The effect of high speed electrons on the structure of polystyrene

Slovokhotova, N.A.; Il'icheva, Z.F.; Kargin, V.A.

doi:10.1016/0032-3950(62)90452-5

Cited by 3 publications

(2 citation statements)

References 6 publications

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“…76 ppm where at least six resonances are observed, see Figure 2. Thus 13 C NMR strongly supports the formation of propyl and vinylidene end groups in agreement with the observations of Slovokhotova et al 19 based on IR analysis of PP irradiated at…”

Section: Resultssupporting

confidence: 79%

A 13C NMR Study of End Groups and Stereoregularity Changes Induced by γ Irradiation of Molten Polypropylenes

Busfield

Hanna

1991

Polym J

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ABSTRACT:Samples of predominantly isotactic and syndiotactic polypropylenes have been irradiated with gamma rays to high doses in the molten state. Solution state 13 C NMR analysis has identified propyl, vinylidene, and isopropyl end groups. The yield of the former shows that the extent of chain scission in isotactic polypropylene is strongly dose dependent with an initial G value of 11.6 reducing to 5.5 at doses greater than 500 kGy. Molecular weight measurements suggest that G(crosslink) is approximately independent of dose with a values of 3.5. The triad sequence contents of the polymers after 2 MGy irradation in the molten state, show that an equilibrium triad distribution has not been achieved, even though the rates of change of triad sequences are virtually zero by this dose. Initial rate kinetics suggests that this is mainly due to the preferential formation of syndiotactic sequences from isotactic ones.KEY WORDS Irradiation / Polypropylene / End Groups / Stereoregularity Changes/ 13 C NMR / Chain Scission / Crosslinking / In recent work 1 -3 we have established that irradiation ofisotactic polypropylene, PP, with gamma or electron radiation induces relatively large changes in the stereochemistry 1 and that both the size and detailed nature of these changes are morphology 2 and dose rate 3 dependent. For example the G values for the loss of pure isotactic pentad sequences when samples of annealed PP were irradiated with gamma radiation, dose rate 4.4kGyh-1 , at ambient temperature and at 200°C (molten sample) were -94 and -283, respectively. When the same sample was irradiated in an electron beam, dose rate 720 kGy h -1 , at ambient temperature, the corresponding G value was -220. The first difference suggests that sterochemical change only occurs in the amorphous regions, as the ratio correlates well with the fraction of amorphous component in the solid state. This is reasonable when * To whom correspondence should be addressed.considering the conclusions of Keller et al. 4 which suggest that neither crosslinking nor chain scission occur within the crystalline regions of polyethylene when subjected to high energy irradiation. The large dose rate effect on the other hand, was explained by a difference in mechanism. An analysis of the full pentad sequence distributions indicated that the deposition of one quantum of energy at the high dose rate resulted in an average of five inversions on mainly alternate monomer units, whilst at low dose rate an energy quantum promoted an average of two inversions on nearby monomer units. In the latter case the distribution was more random, lying somewhere between adjacent and alternate.The detailed chemical mechanism of the inversion is unclear. The observed G values are many times greater that those observed for any other irradiation induced chemical effect in PP,

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Section: Resultssupporting

confidence: 79%

A 13C NMR Study of End Groups and Stereoregularity Changes Induced by γ Irradiation of Molten Polypropylenes

Busfield

Hanna

1991

Polym J

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“…trans-Vinylene groups, which, at that time, were observed after reactor irradiation (γ and neutrons), were not detected under pure γ radiation. 2 The increase of the band at 815 cm -1 was attributed by Slovokhotova et al 8 to cyclohexadiene cross-linked to a phenyl group. Changes in the UV spectrum indicate the formation of conjugated double bonds.…”

Section: Introductionmentioning

confidence: 90%

Irradiation of Atactic Polystyrene: Linear Energy Transfer Effects

et al. 2008

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Atactic glassy polystyrene (PS) has been irradiated in anoxic conditions by electron and ion beams. The induced modifications were followed, in situ, by Fourier transform infrared spectroscopy (FTIR). In-film modifications and hydrocarbon gas release were followed. In-situ measurements allowed one to avoid any spurious oxidation of the films after irradiation and also permitted studying in detail the evolution with dose of the FTIR spectra. The data were quantitatively analyzed, and we present a complete analysis of the effects of the Linear Energy Transfer (LET) on the radiation chemical yields of several radiation-induced modifications (alkynes, allenes, alkenes, benzene, and disubstituted benzenes). For a better understanding of the LET effects, the in-film modifications are compared to H2 release data from the literature and to our measurements of hydrocarbon gaseous molecule yields obtained by us. The overall destruction yield becomes very significant at high LET, and the radiation sensitivity of this aromatic polymer merges with typical values of aliphatic polymers: the radiation resistance conferred at low LET to polystyrene by the phenyl side groups is lost at high LET. This loss of radiation resistance equally affects the aromatic and aliphatic moieties. Monosubstituted alkynes are created above a LET threshold, whereas the other radiation-induced modifications are observed in the whole LET range. Several observations indicate that the phenyl ring is broken at high LET. Comparison of the alkyne yield in PS, polyethylene, and polycarbonate as well as the formation of nitrile bonds in poly(vinylpyridine- co-styrene) are consistent with a cleavage of the phenyl ring as the prominent source of alkynes. As the competing damage mechanisms do not have the same LET evolution, the relative importance of a specific modification on the global damage depends on LET. Some (benzene and disubstituted benzenes) dominate at low LET, while others (in-film alkyne and acetylene release) dominate at high LET.

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The photooxidation of polymers. II. Photolysis of polystyrene

Grassië¹,

Weir²

1965

J of Applied Polymer Sci

106

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SynopsisIn the vacuum photolysis of polystyrene films at 28°C. under 2537 A. radirttion the only gaseous product is hydrogen. At the same time the polymer becomes insoluble and discolors. The intensity exponent of the reaction is unity, the quantum yield of hydrogen is 4.3 X the overall energy of activation is 2.9 kcal./mole, and the rate of photolysis is independent of molecular weight. No hydrogen is produced when 3650 A. radiation is used. These observations can be interpreted in terms of a simple reaction scheme in which the primary effect of the 2537 A. radiation is to liberate hydrogen atoms. The subsequent reaction of these and the polystyryl radicals simultaneously formed in a number of competing steps results in the appearance of hydrogen, the occurrence of crosslinking, and the production of carbon-carbon unsaturation in the main chain which ultimately leads to conjugation and color. These theories are s u p ported by infrared and ultraviolet spectral measurements and by the observation that the rate of photolysis is accelerated by nitrogen.

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The effect of high speed electrons on the structure of polystyrene

Cited by 3 publications

References 6 publications

A 13C NMR Study of End Groups and Stereoregularity Changes Induced by γ Irradiation of Molten Polypropylenes

A 13C NMR Study of End Groups and Stereoregularity Changes Induced by γ Irradiation of Molten Polypropylenes

Irradiation of Atactic Polystyrene: Linear Energy Transfer Effects

The photooxidation of polymers. II. Photolysis of polystyrene

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