Novel azo-containing polymethacrylates bearing spiroacetal-norbornene moiety and methylene spacers: synthesis and characterization

An eight-step synthetic strategy was followed to prepare a series of novel azobenzene-containing methacrylate monomers bearing spiroacetal-norbornene moiety and methylene spacers. Thus, the adduct 2, obtained from cyclopentadiene and acrolein, was converted to 1,3-diol 3. The diol was acetalized with nitrobenzaldehyde 4 under microwave irradiation to obtain nitro compound 5 that was then reduced to amino compound 6. Diazonium salt of 6 was coupled with phenol to produce phenolic compound 7 which was then reacted with n-dibromoalkanes (n=2, 4, 6, 8, 10) to yield bromo compounds 9a–e. Nucleophilic substitution reaction of the bromo compounds with lithium methacrylate produced the methacrylic monomers 12a–e. The monomers were finally homopolymerized via free radical solution method by using AIBN as an initiator (solvent THF, 60°C, 38 h). All the intermediate compounds as well as monomers and polymers were characterized by means of spectroscopic (FTIR, 1H- and 13C-NMR) and thermal (DSC and TGA) techniques. Average molecular weights and molecular weight distributions of the polymers were measured by GPC. The polymers were completely soluble in common organic solvents. The azopolymers showed reversible trans–cis photoisomerization of –NN– bond as indicated by using UV/VIS spectrophotometry.