ISSN:
0022-3832
Keywords:
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Physics
Notes:
The previous paper discusses the effect of physical state during the irradiation on the fate of the polymer radicals produced. Additional experiments relating to trapped radicals in hydrocarbon polymers are discussed. Three different methods of detection were used; namely, infrared absorption at 5.8 μ, electron paramagnetic resonance, and gasuptake by the irradiated polymer. Conditions for producing trapped radicals at room temperature are that the polymer exist in the crystalline, glassy, or highly crosslinked form during irradiation. Radicals trapped in the crystalline or glassy areas can dissipate either as the result of heating the polymer above Tm or Tg or else by exposure to a radical scavenger, e.g., oxygen or ethylene. The lifetime of radicals trapped in Marlex-50 can be many thousands of hours at room temperature. Radical decay will take place even with storage in vacuum if given enough time. The decay is arrested by holding the sample at liquid nitrogen temperature. Loss in radical activity in Marlex-50 when stored in vacuum is due mainly to delayed crosslinking. Trans-vinylene and vinyl do not appear to enter into the reaction responsible for the decay. A comparison of the decay of radicals trapped in unbranched Marlex-50 with that in a branched low-density polyethylene when stored in ethylene, oxygen, and vacuum was made. The results suggest that although radicals are trapped in the crystalline regions of both polymers, there are differences between the two crystals - the crystals in the low-density polymer do not appear to be as tight as those in the Marlex-50. Delayed oxidation reactions occurring in the crystalline regions of irradiated Marlex-50 when stored in oxygen at room temperature require a number of intermediate steps before appearing as carbonyl. An average of 5 molecules of oxygen per polymer radical was used in forming carbonyl. Delayed main chain scissions occur during this process which cause severe embrittlement and loss in physical properties. Significant improvements in physical properties of Marlex-50 can be achieved through irradiation, but radicals must not be left trapped in the polymer.
Additional Material:
7 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1958.1203212502
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