Multi‐Arm Star Polyglycerol‐block‐poly(tert‐butyl acrylate) and the Respective Multi‐Arm Poly(acrylic acid) Stars

Summary: Well‐defined multi‐arm star block copolymers, polyglycerol‐ block ‐poly( tert ‐butyl acrylate) (PG‐ b ‐P t BA), with average arm‐numbers of 17, 27, 36, 66 and 90 arms, respectively, have been prepared by atom transfer radical polymerization (ATRP) of t BA in acetone, using a core‐first strategy. After hydrolysis with excess concentrated HCl in refluxing dioxane, full hydrolysis of the tert ‐butyl ester groups was achieved, resulting in multi‐arm star polyelectrolytes, polyglycerol‐ block ‐poly(acrylic acid) (PG‐ b ‐PAA). The hyperbranched macroinitiators employed were prepared on the basis of hyperbranched polyglycerols via esterification with 2‐bromoisobutyryl bromide. Both CuBr/PMDETA and CuBr/Me 6 TREN catalyst systems have been employed for ATRP of t BA. CuBr/PMDETA was found to permit good control. Polydispersity indices for the new multi‐arm stars were mainly in the range of 1.22 to 1.4, and the absolute M ₙ data were in agreement with the calculated values. Moreover, kinetic curves show a linear dependence of ln([M] 0 /[M] t ) on time, confirming that the polymerizations are controlled. Relationship between arm numbers of the multi‐arm stars and maximum conversion achieved. image Relationship between arm numbers of the multi‐arm stars and maximum conversion achieved.