Polymer Bulletin, Vol.76, No.2, 553-573, 2019
Synthesis and characterization of an A(2)B(2)-type miktoarm star copolymer based on poly(epsilon-caprolactone) and poly(cyclohexene oxide)
An A(2)B(2)-type miktoarm star copolymer with two linear poly(epsilon-caprolactone) (PCL) and two linear poly(cyclohexene oxide) (PCHO) arms was synthesized by using ring-opening polymerization (ROP), click chemistry, and photoinduced cationic polymerization, respectively. The ROP of epsilon-CL with a dihydroxy functional initiator, 3-cyclohexene-1,1-dimethanol, produced a well-defined two-arm PCL with a cyclohexene end-functional group, (PCL)(2)-CH. The subsequent bromination of (PCL)(2)-CH followed by azidation gave a diazido end-functionalized PCL, (PCL)(2)-(N-3)(2). Then, a well-defined two-arm PCL macrophotoinitiator with benzoin end-functional groups, (PCL)(2)-(PI)(2), was prepared by the azide/alkyne click reaction of this (PCL)(2)-(N-3)(2) and PI-alkyne, a separately prepared benzoin photoinitiator bearing a terminal alkyne group. Solid data obtained from the H-1 NMR, FT-IR, GPC, UV, and fluorescence spectroscopic studies proved the successful formation of the macrophotoinitiator having a core connected to two PCL chains and two benzoin photofunctional groups (PI). Finally, a novel A(2)B(2)-type miktoarm star copolymer was synthesized via photoinduced free radical-promoted cationic polymerization of cyclohexene oxide (CHO) monomer using (PCL)(2)-(PI)(2) as photoinitiator. The obtained star copolymer consists of two PCL arms as A blocks and two PCHO arms as B blocks, (PCL)(2)-(PCHO)(2), and was characterized by H-1 NMR, FT-IR, and GPC measurements. The thermal behaviors of all the intermediate and final polymers were studied by thermogravimetric and differential thermal analysis (TG/DTA).
Keywords:Ring-opening polymerization (ROP);Poly(epsilon-caprolactone);Macrophotoinitiator;Click chemistry;Photoinduced free radical-promoted cationic polymerization;A(2)B(2)-type miktoarm star copolymer