Synthesis and Properties of Asymmetric Heteroarm PEO n -b-PS m Star Polymers with End Functionalities

ABSTRACT: We report on the "core-first" synthesis of asymmetric three-and four-arm poly(ethylene oxide) (PEO)-polystyrene (PS) star polymers with functional terminal groups of a general formula PEO nb-PSm with n ) 0, 1, and 2 and n + m e 4. The synthesis was conducted by anionic polymerization of ethylene oxide and followed by atom transfer radical polymerization (ATRP) of styrene. The properties of asymmetric star-shaped macromolecules with different numbers of arms (n ) 1; m ) 2 and 3) and similar lengths of the PEO arm were compared with homoarm star polymers (PEO4 and PS4) and corresponding linear polymers. All star polymers obtained here possessed well-defined architecture with a relatively narrow molecular weight distribution as confirmed by NMR, FTIR, and arm-disassembling techniques. Star polymers showed suppression of melting temperature and lower crystallinity PEO phase due to the presence of a junction point. Preliminary studies demonstrated surface activities of these block copolymers with a rich polymorphism of micellar surface structures expected for amphiphilic block copolymers despite the presence of the bulky terminal functionalized groups

Redistribution of Soil Organic Carbon Induced by Soil Erosion in the Nine River Basins of China

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