. Akad. N a u k SSSR, Otd. khim. nauk, 2256,' 1961 T. I . SAMSONOVA a n d S. Ya. FRENKEL', Kolloid. zh. 20: 67, 1 9 5 8 N. P. PRILEZHAYEV, Organicheskie perekisi. (Organic P e r o x i d e s . ) W a r s a w , 1912 N. A. ZHURAVLEVA, Dissertation, Moscow, 1952 O. P. KOZ'MINA, Zh. obshch, khim. 18: 2016, 1948 K. BAUER, Analiz organicheskikh soyedinenii. (Analysis of Organic Peroxides.)p. 19, Foreign Literature Publishing House, 1953 (Russian translation) V. N. TSVETKOV, K. Z. FATTAKHOV and O. V. KALLISTOV, Zh. exp. i teor. fiz. 26: 351, 1954 V. I. KURLYANKINA and O. P. KOZ'MINA, Vysokomol. soyed. 5: 785, 1963 L. NEBBIA and F. GARRIERI, Chimica e industria 39: 749, 1957 M. M. R. de FOSSE, P. de GRAVE and P. E. THOMAS, Compt. rend. 200: 1450, 1935 F. E. CRITCHFIELD, Analyt. Chem. 31: 1406, 1959 S. A. SHCHUKAREV, S. I. ANDREYEV and I. A. OSTROVSKAYA, Zh. analyt, khim. 9: 354, 1954 A. J. H. v a n d e r W Y K and M. STUDER, Helv. chim. acta 32: 1698, 1949 V. I. KURLYANKINA, A. B. POLYAK and O. P. K 0 Z ' M I N A , Vysokomol. soyed. 2: 1850, 1960

STUDY OF THE ADHESION OF RADIATION-HARDENED POLYESTER RESINS TO HIGHLY ORIENTATED ORGANIC FIBRES* A. I. KURILENKO, G. V. SHIRYAYEVA and V. L. KARPOV t L. Ya. K a r p o v Branch of the Physicochemical I n s t i t u t e (Received 9 November 1964)

THE strength of the adhesive bond between various polymeric fibres and polyester and epoxide resins, hardened by ordinary thermal methods, has been determined previously, and certain relationships were found between adhesion and the nature of the resins and polymers [1]. It seemed of interest to examine the nature of these relationships when the resins are hardened by the radiation method. This problem has received little study. Only two papers concerned with the study of the possibility of increasing adhesion by means of radiation have been published

[2, 3]. The present investigation was made with unsaturated polyester resins hardened by e°Co 7-radiation, and highly orientated fibres. * Vysokomol. soyed. 7: No. 10, 1707-1712, 1965. t E. V. Starodubtseva assisted in the experimental work.