SYNTHESIS OF POLYSTYRENE-BLOCK-POLYOXYETHYLENE FOR USE AS A STABILIZER IN THE EMULSION POLYMERIZATION OF STYRENE

Five well-defined polystyrene-block-polyoxyethylene copolymers were synthesized by anionic polymerization for use as stabilizers in the emulsion polymerization of styrene. The size of the blocks and their relative weight ratios to each other were the main variables. The molecular weights of the blocks varied from M(n)BAR = 1000-7000 for polystyrene, and M(w)BAR = 3000-9000 for polyoxyethylene. The results of the styrene emulsion polymerization with these block copolymers as stabilizers indicate that for efficient anchoring the block length need not be more than 10 monomer units, possibly even less, and that the polyoxyethylene block M(w)BAR = 3000 is just as capable of stabilizing the polystyrene particle as the higher molecular weight blocks. A very important factor was found to be the weight ratio of the two blocks: block copolymers with a polyoxyethylene content between 75 and 90 wt % were effective stabilizers for the emulsion polymerization of styrene