Die Angewandte Makromolekulare Chemie 128 (1984) 173 - I79 (Nr. 2034)

Central Leather Research Institute, Adyar, Madras 600 020, India

Grafting of Ethyl Acrylate onto Gelatin in Water-Isopropanol Medium

Anne George, Ganga Radhakrishnan, and K. Thomas Joseph

(Received 14 May 1984)

SUMMARY: Graft copolymers were synthesized by grafting ethyl acrylate onto gelatin. The

reaction was carried out in water-isopropanol medium (1 : 1 v/v). Reactions take place within 90 min. The resulting product is insoluble in solvents for the respective homo- polymers. Presence of vinyl polymer was confirmed by IR spectra.

ZUSAMMENFASSUNG : Es wurden Pfropfcopolymere durch Pfropfung von Ethylacrylat auf Gelatine her-

gestellt. Die Reaktion wurde in Wasser/Isopropanol (1 : 1 v/v) durchgefuhrt und lief innerhalb von 90 min ab. Das resultierende Produkt ist in den LOsungsmitteln der bei- den Homopolymeren unloslich. Das Vorliegen von Vinylpolymeren wurde durch IR- Spektren bestatigt.

Introduction

Gelatin is one of the most versatile natural products known. It is a material with a wide range of physical properties. These properties are responsible for its numerous and varied applications. The main disadvantages of gelatin films are their change in moisture content with humidity and their hardness which makes the film brittle. Gelatin was therefore graft copolymerized with ethyl acrylate in order to modify its properties. Potassium persulphate has been reported to initiate the graft copolymerization of various vinyl mono- mers onto poly(viny1 alcohol)', casein2, and gelatin3. These studies were carried out in various solvent media like dimethyl sulphoxide, triethanol- amine, and water. In this investigation, it is intended to use this initiator for graft copolymerization of ethyl acrylate onto gelatin in a water-isopropanol medium (1 : 1 v/v).

0 1984 Hiithig & Wepf Verlag, Base1 0003-3146/84/$03.00 173

A. George, G. Radhakrishnan. and K. T. Joseph

Experimental Materials

Ethyl acrylate (Koch Light Laboratories Ltd., England) was first washed with sodium hydroxide (5% solution) to remove the inhibitor, then with water to remove the alkali, and finally dried over anhydrous calcium chloride. Purification was effected by distillation under reduced pressure and nitrogen. The middle fraction of the distillate was collected and stored at 5 "C. Potassium peroxodisulphate (KPS, Riedel de Haen, Germany) was used as obtained. The solvents acetone and isopropyl alcohol were purified and distilled.

Polymerization Procedure

Polymerization was carried out in a water-isopropanol mixture (1 : 1 v/v). Calculated amounts of gelatin, ethyl acrylate. and potassium peroxodisulphate were charged in polymerization ampoules, flushed with a stream of nitrogen, and sealed. The reaction was carried out for 90 min at 60 * 0.1 "C in a thermostat. The polymer was precipitated in ice-cold methanol and was analysed.

Isolation of the Graft Copolymer

The gross polymer obtained consists of unreacted gelatin, graft copolymer, and unbound homopolymer. The homopolymer poly(ethy1 acrylate) (PEA) was removed by soxhlet extraction with acetone and the unreacted gelatin was removed by washing with hot water.

The percentage grafting was calculated as follows:

weight of grafted PEA weight of backbone polymer

Vo Grafting = x loo

The grafting efficiency (GE) was calculated using:

weight of grafted PEA To GE = x loo

weight of grafted PEA + weight of homo-PEA

The rate of grafting (R,) was calculated from the weight of the total polymer formed and the weight of free homopolymer.

Results and Discussion

In order to gain an insight into the mechanism of the reaction, the effect of variables in the synthesis such as monomer concentration, initiator con-

1 74

Grafting of Ethyl AcryIate onto Gelatin

centration, and backbone concentration on graft copolymerization of ethyl acrylate onto gelatin were studied.

Effect of Monomer Concentration

Increase in monomer concentration increases 070 grafting, grafting efficiency, and rate of grafting (Tab. 1 and Fig. 1). Rate of grafting and 070 grafting values are lower compared with the aqueous system4. This is due to

Tab. 1. Effect of monomer concentration on grafting.

EA x lo-' & x 106 Grafting 070 Grafting (mol. 1-l) (mol. I-' * s - l ) efficiency

1 342 6.72 87.05 27.20 2.769 11.24 88.78 30.21 3.692 13.42 89.11 33.46 4.615 17.60 90.48 41.37 5.538 20.16 91.09 46.28 6.461 26.1 1 92.34 51.31

[KPS] = 10 x mole 1 - I ; [Gelatin] = 3.2 x mole 1 - I ; Total volume = 50

m .- c - %

60 5 50 2 0

&O li5

30

20

10

0 IEAI-1OM

Fig. 1. Effect of monomer concentration on grafting. (A) % vs. [EA]; (B) 070 grafting vs. [EA].

175

A. George, G. Radhakrishnan, and K. T. Joseph

the competitive reaction between isopropanol and gelatin for the primary radicals5. The extent of graft copolymerization of EA was less than that of BA6 since homopolymerization of ethyl acrylate is favoured. Similar results were obtained when ethyl acrylate was graft copolymerized onto cellulose in an acetone-water medium'.

Effect of Initiator Concentration

The increase in initiator concentration from 6 x mol - 1-' to 3.0 x lo-' mole I-' increases Yo grafting and grafting efficiency (Tab. 2 and Fig. 2). The lower values in the rates when compared with the aqueous systems could be explained in the light of the mechanism proposed by Ball et al. for the reaction of isopropyl alcohol with the peroxodisulphate ion. From this it could be stated that the primary radicals attack isopropyl alcohol to form isopropyl radicals, hence the availability of primary radicals for the back- bone may be less resulting in less Yo grafting and rate of grafting.

Tab. 2. Effect of initiator concentration on grafting.

[KPS] x 103 q x 106 Grafting 070 Grafting (mol . I-') (mole 1-' . s-l) efficiency

6 10 16 20 24 30

5.01 81.40 25.24 6.92 84.66 31.42 7.94 85.84 38.34

10.23 85.73 41.57 12.02 90.58 42.34 13.18 91.73 43.01

[EA] = 1 . 8 ~ IO-'mol.l-';[Gelatin] = 3 . 2 x 10-4mol~1-';Totalvolume=50 ml; T = 60°C; t = 90 min.

Effect of Backbone Concentration

The concentration of gelatin was varied from 2.2 x mole 1-' to 6.3 mol 1-'. The Yo grafting and rate of grafting increased up to 3.8 x

mol - 1-' and then decreased (Tab. 3 and Fig. 3). The decrease may be x

176

Grafting of Ethyl Actylate onto Gelatin

~

5 10 15 20 25 30

m C .- c - ?

LO E 2

30 ; 20

10

0

m

a,

Fig. 2. Effect of initiator concentration on grafting. (A) % vs. [KPS]; (B) Yo grafting vs. [KPS].

due to termination by gelatin graft radicals when the concentration of gelatin is increased.

Tab. 3. Effect of gelatin concentration on grafting.

[Gelatin] x 10" & x 1 0 6 Grafting % Grafting (mol * 1 - I ) (mole 1- I * S - I ) efficiency

2.2 2.5 3.2 3.8 4.8 6.3

7.00 80.64 18.52 8.12 83.58 21.58 10.43 85.20 25.62 11.92 87.39 29.47 10.66 86.52 22.24 7.64 84.46 19.62

[EA] = 1.8 x lo-' mole 1-I; [KPS] = 10 x low3 mol - 1 - I ; Total volume = 50 ml; T = 60°C; t = 90 min.

Infrared Spectra

Infrared spectroscopy has been found to be a valuable tool in studying graft copolymerization reactions. This technique has been extensively used to establish the proof of grafting and to ensure complete removal of non grafted homopolymer from the grafted products.

177

A. George, G . Radhakrishnan, and K. T. Joseph

Fig. 3. Effect of gelatin concentration on grafting. (A) Rg vs. [GI; (B) Vo grafting vs. [GI.

W V z d

m C .- ..- c :

30 $ 2

25 2

0)

20 m

15

10

5

0

LOO0 3000 2000 1200 800 600 100

FREWENCY CM-'

Fig. 4. IR spectra of pure gelatin (a), gelatin-g-poly(ethy1 acrylate) (b), and poly- (ethyl acrylate) (c).

Pure gelatin has amide absorptions centered around 1650 and 1 550 cm-' (Fig. 4a). Pure poly(ethy1 acrylate) has an absorption due to carbonyl groups centered at 1730 cm-' (Fig. 4b). Fig. 4c shows the spectrum of the graft copolymer having the absorption bands due to amide of gelatin and ester carbonyl groups of poly(ethy1 acrylate).

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Grafting of EthyI Acrylate onto Gelatin

Y. Ikada, Y. Nishizaki, I. Sakurada, J. Polym. Sci., Polym. Chem. Ed. 12 (1974) 1829

* S. Kulasekaran, Y. Lakshminarayana, R. Rajadurai, K. T. Joseph, M. Santappa, Leather Sci. Madras 23 (1976) 385 T. Nagabhushanam, K. T. Joseph, M. Santappa, J. Polym. Sci., Polym. Chem. Ed. 16 (1978) 3287 A. George, G. Radhakrishnan, K. T. Joseph, J. Appl. Polym. Sci. 29 (1984) 703 D. L. Ball, M. Crutchfield, J. 0. Edwards, J. Org. Chem. 25 (1960) 1599 A. George, G. Radhakrishnan, K. T. Joseph, Eur. Polym. J., in press

’ Y. Nakamura, 0. Hinojosa, J. Appl. Polym. Sci. 14 (1970) 789

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