Abdel Rahman, M., Blázovics A., Ágoston M. és mtsai:
A chemiluminescent study for detection of freeradicals in gallbladder bile in gallstone diseases. Ces. a Slov Gastroent., 1995,
Thermal analysis (TA) is useful for studying the
reaction and thermal properties of free radical cured photopolymers. Starting
with reactive liquid monomers, the photocuring reactions are initiated by
the interaction of UV radiation with an added photoinitiator to form free
radicals. The monomers generally are acrylates or methacrylates. Some of the
important characteristics of these systems that can be illustrated by TA methods
are: 1) the polymers are heterogeneous with more than one phase present even
when only one monomer is involved; 2) because of this heterogeneity they have
unusually broad glass transitions; 3) the degree of conversion achieved in
many UV cured systems is in the 60–80% range, so that considerable residual
monomer is often present; 4) partially cured, vitrified samples contain trapped
free radicals that will continue to react slowly; 5) when a partially cured
photopolymer is heated above its current Tg
a reaction exotherm is evident.
Some other aspects of photocuring
are not easily disclosed by thermal analysis. Studying fast photoreactions
by DSC may not give valid kinetic data because the reaction occurs faster
than the DSC instrument time constant. Optical methods (IR, Raman) can be
used to advantage in such cases. While photocuring resins are usually exposed
to light at ambient temperatures, the local temperature in the resin will
be quite elevated, resulting in Tg
values that are much higher than ambient. This has been demonstrated by thermal
modeling of the reaction and verified by infrared thermography.
The effect of gamma-irradiation on some new hydrazones of terpenoids using electron spin resonance (ESR) is reported. Gamma-irradiation of three derivates of hydrazone and of compounds resulting from the condensation of these derivates with terpenoids produces stable free radicals at room temperature. The analysis of the ESR parameters (g-factors and hyperfine coupling) and the simulation performed lead us to conclude that free radicals are of form R–N–NH2 (arising from hydrazine derivates) and R–N–N=R (arising from condensation compounds). The thermal stability of formed radicals is discussed and the activation energy involved in the process of recombination of free radicals is calculated.
Authors:R. Radičević, D. Stoiljković, and J. Budinski-Simendić
The free radical polymerizations of higher n-alkyl methacrylates were not investigated in detail until now. In this work, the courses of the isothermal free radical bulk
polymerization of dodecyl, quatrodecyl and hexadecyl methacrylates were investigated by differential scanning calorimetry.
The effects of the polymerization temperature and the alkyl group length in the esters on the monomer conversions during polymerization
were studied. It was found that the polymerization rate vs. time curves have two maxima. The free radical polymerizations of above-mentioned monomers proceed with slightly expressed
gel effect at the temperatures below 90°C, at initiator concentration 1 mass% in monomer.
Authors:M. Kiss, F. Könczöl, N. Farkas, D. Lőrinczy, and J. Belagyi
The effect of free radicals obtained in hydroxyl and cerium(IV)-nitrilotriacetic acid free radical generating systems on contractile
proteins (actin, myosin and their complexes in glycerinated muscle fibres) was studied using differential scanning calorimetry
and spin trapping electron paramagnetic resonance technique. The analysis of spectra showed that selective attack of thiol
groups – Cys-257 and Cys-374 residues of actin, and among others Cys-707 residue of myosin – and random attack of sidechains
of the main proteins of muscle tissue produced structural and functional changes, which affected the ATP hydrolysis cycle
and very likely the dynamics of actin. The melting curves obtained on protein systems support the view that global conformational
changes accompany the local damage of free radicals.