Mool C. Gupta

Radiation effects on poly(lactic acid)

Abstract The effect of γ-irradiation on poly(lactic acid), PLA, synthesized by the solution polymerization of lactic acid in air and N2 atmosphere, is studied. From the intrinsic viscosity and average molecular weight data of γ-irradiated samples, radiation chemical yields G(s) and G(x) for chain scission and crosslinking respectively were determined. Results indicate that the presence of air causes a decrease in both chain scission and crosslinking. Furthermore, the melting temperature decreased with dose and by using the Flory equation, the value of G (crystalline units) was estimated in air and N2 atmosphere as 19 and 14 respectively.

ELECTRICAL AND OPTICAL PROPERTIES OF CONDUCTING COPOLYMER: POLY(ANILINE-CO-N-ETHYLANILINE)

Copolymers of aniline and N-ethylaniline were prepared by chemical oxidation with ammonium peroxodisulphate in aqueous acidic medium under nitrogen atmosphere. The products have been characterized by solubility, spectroscopic method, and electrical conductivity measurement. The solubility and spectroscopic analysis suggested that the product is a copolymer of aniline and N-ethylaniline. The optical spectra of the homopolymer and copolymer show hypsocromic shift with the increase in dielectric constant of the solvent and with increasing the content of N-ethylaniline in the copolymer. The electrical conductivity of poly(aniline-co-N-ethylaniline) salts was measured as a function of temperature. The conductivity of copolymers decreases with increasing N-ethylaniline content. The conduction mechanism is polaron hopping conduction as similar to the case of polyaniline. Most-probable hopping distance, hopping energy, and localization lengths of copolymers have been compared to those of homopolymers.

Effect of metal oxides on the kinetics of thermal oxidative degradation of nylon-6

Abstract The rate constants and kinetic parameters for the thermal oxidative degradation of nylon-6 in the presence of metal oxides show the existence of a true kinetic compensation effect. This pattern of behaviour amongst metal oxides in the oxdiative degradation of nylon-6 has been linked to the higher oxidation state. The behaviour suggests that the reaction follows a redox or electron transfer mechanism due to tunnelling of electrons.

Chemical synthesis, characterization and transport properties of copolymer: Poly(aniline-co-m-methylaniline)

Abstract Poly(aniline-co-m-methylaniline) were copolymerized by chemical peroxidation of aniline and m-methylaniline in aqueous acidic medium under nitrogen atmosphere at 0–4oC. The molar feed ratio of the monomers were varied to prepare copolymers of different composition. The copolymers product were characterized by solubility, spectroscopic methods, elemental analysis and electrical conductivity measurements. The solubility and spectroscopic analysis suggested that the product is a copolymer of aniline and m-methylaniline. The optical spectra of the copolymer shows hypsochromic shift with the increase in dielectric constant of the solvent and with increasing the content of m-methylaniline in the copolymer chain. The electrical conductivity of copolymer salts were measured as a function of temperature. The conductivity of copolymer decreases with increasing the content of m-methylaniline in the copolymer chain, due to change in coplanarity of polymer and reduction of mobility of charge carrier along the main chain. The conduction mechanism of copolymer is polaron hopping conduction as similar to the case of polyaniline. The coherence, most probable hopping distance, hopping energy and localization length of copolymers have been compared to those of homopolymers.

Estimation of nonisothermal kinetic parameters from a TG curve by the methods of overdetermined system and inflection point

Methods are described to determine nonisothermal kinetic parameters from a TG curve. The first method uses the theory of overdetermined systems while the others use the inflection points. These inflection point methods are an alternative to those described earlier by Viswanath and Gupta.

Studies on Substituted Derivatives of Polyaniline: Effect of Polymerization Conditions on Electrical Conductivity

Abstract Polyaniline, poly(o-methoxyaniline)and poly(N-phenylaniline) were synthesized chemically under different polymerization conditions by peroxodisulphate oxidation in HCl and in a mixture of HCl and CH3CN. The polymer prepared at 0°C, monomer-oxidant ratio 1:1.15 and a strong acidic medium, has the least bandgap and maximum electrical conductivity. The electrical conductivity depends on degree of oxidation and protonation. The bulky substituents increase the torsion angle and hence disorder causes the decrease in the electrical conductivity of polymer.

MELTING BEHAVIOR OF POLYETHYLENE TEREPHTHALATE COPOLYESTER AND POLYSTYRENE BLENDS

The melting behavior of polyethylene terephthalate (PET) copolyester/polystyrene (PS) blends was studied using differential scanning calorimetry. Multiple melting endotherms were observed for the PET copolyester as well as the PET copolyester/PS blend at Tc = 483 and 493 K, respectively. A higher crystallization temperature resulted in the reorganization of the crystalline species and an increase in area under the reorganization peak. Higher melting temperatures for PS-rich blends may be attributed to the formation of a stiffer matrix around the crystallites and the possible inhibition of crystal thickening. Melting behavior shows that the PET copolyester and PS form miscible blends up to 30 wt.% of PS, whereas with the lowering of the isothermal crystallization temperature to 483 K, miscibility was found only up to 10 wt.% of PS.

Standard polynomial method for derivatives: Application to non-isothermal and isothermal kinetics and computer programming for the Sharp—Wentworth and Freeman—Carroll methods

Abstract A method is suggested for obtaining polynomials from experimental data. These polynomial expressions are differentiated to yield first-order derivatives, and these derivatives are used for computing non-isothermal and isothermal kinetic parameters. A single computer program is presented for the Sharp—Wentworth and Freeman—Carroll methods.

Polyarylates: thermal stability in air

Polyarylates were synthesized by the acidolysis of the diacetates of dihydric phenols with diacids using a melt-polymerization technique. These polymers were characterized by solution viscosity, number-average molecular weight and IR spectra. Thermal stability of these polyarylates were studied by dynamic TG in the presence of air. Relative thermal stabilities were compared at the 50% mass loss of a given polymer (Th value). The data presented revealed that there is a definite relationship between the structure of a polymer chain and their thermo-oxidative stability. TheTh values of some of these polyesters were found to be higher than those reported for highly stable fluoro-carbon polymers (e.g. PTFE). It was observed that the polymers with more cyclic structures in a chain tend to be stiffer and more resistant to deformation. A chain backbone consisting of large number of aromatic groups induced chain stiffening because of chain inflexibility, resonance effects and steric effects.

Studies on Substituted Polyaniline Effect of Polymerization Conditions on Transport Properties

Abstract The temperature dependance of the transport properties of polyaniline, poly(o-methoxyaniline) and poly(N-phenylaniline) prepared under different conditions was investigated. The results show that the localization of conducting electrons is least in case of polyaniline and it increases with substituents and with polymerization temperature. The data show that such polymers are a class of 1-D disorder conductor between localization state associated by proton exchange.