Kinetics of spatial structures in the photodegradation of polymers

The formation of spatial structures in photochemical reactions with the resulting creation of stable absorbing products is studied. A theoretical analysis is performed in the approximation of the stationary concentration of intermediate reagents. It is found that in reactions with an arbitrary order of light intensity, accumulation of absorbing products is described by the ‘degradation wave’ of a fixed form.

The wave dynamics determining the degradation velocity is characterized by the single parameter of ‘photoaction’. This parameter depends on the variation law of the incident light intensity, time of action and the chemical reaction mechanism. In the simplest case it is the radiation dose.

The profile forms and the dynamics of their establishment for reactions with different concentration levels of absorbing products are investigated. The conditions for creation of ‘limited degraded layers’ in the polymer are determined.

Experiments in poly(vinyl chloride) (PVC) revealing spatial structures and investigating the product concentration profile in them are considered. It is discovered that in air a three-layer structure forms whose parameters are dependent on the radiation regime. The experimental results are compared with the theory. The possibility of observing spatial layers in polyolefins is discussed.