Abstract: Photoinduced copolymerization of vinyl spiro orthoester(VS)-(2-methylene-1,4,6-trioxaspiro[4,4] nonane)with maleic anhydride(MA) proceeds via formation of the charge transfer(CT) complex as reactive intermediate to produce linearly alternating copolymer, poly(VS-alt-MA) by vinyl type radical polymerization way. It was found that in the mild condition the photopolymeriztion occurs only in the present of radical photoinitiator. The solvent polarity and feed ratio of two monomers significantly affect the polymerization rate, but does not effect on the composition of polymer products. The formation CT complex between VS and MA was further verified by UV absorption spectra. The association constant(K) of CT complex was estimated to be 0.22 mol^-1·L (THF) and 0.19 mol^-1·L(CH₃CN).The small value of K indicates that VS and MA interact to construct a weak CT complex, which is easily affected by polarity of solvents and temperature. The structure of VS/MA copolymer obtained was further determined by IR and ¹HNMR spectra. The results measured clearly demonstrated that the copolymer product possesses a regular alternating structure with original trioxaspiro ring at VS unit in polymer chain. The mechanism of radical alternating photopolymerization of VS with MA was also discussed.

Key words: alternating copolymer, charge transfer complex, vinyl spiro compound, photopolymerization