Well-defined star polymers with mixed-arms by sequential polymerization of atom transfer radical polymerization and reverse addition-fragmentation chain transfer on a hyperbranched polyglycerol core

Mixed-arm star polymers were synthesized by atom transfer radical polymerization (ATRP) and reverse addition-fragmentation chain transfer (RAFT) sequential polymerization using the core first method. The synthesis consisted of three steps: (i) synthesis of a hyperbranched polyglycerol (HPG) core, (ii) ATRP with the first monomer (St, styrene), and (iii) then the polymerization with the second monomer (tert-butyl acrylate, tBA) from the core by the RAFT technique. After the hydrolysis of poly(tBA), poly(acrylic acid) (PAA) arms were obtained. In the whole process, the final products and intermediates were characterized by gel permeation chromatography (GPC), nuclear magnetic resonance spectroscopy (NMR), ultraviolet spectroscopy (UV), Fourier transform-infrared (FT-IR), and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) in detail. The arm number and arm length of polystyrene (PS) and poly(tBA) (PAA) in the star polymers were derived from GPC and MALDI-TOF MS after the cleavage of their ester bond linked to the HPG core: It was found that the initiation efficiency for ATRP of the first St was very high (nearly to 100%) but only when the arm number of PS was less than 66 and the molecular weight (MW) of PS was lower than 1.800 Da, then high initiation efficiency for RAFT of the second tBA could reach to 93%.