Synthesis of hyperbranched poly(tert-butyl acrylate) by self-condensing atom transfer radical polymerization of a macroinimer

Using 2-hydroxyethyl α-bromoisobutyrate as initiator, atom transfer radical polymerization (ATRP) of tert-butyl acrylate leads to poly(tert-butyl acrylate) (PtBA) with a hydroxyl group at one and a bromine atom at the other end. Esterification of the hydroxyl group of these heterotelechelic polymers with acryloyl chloride yields PtBA (Mn = 3 060) with a polymerizable double bond at one end and a bromine atom at the other end which can act as an initiator in ATRP (“macroinimer”). Self-condensing ATRP of such a macroinimer leads to hyperbranched or highly branched PtBA. The polymer was characterized by GPC viscosity measurements. Even at Mw = 78 800, a rather low polydispersity index of Mw/Mn = 2.6 was obtained. A significantly lower value for the Mark-Houwink exponent (α = 0.47 compared to α = 0.80 for linear PtBA) indicates the compact nature of the branched macromolecules.