Synthesis of a well-defined end-chain macrophotoinitiator of poly(ε − caprolactone) by combination of ring-opening polymerization and click chemistry

A novel well-defined end-chain functional macrophotoinitiator of poly(ε − caprolactone) (BPI-PCL) with controlled molecular weight and narrow molecular weight distribution was successfully synthesized by combination of ring opening polymerization (ROP) and “click chemistry”. The synthetic procedure for the preparation of a macrophotoinitiator involves three steps: (1) an azido-functionalized benzoin photoinitiator (BPI-N₃) by transformation of a bromine-end group of BPI-Br compound into an azido group using NaN₃; (2) an alkyne end-functionalized PCL (alkyne-PCL) precursor by ROP of ε − caprolactone (ε − CL) using propargyl alcohol as the initiator and stannous-2-ethylhexanoate (Sn(Oct)₂) as the catalyst; and (3) BPI-PCL through “click reaction” between alkyne-PCL and BPI-N₃ using Cu(I) as a catalyst. The ¹H NMR, FTIR, UV–vis, fluorescence and gel permeation chromatography techniques were used to characterize the chemical structures of the intermediates and the target macrophotoinitiator. The obtained BPI-PCL macrophotoinitiator was used as a precursor in photoinitiated free radical promotedcationic polymerization to synthesize a poly(ε − caprolactone)-poly(cyclohexene oxide) (PCL-PCHO) block copolymer. The thermal behavior of the polymers was studied by differential thermal analysis and thermogravimetric analysis methods.