Free Radical Polymerization Kinetics of Vinylsulfonic Acid and Highly Acidic Properties of its Polymer

Poly(vinylsulfonic acid) (PVS) possesses a high acid content (ion‐exchange capacity in the chemical formula = 9.2 meq · g^?1). Its monomer, vinylsulfonic acid (VSA), had a high acid dissociation ability (Hammett acid function = 0.74 in water), and a high ionic conductivity (0.04–0.11 S · cm^?1). The radical polymerization of VSA with various initiators was kinetically investigated. The ESR spectrum of the VSA polymerization mixture showed a strong signal ascribed to the propagation carbon radical of VSA. The molecular weight of PVS increased with the increasing monomer concentration and decreasing radical initiator concentration to yield the PVS with a molecular weight of 4.0 × 10⁴. Proton‐conductivity of PVS under hydrated and nonhumidified conditions was on the order of 10^?1 and 10^?3–10^?6 S · cm^?1, respectively.

     

Termination Kinetics of Dibutyl Itaconate Free‐Radical Polymerization Studied via the SP–PLP–ESR Technique

Summary: The termination kinetics of dibutyl itaconate (DBI) bulk polymerization was studied via SP–PLP–ESR single pulse–pulsed laser polymerization with time‐resolved detection of free‐radical concentration by electron‐spin resonance, at temperatures between 0 and 60 °C. As is characteristic of PLP experiments, termination rate coefficients, k_t(i,i), are measured for radicals of (almost) identical chain length (CL) i. CL‐averaged 〈k_t〉, for chain lengths up to 200 monomer units, and also kequation/tex2gif-stack-1.gif referring to termination of very small‐size radicals are directly deduced from measured DBI radical concentration vs time traces. At 45 °C, 〈k_t〉 is (3.4 ± 0.6) · 10⁵ L · mol^?1 · s^?1 and kequation/tex2gif-stack-2.gif is (7.2 ± 1.0) · 10⁵ L · mol^?1 · s^?1. Both rate coefficients are independent of monomer conversion up to the highest experimental conversion of 18%. The associated activation energies are E_A(〈k_t〉) = 23.0 ± 3.2 kJ · mol^?1 and E_A(kequation/tex2gif-stack-3.gif) = 27.6 ± 2.8 kJ · mol^?1, respectively. “Model‐dependent” and “model‐free” analyses of radical concentration vs time profiles indicate a pronounced CL dependence of k_t(i,i) for DBI radicals of moderate size, 5 < i < 50. The lowering of k_t(i,i) with CL corresponds to an exponent α close to 0.5 in a power‐law expression k_t(i,i) = kequation/tex2gif-stack-4.gif · i^?a. At higher chain lengths, the variation of k_t(i,i) with CL becomes weaker and may be represented by an α value of 0.16 or even below. These results are consistent with models according to which α varies to a larger extent at low CL and to a smaller extent at high CL with the crossover region between the two ranges being located somewhere around i = 100.

Conversion‐dependence of 〈k_t〉 and kequation/tex2gif-stack-5.gif from laser‐induced photopolymerization of DBI.     

Relationship Between the Free Radical Polymerization Rates of Methacrylates and the Chemical Properties of their Monomeric Radicals

In this study, the rate of photopolymerization (R_p) of 21 alkyl methacrylates is correlated with the chemical properties of their monomeric radicals by making use of the enthalpic and polar effects of these radicals. Based on these properties, a general non‐linear expression is derived by optimizing the radicals and evaluating both their stability and polar effects, via the radical electrophilicity, using density functional theory. The expression performs quite well in predicting R_p for 16 of the 21 methacrylates with an R² value of 0.9384, but does not hold for too unstable and/or too nucleophilic radicals. Increasing the stability or decreasing the nucleophilicity of the monomeric radical results in a higher polymerization rate; in addition, the influence of the polar effects becomes larger for more stable radicals. Methacrylates containing a pendant phenyl, where π–π stacking plays an important role, are experimentally found to have a higher polymerization rate than predicted.

     

胆道梗阻后胆汁中自由基反应及其在胆石形成中的作用

作者通过临床标本及动物实验,观察胆汁中超氧化物歧化酶(SOD)、过氧化脂质(LPO)、β-葡萄糖醛酸苷酶(β-G)、总胆红素(TB)及总蛋白(P)等的变化,对胆道梗阻后胆汁中自由基反应及其在胆石形成中的作用进行了研究。结果发现:原发性肝胆管结石和/或胆道梗阻病人术中胆汁的SOD和LOP升高,显示自由基反应增强,切除病灶或解除梗阻后则逐渐下降。动物实验证明,兔胆道梗阻后,同样使胆汁中SOD和LPO显著上升,并伴随有组织性β-G,TB,及P的含量明显增加。组织性β-G和TB变化与SOD相关。提示胆道梗阻,胆管内压增高,可通过增强自由基反应途径使胆汁成份发生变化,导致胆石形成。     

ESR Detection of Propagating Radical Species during RAFT‐Mediated Polymerization

Summary: ESR spectroscopy directly detected both propagating and intermediate radicals during RAFT‐mediated reactions of styrene and methyl acrylate. Their nature and concentrations during the initialization period were significantly different from those thereafter. The dominant radicals during the initialization period were initiator‐ and R‐group derived, and the intermediate radicals were both different and of lower concentration than during the subsequent steady state polymerization.

     

快速减压后大鼠肺组织自由基含量的变化

采用ＥＰＲ波谱义测定肺组织内自由基变化以评价快速减压对肺的损伤。把ＳＤ大鼠在０．５ＭＰａ空气中暴露６０ｍｉｎ，用１ｍｉｎ匀速减至常压，然后分别在４５ｍｉｎ和９０ｍｉｎ时腹腔放射处死，取肺０．７５ｇ匀浆后用ＥＰＲ波谱仪测定维生素Ｃ自由基强度。结果显示减压后４５ｍｉｎ肺组织内ＶＣ强度无明显变化，减压９０ｍｉｎ组的肺组织内ＶＣ强度明显增高，表明快速减压可引起肺组织自由基增加。     

家兔MSOF时氧自由基与微循环改变

对8只MSOF兔做了全血及组织匀浆中SOD、MDA、GSH含量测定,同时做了球结膜微循环动态观察。结果显示:兔MSOF时,血SOD、GSH显著降低,MDA显著升高,肝组织匀浆中SOD含量下降,MDA升高。肾组织匀浆中MDA显著升高,GSH显著降低,脑组织匀浆中MDA也显著升高。并观察到兔MSOF时球结膜微循环的形态、流态、襻周状态加权积分值均较正常时显著升高。     

Kinetic and ESR studies on radical polymerization. Radical polymerization behavior of N-octadecylmaleimide in benzene

The polymerization of N-octadecylmaleimide ( 1 ) initiated with azodiisobutyronitrile ( 2 ) was investigated kinetically in benzene. The overall activation energy of the polymerization was calculated to be 94,2 kJ·mol^?1. The polymerization rate (R_p) at 50°C is expressed by the equation, R_p = k[ 2 ]^0,6[ 1 ]^1,7. The homogeneous polymerization system involves ESR-detectable propagating polymer radicals. Using R_p and the polymer radical concentration determined by ESR, the rate constants of propagation (k_p) and termination (k_t) were evaluated at 50°C. k_p (33 L · mol^?1 · s^?1 on the average) is substantially independent of the monomer concentration. On the other hand, k_t (0,3 · 10⁴ – 1,0 · 10⁴ L · mol^?1 · s^?1) is fairly dependent on the monomer concentration, which is ascribable to a high dependence of k_t on the chain length of rigid poly( 1 ). This is the predominant factor for the high order with respect to the monomer concentration in the rate equation. In the copolymerization of 1 (M₁) and St (M₂) with 2 in benzene at 50°C, the following copolymerization parameters were obtained: r₁ = 0,11, r₂ = 0,09, Q₁ = 2,1, and e₁ = +1,4.     

Flies,worms and the Free Radical Theory of ageing

Drosophila and Caenorhabditis elegans have provided the largest body of evidence addressing the Free Radical Theory of ageing, however the evidence has not been unequivocally supportive. Oxidative damage to DNA is probably not a major contributor, damage to lipids is assuming greater importance and damage to proteins probably the source of pathology. On balance the evidence does not support a primary role of oxidative damage in ageing in C. elegans, perhaps because of its particular energy metabolic and stress resistance profile. Evidence is more numerous, varied and consistent and hence more compelling for Drosophila, although not conclusive. However there is good evidence for a role of oxidative damage in later life pathology. Future work should: 1/ make more use of protein oxidative damage measurements; 2/ use inducible transgenic systems or pharmacotherapy to ensure genetic equivalence of controls and avoid confounding effects during development; 3/ to try to delay ageing, target interventions which reduce and/or repair protein oxidative damage.