Abstract
Cobalt mediated radical polymerization (CMRP) was used to prepare the well-defined poly(vinyl acetate) (PVAc) as the macro-initiator in reverse atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) and styrene (Sty) for the synthesis of block copolymers of PVAc-b-PMMA and PVAc-b-PSty with the linearly increased molecular weight and smoothly shifted GPC traces. The chain extension from PVAc to PMMA or PSty via this hybridization of CMRP and ATRP required no difunctional initiator nor further chain end modification and was as simple as the regular chain extension in reverse ATRP process. Since the cobalt complex bonded to the chain end of PVAc was dissociated during the ATRP process, this method also efficiently solved the issue of metal removal in CMRP process. Another section was focused on the ligand steric effect to the control efficiency of vinyl acetate radical polymerization. Cobalt(II) Salen complexes with different ligands were used to mediate the polymerization of vinyl acetate. The VAc polymerization with the complex of CoII(salophen), which has a planar structure, showed a significant molecular weight deviation and a low control efficiency (Mw/Mn = 1.42). On the other hand, CoII(et-salen) and CoII(salcomic) mediated the VAc polymerization with linear increased molecular weight versus conversion and a relatively low polydisperity (Mw/Mn = 1.34 and 1.32). The CoII(Salen*) showed the best control to VAc polymerization (Mw/Mn < 1.20).