Synthesis and characterization of macrophotoinitiators of poly(ε-caprolactone) and their use in block copolymerization

Novel end-chain and midchain functional macrophotoinitiators of poly(ε-caprolactone) have been synthesized. For this purpose, mono- and dihydroxy functional photoinitiators namely, benzoin (B) and 2-hydroxy-2-methyl-1-phenyl propan-1-one (HMPP), Darocure 1173, and 2-hydroxy-1-[4-(2-hydroxyethoxy)phenyl]-2-methyl propan-1-one (HE-HMPP), Irgacure 2959, respectively, were used as initiators for the stannous-2-ethylhexanoate (Sn(Oct)₂) catalyzed living ring-opening polymerization of ε-caprolactone. The gpc and IR, H NMR, UV, and fluorescence spectroscopic studies revealed that low-polydispersity poly(ε-caprolactone) with desired photoinitiator functionality at the end or in the middle of the chain were obtained. These prepolymers were used to induce radical polymerization of methyl methacrylate (MMA) upon irradiation via α-cleavage of the incorporated phenyl ketone groups. While end-chain functional macrophotoiniators led to the formation of both homo and block copolymers, only block copolymers of ε-CL and MMA were formed with midchain functional macrophotoinitiator. Successful blocking has been confirmed by a strong change in the molecular weight of the prepolymer and the block copolymer as well as by NMR spectral measurements.