Chemical reactions of benzophenone photoirradiated in 1,2-polybutadiene

The photolysis of benzophenone (BP) in 1,2-polybutadiene (1,2PB) was studied at low radiation intensity in order to clarify some aspects of BP photochemistry and of 1,2PB photocrosslinking. The expected primary photoreactions of hydrogen abstraction and carbonyl-vinyl cycloaddition were observed. In addition, it was established that the appearance of light absorbing transients (LATs) is not as significant as in polar media, and that the kinetics of BP consumption are more complicated than for a pseudo monomolecular process. Theories are available for reactions between excited species and BP molecules in ground state. An approximate kinetic model was developed by defining a global BP consumption as the sum of the photoreduction and a BP concentration-dependent term. It was also found that the polymerization of vinyl groups in 1,2PB is probably the most significant crosslinking process and that almost all BP-originating products are bonded into the network of crosslinked chains. Observations of the photolysis of BP in 3-methyl-1-butene were used to estimate what happens in the polymer.

► The photolysis of benzophenone under the 365 nm radiation in 1,2-polybutadiene does not follow a pseudo-monomolecular kinetics.
► The reaction mechanism and a corresponding approximate kinetics model were developed.
► The formation of light absorbing transient during irradiation become almost negligible in 1,2-polybutadiene.
► The final 1,2-polybutadiene network contains the photoproducts derived from benzophenone that are linked to the polybutadiene chains.
► The polymerization of vinyl groups of polybutadiene is a significant crosslinking path.