Wu Jilan

Study on radiation-induced grafting of styrene onto chitin and chitosan

Abstract Radiation-induced grafting of styrene onto chitin and chitosan powder was performed at room temperature. The effect of various conditions such as absorbed dose, solvent and oxygen on grafting was investigated. The grafting yield increased with the increase in absorbed dose. At the same dose, the grafting yield of styrene on chitosan was higher than that on chitin. The grafting reaction was promoted in the presence of methanol, and oxygen delayed the grafting reaction but did not inhibit it completely. In order to study the mechanism of grafting reaction and analyze the grafted samples, the grafted products were extracted first by benzene, then they were hydrolyzed in the presence of acid and separated by thin layer chromatography (TLC). Three different kinds of polystyrene (PS), i.e. PS grafted onto chitin, PS embedded in chitin and PS in grafting solution were gained. The variation of their molecular weight (MW) and width index of molecular weight distribution (Mw/Mn) determined by gel permeation chromatography (GPC) at different grafting conditions is discussed.

Study on oxidation of polymers treated by high let radiation

Abstract The oxidation of medical silicone rubber and segmented polyether urethane which were bombarded with 1∼1.2 MeV Si + or F + at the dose of 5 × 10 14 ions/cm 2 was studied. In XPS measurements, it was found that the oxygen concentration on the surface of the implanted polymeric membranes had been increasing in three months at least. ESR measurement showed that some free radicals existed in these membranes and their quantities decreased with time. Chemical analysis proved that peroxides were generated in the γ irradiated membranes. The reason for the increasing of oxygen concentration was that free radicals combined with oxygen in the air and produced peroxides on the membrane surface. Moreover, in order to demonstrate the radiation mechanism, low LET (γ rays) radiation of such polymeric membranes was carried out for comparison

Reactions and kinetics of baicalin with reducing species, H, e−solv and α-hydroxyethyl radical in deaerated ethanol solution under γ-irradiation

Abstract Baicalin (β- d -Glucopyranosiduronic acid, 5,6-dihydroxy-oxo-2-phenyl-4H-1-benzopyran-7-yl) is a naturally occurring flavonoid of pharmacological importance and one of typical Chinese herbs. The γ-radiolysis of baicalin in the deaerated liquid ethanol was studied. The G values of H 2 and 2,3-butanediol decrease with increasing baicalin concentration indicates that baicalin is able to scavenge reducing species, H and α-hydroxyethyl radicals, efficiently. Two γ-radiolytic products of baicalin—mono hydroxyethyl and dihydroxyethyl derivatives—formed and were isolated; their structures are determined as well. A reasonable mechanism of γ-radiolysis of baicalin is proposed as well as the relevant rate constants obtained. The rate constant of baicalin with α-hydroxyethyl radicals is 3 × 10 4 mol −1 ·dm 3 ·s −1 , and that of H atoms with baicalin is 7 × 10 3 times as large as that with ethanol.

Selecting ethanol as a model organic solvent in radiation chemistry-I. Radiolysis of acetone-ethanol system

Abstract Radiolysis of acetone-ethanol solution [Zhang, Wu and Zhou (1994) Radiat. Phys. Chem. 43, 335] has been further studied in this work. The dependences of G values of the final γ radiolytic products such as H 2 , 2,3-butanediol and acetaldehyde on acetone concentrations in liquid ethanol were obtained. New information was provided that except the detected new product 2-methyl-2,3-butanedio (Zhang et al. , 1994), another new final product isopropanol was also found and material balance between intermediates and major final products was obtained. In addition, a ratio of rate constants k (e s − + CH 3 CHO)/ k (e s − + CH 3 COCH 3 ) = 0.96 was calculated by computer simulation, which is in good agreement with the result obtained from pulse radiolysis experiments [Milinchuk and Tupikov (1989) Organic Radiation Chemistry Handbook ].

Radiation synthesis of a water-soluble temperature sensitive polymer, activated copolymer and applications in immobilization of proteins

Abstract In this work the radiation polymerization of N-isopropylacrylamide (NIPAAM) in aqueous solutions has been carried out and a water-soluble, temperature sensitive polymer and copolymer were obtained by using γ-rays from Co-60 source at room temperature. We have gained the optimum dose and dose—rate of radiation synthesis of linear polyNIPAAM through determining conversion yield and viscosity. In order to immobilize protein (BSA) and enzyme (HRP) into this water-soluble polymer, we prepared an activated copolymer, poly ( N-isopropylacrylamide-co-N-acryloxysuccinimide). The BSA and HRP has been immobilized onto the activated copolymer. The BSA (HRP) / copolymer conjugates still kept the original thermally sensitive properties of the linear polyNIPAAM. The conjugation yield of BSA to the activated copolymer decreased with increasing of dose. The thermal stability of the immobilized HRP was stable at 0 °C for a long time and has, at least, 4 days stability at room temperature. Immobilized HRP activity was lowered when the temperature was raised above its LCST. This phenomenon was reversible and the immobilized HRP regained activity below its LCST. The optimum pH of the immobilized HRP shifted from ca.5 upward to ca.7.

Study of baicalin scavenging hydroxyethyl peroxyl radicals by radiolysis of aerated ethanol-baicalin system

Abstract The reaction of baicalin (β- d -glucopyranosiduronic acid, 5,6-dihydroxy-oxo-2-phenyl-4H-1-benzopyran-7-yl) scavenging hydroxyethyl peroxyl radicals (RO 2 . ) was studied with the aid of radiolysis of aerated ethanol. Two main stable products were separated by reverse HPLC and their possible molecular structures were derived from their UV, IR and FAB-MS spectra. The dependence of G (H 2 O 2 ), G (CH 3 CHO) and G (-baicalin) on the concentration of baicalin showed that one baicalin molecule could inhibit the formation of one H 2 O 2 molecule and two CH 3 CHO molecules. A possible reaction mechanism between baicalin and RO 2 . radical was suggested.

Study of radiation grafting of styrene on cotton cellulose

Abstract Direct and preirradiation graft of styrene on cotton cellulose were studied in respects of molecular weight (Mn), molecular weight distribution (Mw/Mn) of grafted side chains and reaction kinetics. Effects of total dose, dose rate, concentration of monomer and acidity in the systems on Mn and Mw/Mn of the grafted side chains were investigated by means of direct radiation grafting. Preirradiation grafting of the same systems was studied as well.

The reaction of alpha-hydroxyethyl radical in aqueous solution and ethyl alcohol

Abstract The dependences of G values of the final γ-radiolysis products such as H 2 , 2,3-butanediol and acetaldehyde on the absorbed dose in aqueous ethanol solution and on acetone concentration in liquid ethanol were studied. It was found that α-hydroxyethyl radical can undergo both recombination reaction and disproportionation reaction at the almost same rate in aqueous ethanol solution, but only go through the recombination reaction in liquid ethanol. When increasing acetone concentration, the G (CH 3 CHO) value rises and G ((CH 3 CHOH) 2 ) value decreases. A new final product, 2-methyl-2,3-butanediol, is found in the irradiated acetone-ethanol system.

The examination of TBP excited state by pulse radiolysis

Abstract With pulse radiolysis as well as flash photolysis, acetophenone and benzophenone have been employed as probles in the determination of the yield of tributyl phosphate excited species (TBP∗) in this work. The yield of e s , G ( e s ) has been determined to be about 1.0 and the total measured yield of TBP∗ has been estimated to be 1.9. Meanwhile, estimations are also obtained for the rate constants of the following reactions: dissociative electron capture ( e s +TBP→C 4 H 9 • +(C 4 H 9 O) 2 P(=O)O − ) ( k 1 =9.62×10 5 s −1 ), hydrogen abstraction by triplet benzophenone from TBP to give ketyl radical of benzophenone (BH) ( k 1 =6.0×10 5 s −1 ). The ratio of the rate constant of the decomposition of TBP∗ to that of the reaction of the energy transfer from TBP∗ to benzophenone is 9.6×10 −4 moldm −3 .

Research on radiation stability of polypropylene

Abstract The effect of isotacticity of polypropylene(PP) on its radiation stability has been investigated in the present work. It was found that (1) The G value of H 2 and CH 4 is smaller if isotacticity of PP is higher; (2) It is easier to be crosslinked by radiation for the PP with higher isotacticity; (3) The shape of DSC peak changes smaller after irradiation for PP with higher isotacticity. These results have been explained by the measurement of 13 C-NMR and small angle X-ray scattering.