M.H. Rao

Pulse radiolysis study of initiation and propagation in radiation induced polymerisation of cyclohexyl methacrylate

Abstract Initiation and individual propagation rate constants for the first few steps are determined for e - aq , OH radical and H atom reactions with cyclohexyl methacrylate as the monomer using the technique of pulse radiolysis. Though the rate constants for initiation are higher, the propagation rate constants for the transient species formed by reaction of OH radical and H atom are lower compared to that by reaction of e - aq with the monomer. It is also observed that in the case of e - aq reaction the first propagation step is about an order of magnitude faster than the second propagation step and propagation through radical-anionic form is much faster than its radical counterpart.

Pulse Radiolysis Study of Initiation, Dimerization, and Propagation Steps of 3,3-Dimethylacrylic Acid in Aqueous Medium

Abstract Rates of initiation, dimerization, and first propagation steps originating from the hydrated electron and hydroxyl radical reactions with 3,3-dimethylacrylic acid monomer have been investigated using the technique of pulse radiolysis. The initiation step for the protonated monomer is found to be faster than that of the deprotonated form. The dimerization step is about two orders of magnitude faster than the first propagation step. Radical species are more reactive than the corresponding radical-anionic species, and the β-protonated electron adduct to the monomer is found to propagate faster than other electron adduct species. The different transient species have been characterized by their absorption spectra, λmax, extinction coefficient, pK, and redox behavior. Based on these observations, the most probable structures are suggested.

Free-Radical Species from Methyl Vinyl Ketone in Aqueous Solution: A Pulse Radiolysis Study

Abstract Transient species (T1 and T2), formed respectively by the reactions of hydrated electrons and hydroxyl radicals with methyl vinyl ketone monomer in aqueous solution, were characterized by their spectra, redox behavior, and decay kinetics. These were found to have λmax at 290 and 310 nm with low extinction coefficient values of 94 and 70 m2/mol, respectively. Rate constants for the reactions of methyl vinyl ketone with eaaq- and OH were found to be 3.2 × 109 and 7 × 108 dm3·mol−1·s−1, respectively. the first propagation step for species T2 was found to be much faster (κpl ∼ 1.5 × 106 dm3·s−1 than that for species T1 (κpl∼7.0 × 105 dm3·mol−1·s−1). Both were found to be reducing in nature, and the rate constants for the reduction of thionine and safranine with these species were determined. the most probable structures of these species are suggested.

Transient species involved in radiation polymerization of aqueous divinyl sulfone : a pulse radiolysis study

Abstract Initiation and individual propagation rate constants for the first few steps originating from hydrated electron and hydroxyl radical reactions with divinyl sulfone as the monomer have been determined using the technique of pulse radiolysis. The transient species formed by the reaction of hydrated electrons with divinyl sulfone propagate at a faster rate than the species formed by hydroxyl radical reaction. The first propagation step is found to be more than an order of magnitude faster than the second propagation step. The different transient species have been characterized by their absorption spectra, λ max , extinction coefficient, p K and redox behavior. Based on these, their most probable structures have been inferred.

Radiation polymerisation of cyclohexyl methacrylate—II. role of ionic and radical scavengers

Abstract Radiation polymerisation of cyclohexyl methacrylate has been carried out in the presence of scavengers i.e. biphenyl, cyclohexanol and benzoquinone. In presence of biphenyl and cyclohexanol which are scavengers for electrons and anions no induction period was observed and the rates of polymerisation and molecular weights decreased to the same extent. In presence of benzoquinone, a scavenger for both anions and free radicals, an induction period was observed, decreasing both the molecular weights and the rates of polymerisation. From these results it is evident that the polymerisation takes place both by anions and free radicals. A very high chain transfer constant ( K tr / K p ) to benzoquinone equal to 23.06 was obtained.

Radiation polymerisation of cyclohexyl acrylate in presence of hydroquinone—III

Abstract Radiation initiated polymerisation of cyclohexyl acrylate has been studied at various dose rates, temperature and scavenger concentration. The dose rate exponent is found to be 0.77 indicating the possibility of chain transfer to hydroquinone. GPC chromatogram showed that the low molecular weight fraction was suppressed completely in the initial stages, indicating the possibility of hydroquinone acting as a chain transfer agent for free radicals. The molecular weight determined is independent of dose rate but increased with conversion. The intrinsic viscosity of the polymer decreased with increase in conversion indicating the possibility of branching as the conversion increases due to chain transfer to the polymer.

Radiation polymerisation of cyclohexyl acrylate—I

Radiation polymerisation of cyclohexyl acrylate has been studied at various dose rates. The rate of polymerisation of cyclohexyl acrylate is an order of magnitude higher than any of the acrylates reported so far. The kp/kcase12t values determined are in the range of some of ionic initiated polymerisations induced by radiation. GPC chromatogram shows two distinct peaks of equal area which are identified with free radical and ionic initiations.

Radiation polymerisation of cyclohexyl acrylate in presence of cyclohexanol—II

Abstract Radiation polymerisation of cyclohexyl acrylate in presence of cyclohexanol has been studied at various dose rates. The dose rate exponent determined ∼0.66 indicates the possiblity of the existence of the chain transfer to cyclohexanol. GPC chromatogram shows the presence of the low molecular weight polymer suppressing the high molecular weight fraction. These results suggest that the origin of the low molecular weight polymer could be through free radical initiation. High molecular weight fraction which is due to ionic initiation is suppressed completely indicating the possibility of cyclohexanol acting as a chain transfer agent for ions.

Gamma radiolysis of polycyclohexyl methacrylate

Abstract Polycyclohexyl methacrylate prepared by gamma ray initiation of cyclohexyl methacrylate was found to be a degrading type of polymer. The radiolytic products of the polymer are carbon monoxide, carbon dioxide, hydrogen, cyclohexyl formate, cyclohexane, and cyclohexanol with small traces of methane and cyclohexene. On the basis of the yields obtained, i.e. cyclohexane, cyclohexanol, cyclohexyl formate, and hydrogen, a mechanism has been proposed for the radiolytic degradation of the polymer. On the basis of the proposed mechanism for degradation, G (scission) should be ≈2.82. But the measured value using the molecular weight-radiation dose relationship is only ≈2.41. This indicates that the measured value is actually [ G ( S ) - G ( X )] and not G ( S ) alone and some amount of crosslinking is also taking place along with degradation.