Solid-state photopolymerization of octadecyl sorbate to yield an alternating copolymer with oxygen

The crystals of octadecyl sorbate (ODS) were irradiated with sunlight or with a high-pressure Hg lamp to yield polymers with a molecular weight of 2.6-7.2 x 10(3). ESR spectroscopy confirmed that the propagating species is of allylic structure during the photopolymerization of ODS in the crystalline state, and that it is long-lived because of the immobility of the polymer chain produced. An alternating copolymer of ODS with oxygen is produced during the polymerization in air and the repeating unit of ODS in the resulting copolymer consists exclusively of 5,4-structure, when ODS crystals obtained by recrystallization from ethanol were used. Bulk polymerization of ODS provides a high molecular weight poly(ODS) with predominant trans-5,2-structure in the presence of a radical initiator in the melt. ODS crystals obtained from hexane or chloroform afford polymers consisting of both 5,4- and 5,2-structures.