K. S. V. Srinivasan

Synthesis, characterization, and studies on the solid-state crosslinking of functionalized vinyl cinnamate polymers

Functionalized vinyl cinnamate monomers were synthesized by the reaction between hydroxyethylacrylate (HEA) and substituted cinnamoyl chlorides possessing electron releasing and withdrawing functional groups like chloro, methoxy, and nitro groups at the para position of the aromatic ring. The structures of these monomers were characterized by Fourier transform infrared (FTIR), 1H-, and 13C-NMR spectral techniques. The homopolymers of the synthesized monomers were obtained by the free radical solution polymerization in dimethylformamide (DMF) at 80°C for 12 h using azobisisobutyronitrile (AIBN) as a radical initiator. The sensitivity of these polymers towards light was studied by monitoring the photocrosslinking nature of the polymers by ultraviolet (UV) and FTIR techniques. The effect of the functional groups on the crosslinking efficiency was studied and compared with that of the unsubstituted polymer. The cyclobutane-type addition mechanism involved in the photocrosslinking phenomena was confirmed by the above spectral studies in the functionalized vinyl cinnamate polymers.

Synthesis, characterization, and reactivity ratio studies on new sulfide copolymers containing ethylbenzene units

Abstract Soluble new sulfide copolymers were synthesized readily by the polycondensation of ethylene dibromide (EDB) (or methylene dibromide (MDB)) with styrene dibromide (SDB) and sodium sulfide (Na2S) in the presence of phase transfer catalyst. The copolymers were characterized by using Fourier transform-infrared, 1H NMR, 13C NMR, gel permeation chromatography, and thermogravimetric analysis (TGA) techniques. The copolymer composition obtained from the 1H NMR spectra led to the determination of reactivity ratios. The analysis of reactivity ratios revealed that both EDB and MDB are more reactive than SDB towards Na2S, and copolymers formed are random in nature. Furthermore, it also gave an insight on the microstructure of the copolymers that both poly (ethylene sulfide-co-styrene sulfide) (p(ES-co-SS)), and poly(methylene sulfide-co-styrene sulfide) (p(MS-co-SS)) copolymers have more of blocky structure with increase in the concentration of ethylene sulfide (ES) or methylene sulfide (MS) units in the respective copolymers. The TGA was used to find out the thermal stability of these polymers. The XRD data indicated an increase in the amorphous content of the copolymers with an increase in the concentration of styrene sulfide (SS) units and thereby resulting in most of these copolymers being soluble in common organic solvents. The solubility and molecular weight of the polymers formed were dependent on the concentration of SDB taken in the feed.

Kinetic and mechanistic studies on the block copolymerization of methyl methacrylate initiated by ce4+-poly (ethylene glycol) redox system

The kinetic and mechanistic features of tetravalent cerium-poly( ethylene glycol) ( PEG, molecular weight 6000) redox couple initiated block copolymerization of methyl methacrylate (MMA) have been investigated in aqueous acidic medium in the temperature range 30-50°C. The block copolymerization behavior as a function of [Ce 4+ ], [PEG], [MMA], [H + ], [NO 3 - ], as well as temperature, have been studied. The overall rate of polymerization (Rp), the rate of disappearance of Ce 4+ (R Ce ), and the number average molecular weight (M n ) have been determined from gravimetry, cerimetry, and gel permeation chromatography, respectively. Rp has been found to bear a square dependence on [MMA] and independent of both [Ce 4+ ] and [H + ]. R Ce has been found to be directly proportional to [Ce 4+ ] and [H + ], and independent of [MMA]. Both Rp and R ce have been found to be retarded on adding nitrate ions, while increase of temperature accelerated the rates. The M n of the block copolymer has been found to depend on [Ce 4+ ] , [PEG], [MMA], and [H + ] as well as on temperature. A plausible reaction scheme has been derived and suitable kinetic expressions have been evaluated based on these observations. It has been concluded that by varying the temperature and concentration of the components of the redox system, it is possible to control the rate of polymerization and the molecular weight of the resulting block copolymer.

Block copolymerization initiated by Mn(III)-poly(ethylene glycol) redox system : general features and kinetics

The kinetics and mechanism of thermal polymerization of acrylonitrile initiated by Mn(III) pyrophosphate — poly(ethylene glycol) (PEG, molecular weight 6000) redox system in aqueous sulfuric acid medium was studied in the temperature range 30–60°C. The overall rates of polymerization and the disappearance of Mn3+ were determined. The polymerization was initiated by the organic free radical produced from the Mn3+-PEG reaction and the termination was by the metal ions. The rate of polymerization of acrylonitrile was found to be directly proportional to the square of the monomer concentration and first power of PEG concentration, and inversely proportional to the concentration of Mn3+. The rate of manganic ion disappearance was found to be directly proportional to manganic ion concentration and PEG concentration, and independent of the monomer concentration. Based on these observations, a plausible reaction scheme was suggested and suitable kinetic expressions were evaluated.

Grafting of methyl methacrylate onto cellulose nitrate initiated by benzoyl peroxide

It has been observed that grafting of vinyl monomers onto cellulose nitrate in solution takes place using benzoyl peroxode. The graft copolymer was isolated from the unreacted backbone and homopolymer by selective solvent extraction. The effect of variables, such as the initiator concentration, the monomer concentration and the reaction time on the percent grafting and the grafting efficiency, were discussed. A probable mechanism for grafting of vinyl monomers to cellulose nitrate in solution has been proposed.