Notes. Free radical graft polymerization of methyl methacrylate from polyvinyl alcohol using FeCl 3 /K 2 S 2 O 5 redox pair

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1 Indian Journal of Chemistry Vol. 46A, September 7, pp Notes Free radical graft polymerization of methyl methacrylate from polyvinyl alcohol using FeCl 3 /K 2 S 2 O 5 redox pair P Chowdhury, Md A Ali & K Roy Department of Chemistry, Siksha-Bhavana Visva-Bharati, Santiniketan , India pranesh_2@yahoo.co.in Received 22 March 6; revised 9 June 7 Ferric chloride/potassium metabisulfite redox pair initiated free radical polymerization of methyl methacrylate has been carried out in aqueous medium both in presence and absence of polyvinyl alcohol (PVOH). The percentage of homopolymer formation is very low in absence of PVOH. However, the presence of PVOH (.1%) gives rise to more than 7 % yield of polymethyl methacrylate homopolymer. About % graft copolymer (PVOH-g-PMMA) is achieved at C using 1. % PVOH. Free radical polymerization (both homopolymer and graft copolymer) is decreased with the increase of temperature. Homopolymer formation and graft copolymerization have been confirmed by FT-IR studies. A reaction scheme has been proposed to elucidate the role of ferric ion and metabisulfite ion. IPC Code: Int Cl. 8 C8F4/; C8F16/6; C8F265/ Graft modified polyvinyl alcohol (PVOH) possesses great potential as unique polymeric material for several applications, such as biomedicine, adhesive, painting, etc 1. Graft co-polymerization of alkyl methacrylate and alkyl acrylates from PVOH has been conducted mostly in aqueous medium and are initiated mainly by ceric 2-8, cupric 9-12, peroxydisulphate 13 and diperiodato nicklate 14, 15 ions. Very little work has been done on vinyl grafting using ferric ion. Sanjay et al. 12 have used ferric ion along with hydrogen peroxide as an initiator for vinyl grafting of PVOH. Ferrous ion in presence of hydrogen peroxide (Fenton s reagent) has been reported as an effective initiator for vinyl grafting 16. Konar et al. 17 have used ferric chloride / potassium metabisulfite redox pair for free radical vinyl polymerization (without polyvinyl alcohol). PVOH, being long chain macromolecules, can act as a protective colloid or as a suspending agent in the suspension polymerization. Thus, it is important to investigate the effect of PVOH on ferric ion initiated polymerization of methyl methacrylate. Previously, we have reported the effect of PVOH on ceric ion initiated polymerization and graft co-polymerization of vinyl monomers 18. The present investigation deals with the detailed study of the effect of polyvinyl alcohol on the free radical polymerization and graft polymerization of methyl methacrylate using ferric chloride and potassium metabisulfite redox pair in aqueous medium. The effect of temperature on the free radical polymerization has been investigated. A probable reaction mechanism has been suggested to elucidate the role of ferric ion in free radical polymerization. Experimental Polyvinyl alcohol (PVOH, Burgoyne Burbidges Company, Mumbai, India, viscosity average molecular weight = 161, degree of hydrolysis = mol %, viscosity = cps) was used. Methyl methacrylate (MMA, Merck, Schuchardt) was purified before use 5. Ferric chloride (Qualigens, Mumbai, India) and potassium metabisulfite (Merck, Mumbai, India) were used as received. Graft polymerization Graft polymerization was carried out in a twonecked round bottom flask kept in a constant temperature water bath maintained at C. A definite amount of polyvinyl alcohol (PVOH) was soaked with the required amount of methyl methacrylate (MMA) for 15 min before graft polymerization was started. Doubly distilled water (95 ml) was then added to the reaction mixture and it was allowed to attain the required temperature. Freshly prepared FeCl 3 solution (.6 ml, 5%) and K 2 S 2 O 5 solution (4. ml,.5%) (FeCl 3 / K 2 S 2 O 5 = 2:1, mole ratio) were then added carefully. After the specified time interval, the reaction was arrested by quenching with hydroquinone. In order to separate the homopolymers from grafted polymers, the samples were extracted with acetone in Soxhlet apparatus for 4 h to dissolve all the homopolymer. The colorless product was dried under vacuum at 5 C for more than 24 h to a constant weight. Similarly, unreacted PVOH was removed by extracting with water for 2 h. Characterization of graft copolymer FTIR spectra of the samples (Using KBr pellets) were recorded on a Shimadzu (model No. 85)

2 NOTES 1415 Fig. 1 FTIR spectra of (a) PVOH, (b) PMMA, and, (c) grafted PVOH. FTIR system in the range of - cm -1. Thermogravimetric analysis (TGA) was conducted using a Stantum Redcraft thermal analyzer (STA-78) in air at a rate of 1 C / min. The ph of the system was measured using a ph meter (Elico India, model 11). Flow time of the polymer solution was counted in ethyl acetate using Ubblehode viscometer at room temperature. Intrinsic viscosity of polymethyl methacrylate (homopolymer) in ethyl acetate at 3 C was determined graphically using flow time data. The viscosity average molecular weight, M v was estimated using Eq (1) 19. [η] = (M v ).75 (1) Swelling coefficient (q) was determined by swelling the sample in acetone at room temperature for 72 hrs according to Eq.2 (refs 6 9) q = (m m ) /m.d (2) where m, m and d are the weights of the swelled sample, the original sample and density of the solvent respectively. The percentage of grafting (PG), grafting efficiency (GE) and percentage of homopolymerization (H) and rate of polymerization (R) were used to evaluate the graft polymerization according to the following relationship 16, 18. Weight of PMMA grafted PG = 1 Weight of PVOH taken (3) Weight of PMMA grafted GE = 1. (4) Weight of MMA taken Weight of PMM homo-polymer H = 1 (5) Weight of MMA taken -1-1 Weight of polymer formed R = Mol. wt. of MMA x time x volume (6) (mol.h. L ) 1 Results and discussion The presence of PMMA on the PVOH molecules was verified by the FTIR spectra of PVOH, PMMA and grafted PVOH (Fig. 1). The spectra of both PVOH and grafted PVOH show a characteristic broad absorption band of the hydroxyl group around cm -1. This is attributed to the O-H bond stretching vibration 16,18, of PVOH. The spectrum of the grafted PVOH exhibits a strong absorption band at 173 cm -1, which is absent in the spectrum of PVOH.

3 1416 INDIAN J CHEM, SEC A, SEPTEMBER 7 H (%) Poly vinyl alcohol (g/dl) PG (%) Fig. 2 Effect of polyvinyl alcohol at a fixed amounts of other reagents. [ MMA =.94 %, FeCl 3 /K 2 S 2 O 5 = 2, Temp. = C, Time =3 h ]. Curves 1 and 2 indicate plots of percentage of grafting (PG) and percentage of homopolymerization (H) respectively]. The peak near 173 cm -1 may be associated with the C=O stretching vibration of an ester group,21 from MMA. The appearance of a new peak at 173 cm -1 in the resulted copolymer provides strong evidence of grafting. The effect of polyvinyl alcohol (PVOH) on the percentage of homopolymerization (H) and percentage of grafting (PG) are shown in Fig. 2. PVOH was varied from to 1.2 g /dl at a fixed level of other components. The polymerization system having no PVOH provided low ( %) homopolymer formation. Konar et al. 17 reported 25% conversion at the same reaction conditions. The yield of homopolymer (H) increases with the increase of PVOH, reaches a maximum at.1 g /dl and then decreases with further increase of PVOH. The PVOH level of.1 g/dl seems to be critical concentration for homopolymerization. About 71% homopolymerization was found at this critical concentration. PVOH being long chain macromolecules, may act as protective colloid or as suspending agent in the suspension polymerization where it adsorbs on the suspended particles. As a result,.1% PVOH could stabilize the PMMA sol. The uniqueness of this suspending agent is that the polymerization system requires no N 2 gas or inert atmosphere. At.4% of PVOH, the rate of homopolymerization decreased and the graft polymerization just starts. The extent of graft polymerization was maximum at 1.% with low homopolymerization. The formation of graft polymerization at relatively higher concentration of PVOH, may well be understood from the mechanism suggested in Eq.12. The effect of polyvinyl alcohol on the induction period, rate of polymerization, rate of grafting and viscosity average molecular weight are given in Table 1. Induction period of polymerization decreased in presence of PVOH, while rate of polymerization and viscosity average molecular weight of the polymer increased due to addition of PVOH. Thus, it may be concluded that the presence of PVOH can control the rate, yield and nature of polymerization. A study on effect of monomer on grafting polyvinyl alcohol at a fixed level of other reagents was carried out. The percentage of grafting increases steeply with the increase of monomer (MMA) level up to.94% and then increases slowly. The increase of grafting level may be explained with the help of Eqs 13 and 14. It may be noted that homopolymerization restricts the grafting level at more than.94% MMA. Study on the effect of FeCl 3 / K 2 S 2 O 5 (I/P) mole ratio on grafting PVOH at fixed level of other reagents shows that the PG increases gradually with the increase of I/P mole ratio up to 2 and then it reaches a plateau. Eqs 7 9 may substantiate the increase of PG. The I/P mole ratio = 2 leads to the formation of 1:1 complex of Fe 3+ with HSO 3 - ion. The complex then produces the S (O 2 )O ion radicals on Initiator a PVOH (%) Induct-ion time (min) Table 1 Polymerization data of methyl methacrylate Time (h) H (%) at C PG(%) at C η M v x1-3 R x1 2 (mol/h/ L) A+B A+B A+B 1. 3 < a A = 4 ml of.5 % K 2 S 2 O 5 and B =.6 ml of 5 % FeCl 3 solution. [FeCl 3 ]/[K 2 S 2 O 5 ]=2

4 NOTES 1417 decomposition. The ion radical ultimately leads to polymerization. Free radical polymerization and graft polymerization It was observed that when potassium metabisulphite (K 2 S 2 O 5 ) is added to the ferric chloride solution in 1:2 mole ratio, an orange red color solution was produced at C. The orange red solution is capable of producing free radicals that can initiate vinyl polymerization. It is known that K 2 S 2 O 5 when added to water, gives bisulphite 22,23, HSO 3 ion and the orange red color appears to be due to formation of a complex between Fe +3 ions and HSO 3 ions 23. HSO 3 ion is known to have two tautomeric forms in equlibrium 22. S 2 O 5 = + H 2 O = 2 HSO 3 (7) H S(O 2 )O (structure 1) = HO S(O)O (structure 2) (8) Fe 3+ + H S(O 2 )O = [Fe{ H S(O 2 )O}] 2+ Fe 2+ + H + + S (O 2 )O (9) The ph of the salt solution at C and 3 C were measured and it was found that the ph of the medium decreases when FeCl 3 reacts with bisulphate. The decrease in ph of the reaction medium is probably due to decomposition of the iron complex (Eq.9). The radical anion (S O 3 ) produced is probably responsible for the formation of free radical (Eq.1) that can initiate polymerization. At low levels of PVOH (<.1%), the system produces homopolymers predominantly (Eq.11). At higher levels of PVOH (>1.%), both homopolymer and graft copolymer are produced (probably via Eqs 12 14)(refs 16, ) S O 3 ( R) + (n+1) CH 2 =C(Me)COOCMe ( M) O 3 S (CH 2 C(Me)COOMe) n CH 2 C (Me) COO-Me ( RM n M ) (1) red coloration of the FeCl 3 /K 2 S 2 O 5 mixture vanishes almost instantaneously indicating no formation of iron complex. The chemical test 24 revealed the formation of bisulfate and ferrous ion at 3 C (Eq.15). Since no free radical is formed at higher temperature no polymer is obtained. The structures 1 and 2 of the bisulfite ion are responsible for its reducing property 17 and complex formation ability 22 respectively. 2 Fe 3+ + H-SO 3 + H 2 O = HSO H Fe 2+ (15) Thermal properties of the homopolymers and grafted polymers are shown in the Fig. 3 in the form of dw(%)/dt versus T plots. All the samples undergo more or less same weight loss at 9 C. The weight loss at this temperature is due to loss of moisture. Both PVOH and PMMA show two stages degradation while the grafted polymer exhibits three stages degradation. Thermal stability of the grafted PVOH is higher than the individual homopolymers. The above study shows that in the absence of polyvinyl alcohol, the yield of polymethyl methacrylate (PMMA) using FeCl 3 /K 2 S 2 O 5 pair in aqueous medium dw (%) / dt 1 8 PVOH RM n M Homo-polymer (11) CH 2 CH(OH) + RM n M CH 2 C (OH) ( P ) + RM n MH (12) P + (x+1) M P M x M (13) 2 P M x M Graft copolymer (14) Both homopolymer and graft copolymer are formed at C. No polymer was formed at higher temperature (3 C). At room temperature (3 C), the Temp. ( O C) Fig. 3 The dw(%)/dt versus temperature plots of PVOH. [ (1) Low molecular weight PMMA; (2) higher molecular weight PMMA; and, (3) grafted PVOH].

5 1418 INDIAN J CHEM, SEC A, SEPTEMBER 7 is very low. However,.1% of polyvinyl alcohol (PVOH) gives rise to more than 7% yield of PMMA. About 61% graft copolymer (PVOH-g-PMMA) is achieved at C using 1.% or more PVOH. The extent of free radical polymerization (both homopolymerization and graft polymerization) decreases with increase in temperature. The ability to form the 1:1 complex with bisulfite ion at C makes the ferric ion to act as a suitable initiator for both homo and graft polymerization. The optimum [FeCl 3 ]/[K 2 S 2 O 5 ] mole ratio was found to be 2:1. References 1 Carlotti S J, Beaune O G & Schue F, J Appl Polym Sci, 81(1) Jana S C, Maiti S & Biswas S J, J Appl Polym Sci, 78() Robson F S, Dantiki S & Leslie J G, J Macromol Sci Chem, 24 (1987) Guo Z, Zhichao Z & Fengcho X, J Appl Polym Sci, 75() Chowdhury P & Banerjee M, J Appl Polym Sci, 7(1998) Chowdhury P, Indian J Chem Technol, 5(1998) Chowdhury P & Pal C M, Eur Polym J, 35(1999)27. 8 Chowdhury P & Chowdhury N D, J Polym Mater, 16(1999) Goddart P, Wertz J L, Biebuyck J J & Merrier J P, Poly Eng Sci, 29( 1989) Higashi F, Cho C S & Kakinoki H, J Polym Sci Chem Ed, 17(1997) Sumita O, Fukada A & Kuze E, J Polym Sci Chem Ed, 18(198) Sanjay N, Ramkrishna B, Aditya J & Anil K, Polymer, 34 (1993) Chiang W Y & Hu C M, J Appl Polym Sci, 3(1985) Liu Y, Liu X, Deng K & Liu Z, J Appl Polym Sci, 87(3) Mishra B N, Mehata I K, Kanthural M & Panjloo S, J Polym. Sci Part A Polymer Chem, 25(1987) Chowdhury P & Ali M A, J Appl Polym Sci, 97(5) Banerjee M & Konar R S, Indian J Chem, 19(198) Chowdhury P & Ali M A, J Polym Mater, 22(5) Immergut E H & J.Brandrup, Polymer Handbook (Interscience, New York), 1975, chapter 4, page 1. Dyer J R, Application of Absorption Spectroscopy of Organic Compounds (Prentice-Hall of India Pvt. Ltd., New Delhi), 1991, p Williams D H & Fleming I, Spectroscopic Methods in Organic Chemistry, 4 th Edition (Tata Mc Graw-Hill, New Delhi) 1988, p Cotton F A & Wilkinson G, Advanced Inorganic Chemistry (John Wiley, New York) 1972, Greenwood N N & Earnshaw A, Chemistry of Elements, 2 nd Edition (Butterworth-Heinemann, Oxford) 5, p Vogel A G, A Textbook of Macro and Semimicro Qualitative Inorganic Analysis, 4 th Edn (Orient Longman, Calcutta) 1977, p. 248.

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