Two-arm PCL and PLLA macrophotoinitiators with benzoin end-functional groups by combination of ROP and click chemistry and their use in the synthesis of A2B2 type miktoarm star copolymers

Abstract

Novel and well defined macrophotoinitiators with two-arm poly(ε−caprolactone) (PCL) and poly(l-lactide) (PLLA) chains bearing two benzoin photofunctionalities (BPI) at the connection point of the polymer chains have been synthesized by combination of ring opening polymerization (ROP) and click chemistry. Initially, dibromo end-functionalized two-arm PCL, (PCL)2-(Br)2, and PLLA, (PLLA)2-(Br)2, were synthesized by ROP of ε−caprolactone and l-lactide monomers in bulk, using 2,2-bis(bromomethyl)-1,3-propanediol as the initiator and stannous-2-ethylhexanoate, (Sn(Oct)2), as the catalyst. Then, the terminal bromines of the polymer arms were converted into azide groups with sodium azide (NaN3). Subsequently, well-defined two-arm PCL and PLLA macrophotoinitiators with benzoin end functional groups [(PCL)2-(BPI)2 and (PLLA)2-(BPI)2] were obtained from the click reaction between diazido end-functionalized (PCL)2-(N3)2 and (PLLA)2-(N3)2 polymers and an alkyne-terminated benzoin photoinitiator (BPI-alkyne) which was synthesized from benzoin and propargyl bromide. The 1H NMR, FT-IR, GPC, UV, and fluorescence spectroscopic studies revealed that two-arm poly(ε−caprolactone) and poly(l-lactide) having benzoin photofunctional groups bound to the linking point of the chains were obtained. These polymers were then used as macrophotoinitiators for the photoinduced free radical promoted cationic polymerization of cyclohexene oxide (CHO) monomer to synthesize A2B2 type miktoarm star copolymers comprised of PCL or PLLA as A blocks and PCHO as B blocks.