Spin-labeled polyethylene

ESR spectra of spin-labelled polyethylene and polypropylene mentioned above were observed at various temperatures and the molecular motions at chain ends were discussed. 

Vivatpanachart et al. concluded that exclusion of the chain end from the crystalline region should be a cause of the down shift of the transition temperature after annealing in the case of fractured spin-labelled polyethylene this was based on the comparison of annealing effects in low- and high-density polyethylenes. However, the crystalline structure of isotactic polypropylene should be more bulky than polyethylene since the former has a 3, helix and the latter a planar zig-zag conformation. Therefore, it is reasonable that the spin-labelled chain end of isotactic polypropylene can be included in the thickened crystals after annealing this is a cause of the annealing effect mentioned above, the high temperature shift of the transition temperature. 

Polyethylene films containing carbonylhydrazide groups were treated by radical IV (R = -N=C=S) [91]. The spin-labelled polyethylene was obtained hy the following reaction ... 

Fig. 9.17. Plots of C spin-lattice relaxation times Ti against inverse absolute-temperature for C-labeled polyethylene adsorbed on the surface of silica gel [23].

Glass-Rubber Transition Detected by the Spin Label Method for Polyethylene (PE) Crystallinity Dependence... 

As mentioned already in Sect. 2, changes of the principal value of the g-tensor also give important information on molecular motion in polymeric chains. The spectrum of peroxy radicals shows a typical g-anisotropy and the study on molecular motion by observing peroxy radicals is, therefore, a kind of spin label study of the materials containing peroxy radicals. In the course of studying the oxidation of irradiated polyethylene, an interesting feature of the ESR spectrum of peroxy radicals was found. 

It is interesting to note the annealing in the case of isotactic polypropylene. As shown in Fig. 10.9., heat treatment results in an up shift of the narrowing temperature in region II On the other hand, however, an effect of annealing appeared in the down shift of the transition (narrowing) temperature in the case of fractured polyethylene A similar phenomenon was also reported by Bullock et al. for polyethylene by the spin label method... 

Spin labels were grafted on polyethylene under y-radiolysis in the presence of PBN [116] ... 

The simplest method of spin labelling is to utilise a functional group on the polymer to attach the label, usually via a condensation reaction (Scheme 1). Labels can also be introduced by less rect methods. For example, the Keana synthesis [6] (Scheme 2) has been used to label polyethylene that had been copolymerised with a small amount of carbon monoxide [7]. Polystyrene has been labelled by reacting the lightly lithiated polymer with either 2-methyl-2-nitrosopropane or nitrosobenzene (Scheme 3) [8]. 

It was established that CDs labelled with TEMPO derivatives, Le. spin labelled CDs 32-34 undergo interaction with PEG 600 (PEG = polyethylene glycol) and with PPG 425 (PPG = polypropylene glycol) in concentrated aqueous solutions. The EPR spectra of 32-34 are changed when they are complexed with PEG or PPG. It was observed that the relationship between rotational correlation times (t) and solvent viscosity caimot be described by the Debye-Stokes-Einstein equation, this fact being due to self-aggregation of alkylene glycols in concentrated solutions. However the use of the fractional Debye-Stokes-Einstein equation, i.e. the relationship between relative x values and relative viscosity is in accordance with the experimental data [77]. 

Bullock AT, Cameron GG, Smith PM. Electron spin resonance studies of spin-labeled polymers. 10. Polyethylene containing ketone side groups. Macromolecules 1976a 9 650-653... 

For this reason, the study in question19 examined a sample of high-density polyethylene that was iso topically labelled with, 3C so as to produce isolated 13C spin pairs. Static 13C powder lineshapes were then observed as a function of temperature. Analysis of these by lineshape simulation shows that, indeed, the polyethylene chains do undergo 180° chain flips. The static lineshapes in this case result from the sum of chemical shift anisotropy and dipolar coupling. However, the chemical shift anisotropy is known and, as mentioned previously,... 

Experimentally, we do not have any data on the diffusion of trapped chains in a network. What is available is the diffusion coefficient of a labeled chain in polyethylene melts, measured by two techniques 1) from nuclear spin resonance data, and 2) using deuterated chains as labels, the local concentrations of deuterated/protonated species being probed by infrared measurements. ... 

Figure 3.27 The two-dimensional spin exchange spectrum for semicrystalline polyethylene. The signals along the diagonal are labelled for the crystalline (c) and amorphous (a) peaks. The cross-peaks ac and ca result from exchange between the crystalline and amorphous fractions. Reprinted with permission from ref. 33.

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