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State of the Art of Polymer Research in India, III : Physical Chemistry of Polymers

The oxidative cleavage of some aliphatic ketoximes by thallium(III) acetate was studied in the temperature range of 20-40°C. The reactions were followed by determination of the rates of disappearance of thallium(III) acetate for variations in [substrate], [Tl(III)], [H + ], ionic strength, temperature, etc. The reactions were found to be totally second order-first order with respect to each reactant. The second-order rate constants and thermodynamic parameters were evaluated and discussed. The mechanism proposed involves one-electron oxidation to the iminoxy radical followed by an another one-electron oxidation to the hydroxynitroso compound which dimerizes and decomposes to give the carbonyl compounds and hyponitrous acid.

The species distribution and stability constants were evaluated for six mixed imidazole (A)-dipeptide (B) complexes of Cu(II) in aqueous perchlorate medium at I = 0.15 M (NaClO 4 ) and 37 °C from pH titration data. The dipeptides used are glycylglycine, glycyl-L-alanine, L-alanylglycine, glycyl-L-leucine, L-leucylglycine and glycinamide. In addition to the binary complex species CuA, CuA 2 , CuA 3 , CuA 4 , CuB, CuBH −1 , CuB 2 H −1 , three mixed complexes CuA 2 B, CuA 2 BH −1 and CuABH −1 were detected in each system. However in the glycinamide secondary ligand (B) system, the mixed species CuAB formed instead of CuABH −1 . The stability order found for these complexes is discussed in terms of the steric effects due to side chain substituents in the dipeptide (B) ligands. The results suggest that mixed-coordination enhances the stability of the complexes. The amide deprotonated dipeptides (B) appear to be tridentate in the CuA 2 BH −1 and CuABH −1 complexes.

The kinetics of the base hydrolysis of some trans-halogenoaminebis(dimethylglyoximato)-cobalt(III) complexes (amine-pyridine or γ-picoline; halogen-chloride or bromide ion), have been studied at 30°C and 0·1 M ionic strength at 8 < pH < 13. The kinetic data were found to obey the following rate equation: kobs = (ka + kbK[OH−] + kcK[OH−]2)(1 + K[OH−])−1. The rate constants and activation parameters for the aquation of these complexes have also been determined at 0·1 M ionic strength. The bromo complexes are found to undergo hydrolysis at a lower rate than the chloro complexes. The results have been interpreted in terms of a dissociative interchange mechanism for hydrolysis.

Etude des reactions de decomposition de Cr(O 2 ) 2 en (H 2 O) et Cr(O 2 ) 2 (dien). Les produits et leurs proportions varient en fonction de [H + ]

The polymerization of acrylonitrile (M) initiated by the Ce(IV)–acetophenone (AP) redox pair has been studied in acetic–sulfuric acid mixtures in a nitrogen atmosphere. The rate of polymerization is proportional to [M]3/2, [AP]1/2 and [Ce(IV)]1/2. The rate of disappearance of ceric ion,–RCe, is proportional to [AP], [M], and [Ce(IV)]. The effect of certain salts, solvent, acid and temperature on both the rates have been investigated. A suitable kinetic scheme has been proposed, and the composite rate constants kp2(k/k/t) and k0/ki are reported.

Poly(acrylonitrile-co-methyl methacrylate) films were oxidized in an air oven and in an oxidation chamber at temperatures of 80 to 200°C. Differential thermal analysis of these oxidized films showed that the exothermic peaks increased with increasing oxidation temperature. The change of viscosity, the insolubility in dimethylformamide and IR analyses indicate both intramolecular and intermolecular reactions.

Polymerisation of methyl acrylate (MA) initiated by O 2 -ascorbic acid (AA)-Cu 2+ system was studied in aqueous medium at 40°C. The rate of polymerisation R p , was found to increase, remain constant, and then decrease with increasing [Cu 2+ ]. R p was found to depend on [Cu 2+ ] 0,6 , [AA] 0 , [O 2 ] 0,6 , and [MA] 1,3 in the increasing region, on [Cu 2+ ] 0 , [AA] 0 , [O 2 ] 0,6 , and [MA] 1,6 in the constant region and on [Cu 2+ ] -0,9 , [AA] 0 , [O 2 ] 0,7 , and [MA] 2,0 in the decreasing region. Rate laws were derived assuming a plausible reaction mechanism for the different regions. R p increased with ionic strength and decreased with [H 2 SO 4, ]. An initial increase, then steady state followed by a decrease in rate with temperature was noticed in the range 25-55°C. k p /k t ½ values were calculated and compared with literature values. Chain lengths were determined viscometrically.

The mechanism of the polymerization of acrylamide in aqueous medium initiated by the glycerol (R)/Ce(IV) redox system was studied. The rate of monomer disappearance was found to be directly proportional to [M] 3/2 , and R ½ at lower concentrations of Ce(IV). The rate of the disappearance of ceric ions was found to be inversely proportional to [M] and directly proportional to [Ce(IV)] and [R]. Consistent with the findings of earlier investigations, a complex formation between monomer, acrylamide, and ceric ion is indicated. The experimental results show the termination to be mutual. On the basis of these and other kinetic results, an appropriate mechanism is proposed. At higher concentration of Ce(IV), a different mechanism seems to operate. The rates of disappearance of both the monomer and ceric ions are retarded on addition of anions like HSO 4 − , SO 4 −− , or ClO 4 − , but they are accelerated on the addition of Mn(II) ions. Interpretations of the above observations are furnished.

The kinetics of γ-radiation-induced bulk polymerization of methyl phenoxymethacrylate and methyl paracresoxymethacrylate was studied at dose rates of 0.3 and 0.075 Mrad/h and at temperatures of 0 and 30°C. The polymerization was first order with respect to the monomers and the rate of polymerization had a direct dependence on dose rate. The activation energy value for the polymerization of methyl phenoxymethacrylate was 1.2 and 0.7 kcal/mol for methyl paracresoxymethacrylate. The polymerization proceeded predominantly by an ionic mechanism.

The kinetics of the thermal polymerization of methyl acrylate (MA) and acrylamide (AAM) initiated by manganic ion in aqueous sulfuric acid medium has been studied. The rate of disappearance of [monomer] (Rp) was found to bear a square dependence on monomer and to be independent of [Mn2+] in the case of both the systems. Rp for acrylamide increased with the increase in [H+] but that for methyl acrylate remained almost constant. The degree of polymerization of the polymers (Xn) determined viscometrically was directly proportional to the [monomer] and inversely proportional to [Mn3+], for both systems. Xn increased with an increase in [H+] in the case of acrylamide and decreased in the case of methyl acrylate. Suitable reaction schemes to explain these experimentally observed facts have been proposed. Kinetic and thermodynamic parameters are also evaluated.

The kinetics of polymerization of acrylamide (AM), acrylic acid (AA), and acrylonitrile (AN) initiated by the redox system Mn 3+ -diglycolic acid (DGA) was studied. All three systems followed the same mechanism; namely, initiation by an organic free radical arising from the oxidation of diglycolic acid and termination by the interaction of polymer radicals with Mn 3+ ion. The rate coefficients k i /k 0 and k p /k t were related to monomer and polymer radical reactivity, respectively. An inverse relation between monomer and polymer radical reactivity was observed. Monomers with higher Q values gave higher k i /k 0 values but lower k p /k t values. The e values of the monomers were important in determining the reactivities of monomers with nearly the same Q values.

The kinetics and product analyses of the amine exchange reactions of two 2-aminopyridine derived Schiff-base ligands and their monomeric bischelate and dimeric copper(II) complexes have been studied. The Schiff-base ligands investigated underwent amine exchange reactions with n-butyl, cyclohexyl, t-butyl amines. The coordination of the Schiff-base ligands to copper(II) rendered the amine exchange reactions slower. With n-butyl and cyclohexyl amines, parallel first- and second-order terms on their concentrations are observed for the amine exchange reactions of copper(II) bischelates and dimer. The kinetic data favor a mechanism involving a rate-limiting elimination of 2-aminopyridine from a diaminoacetal intermediate in preference to a scheme in which a dissociation of the complexes into free ligands and Cu(II) may precede the amine exchange. The steric factors influence the amine exchange reactions of Cu(II) bischelates with the bulkier amines reacting slower as given by the order t-butylamine (3.3 ± 0.3 × 10−3 dm3/mol·s) < cyclohexylamine (0.2 ± 0.03 dm3/mol·s) < n-butylamine (2.2 ± 0.2 dm3/mol·s). The bulkiness of the t-butyl group and the constraints imposed by the changes in the coordination geometry of Cu(II) on amine exchange not only render the reactions of Cu(II) bischelates slower but also make the formation of the mixed adduct ([N-(5-methyl)-2-pyridyl salicylaldimine][N-t-butyl salicylaldimine] Cu(II)) more favored.

The stability constants of the ternary uranyl ion complexes involving dicarboxylic acids were determined by pH metric titrations at a temperature of 31 ± 0·1°C and an ionic strength, μ = 0·1 M (NaClO4). The stability values clearly show the discriminating qualities of uranyl ion-dibasic acid 1:1 complex toward the secondary ligand to be coordinated. The values of log K2YX are inversely related to the product of the acid dissociation constants of the secondary ligands. The overall stability is found to be dependent on the binary stabilities. Ring size of the chelates formed by the secondary ligands is found to influence the formation of ternary complexes.

Three aromatic polyamides containing alkyl and ether linkages in the main chain were synthesized, using low-temperature solution and interfacial polycondensation procedures, and were characterized by viscosity, solubility, UV, IR, TGA, and DSC studies. Fibers were spun using a laboratory-scale wet spinning unit and their mechanical and morphological properties studied. The results were correlated with structure and spinning conditions.

The kinetics and mechanism of polymerization of acrylamide (AM) initiated by manganese (III) acetate (MTA)-diglycolic acid (DGA) redox system in aqueous sulfuric acid were studied in the temperature range 20-35°C. The overall rates of polymerization and the disappearance of Mn 3+ and the kinetic chain lengths of polyacrylamide were determined. The polymerization reaction is initiated by the organic free radical arising from the Mn 3+ -diglycolic acid reaction and the termination is by the metal ions. The rate of polymerization of acrylamide was found to be proportional to the first power of monomer and diglycolic acid and independent of manganese(III) acetate. The various rate parameters were evaluated.

By exposure to ultraviolet and gamma radiation and by the usual methods of thermal polymerization, the stereospecific polymerization of methyl aryloxymethacrylates was carried out at different temperatures in several solvents. Triad tacticity values of the polymers obtained by free-radical and ionic routes were computed from nuclear magnetic resonance spectral data. Results of this investigation support our earlier observation that, under the conditions used, heterotactic content is the maximum in most of these polymers, thereby justifying the high steric effect of the bulky and polar aryloxy side chain which offers equal isotactic and syndiotactic placements.

The rates of the individual reactions of 2-methylol-4-t-butylphenol with 4-t-butylphenol were measured under varying mole ratios of reactants in the presence of different acid catalysts (5.0×10 −3 N to 2.0 ×10 −4 N) at five different temperatures (60, 65, 70, 75, and 80°C). In all the experiments, the reactions were found to obey second-order rate law. The values of the Arrhenius parameters and the entropy of activation for the overall reaction were calculated. The relative catalytic efficiencies of the acid catalysts followed the order HNO 3 >HCl>H 2 SO 4 .

Kinetic evidence for inner sphere oxidative path was observed in the oxidation of hexacyanoferrate(II) by peroxodiphosphate at pH = 10 and 26°C. The reaction obeys the rate law suggesting the mechanism Added free ligand, CN − , effects a remarkable decrease in the reaction rate in accordance with the rate law. Effect of pH on the reaction rate was studied and evidence for free radical intermediates was obtained.

Four coloured polyamides containing azo-p-phenylene units were synthesised from 4,4′-azodibenzoic acid and four aromatic diamines employing both interfacial and solution polymerization procedures. The polymers were characterized by their UV and IR spectra, by inherent viscosity measurements and by solubility data. The stability in conc. sulfuric acid and the thermal behaviour are discussed.

Poly(buty1 methacrylate-co-acrylonitrile) of 1:1 molar composition has been prepared by bulk polymerization process using 2,2'-azoisobutyronitrile (AIBN) as the initiator and fractionated using ethyl methyl ketone and methanol as the solvent and the precipitant respectively. The identical value of the refractive index increments (dn/dc) of these fractions indicated their homogeneity in chemical composition. The dilute solution properties of these fractions in N,N-dimethylformamide (DMF), ethyl methyl ketone (MEK), and acetone have been investigated employing light-scattering, osmometry and viscometry techniques. The following Mark-Houwink relationships have been established at 25°C: DMF:[η]=1,538·10 hypehn;2·MW0.73 MEK:[η]=7,096·10 hyphen;2·MW0.56 Acetone:[η]=7,852·10 hyphen;2·MW0.72. The unperturbed dimensions for the copolymer have been evaluated and compared with those for the constituting homopolymers. A solvent dependence of the unperturbed dimension has been observed. The steric factor, σ, was found to be 2,64 in DMF and 2,48 in MEK for poly(buty1 methacrylate-co-acrylonitrile) compared to a value of 2,20 for poly(acrylonitri1e) in DMF, and 2,09 for poly(buty1 methacrylate) in MEK which suggests the greater stiffness of the copolymeric chain compared to the constituting homopol ymers.

The polymerization of acrylonitrile was studied in aqueous sulfuric acid with the redox initiator system, ceric ammonium sulfate/glycerol at 15–25°C. The initiation was effected by the ceric ion and the radical produced from the reaction of Ce4+ with glycerol. At lower concentrations of Ce4+, the rate of monomer disappearance was proportional to [M]1,5, [G]0,5, and [Ce4+]0,5, and the rate of ceric ion disappearance was directly proportional to [Ce4+] and [G]. The results were explained by a kinetic scheme involving the oxidation of substrate by Ce4+ to give the primary radical and further reaction of the latter with Ce4+ to give the final product, and initiation of polymerization both by Ce4+ and the primary radical. The initiation by Ce4+ was found to be negligible as compared to that by the primary radical. The termination step is postulated to be mutual at lower concentrations of Ce4+ and linear at higher concentrations of Ce4+. The induction period and the rate of polymerization was compared with those of other polyol systems, such as sorbitol and mannitol.

The kinetics of γ-radiation-induced solution polymerization of methyl phenoxymethacrylate (MPMA) and methyl p-cresoxymethacrylate (MCMA) in toluene has been studied at 30 and 0°C and at dose rates of 0.3, 0.15, and 0.75 Mradh -1 . The rates of polymerization, which were found to increase with increasing monomer concentration, have direct dependence on dose rate and [monomer] and have inverse dependence on [solvent]. The apparent energies of activation measured at 0.3 Mrad h -1 for MPMA and MCMA respectively are: 46.8 kJ mol -1 and 11.7 kJ mol -1 . The polymerization proceeded in spite of the presence of the inhibitor p-hydroxyphenyl methyl ether (PHME). This suggests that the mechanism of polymerization may be predominantly ionic. A suitable reaction scheme has been proposed.

Synthesis and characterisation bynmr spectroscopy of oligomers derived from 2-hydroxy ethyl acrylate (hea) and 2-hydroxy propyl methacrylate (hpma) and 1,6-bexamethylene diisocyanate (hdi) are briefly discussed.

High polydispersity values obtained for the molecular weights, as determined by light scattering, osmometry, and GPC, of polymers prepared by different methods from the monomers recently synthesised indicate the presence of large quantities of low molecular weight species besides the high molecular weight species besides the high molecular weight species. Intrinsic viscosity data were used to evaluate Mark–Houwink constants K and “a” for this new series of monomers. DSC analyses show that the polymers have low Tg. X-ray diffraction studies made on the fibers show a high percentage of crystallinity in poly(methyl α-phenoxymethacrylate).

Polymerization of vinyl monomers initiated by chromic acid-reducing agent (glycerol, sorbitol and mannitol) systems was studied at 35-45°C in perchloric acid medium. Chromic acid alone did not initiate polymerization. On the basis of the experimental results embodying the dependences of various variables on the rate of polymerization R and the rate of chromium(VI) disappearance -RCr, a reasonable kinetic scheme has been suggested. The order of the reactivity of different polyhydroxy alcohols is: glycerol > sorbitol > mannitol. The scheme is consistent with linear termination and the formation of a radical intermediate resulting from the oxidation of the reducing agent by Cr(VI).

The kinetics of redox -initiated polymerization of acrylic acid (AA) by the systerm Mn 3+ -isobutyric acid (IBA) in sulfuric acid was studied in the temperature range of 35-50°C. The overall rates of polymerization (R p ), disappearance of manganic ion (−R m ), and degree of polymerization (X n ), were measured with variation in [monomer], [Mn 3+ ], [IBA], H + , μ, [Mn 2+ ], and temperature. The polymerization is initiated by the organic free radical that develops from the Mn 3+ -isobutyric acid oxidation reaction. Two types of termination reactions, one by the metal ion (Mn 3+ ) and the other by the MN 3+ -isobutyric acid complex are proposed to explain the kinetic results. The various rate parameters were evaluated an discussed.

Studies were carried out on grafting of various vinyl monomers to nitrocellulose by ceric ions. It was observed that graft copolymerization occurred only with methyl methacrylate (MMA) and methyl acrylate monomer. The variables such as initiator concentration, monomer concentration, time of grafting, and nitrocellulose content on grafting of MMA are discussed. By hydrolyzing away the nitrocellulose backbone, the grafted poly(methyl methacrylate) branches were isolated and the >c=o peak at 1740 cm −1 in the infrared spectra of these isolated branches gave definite evidence of grafting. The molecular weight of isolated branches has been determined by viscometry. The probable mechanism of grafting may be at the α-carbon atom of primary alcohol or at a C 2 -C 3 glycol group of the anhydro glucose unit or at the hemiacetal group of the end unit of nitrocellulose, as nitrocellulose is formed by the partial nitration of cotton cellulose.

Solution blending of n-butyl methacrylate-ethyl acrylate copolymers with chlorinated rubber was investigated. The tensile properties of the blends were studied; it was concluded that the blends serve as good film forming materials.

The kinetics of the reactions of hydrogen provide with two chromium(IV)-depetoxo complexes Cr(O 2 ) 2 (H 2 O) (O 2 ) 2 (dien) have been investigated in aqueous acidic media 10°C l=1.00 (NaClO 4 ).

Additives are generally added to spin dope in wet spinning to facilitate mechanical operations, increase solid content, and effect gelation to precede phase separation. Besides these advantages, they have an effect on the cross section of PAN fibers. Organic compounds (hydrochlorides of aryl, alkyl secondary amines, etc.) change the cross section to a bean shape, whereas a nonsolvent (water) and inorganic compounds (calcium salts, borax, boric acid, etc.) retain the circular cross section of PAN fibers. The change in cross section can be attributed to the change in skin and core effects at different pH values of the spin dope in the presence of the additives.

Amyloglucosidase was immobilized on a copolymer of methyl methacrylate and 2-dimethylaminoethyl methacrylate. The resulting immobilized amyloglucosidase has 19% of the soluble enzyme specific activity. The pH optimum of immobilized amyloglucosidase is shifted towards acidity by 1.9 units. The temperature optimum of immobilized enzyme is shifted upward by 5°C. The immobilized amyloglucosidase has the maximum stability at pH 4.6, whereas the soluble enzyme has maximum stability at pH 5.5. While soluble amyloglucosidase has a maximum thermal stability at 50°C, the stability of the immobilized amyloglucosidase steadily decreases with the increase in temperature.

Oxygen as a promoter of radical polymerisation of ethyl acrylate was studied in the aqueous medium. Cu2+ was chosen as the catalyst for the ascorbic acid (AA)—02 redox reaction, constituting a three component initiating system. The rate of polymerisation, Rp, was observed to increase, remain constant and then decrease with increasing [Cu2+]. Rp increased with [O2] upto ∼ 6.5 × 10−4M and thereafter remained constant. [AA] > 1.2 × 10−3M did not influence the rate. Rp always increased with monomer [M] at fixed [Cu2+], [O2] and [AA]. However, the order with respect to [M] increased with increasing [Cu2+]. The rate of polymerisation increased with ionic strength, μ and decreased with [H2SO4]. There was an initial increase in Rp followed by a decrease with increasing temperature. Conditions were identified where Rp depended only on [Cu2+] and [M] or [M] only for industrial exploitation. Kinetic chain length of the polymers obtained under various experimental conditions were determined viscometrically.

Kinetics of grafting of poly(butyl acrylate) onto gelatin was studied with H 2 O 2 - ascorbic acid redox systm. Percent grafting, grafting efficiency, R g , and R h were determined as a function of time, temperature, initiator, monomer, and backbone concentration. It was found that R g depends on first power of monomer concentration and 0.5 power to the initiator concentrations. A detailed kinetic scheme is proposed to explain these results.

Poly(methacrylonitrile-co-styrene) (PMANS) and Poly(acrylo-nitrile- co- styrene) (PANS) having 1:1 composition were prepared with free-radical initiators. The polymers were fractionated into fractions having narrow molecular weight distribution. The dilute solution properties of the fractionated copolymers were studied by light scattering, viscometry, and osmometry in solvents (methyl ethyl ketone, dimethylformamide, and acetone), [n]-M w and(r2)w l/2−M w relationships have been established. The validity of the various graphical methods for the determination of Flory′s constant, K θ were observed. From the values of the steric factors it was noticed that the copolymer coil of PANS is stiffer than that of PMANS.

Equilibrium studies on mixed-ligand complexes of uranyl ion with carboxylic acids, malonic, diglycollic, maleic, crotonic, glycollic, thioglycollic and mercaptopropionic, as ligands were carried out by the pH titration method at 31 ± 0·1°C and ionic strength μ = 0·1 mol dm −3 (NaClO 4 ). Different equilibrium constants, characteristic of mixed-ligand complexes were calculated. In most of the systems studied, ternary complexes were found to be more stable than the corresponding binary complexes. The stabilities of ternary complexes appear to depend on the size of the chelate ring; the difference in stabilities of 1:1 and 1:2 binary complexes; the nature of the donor atom and the charge neutralization if any. In general, the stability is attributed to the unsymmetrical nature of the ternary complex.

The polymerization of acrylonitrile (AN) initiated by oxygen-ascorbic acid (AA)-ferric ion system was studied in dil. HNO3 at 40°. The rate of polymerization, Rp, was found gravimetrically. In the [Fe3+] range, (2–5 × 10−5 M, Rp was proportional to [AN]1.5 ± 0.05, [O2]0.5 ± 0.02 [AA]0 and [Fe3+]0; for [Fe3+] = (5–30) × 10−5 M, it was proportional to [AN]1.8 ± 0.05, [O2]0.6 ± 0.02, [AA]0 and [Fe3+]−0.9 ± 0.05. A plausible reaction scheme is proposed and rate law presented to explain these results. Rp increased with ionic strength and [HNO3] (up to ∼0.25 M). An initial rate increase with temperature followed by a decrease was noticed. Chain lengths of the polymers were determined viscometrically.

Methyl methacrylate was polymerized in aqueous medium initiated by a copper(II)-ascorbic acidoxygen system at 40°C and a kinetic study of the reaction is presented. The rate of polymerization, Rp showed an increase, constancy and then a decrease with increase in the [Cu2+]. The order with respect to [Cu2+] was 0.5 in the rate increase region. The order in monomer concentration changed gradually from 1.0 to 2.0 with increase in [Cu2+]. Rp became independent of ascorbic acid (AA) concentration and oxygen concentration at high concentrations. These results indicate that termination by mutual interaction of chain radicals predominates at low [Cu2+] while termination was exclusively by metal ions at high [Cu2+]. Rp was also observed to increase with temperature and ionic strength and to K p K t 1 2 value was calculated and compared with literature values. Chain lengths were determined by viscometry for the polymers obtained under various experimental conditions.