Polyethylene model compounds

Very recently. LET effects on fluorescence lifetimes of low molecular polyethylene model compounds (n-alkane) have been studied by many kinds of pulse radiolysis - methods such as electron beam, ion beam and synchrotron radiation (SR) [40] pulse radiolysis techniques [41]. Figure 10 shows time profiles of the fluorescence from neat n-dodecane liquids irradiated many kinds of radiation with different LET. The fluorescence lifetimes from irradiated neat... 

Very recently LET effects of ion beams on both standard polymers such as polystyrene and low molecular polyethylene model compounds (n-alkanes) have been studied by time-resolved spectroscopic methods, that is, ion beam pulse radiolysis techniques. Further basic studies are necessary so that the detailed mechanisms of ion beams on polymers can be clarified, especially LET effects and high density excitation effects. 

Model Compounds. Many of the complexities associated with practical polymers and the many simultaneous reaction pathways can be avoided by using model compounds. A typical one is eicosane (n-C20Hi 2) which forms single crystals similar to those in the crystalline regions of polyethylene (58-60). More work is needed on similar compounds and on low molecular weight oligomers to establish both the species produced and the kinetics of their reactions (61,62). 

Figure 2. Adiabatic potential curves in the main chain scission of a model compound of polyethylene ethane (9) Alg (O) Alu (U) A2g (Q) A2u (A) Eg (A) Eu (-------------------------) singlet (---) triplet (4)...

The intramolecular mobility, which yields many other conformations between these two extremes, is the basis for viscoelasticity in polymers. Pendant groups, such as the methyl group in isobutane, and lower temperatures decrease the mobility of model compounds such as ethane as well as the polymer chains of polyethylene. 

In order to investigate the structure of crosslinked polyethylene by, 3C NMR the model compound l,l,2,2-tetra(tridecyl)ethane, i.e. two molecules of n-C27H56 linked at the C-14 atoms, was prepared. The tertiary 13C-14 atoms give rise to a resonance signal at 39.5 ppm. Spectra of long chain n-paraffins eicosane (C20H42) and hexacosane (C26H54) exposed to 5 MGy y-radiation above their respective... 

Effect of Chemical Modification with Polyethylene Glycol on the Brightness Stability of Lignin Model Compounds and High-Yield Pulp... 

In evaluating the energetics of oxidizers, it is apparent that the perchlorate salts are more desirable than nitrate salts. Therefore one would expect that attempts would be made to incorporate the perchlorate group into binder structures. The study of perchlorate esters was not pursued when it was found that simple model compounds obtained from alcohols and perchloric acid were excessively shock sensitive. However, when the C104 group existed in ionic or salt-like form, these materials were found to be far less sensitive. Bell Aerosystems Corp., in conjunction with the Food Machinery Corp. prepared the polyethylene hydrazine perchlorates. 

The linear polyethers are model compounds to show the effect of the insertion of one oxygen atom at different positions into the polyethylene -CH2-CH -repetitive unit. What will be the influence on the polymer XPS valence band spectrum, compared to the one of polyethylene (Figure 2) Our study was conducted on three materials poly(methylene oxide) or PMO, poly(ethylene oxide) or PEO, and poly(tetramethylene oxide) or PTMO, that are... 

I = 21 y = 0.394 r = 0.9476 F = 49.8 where log P is the hydrophobicity, bondrefr is the molecular refractivity, delta is the submolecular polarity parameter, ind indicator variable (0 for heterocyclics and 1 for benzene derivatives). Calculations indicated that PBD-coated alumina behaves as an RP stationary phase, the bulkiness and the polarity of the solute significantly influencing the retention. The separation efficiency of PBD-coated alumina was compared with those of other stationary phases for the analysis of Catharanthus alkaloids. It was established that the pH of the mobile phase, the concentration and type of the organic modifier, and the presence of salt simultaneously influence the retention. In this special case, the efficiency of PBD-coated alumina was inferior to that of ODS. The retention characteristics of polyethylene-coated alumina (PE-Alu) have been studied in detail using various nonionic surfactants as model compounds.It was found that PE-Alu behaves as an RP stationary phase and separates the surfactants according to the character of the hydrophobic moiety. The relationship between the physicochemical descriptors of 25 aromatic solutes and their retention on PE-coated silica (PE-Si) and PE-Alu was elucidated by stepwise regression analysis. 

The estimation of chemical shifts by examining the spectra of model compounds is not always feasible, and the prediction models fail to distinguish between two or more stereosequences as they cannot always be distinguished on the basis of intensity alone. To overcome these limitations, large numbers of organic compounds have been analyzed by NMR and their chemical shifts have been used to determine a set of empirical correlations that are used to determine the structure based on the polymer s NMR spectrum. The carbon chemical shifts of hydrocarbon-based polymers such as polyethylenes can be predicted by empirical additivity rules such as ... 

There is an enormous body of work on quasielastic neutron scattering from polymers [1,2]. There is a smaller literature on neutron vibrational spectroscopy of polymers but this has had a significant impact on the characterisation of these materials. Crystalline or semi-crystalline polymers are the most important class of polymers commercially. The most-studied and technologically most important of these is polyethylene and this will be considered in some depth and we will highlight the use of the n-alkanes as model compounds ( 10.1.2). We will then see how these concepts can be transferred to polypropylene ( 10.1.3), nylon ( 10.1.4), and conducting polymers ( 10.1.5). Non-crystalline polymers ( 10.2) have been much-less studied by INS. As examples, we will consider polydimethylsiloxane ( 10.2.1) and advanced composites ( 10.2.2). 

Molecular weight cutoff It refers to be smallest molecular weight of a macrosolute for which the membrane shows at least 90% rejection. This value is typically determined imder a set of well-defined conditions using model compounds (e.g., polyethylene glycols, dextrans and proteins such as BSA) at low concentration. 

Time resolved spectroscopy has developed assignments of intermediate species in radiation chemistry as revealed in the other sections. However, because solid polymers are less transparent, the works obtained so far seem to be limited mainly to polymer solution systems or liquid model-compounds. The lifetime of intermediates depends on LET the fluorescence lifetime of n-dodecane is shorter for higher LET radiation [83], which was studied as liquid model compounds for polyethylene. The observation is attributed to scavenging upon encountering of intermediates. Light emission from excimers of solid polystyrene has constant lifetime irrespective to LET [84], whereas polystyrene... 

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