Please use this identifier to cite or link to this item: http://localhost:8081/xmlui/handle/123456789/1420
Title: STUDIES ON GRAFT COPOLYMERIZATION OF COMONOMERS ONTO CELLULOSE
Authors: Khandekar, Keerti
Keywords: CHEMISTRY;GRAFT COPOLYMERIZATION;COMONOMERS;CELLULOSE
Issue Date: 2005
Abstract: The surface modification of material is a useful technique to impart additional properties for specific applications. The modification of natural and synthetic polymers has been reported by various techniques but graft copolymerization has been found to be easiest .and useful technique to modify the bulk and surface properties of polymers. The graft copolymerization has been used to develop material for potential applications in textile, biomedical and membrane technology. The graft copolymerization using single monomer has been carried out either growing a polymer chain on backbone of polymers or by grafting a polymer chain on backbone of polymers. But the modification by grafting with preformed polymer chains has been proved to be of limited use as grafting by this technique is difficult and provided limited choice for distribution of grafted chains on polymer surface. Similarly, the graft copolymerization of single monomer has been found to be less useful than graft copolymerization carried out with mixture of monomer. The binary graft copolymerization increases, the graft yield and also provides opportunities to influence the grafting of monomers, which otherwise show low affinity for graft copolymerization. The graft copolymerization has been accomplished with various methods but in presence of eerie ammonium nitrate has been found to be more effective as it inhibits the formation of ungrafted homopolymers. In view of these reports, the graft copolymerization of acrylamide has been recorded in presence of different alkyl acrylates using eerie ammonium nitrate as initiator in presence of nitric acid. The individual graft copolymerization of 11 aerylamide has also been carried out to compare the effect of added comonomer in the reaction mixture. The graft copolymerization of aerylamide and methyl acrylate comonomers has been carried out at different feed molarity ranging from 5.0 x 10"2 mol dm"3 to 50.0 x 10"2 mol dm"3 at a constant concentration of eerie ammonium nitrate (7.0 x 10"3 mol dm"3) and nitric acid (6.0 x 10"2 mol dm"3). The effect of feed molarity on graft yield (%Gy) and other grafting parameter has been studied. To ascertain the participation of eerie (IV) ions, the effect of feed molarity on eerie (IV) ions disappearance was also studied. During feed molarity variation, the fraction of aerylamide was kept constant (fMm = 0.6) to maintain a constant monomer-monomer interactions in the reaction mixture. The graft yield has also been studied at different feed compositions (fAAm) ranging from 0.2 to 0.8 and reactivity ratio of aerylamide (n) and methyl acrylate (r2) comonomers has been evaluated using composition of grafted chains obtained at different feed compositions. The arrangement of sequence length (mM) in the grafted chains has been proposed on the basis of elemental analysis and the product of reactivity ratio of aerylamide (n) and methyl acrylate (r2). The effect of reaction time, temperature and concentration of eerie ammonium nitrate on graft copolymerization of aerylamide and methyl acrylate has been carried out and data were used to determine the dependence of rate of graft copolymerization (RP) on concentration of eerie ammonium nitrate and comonomers. The energy of activation for graft copolymerization of aerylamide and methyl acrylate has been determined from Arrhenious plot, which has been found to be 6.95 k J mol" 1. The low energy of activation for graft copolymerization in presence of methyl in acrylate comonomer has clearly suggested that the presence of comonomer has facilitated the graft copolymerization. The effect of addition of nitric acid, nitrate ions and hydrogen ions on graft copolymerization has been studied to analyze the variation in activity of eerie (IV) ions for graft copolymerization of aerylamide and methyl acrylate comonomers. The nitric acid and hydrogen ions concentration has shown high graft yield at 6.0 x 10"2 mol dm"3 and 12.0 x 10"2 mol dm"3 concentration respectively at constant concentration of comonomers (30.0 x 10"2 mol dm"3) and eerie ammonium nitrate (7.5 x 10"3 mol dm"3), whereas the addition of nitrate ions under similar experimental conditions has shown a continuous decreasing trend. The grafted cellulose has been analyzed for thermal stability by TGA and DTA analysis and found that graft copolymerization has increased the thermal stability of cellulose. The increase in thermal stability of cellulose on graft copolymerization of single monomer and mixture of monomers has been evaluated, in terms of initial decomposition temperature (T|), final decomposition temperature (Tf) and temperature of maximum decomposition (Tmax). The thermal stability of cellulose was also characterized by energy of activation for decomposition (Ea) for pure cellulose (202.33 k J mol"1) and cellulose grafted with aerylamide (283.80 k J mol"1), methyl acrylate (261.09 k J mol"1) and grafted with mixture of aerylamide and methyl acrylate (266.81 k J mol'1), which has clearly indicated that graft copolymerization has increased the thermal stability of cellulose. The graft copolymerization of aerylamide and methyl methacrylate comonomers has also been studied and concentration of comonomers (45.0 x IV 10"2 mol dm"1), eerie ammonium nitrate (8.0 x10"3 mol dm"3), nitric acid (9.0 x 10"2 mol dm"3) and hydrogen ions (16.0 x 10"2 mol dm"3) for maximum graft-yield has been evaluated. The overall graft yield has been found to be low for acrylamidemethyl methacrylate comonomer system in comparison to acrylamide-methyl acrylate cononomer system, which has been attributed to the methyl substituent on methyl methacrylate comonomer. The analysis of grafted chains obtained with acrylamide-methyl methacrylate comonomer system has shown that the fraction of aerylamide has been found to be higher (FAAm = 0.57) than observed with acrylamide-methyl acrylate comonomer system (FAAm= 0.55) at same feed composition (fAAm= 0.6). This has indicated that methyl methacrylate has shown more synergistic effect on aerylamide for graft copolymerization in comparison.to methyl acrylate comonomer. The arrangement of sequence lengths (mM) of aerylamide and methyl methacrylate monomers in the grafted chains (m M) has been proposed on the basis of product of reactivity ratio (n.r2) and the composition of grafted chains obtained with elemental analysis. The sequence length of aerylamide (mM,) has been found to be higher (2.08) in aerylamide -methyl methacrylate comonomer system in comparison to acrylamide-methyl acrylate comonomer system (1.88) at the same feed composition (f^m = 0.6). The rate of graft copolymerization has shown a square dependence on concentration of monomers and shown fractional order (0.5) with eerie ammonium nitrate. These observations have indicated for almost similar mechanism for graft copolymerization of acrylamide-methyl methacrylate comonomers as was operating with acrylamide-methyl acrylate system. The energy of activation for graft copolymerization of acrylamide-methyl methacrylate has bee found to be high (14.19 kJ mol"1) in comparison to acrylamide-methyl acrylate comonomer system (6.95 k J mol"1) indicating the effect of methyl substituent on graft copolymerization. The thermal analysis of grafted cellulose has clearly indicated that the graft copolymerization of acrylamide-methyl methacrylate comonomer has increased more thermal stability of cellulose (351.62 k J mol"1) than observed with graft copolymerization of acrylamide-methyl acrylate comonomers onto cellulose (266.81 kJ mol"1). The graft copolymerization of aerylamide has also been studied in presence of ethyl methacrylate comonomer by varying the feed molarity from 7.5 x 10"2 mol dm"3 to 60.0 x 10"2 mol dm"3 and varying the concentration of eerie ammonium nitrate from 1.5 x 10"3 mol dm"3 to 12.0 x 10"3. The graft yield was maximum at a feed molarity of 37.5 x 10"2 mol dm"3 and at 7.5 x 10"3 mol dm"3 concentration of eerie ammonium nitrate. The graft yield in acrylamide-ethyl methacrylate comonomer system has been found to be high in comparison to acrylamide-methyl methacrylate comonomers but found to be low in comparison to acrylamide-methyl acrylate comonomer system. The mole fraction of aerylamide (FAAm) monomer in the grafted chains has been found to higher (0.56) in comparison to methyl acrylate comonomer system (0.55) but lower than methyl methacrylate comonomer system (0.57). This variation in mole fraction (FAAm) has provided indications for relative, synergistic effect of added comonomer. The ethyl methacrylate comonomer has shown more affinity for grafting than methyl methacrylate comonomer. The sequence length of VI aerylamide monomer (mMi) with ethyl methacrylate (mM2) comonomer has been found to be lower (1.88) than in presence of methyl methacrylate comonomer (2.08) but was high in comparison to methyl acrylate comonomer (1.80). The overall graft yield with acrylamide-ethyl methacrylate-comonomer has been found to be high in comparison to individual grafting of aerylamide and ethyl methacrylate monomers. The effect of reaction time and temperature on graft copolymerization of acrylamide-ethyl methacrylate comonomers has also been studied successfully and energy of activation (Ea) has been estimated (9.63 k J mol"1), which was lower than methyl methacrylate comonomer system (14.19 kJ mol'1) but higher in comparison to methyl acrylate comonomer system (6.95 kJ mol"1). The graft yield was maximum at 7.5x10"2 mol dm"3 concentration of nitric acid and at 14.0x10"2 mol dm"3 concentration of hydrogen ions. The graft yield and other grafting parameters have shown a continuous decreasing trend on varying the concentration of nitrate ions. The cellulose has shown a significant increase in thermal stability on graft copolymerization of ethyl methacrylate and its mixture with aerylamide monomer. The thermal stability of cellulose grafted with acrylamide-ethyl methacrylate comonomers has been found to be low (Ea =278.99 kJ mol"1) in comparison to acrylamide-methyl methacrylate comonomer system (Ea =351.62 kJ mol"1). This has been due to ester ethyl group of ethyl methacrylate comonomer. In order to investigate the effect of size of ester alkyl group of comonomer on synergistic graft copolymerization of aerylamide and on thermal stability of grafted cellulose, the graft copolymerization of aerylamide has been studied in Vll presence of ethyl acrylate comonomer. The graft,yield has increased in presence of ethyl acrylate and found to be maximum at a feed molarity of 30.0 x 10"2 mol dm"3. During concentration variation of eerie ammonium nitrate and nitric acid the maximum graft yield was obtained at 6.0 x 10"3 mol dm"3 and 5.0 x 10"2 mol dm"3 respectively. The composition of grafted chains has shown variations on varying the feed composition (fAAm) and reaction temperature. The fraction of aerylamide (FAAm) in the grafted chains has been found to be low (0.52) in comparison to other comonomers used for graft copolymerization with aerylamide. The • sequence length (m M-i) of aerylamide was also low (1.59) in comparison to ethyl methacrylate (1.88) and methyl acrylate (1.80) comonomers. The arrangement of sequence lengths of aerylamide (mMi) and ethyl acrylate (mM2) in the grafted chains was in alternate fashion as proposed on the basis of product of reactivity ratios of aerylamide and ethyl acrylate monomers (n. r2). The arrangement was confirmed by determining the composition of grafted chains by elemental analysis. The affinity of graft copolymerization of aerylamide and ethyl acrylate comonomers onto cellulose has been evaluated in terms of graft yield and ' energy of activation for graft copolymerization, which has been found to be low (5.57 kJ mol"1) in comparison to other comonomer systems. This has clearly indicated that ester alkyl group of ethyl acrylate has increased the extent of graft yield and has shown comparatively high synergistic effect on graftcopolymerization of aerylamide. However, the synergistic effect of ethyl acrylate on aerylamide has been found to be low in comparison to other comonomers. The graft copolymerization of acrylamide-ethyl acrylate comonomers has Vlll increased the thermal stability of cellulose (Ea = 249.39 k J mol"1) in comparison to pure cellulose (Ea = 202.33 k J mol'1) but the increase in thermal stability has been found to be low in comparison to other comonomer systems, which has indicated that the ester alkyl group has facilitated the decomposition of grafted chains. In order to confirm the effect of ester alkyl group on graft yield and thermal stability of cellulose, the graft copolymerization of aerylamide has been carried out in presence of butyl acrylate with a larger ester alkyl group in comparison to other comonomers used with aerylamide for graft copolymerization onto cellulose. The acrylamide-butyl acrylate comonomers have shown maximum graft yield at a feed molarity of 28.0 x 10"2 mol dm"3 and at 5.0 x 10"3 mol dm"3 concentration of eerie ammonium nitrate. The graft yield has been found to be maximum at 4.0 x 10"2 mol dm"3 concentration of nitric acid and at 4.0 x 10"2 mol dm"3 concentration of hydrogen ions. The fraction of aerylamide (FAAm) in the grafted chains has been found to be low (0.49) in comparison to grafted chains obtained with other comonomers. The overall graft yield was high in comparison to individual graft copolymerization of aerylamide and butyl acrylate but the synergistic effect of butyl acrylate on graft copolymerization of aerylamide onto cellulose has been found to be lowest. The sequence length of aerylamide (mMi) in the grafted chains was also lowest (1.45) and arranged in alternate fashion with butyl acrylate sequence length (nTM2). The arrangement of sequence length of aerylamide (fnMi) and butyl aerylamide (nTM2) has been confirmed by elemental analysis of grafted chains. The affinity of acrylamide- IX butyl acrylate comonomers for graft copolymerization on cellulose has been evaluated by energy of activation (Ea) for graft copolymerization using rate constant obtained as a function of temperature. The energy of activation for graft copolymerization of acrylamide-butyl acrylate comonomers has been found to be lowest (4.69 kJ mol"1), which indicated for high affinity of acrylamide-butyl acrylate comonomers. The graft copolymerization of acrylamide-butyl acrylate comonomers has also shown increasing effect on thermal stability of cellulose as clear from the energy of activation for decomposition of acrylamide-butyl acrylate comonomers grafted cellulose (235.25 k J mol"1) in comparison to pure cellulose (202.33 k J mol"1). Although graft copolymerization of acrylamide-butyl acrylate comonomers has increased the thermal stability of cellulose but the increase in thermal stability on graft copolymerization of acrylamide-butyl acrylate comonomer system has been found to be lowest, which has clearly suggested that ester butyl group of butyl acrylate comonomer has played a significant role in controlling the thermal stability of the cellulose. These investigations have clearly indicated that the presence of added comonomer has controlled the extent of grafting and also the composition of grafted chains, which has been attributed to synergistic effect of added comonomer in the reaction mixture. The method of graft copolymerization with binary mixture of comonomers had provided sufficient opportunities to tailor the surface properties of the polymers.
URI: http://hdl.handle.net/123456789/1420
Other Identifiers: Ph.D
Research Supervisor/ Guide: Gupta, K. C.
metadata.dc.type: Doctoral Thesis
Appears in Collections:DOCTORAL THESES (chemistry)

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