Electron spin resonance study of γ-irradiated poly(methacrylic acid)

Low temperature relaxations in poly(methacrylic acid) (PMAA) have been studied by electron spin resonance (ESR) spectroscopy. The observed 8 line ESR spectra of irradiated PMAA in the temperature range 77-300K (LNT-RT) is attributed to the free radicals of the type ～ CH₂? CH? CH₃. Assignment of ESR spectra to free radicals has been made on the basis of magnetic parameters employed to simulate ESR spectra at different temperatures. Further, ESR spectra below LNT have been simulated, using the set of parameters employed to simulate the experimental spectrum at LNT. Magnetic parameters of the ESR spectra at LNT and below LNT indicate γ- and δ-relaxations of PMMA chains. © 1994 John Wiley & Sons, Inc.     

Electron spin resonance study of γ-irradiated poly(acrylic acid)

Electron spin resonance (ESR) spectra of poly(acrylic acid) (PAA) γ-irradiated in air at room temperature and recorded at room temperature and at liquid-nitrogen temperature have been studied to identify the radiation products. The ESR spectra are composed of eight lines with hyperfine splittings of 23 ± 1 G and 11 ± 1 G. The method of least-squares total curve fitting, employing the Lorentzian line shape function, to the observed spectra enabled the assignment of the spectra. Computed spectra obtained by the superposition of a singlet and the spectra due to chain radicals are considered to give the best fits to the observed ESR spectra. The singlet is assigned to the radicals COOH, and the component 10-line spectra are assigned to the chain radicals CH₃? CH? CH₂ ～ and/or ～ CH₂? CH? CH₂ ～. The observed change in line shape with temperature of the ESR spectra is attributed to the hindered oscillations of the methyl groups about the C_α? C_β bond axis of the chain radicals. The existence of the methyl groups is confirmed by the measurement of infrared absorption.     

Electron spin resonance of γ-irradiated poly(ethylene 2,6-naphthalene dicarboxylate)

The two types of radicals trapped in γ-irradiated poly(ethylene 2,6-naphthalene dicarboxylate) (PEN 2,6) have been identified by ESR as ? O? CH? CH₂? O? (radical I) and a radical located on the naphthalene ring (radical II). The relative concentrations of radicals in the gross polymer are 10–20% radical I and 80–90% radical II. Similar trapped radicals have been identified in γ-irradiated poly(ethylene terephthalate) (PET), a structurally related polymer which differs only in the aromatic moiety, but the relative radical concentrations are quite different. These results are discussed in relation to the radiation resistance of the two polymers.     

Thermal and photo-induced phenomena in γ-irradiated poly(methyl methacrylate)

ESR spectra and optical absorption spectra of γ-irradiated poly(methyl methacrylate) (PMMA) at 77°K and the photo- and thermal bleaching behavior have been studied. γ-Irradiation of PMMA yields a singles spectrum with a line width of 6 G which is bleachable with visible light. This species is assigned to the polymer cation. The unbleached species consists mainly of a four-line spectrum and is assigned to a polymer radical having a different CH₂ conformation from the usual nine-line spectrum. On subsequent warming to room temperature, the spectrum changes into the nine-line spectrum. γ-Irradiation of PMMA containing biphenyl as an additive at 77°K gives biphenyl cation. Yield of polymer radical is reduced by the addition of biphenyl and 2-methyltetrahydrofuran. A mechanism is proposed which is consistent with the experimental results.     

Synthesis of poly(γ-methoxypropylmethylsilylene) and poly(γ-methoxypropylmethylsilylene-co-di-n-hexylsilylene)

The synthesis of γ;-methoxypropylmethyldichlorosilane, and its subsequent polymerization and copolymerization with di;-n;-hexyldichlorosilane through the reductive coupling with sodium has been accomplished. The resulting polymers contain methyl ether side groups that allow further synthetic transformations on the polysilane backbone. For poly (γ;-methoxypropylmethylsilylene) these groups impart solubility characteristics different than typical alkyl and aryl substituted polysilanes. These new polymers and copolymers have been characterized by GPC and ¹H-, ¹³C-, and ²⁹Si-NMR. © 1994 John Wiley & Sons, Inc.     

An electron spin resonance (ESR) and simultaneous electrochemical and electron spin resonance (SEESR) spectroscopic study of motion, stability and potential controlled release of radical guests from the β-cyclodextrin inclusion polymer

The influence of molecular inclusion and separation of radical guests inside the amorphous β-cyclodextrin host polymer (β-CDP) matrices on the motion and stability as well as controlled potential release of radicals was studied by electron spin resonance spectroscopy (ESR) and simultaneous electrochemistry and electron spin resonance (SEESR) spectroscopy. A pronounced restriction of rotational motion was observed for the included stable protonated form of the 4-amino-2,2,6,6-tetramethylpiperidine-1-oxyl (4-amino-TEMPO) free radical and a partial restriction of motion of the NN,N',N'-tetramethyl-1,4-phenylenediamine (TMPD^.+) radical (generated ex situ by controlled potential electrolysis), while virtually no restriction was found in the case of the methyl (MV^.+) and heptyl viologen (HV^.+) monocation radicals as well as of the 2-nitrotoluene anion radical (2NT^.− ). The MV^.+, HV^.+ and 2NT^.− unstable radicals were electrochemically generated inside the β-CDP film coat at a Pt flag electrode. The rate of the open-circuit decay of the included unstable radicals was markedly decreased as compared with their decay at the bare electrode. It was also found that the extent of inclusion of alkyl viologens was governed by their ionic charge, i.e. the higher the charge of the ion the weaker its inclusion.     

Ionic species in γ-irradiated poly(methyl methacrylate) at 77°K

Ionic species in poly(methyl methacrylate) (PMMA) have been studied by optical absorption and ESR spectrometry. γ-Irradiation of PMMA containing aromatic solutes gave rise to the absorption spectra of corresponding cation radicals. The G value for the formation of cation radicals was determined to be 1.5. Anionic radicals of the solutes were not detected for the aromatic solutes studied. Anionic species of pure PMMA were identified by both absorption spectra and ESR spectra. It has an absorption maximum at 440 nm. A sharp singlet with a line width of about 5 G which was found by ESR spectrometry was tentatively assigned to the trapped electron of PMMA. The results show that a large number of electron traps in PMMA may exist on the ester side chain themselves.     

The grafting of acrylamide onto poly(ε‐caprolactone) and poly(1,5‐dioxepan‐2‐one) using electron beam preirradiation. II. An in vitro degradation study on grafted poly(ε‐caprolactone)

Acrylamide was graft polymerized onto the surface of a biodegradable semicrystalline polyester, poly(ε‐caprolactone). Electron beam irradiation at a dose of 5 Mrad was used to generate initiating species in the polyester. The degradation in vitro at pH 7.4 and 37°C in a phosphate buffer solution was studied for untreated, irradiated and acrylamide‐grafted polymers. In the case of poly(ε‐caprolactone), all materials showed similar behavior in terms of weight loss. No significant decrease in weight was observed up to 40 weeks, after which the loss of weight accelerated. The main differences in degradation behavior were found for the average molecular weights, M̄_n and M̄_w. Virgin poly(ε‐caprolactone) maintained M̄_n and M̄_w up to about 40 weeks, whereas the irradiated and grafted poly(ε‐caprolactone) showed similar continuous declines in M̄_n and M̄_w throughout the degradation period. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1651–1657, 1999     

Electron paramagnetic resonance spectroscopy of γ-irradiated cellulose and related compounds

EPR studies were carried out on different irradiated cellulosic materials. The shape of the EPR spectrum was found to depend upon the fine structure of cellulose. The peak-to-peak distances of the large peaks on the differential curves were found to be 23.3 and 24.8 gauss, respectively, for the amorphous and recrystallized cellulose. The number of free radicals present per unit weight in the recrystallized cellulose and in the amorphous cellulose were found to be in the ratio of 2.1:1. The EPR spectrum of a sample of irradiated cotton crystallites which was soaked in acetone before being dried was markedly symmetrical, in contrast to the EPR spectra of samples of cotton linters and of cotton crystallites dried from water, and was considered to be a reflection of the lower intermolecular bonding in the former. For corresponding doses, the free radicals on cotton crystallites have the highest g value, followed by cotton linters, followed by regenerated cellulose I. The g value decreased as the irradiation dose was increased.     

The preparation of poly(N-acetyl-α-amino acrylic acid) [poly(N-acetyl dehydroalanine)] and poly(α-amino acrylic acid) (polydehydroalanine)

Poly(N-acetyl-α-amino acrylic acid) was prepared by a free radical polymerization reaction. Mild alkaline hydrolysis of the polymer product yielded a second polymer poly(α-amino acrylic acid) (polydehydroalanine). Both polymers exhibited certain polyelectrolyte behavior, although the latter did not behave as expected for an amphoteric polyelectrolyte.     

High resolution electron microscopy of β‐poly(ethylene naphthoate)

The β phase of poly(ethylene naphthoate) is suggested by high resolution electron microscopy and electron diffraction data to be monoclinic, with a = 1.320 nm, b = 0.962 nm, c = 1.300 nm, α = 131.50°, β = 90°, and γ = 90° and space group P2₁/n 1 1. A model structure has been presented which accounts quantitatively for the observed intensities of the hk0 reflections and provides qualitative agreement with the hkl data.     

ESR study of γ-irradiated 1,3,5-trithiane and its derivatives

Radicals formed in γ-irradiated 1,3,5-trithiane and its derivatives at room temperature have been studied by ESR spectroscopy. ESR evidence establishes that 1,3,5-trithiane as well as α- and β-2,4,6-trimethyl-1,3,5-trithiane yield radicals mainly by loss of the hydrogen atom, whereas α- and β-2,4,6-triphenyl-1,3,5-trithiane and 2,4,6-trimethyl-2,4,6-triphenyl-1,3,5-trithiane produce radicals that are parent radical cations, which are also present in small amounts in aliphatic trithianes. Furthermore, in all the spectra examined R–S^.-type radicals are observed. The probable initiation process of radiation-induced 1,3,5-trithiane polymerization is discussed briefly.     

Simulation study of poly(γ-benzyl-l-glutamate) in dimethylformamide

We perform atomistic Molecular Dynamics simulations of Poly(γ-Benzyl-L-Glutamate) (PBLG) in Dimethylformamide (DMF) to study the structure and some dynamic aspects of the complex side chain - solvent interface. In addition, we investigate the elastic behavior of PBLG with the emphasis on the determination of the persistence length.