An arm-first approach to cleavable mikto-arm star polymers by RAFT polymerization

Redox-cleavable mikto-arm star polymers are prepared by an "arm-first" approach involving copolymerization of a dimethacrylate mediated by a mixture of macroRAFT agents. Thus, RAFT copolymerization of the monomers BMA, DMAEMA, and OEGMA, with the disulfide dimethacrylate cross-linker (DSDMA), bis(2-methacryloyl)oxyethyl disulfide, mediated by a 1:1:1 mixture of three macroRAFT agents with markedly different properties [hydrophilic, poly[oligo(ethylene glycol) methacrylate] - P(OEGMA)_8-9; cationizable, poly[2-(dimethylamino)ethyl methacrylate] - P(DMAEMA); hydrophobic, poly(n-butyl methacrylate) - P(BMA)] provides low dispersity mikto-arm star polymers. Good control (D strok sign < 1.3) is observed for the target P(DMAEMA)/P(OEGMA)/P(BMA) (3:3:1) mikto-arm star, a double hydrophilic P(DMAEMA)/P(OEGMA) (3:3) mikto-arm star and a hydrophobic P(BMA) homo-arm star. However, D strok sign for the target mikto-arm stars increases with an increase in either the ratio [DSDMA]:[total macroRAFT] or the fraction of hydrophobic P(BMA) macroRAFT agent. The quaternized mikto-arm star in dilute aqueous solution shows a monomodal particle size distribution and an average size of ≈145 nm. Low dispersity redox-cleavable mikto-arm star polymers with a cross-linked core containing disulfide bonds are synthesized by cross-linking copolymerization mediated by three different arm macroRAFT agents (hydrophilic, cationizable, and hydrophobic). The dispersity of the stars increases with an increase in [cross-linker]:[total macroRAFT] or the fraction of hydrophobic macroRAFT agent.