1-HEPTENE, 3-HEPTENES AND CUMENE AS MODEL COMPOUNDS OF SBS BLOCK-COPOLYMERS - STUDY OF THEIR PHOTOREACTIONS IN THE PRESENCE OF PHOTOINITIATORS OF POLYMERIZATION

The photoreactions of 1-heptene, 3-heptene and cumene in the presence of unimolecular and bimolecular reaction photoinitiators (1,1-dimethox y-1-phenyl-acetophenone, DMPA, and benzophenone, BP) has been investig ated. Quantum yields of the reactions and identification of the photor eaction products has permitted to elucidate the steps and the mechanis m of the mentioned photoreactions. This helps to know the reactions wh ich take place in more complicated systems, such is the case of the ph otopolymerization of acrylic monomers in SBS block copolymer matrices, of which these compounds could serve as models. For heptene derivativ es, the photoreaction in the presence of BP takes place through direct abstraction of an allylic hydrogen atom, and in minor extension, of o ther hydrogen atoms of the heptene aliphatic chain. As the main form o f termination, the heptenyl and the ketyl radicals formed coupled insi de the solvent cage. Photoreaction in the presence of DMPA occurs by d irect attack of the radicals formed from the initiator (PhCO., Ph(MeO) (2)C-., and CH3.) to the heptene double bond. When this double bond is terminal oligomerization occurs. For cumene, the photoreaction takes place through direct abstraction of the benzylic hydrogen atom in both cases. (C) 1997 Elsevier Science S.A.