From well defined star-microgels to highly ordered honeycomb films

Star-microgels were prepared in a two-step process known as the arm first approach by Atom Transfer Radical Polymerization (ATRP). Living linear poly(methyl methacrylate) (PMMA), with molecular weight (Mn) of 10000 and 20000, was reacted with ethylene glycol dimethacrylate (EGDMA) as crosslinker and varying amounts of methyl methacrylate (MMA) as spacer, under ATRP conditions, to produce star-microgels with Mn ranging from 0.3 × 106 to 1.0 × 106 and number of arms, n(arms) from 11 to 74. As Mn of the arm was increased, a decrease in molecular weight and in the number of arms in the microgel was observed. Star-microgels, with MMA spacer incorporated in the core, were found to have lower molecular weight and lower arm number. The microgels were used as precursors to form honeycomb films. The films were cast under conditions of high humidity which produces condensed water droplets which act as the template for a precipitating polymer. This is the first report of the use of well defined star-microgels to cast highly ordered porous films. It is shown that the pore diameters decrease with increasing number of PMMA arms and with increasing molecular weight of the star-microgel.