Synthesis and Polymerization of N-(L-Menthylcarboxylatomethyl)maleimide

A new type of optically active N-(L-menthylcarboxylatomethyl)maleimide (MGMI) was synthesized from maleic anhydride, glycine, and L-menthol. Radical homopolymerization of MGMI was performed at 50°C for 24 h to give optically active polymer having [α]_D = -57°. Radical copolymerizations of MGMI (M ₁) were performed with styrene (ST, M ₂), methyl methacrylate (MMA, M ₂) in benzene at 50°C. From the results, the monomer reactivity ratios (r ₁, r ₂) and the Alfrey-Price Q, e values were determined as follows: r ₁ = 0.16, r ₂ = 0.006 for the MGMI-ST system; r ₁ = 0.15, r ₂ = 1.65 for the MGMI-MMA system, and Q ₁ = 0.72, e ₁ = 1.59 calculated from the MGMI-MMA system. Anionic homopolymerizations of MGMI were also carried out. Chiroptical properties of the polymers were investigated.     

Scission induced by circular shear and heat conduction in an elastomeric cylinder

Constitutive equations for the thermo-mechanics of elastomeric materials generally assume that they do not undergo microstructural change. A constitutive theory is discussed here which accounts for such changes arising from continuous scission of macromolecular junctions of elastomeric networks due to deformation and high temperatures and the subsequent cross-linking of molecules into new networks with new reference states. The total stress is the superposition of the stresses in the remainder of the original network and in each subsequently formed network. Each network acts as a temperature-dependent non-linear elastic material. The interaction of this material response with inhomogeneous deformation and temperature fields is studied for finite circular shear of a cylinder. Numerical results illustrate how the mechanical response of the cylinder depends on the temperature dependence of both the scission–cross-linking process and the properties of the elastic networks.     

Chemorheological response of elastomers at elevated temperatures: Experiments and simulations

An experimental study and a method for simulating the constitutive response of elastomers at temperatures in the chemorheological range (90-150 °C for natural rubber) are presented. A comprehensive set of uniaxial experiments for a variety of prescribed temperature histories is performed on natural rubber specimens that exhibit finite elasticity, entropic stiffening with temperature, viscoelasticity, scission, and oxygen diffusion/reaction effects. The simulation approach is based on a multi-network framework for finite elasticity, isothermal incompressibility, thermal expansion, and temperature-induced degradation. The model extends previous work to account for kinetics of scission for arbitrary time-varying temperature histories and incorporates the effects of viscoelastic relaxation and diffusion-limited oxidative scission. The model is calibrated to experiments performed on a commercially-available filled natural rubber material, and numerical simulations are compared favorably to experiments for a variety of temperature histories.     

Combined deformation- and temperature-induced scission in a rubber cylinder in torsion

When an elastomeric material is deformed and subjected to temperatures above some characteristic value T_cr (near for natural rubber), it undergoes time and temperature dependent chemical changes consisting of scission and crosslinking of its macromolecular structure. The process continues until the temperature decreases below T_cr. Experiments carried out in uniaxial extension have shown that the chemical changes are independent of stretch ratio within moderate stretches. It is reasonable to expect that the chemical changes would be affected by sufficiently large deformations, an interaction referred to as ‘mechanochemistry’. A kinetic theory of the breakdown of solids by Zhurkov [Kinetic concept of strength of solids, Int. J. Fract. Mech. 1 (1965) 311-323. [15]] attributes this interaction to the lowering of activation energy by mechanical work.In a recent constitutive theory, an expression was developed that relates the chemical kinetics of scission of the original elastomeric network to time, temperature and activation energy. The kinetic theory of Zhurkov suggests a method for modifying this expression to account for the influence of deformation. This is explored in the case of simple shear deformations, such as those occurring during torsion of elastomeric cylinders held at fixed length. Using the approach of Penn and Kearsley [The scaling law for finite torsion of elastic cylinders, Trans. Soc. Rheology 20 (1976) 227-238. [16]], it is shown that experiments in torsion can be used to determine the influence of shear deformations on the chemical kinetics of scission.     

The Th fission valleys

One of the interesting problems in the nuclear fission studies is the nature of the asymmetry of the fission fragment mass distribution (FFMD). In connection with recent experiments, the valleys on the potential energy surface of ²²⁶Th have been considered. The pre-scission nuclear shape calculated as a result of the minimization in multi-dimensional space of the deformation parameters with two constrains is shown to be of the type considered by Brosa et al.     

Effect of the phenolic antioxidants on the structure of gamma-irradiated model polyethylene

High energy radiation has been successfully employed to modify the chemical structure of commercial polymers. It induces at least two types of reaction in polyethylene: crosslinking and chain scission. In addition the efficiency of the radio-induced reactions can be affected by the presence of antioxidants. The purpose of this work is to study the effect of the irradiation on a model polyethylene containing a phenolic type antioxidant. Samples containing 0.1% and 1% by weight of Irganox 1010 (Ciba-Geigy) were irradiated under vacuum at room temperature with different doses of gamma rays from a ⁶⁰Co source. Changes in structure and the average molecular weight were followed by gel permeation chromatography and low angle laser light scattering. The critical doses for gelation were determined as a function of the antioxidant concentration. Theoretical calculations to predict the evolution of molecular structure with extent of radiation were performed using a probability model. The agreement between the calculated and the measured molecular weights is very good.     

Electron irradiation induced microstructural modifications in BaCl2 doped PVA: A positron annihilation study

Thin films of pure and 10 wt% BaCl₂ doped poly(vinyl alcohol) (PVA) were prepared by solution casting method. These films were subjected to electron irradiation for different doses ranging from 0 to 400 kGy in air at room temperature. The effect of electron irradiation on the optical and free volume related microstructures of these polymer films was studied using positron annihilation lifetime spectroscopy, FTIR and UV-vis techniques. The FTIR spectral studies indicate that the electron irradiation induces chemical modifications within the doped PVA, which results in chain scission as well as cross-linking of the polymer. The positron lifetime study on these irradiated polymers shows that the chain scissions and cross-linking within the polymer matrix affect the free volume content and hence the microstructure. The UV-vis optical absorption studies show that the induced microstructural change by electron irradiation also modifies the optical properties. Using UV-vis spectra, the optical energy band gap was estimated and it decreases with increase in electron dose. A correlation between positron results and optical results is obtained and electron irradiation induced microstructure modifications within the doped polymer are understood. The results highlight the usefulness of positron annihilation technique in the study of the microstructure of irradiated polymers.     

A novel donor-π-acceptor anthracene monomer: Towards faster and milder reversible dimerization

A novel functional 2,6-substituted donor-acceptor anthracene derivative, bearing a long alkyl spacer and a polymerizable end-group, is synthesized from readily available compounds. This monomer possesses conjugated electron donor and acceptor moieties to achieve UV absorption and anthracene dimerization at higher wavelengths and under milder conditions, than anthracene and other reported anthracene derivatives. The compound was shown to absorb at higher wavelengths and dimerize much faster compared to most 9-substituted anthracenes. The fast photochemical and relatively slow thermal scission of the dimers were studied and related to the chemical structure, i.e. the 2,6-substitution.     

Novel Copper(II) Thiodibenzoic Acid Coordination Polymers by in situ Extrusion of Sulfur from 2,2′‐Dithiodibenzoic Acid and the Unique Oxidation of Disulfide to Sulfate

Slow diffusion reaction of 2,2′‐dithiodibenzoic acid (dtdb) with CuCl₂ in the presence of N‐donor ligands results in the formation of different coordination polymers where both S–S and C–S scission and oxidation of S is observed. X‐ray diffraction analysis of [Cu(tdb)(phen)(H₂O)]₂ · 2H₂O.2DMF] ( 1 ), [Cu(tdb)(py)₂(H₂O)]₂ ( 3 ), and [Cu(tdb)(bipy)(H₂O)]₂ · 0.5H₂O ( 4 ) (tdb = thiodibenzoic acid, phen = phenanthroline, py = pyridine, bipy = 2,2′‐bipyridine) show that the metal ions are coordinated to the carboxylate oxygen atoms of the in situ generated tdb ligand in a monodenate fashion. In [Cu(phen)(SO₄)₂(H₂O)₂]_n ( 2 ) and [Cu(bipy)(SO₄)₂(H₂O)₂]_n ( 5 ), the sulfur is oxidized to sulfate ions prior to coordination with the metal. Complex 1 has a dimeric structure with π–π interactions between the phen ligands, whereas 3 and 4 form 1D polymeric chains.     

Gamma polymorph and branching formation as inductors of resistance to electron beam irradiation in metallocene isotactic polypropylene

The influence of a wide dose range of electron beam (EB) irradiation is analyzed on films obtained from metallocene isotactic polypropylene (iPP) under two different thermal processing conditions. A greater irradiation resistance is observed in those films with content in γ crystallites higher than in α monoclinic entities in terms of melting temperature variation with irradiation. This change is on the order of 0.5 °C per 100 kGy in slowly crystallized films while a value of 1.5 °C per 100 kGy is found in quenched specimens. On the other hand, dual studies on films and pellets have proved that branching takes place in this metallocene iPP. The scission processes that occur during irradiation cannot account by themselves for the observed changes in molecular weight distribution as demonstrated by simulation. The observed changes in the rheological behaviour of the irradiated iPP corroborate that increasing degrees of branching are generated by the irradiation process.