ISSN:
0022-3832
Schlagwort(e):
Chemistry
;
Polymer and Materials Science
Quelle:
Wiley InterScience Backfile Collection 1832-2000
Thema:
Chemie und Pharmazie
,
Physik
Notizen:
A general expression for the crosslinking efficiency in saturated polymers by added free-radical initiators is derived on the basis of a steady-state kinetic treatment of the following reactions: (a) dissociation of initiator to form R· radicals; (b) transfer to produce P· polymer radicals; and (c) the three recombination reactions of P· and R· radicals, only one of which (P· + P·) produces a polymer crosslink. The instantaneous crosslinking efficiency (crosslinks formed per molecule of initiator decomposed) is given by: C = (k[I]1/2 + 1)-2, where [I] is the instantaneous concentration of initiator and k is constant for a given polymer-initiator system at constant temperature. Depending on the value of k[I]1/2 compared to unity, C may vary from zero to unity. An average value C̄ of C and therefore the crosslink concentration for any degree of decomposition of the initiator is given by an integrated form of the above expression. These kinetic expressions are confirmed by experimental results on the crosslinking of a polydimethylsiloxane polymer by benzoyl peroxide at 125°C. (previously reported work) and by dicumyl peroxide at 170°C. (present work). Both experiment and theory suggest that with polymers such as dimethylsiloxanes, which are more resistant to free-radical attack, ionizing radiation may have unique advantages over conventional chemical initiators for the production of polymer radicals for crosslinking or graft polymerization.
Zusätzliches Material:
4 Ill.
Materialart:
Digitale Medien
URL:
http://dx.doi.org/10.1002/pol.1960.1204214012
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