Photochemistry of ketone polymers. XIV. Studies of ethylene copolymers

Studies have been made of the photochemistry of ethylene copolymers with carbon monoxide (CO), methyl vinyl ketone (MVK), and methyl isopropenyl ketone (MIPK) in solid films. Infrared (IR) evidence is presented to show that a variety of unexpected ketone structures is present in these polymers as a result of 1,5‐hydrogen transfer or “back‐biting” during the high‐pressure polymerization reaction. These additional structures complicate the analysis of the quantum yield data. The overall quantum yield for carbonyl disappearance (ϕ‐co) which increases from 0.074 to 0.24 to 0.26 in the series PE‐1% CO, PE‐2% MVK, and PE‐20% MIPK reflects the increasing stability of the alkyl radicals produced from the type I process in the respective ketone structures. It is also shown that ketone groups located in the backbone of the polymer, as in the 1% CO copolymer, have lower quantum yields for photochemical reactions, particularly those that produce free radical intermediates. Studies of the gaseous products from extensive photodegradation under nitrogen show that in all three cases carbon monoxide is the major product (46‐65% of the total). Acetaldehyde and methane, expected from the type I reaction, are major products only for the MVK and MIPK copolymers. Reaction schemes are presented to explain the major products observed.