Photolysis of Poly[1-(4-substituted phenyl)-2-propen-1-one] in the solid phase

Abstract

Photolysis of poly[1-(4-substituted phenyl]-2-propen-1-ones] in film of thickness 5–10 μm was followed by automatic viscometry, lowangle laser light scattering (LALLS) and gel permeation chromatography (GPC) under irradiation at 313 and 285·8 nm in air. The substituents in position 4 of the benzene ring were: H, fluoro, chloro, methoxy and ethyl. The monitoring of degradation by automatic viscometry and LALLS enabled determination of the Mark-Houwink parameters α and K for the above polymers in chlorobenzene at 25°C as follows. H: α = 0·76 ± 0·03, K = 3·8 × 10⁻³; 4-F: α = 0·69 ± 0·02, K = 6·1 × 10⁻³; 4-Cl: α = 0·79 ± 0·03, K = 1·4 × 10⁻³; 4-C₂H₅: α = 0·85 ± 0·03, K = 1·3 × 10⁻³; 4-OCH₃: α = 0·75 ± 0·06, K = 2·3 × 10⁻³. The plots of main chain scission versus time were curved, which indicates inhibition at the later stage of degradation. The initial quantum yields of main chain scissions are about 0·08 except for the 4-methoxy derivative, in which case strong oxygen quenching causes the quantum yield to lie one order of magnitude lower. The unsaturated ketone formed during photolysis quenches the main chain scissions with Stern-Volmer constants which lie within the range 50–150 mol⁻¹ for the polyketones under study.