ISSN:
0360-6376
Keywords:
Physics
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Polymeric methacrylates functionalized with free methacryloyl groups are efficiently crosslinked in the presence of transition-metal carbonyls on UV irradiation of the polymeric solid. The reaction proceeds by a radical chain mechanism with a kinetic chain length of about 10 in a solvent-free polymer containing 10-3 mole of methacryloyl groups per cm3. The chain length increases steeply when the glass transition of the polymer is reached, either by plastification or by an increase in temperature. The temperature dependence of the crosslinking yield below the glass transition is consistent with an activation energy of about 9 kcal mole-1. The addition of acrylic monomers enhances chain propagation by up to an order of magnitude. Postirradiative crosslinking in the matrix comes to a standstill well before all acrylic groups or radicals have been exhausted: if, after cessation of the primary reaction, the matrix is briefly heated, a second crop of crosslinks is obtained without further exposure. The system behaves thus as if the radicals had been removed into traps from which they can be set free by thermal activation. From an analysis of the reaction kinetics it appears that in the glassy polymer 90% of the radicals are inactivated in this way. Radical recombination, however, is the principal mechanism of chain termination above the glass transition. From the kinetic data, diffusion coefficients for polymer-bound groups are found to be in the range of 10-17-10-16 cm2 sec-1 in the glassy polymer at room temperature. They are of the order of 10-14 cm2 sec-1 in plasticized films above the glass transition.
Additional Material:
8 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/pol.1979.170171021
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