Synthesis and characterization of star-shaped polymers by atom transfer radical polymerization

Abstract

Precisely controlled star-shaped polymers have been attracting interest as new polymeric materials due to their unique properties resulting from three-dimensional structures. However, construction of star-shaped polymers requires elaborated synthetic steps such as coupling of several well controlled linear polymer chains with a core molecule. Recently developed atom transfer radical polymerization opens a way to make star-shaped polymers efficiently. In this study, the star-shaped poly(MMA)s with well-defined molecular weight (~16,000) and narrow polydispersity (＜1.25) were prepared in high yield by $NiBr_2(PPh_3)_2$. The polymerizations were carried out with multifunctional initiators which were prepared from 2-bromoisobutyryl bromide and phloroglucinol or pentaerithritol in bulk at 90 ℃. The star-shaped poly(MMA-co-HEMA)s with well-defined molecular weight (~12,000) and narrow polydispersity (＜1.30) were also prepared in high yield by CuBr/2,2’-bipyridine. The polymerizations were carried out with multifunctional initiators which were prepared from 2-bromoisobutyryl bromide and phloroglucinol or pentaerithritol in N,N-dimethyl formamide at 90℃. Investigation of the physical properties of the polymers revealed that the synthesized well-defined star-shaped poly(MMA-co-HEMA)s had a higher thermal stability than the poly(MMA) presumably due to the increased hydrogen bonding by hydroxyl groups of HEMA monomer unit.