SynopsisThe radiation crosslinking of poly(viny1 chloride), PVC, with trimethylolpropane trimethacrylate, TMPTMA, has been examined. The polyfunctional TMPTMA undergoes rapid polymerization incorporating the PVC into a three-dimensional ne work. The kinetics and mechanism of these treatment. The gel was rapidly formed with a TMPTMA polymerization rate greater than that of the PVC grafting reaction. Only 3040% of the available bonds were used in the initial polymerization. The remaining 60-70% of the double bonds predominantly react in the final stages of crosslinking (80-100% gelation). The macroscopic properties (e.g., solubility, glass transition temperatures, mechanical characteristics, etc.) of the PVC-TMPTMA blend are discussed in terms of the molecular crosslinking mechanism. The effect of thermal treatment, during and after irradiation. on the reaction rates and mechanism is examined.crosslinking reactions were studied with particu > ar reference to dose dependence and thermal

SynopsisThe radiation crosslinking of poly(viny1 chloride) (PVC) blended with trimethylolpropanetrimethacrylate (TMPTMA) has been examined. The polyfunctional TMPTMA undergoes polymerization incorporating the PVC into a 3-dimensional network. The kinetics and mechanisms of these crosslinking reactions were studied with particular reference to dependence on radiation dose and blend composition. The crosslinking rate was found to be proportional to the TMPTMA concentration. As the TMPTMA concentration decreased, soluble graft copolymers were produced in addition to insoluble networks. A gel permeation chromatography technique provided compositional information on the gel and sol fractions. The competition between polymerization, grafting, and degradation reactions was examined.

An intein-driven protein splicing approach allowed for the covalent linkage between the N- and C-termini of a polypeptide chain to create circular variants of the endo-β-1,3-1,4-glucanase, LicA, from Bacillus licheniformis. Two circular variants, LicA-C1 and LicA-C2, which have connecting loops of 20 and 14 amino acids, respectively, showed catalytic activities that are approximately two and three times higher, respectively, compared to that of the linear LicA (LicA-L1). The thermal stability of the circular variants was significantly increased compared to the linear form. Whereas the linear glucanase lost half of its activity after 3 min at 65 °C, the two circular variants have 6-fold (LicA-C1) and 16-fold (LicA-C2) increased half-life time of inactivation. In agreement with this, fluorescence spectroscopy and differential scanning calorimetry studies revealed that circular enzymes undergo structural changes at higher temperatures compared to that of the linear form. The effect of calcium on the conformational stability and function of the circular LicAs was also investigated, and we observed that the presence of calcium ions results in increased thermal stability. The impact of the length of the designed loops on thermal stability of the circular proteins is discussed, and it is suggested that cyclization may be an efficient strategy for the increased stability of proteins.

SynopsisThe radiation chemistry of poly(viny1 chloride) (PVC) blended with trimethylolpropanetrimethacrylate (TMPTMA) and diundecyl phthalate (DUP) has been examined. This three-component mixture contains a base resin (PVC), a crosslinking sensitizer (TMPTMA), and a physical modifier (DUP). These are the basic components in any radiation-curable coating. The kinetics and mechanism of the crosslinking reactions were studied with reference to the dependence on radiation dose and blend composition. The polyfunctional TMPTMA underwent polymerization incorporating the PVC into a 3-dimensional network. DUP remained chemically inert during the irradiation, not being bound to the network. However, DUP by plasticizing the macromolecules and diluting the monomer, changed the kinetics extensively. DUP enhanced TMPTMA homopolymerization, TMPTMA grafting, and PVC crosslinking reaction rates. The effect on the competition between polymerization, grafting, and degradation reactions was examined in terms of enhanced mobility of the reacting species. The influence of these kinetic considerations in selecting a blend composition for a coating application was discussed.

SynopsisBlends of poly(viny1 chloride) (PVC) with polyfunctional monomers may be crosslinked by ionizing radiation. The physical properties of PVC blended with trimethylolpropanetrimethacrylate (TMPTMA) and diundecyl phthalate (DUP) were studied. The TMPTMA monomer crosslinked the blend by homopolymerization and/or grafting to PVC. The plasticizer, DUP, was chemically inert under irradiation but, by plasticizing the macromolecules and diluting the monomer, changed the kinetics extensively. Characteristics of the glass transitions and the tensile mechanical properties have been correlated with blend composition and radiation dose. Before irradiation, poly(viny1 chloride) was plasticized by both DUP and TMPTMA monomer. The increase in glass transition temperature and mechanical strength following irradiation to 5 Mrad was correlated with the TMPTMA content of the blend. Both the molecular structure of the network and the DUP content of the blend were factors in determining the physical properties of the final crosslinked blend. The molecular structure was determined by the kinetics of the crosslinking reactions, which in turn were determined by the blend composition. A molecular interpretation consistent with the physical properties, chemical kinetics, and mechanism of the crosslinking system has been presented.